CHAPTER SEVEN
Myocardial Diseases
Hypertrophic Cardiomyopathy
Hypertrophic cardiomyopathy (HCM) is a disease that primarily affects cats. It is rare for other animal species to develop this disease (1–7). It is characterized by unexplained concentric left ventricular hypertrophy where the left ventricular chamber is not dilated and is often smaller than normal (8–12). Diastolic failure secondary to impaired relaxation is a common complication resulting in elevated left ventricular filling pressure and a dilated left atrial chamber (8). Left ventricular outflow obstruction is also a common occurrence (8). In man this disease has a 10 to 15% rate of progression to dilated cardiomyopathy (8).
Two-Dimensional and M-mode Evaluation
Left Ventricular Chamber
The hypertrophy in cats displays varying morphologies. Most cats present with symmetric hypertrophy with both the ventricular septum and the free wall affected to a similar degree (Figures 7.1, 7.2). About as many cats however, present with asymmetric hypertrophy affecting primarily the septum (Figures 7.3, 7.4). Fewer cats (17%) present with asymmetric hypertrophy affecting the left ventricular free wall (Figures 7.5, 7.6). In other cases, only the apex, midventricular areas, segmental areas of marked transitions between normal thickness, and increased thickness or the very base of the septum are hypertrophied (Figure 7.7) (13,14). Asymmetric septal hypertrophy was the most common form of hypertrophy in one study in dogs with HCM with 80% of 20 dogs in one study displaying this asymmetry (6). Infarction and aneurysmal dilation of the left ventricular apex may develop (14). Although this has not been studied in the cat, in man there is no correlation between the degree of hypertrophy and clinical signs of heart failure (15). The degree of hypertrophy does correlate with the incidence of sudden death in man however (16).
Hypertrophic Cardiomyopathy
Features
Concentric LV hypertrophy
Most have symmetric or just VS hypertrophy
LA does not have to be dilated.
Most have obstruction to outflow.
SAM seen
Systolic aortic valve closure seen
Elevated fractional shortening
Figure 7.1 Symmetric concentric left ventricular hypertrophy is the most common form of hypertrophy pattern in cats with hypertrophic cardiomyopathy. Here the septum and free wall are of
similar thickness. The hypertrophy is severe. This image also shows systolic anterior motion of the mitral valve (arrow) and a dilated left atrium. RV = right ventricle, LV = left ventricle, AO = aorta, LA = left atrium, plane = right parasternal long-axis left ventricular outflow view.
Figure 7.2 This M-mode of the left ventricular chamber in a cat with hypertrophic cardiomyopathy shows severe symmetric hypertrophy with elevated fractional shortening. RV = right ventricle, LV = left ventricle, VS = ventricular septum, LVW = left ventricular wall.
Figure 7.3 Asymmetric hypertrophy is seen almost as often as symmetric hypertrophy. This cat has a thicker septum than free wall (arrow), and the septum bulges into the outflow tract probably creating outflow obstruction despite mild hypertrophy. RV = right ventricle, LV = left ventricle, LA = left atrium, AO = aorta, plane = right parasternal left ventricular outflow view.
Figure 7.4 Septal hypertrophy (arrow) is seen in this cat with hypertrophic cardiomyopathy. RV = right ventricle, LV = left ventricle, AO = aorta, LA = left atrium, plane = right parasternal long-axis left ventricular outflow view.
Figure 7.5 Asymmetric hypertrophy affecting the left ventricular free wall in this M-mode is seen infrequently with hypertrophic cardiomyopathy. There is an effusion above the right ventricular wall. RV = right ventricle, LV = left ventricle.
Figure 7.6 (A) Asymmetric hypertrophy affecting the left ventricular wall is seen on this transverse view of the left ventricular chamber. (B) Severe asymmetric hypertrophy involving the left ventricular wall is appreciated on this right parasternal long-axis view of the left ventricle. (C) Hypertrophy of only the left ventricular free wall is seen in this cat. The septum is normal. Plane = left cranial longaxis four chamber, LVPW and LVW = left ventricular free wall, RV = right ventricle, RA = right atrium, LA = left atrium, LV = left ventricle, VS = ventricular septum, PL = pleural effusion.
Figure 7.7 Focal basilar hypertrophy of the interventricular septum (measurement) is seen in this cat. RV = right ventricle, VS = ventricular septum, LV = left ventricle, LVW = left ventricular wall, AO =
aorta, LA = left atrium, plane = right parasternal long-axis left ventricular outflow view.
The hypertrophy may obstruct flow in the left ventricular outflow tract. This occurs primarily when the base of the ventricular septum impinges upon the outflow tract, and it may occur when extensive free wall thickening displaces the mitral valve upward into the outflow tract. Abnormally long mitral valve leaflets are a cause of left ventricular outflow obstruction in man (8,17). Cats with symmetric hypertrophy or hypertrophy primarily affecting the septum tend to have a significantly higher incidence of murmurs, probably associated with outflow tract obstruction (13). Hearts with midventricular hypertrophy may have midcavity obstruction associated with contraction (9,10,12,13,17). Significant right ventricular hypertrophy in addition to the LVH has been seen in several cats (12).
Large prominent papillary muscles are common in cats with hypertrophic cardiomyopathy. Using either of the area methods to measure papillary muscle size, a papillary muscle area of greater than .8 cm2 exceeds that found in normal cats (Figure 7.8). This is not specific to hypertrophic cardiomyopathy and may reflect enlargement of the papillary muscles secondary to other causes of left ventricular hypertrophy (18).
Figure 7.8 (A) Papillary muscle size assessed by direct trace of the muscles. (B) Papillary muscle size assessed by tracing the interior surface of the left ventricular chamber around the papillary muscles and (C) tracing the interior surface through the papillary muscles. The total papillary muscle area is obtained by subtracting the two areas (A–B). (D) Measurement of papillary muscle width and height is shown. Plane = right parasternal transverse left ventricle, RV = right ventricle, LV = left ventricle.
Left Atrium
Left atrial size may or may not be increased in animals with hypertrophic cardiomyopathy (Figure 7.9). Left atrial enlargement is considered to be an indicator of severity and chronicity of diastolic failure in man (19,20). The larger the left atrium, the worse the prognosis. The cause of left atrial enlargement is typically secondary to diastolic dysfunction but may be because of systolic failure or abnormal mitral valve function (13,17).
Figure 7.9 Left atrial dilation is present on this transverse two-dimensional image of the heart base in a cat. This may be seen in animals with hypertrophic cardiomyopathy secondary to diastolic or systolic dysfunction. RV = right ventricle, AO = aorta, LA = left atrium, LAU = left auricle, PA = pulmonary artery, plane = right parasternal transverse heart base.
Left Ventricular Outflow Obstruction
Systolic anterior motion (SAM) of the mitral valve occurs in the presence of moderate to severe left
ventricular outflow tract obstruction. Several theories exist for the underlying cause of SAM. High velocity flow within an outflow tract narrowed by a hypertrophied septum creates a Venturi effect and tends to pull one or both mitral valve leaflets into the outflow tract (17,21,22). The presence of abnormal ventricular architecture and papillary muscle misalignment may allow the septal or parietal mitral valve leaflets to be pushed into the outflow tract during systole (8,17,22–26). Alignment of the subauricular papillary muscle into the middle of the ventricular chamber may also play a role in the development of SAM. This displacement causes the flow of blood to slip in under the septal leaflet pushing it into the outflow tract like a cowl (23). In man reports of elongated mitral leaflets, direct papillary muscle attachment to the septal mitral leaflet, and short chordae tendinae are all associated with obstruction to left ventricular outflow (27). There is reason to believe that SAM contributes substantially more to any outflow obstruction than the hypertrophied ventricular septum (23). Systolic anterior motion of the parietal mitral valve leaflet secondary to a hyperdynamic state without left ventricular hypertrophy has been documented (26). Outflow tract obstruction is worsened by volume contraction, decreased afterload (aortic pressure), and increased contractility, which all allow the left ventricular chamber to achieve smaller systolic dimensions and decrease tension on chordae tendinae allowing the mitral valve leaflet to move up into the outflow tract (8,23,28).
The degree and duration of septal contact during systolic anterior mitral valve motion correlate with severity of dynamic outflow obstruction.
Although muscular septal hypertrophy and SAM are the most common causes of left ventricular obstruction, midventricular obstruction may occur. This is usually caused by severe hypertrophy that allows the septum and free wall to meet each other during systole resulting in cavity obliteration. Often a severely hypertrophied papillary muscle is caught between the two walls (29). Identification of midventricular obstruction is possible with color-flow Doppler that shows turbulence within the middle of the ventricular chamber and with PW Doppler, that defines an aliased signal at the point of obstruction. The increase in midventricular velocity may not reflect true obstruction and may simply be the result of high velocity flow secondary to a small hyperdynamic chamber (22).
An experienced eye can detect systolic anterior motion on real-time two-dimensional images, but the motion is easier to detect and document on M-mode images of the mitral valve (Figures 4.101, 7.1, 7.10, 7.11, 7.12). The duration of mitral valve septal contact is directly correlated to severity of the outflow tract gradient (10,30,31). Longer apposition with the septum indicates more severe obstruction. Late peaking SAM with little if any contact suggests mild obstruction to flow. Small gradients will not create any SAM (9,10,32–34). Left ventricular outflow obstruction because of SAM is dynamic in nature and may not be present at rest (17).
Figure 7.10 Mild systolic anterior motion associated with increased velocity of blood flow in the left ventricular outflow tract is seen on this cat’s M-mode (arrow). The amplitude and duration of SAM is related to the degree of obstruction. Obstruction here is mild. There is also severe right ventricular hypertrophy. RV = right ventricle, LV = left ventricle, VS = ventricular septum.
Figure 7.11 The systolic anterior motion barely touches the septum in this cat, but its duration is long. This probably correlates with a moderate degree of outflow tract obstruction (arrow).
Figure 7.12 Systolic anterior mitral valve motion is seen on this feline long-axis two-dimensional image. The septal leaflet of the mitral valve is displaced into the left ventricular outflow tract (arrow). RV = right ventricle, VS = ventricular septum, AO = aorta, LV = left ventricle, LVW = left ventricular wall, LA = left atrium.
Systolic anterior motion may be the cause of left ventricular outflow obstruction and the resultant concentric left ventricular hypertrophy in young dogs (1). The systolic anterior mitral valve motion may be due to abnormalities of the mitral apparatus. Redundant valve tissue was seen in several of these dogs. The hypertrophy and systolic anterior motion resolved with beta-blocker treatment in dogs that lived (1).
It is important to point out that SAM may be seen in patients without HCM. It is reported in patients with elevated right ventricular pressure caused by pulmonic stenosis, tetralogy of Fallot, and pulmonary hypertension (35). All of these patients had left ventricular volume contraction, and the abnormal left ventricular geometry is thought to be the cause of the SAM. Outflow gradients were present in most cases, and even when peak flow velocity was normal, the flow profile showed late peaking velocity (35). Systolic anterior mitral valve motion is also reported in association with a handful of other situations: transposition, double chamber right ventricle, anomalous papillary muscles, conotruncal abnormalities, systemic hypertension, and anemia (21,36–40).
SAM may be seen with right ventricular pressure overload presumably due to poor LV preload and altered LV geometry.
Aortic valve motion may be altered in people and cats with hypertrophic obstructive cardiomyopathy. Ejection time increases in direct proportion to the degree of subvalvular dynamic obstruction. There is evidence of early systolic closure of the aortic valve corresponding to the decrease in forward flow as the dynamic obstruction occurs (Figures 4.97, 7.13) (10,32,41–43). This motion is also called midsystolic notching or midsystolic closure. This motion usually involves only one or two of the aortic valve cusps, and M-mode images of the aortic valve taken from parasternal long-axis views may not show it while M-modes obtained from transverse views may. This motion may be seen with dynamic hypertrophic obstructive cardiomyopathy or with fixed subaortic obstruction (stenosis). There is no correlation with the severity of the pressure gradient. Early aortic valve closure has been reported with ventricular septal defect and double outlet right ventricle (41).
Figure 7.13 Systolic closure of the aortic valve on M-mode images occurs when dynamic obstruction reduces flow through the valve (arrow) in this cat with hypertrophic cardiomyopathy. AO = aorta, LA = left atrium.
Systolic Function
Fractional shortening in HCM is typically increased, and the hearts are very visibly hyperdynamic (Figure 7.2) (44). This is not necessarily indicative of increased intrinsic contractility but may only be secondary to altered loading conditions in the heart. Paradoxically this increase in function often impedes cardiac output as dynamic obstruction is aggravated by the hyper contractile septum. Only in rare cases, as end-stage HCM is reached, does function of the septum or free wall decrease. With advances in tissue Doppler imaging, systolic dysfunction can be identified before fractional shortening and ejection fraction decrease (21). In one study, 72% of cats with fractional shortenings less than 30% were dead 3 months after their initial examination (Figures 7.14, 7.15) (13). Whether these cats have reduced fractional shortenings because of systolic dysfunction alone or diastolic disease, which has progressed to include systolic dysfunction is not known.
Figure 7.14 Left ventricular function in this cat with hypertrophic cardiomyopathy is decreased as seen by poor septal and free wall thickening during systole. RV = right ventricle, VS = ventricular septum, LV = left ventricle, LVW = left ventricular wall.
Figure 7.15 The left ventricular chamber has started to dilate, and function is very poor in this hypertrophic cardiomyopathy. RV = right ventricle, LV = left ventricle VS = ventricular septum, LVW = left ventricular wall.
Doppler Evaluation of HCM
Evaluation of Outflow Obstruction
A pressure gradient across the left ventricular outflow tract in man is now considered a predictor of complications, disease progression, and death (17,22,45). This predictive feature was present when outflow gradients reached 30 mm Hg or greater, and prognosis did not become worse with worsening pressure gradients (17,46). There also appears to be a direct relationship between left ventricular outflow obstruction and both systolic and diastolic dysfunction in humans with hypertrophic
cardiomyopathy. The gradient correlated with left ventricular filling pressure, hypertrophy, and left atrial size (46).
The obstruction to outflow seen in many cases of HCM occurs primarily during late systole. Spectral Doppler displays show this nicely by dagger-shaped late peaking velocity on left ventricular outflow tract flow profiles (Figure 7.16) (10,33). This late-peaking maximal velocity correlates with the increased flow velocity as the septum narrows the outflow tract or SAM obstructs flow. Pressure gradients are measured using the Bernoulli equation. Outflow obstruction is subvalvular, and the Doppler cursor is not necessarily aligned with the wall of the aorta to record peak velocity. Align the cursor with the outflow tract, using color-flow Doppler to define the orientation of the turbulent flow. A low frequency transducer may define high outflow flow velocity that is not found with high frequency high-resolution transducers. Occasionally there is obstruction in the middle of the ventricular chamber. A late-peaking outflow profile is seen if the middle of the chamber is interrogated or when the continuous-wave Doppler beam crosses that portion of the chamber while evaluating the outflow tract. Pulsed-wave Doppler should be used to interrogate the midventricular area for obstruction (Figure 7.16). Color-flow Doppler aids in identifying this. Midventricular obstruction should be considered when there is no SAM and secondary mitral regurgitation but there is a murmur (22,29).
Late peaking ventricular outflow profiles are seen with dynamic outflow obstruction.
Figure 7.16 (A) Dynamic left ventricular outflow obstruction in cats with hypertrophic cardiomyopathy results in increased aortic flow velocities and a late peaking velocity (arrows). Flow velocity here is mildly increased at approximately 2.5 m/sec. (B) Mid-ventricular obstruction may occur, which creates a late peaking flow profile (small arrows) in the middle of the left ventricular chamber. Pulsed-wave Doppler (long arrow on 2D image) is necessary to isolate the location of increased velocity and obstruction. Plane = apical five-chamber view, LV = left ventricle, RV = right ventricle, AO = aorta, LA = left atrium, RA = right atrium.
Systolic anterior motion is not only responsible for obstruction to left ventricular outflow, but also for resultant mild to moderate mitral regurgitation as the valve leaflets are pulled out of a properly closed position (17). The mitral regurgitant jet is directed toward the lateral wall of the left atrium, and seeing a jet directed away from the outflow tact should provide a hint that SAM is present (Figures 7.17, 7.18). The presence and degree of regurgitation is directly related to SAM. The greater the obstruction, the greater the degree of SAM the greater the degree of insufficiency (17,27). Alleviation of the outflow tact obstruction results in reduction or elimination of the SAM and mitral insufficiency (32,34). There are patients with mitral insufficiency unrelated to their hypertrophic disease however, and this should be suspected when the regurgitant jet is not directed downward toward the lateral wall of the left atrium away from the outflow tract and is centrally directed instead (17,27).
Figure 7.17 Aliased color-flow signals within the left ventricular outflow tract (large arrow) and left atrium (small arrow) reveal the presence of obstruction to flow and mitral insufficiency respectively in this cat with hypertrophic cardiomyopathy. The hypertrophy in this heart is symmetric. RV = right ventricle, VS = ventricular septum, LV = left ventricle, AO = aorta, LA = left atrium, LVW = left ventricular wall, plane = right parasternal left ventricular outflow view.
Figure 7.18 A small jet of mitral insufficiency (small arrow) is seen secondary to left ventricular outflow obstruction (large arrow) and systolic anterior motion in this cat with hypertrophic cardiomyopathy. This cat has symmetric hypertrophy. RV = right ventricle, LV = left ventricle, AO = aorta, LA = left atrium, plane = right parasternal left ventricular outflow view.
When color-flow or an imaging Doppler probe is not used, it is easy to record mitral regurgitation flow as opposed to left ventricular outflow from left apical five-chamber views of the heart. Mitral regurgitation starts earlier in the cardiac cycle near the beginning of the QRS complex. Aortic flow starts later during the latter part of the QRS complex (Figure 10.22). When the late-peaking flow profile is seen, you know it is the outflow tract and not mitral insufficiency.
Evaluation of Diastolic Function
Pulsed-Wave Doppler Evaluation of Diastolic Function
While systolic function is generally not impaired in patients with HCM, diastolic dysfunction is a common abnormality. Diastolic dysfunction is the result of impaired myocardial relaxation, restriction to left ventricular filling, and increased left ventricular filling pressures (47). Diastolic failure is a major factor in the development of congestive heart failure in feline cardiomyopathy (48). Assessment of left ventricular diastolic function involves the Doppler evaluation of transmitral flow, isovolumic relaxation time, pulmonary venous flow, and myocardial motion.
Impaired myocardial relaxation is reflected in the rate of relaxation, and isovolumic relaxation time will be increased (12,49,50). The left ventricular filling pattern of most patients, both animals and human with HCM, is abnormal. It shows decreased early filling (E) and a larger late diastolic filling component (A) with the atrial contraction (Figures 4.73, 7.19, 7.20) (50). Mitral valve early diastolic deceleration time is prolonged in HCM, and this is reported as an early predictor of disease development (50–52). The increased deceleration time reflects impaired left ventricular filling associated with delayed relaxation and results in a larger atrial contribution to left ventricular volume and a decreased E : A (10,47,52,53). Increased heart rate results in summation of E and A transmitral flow. The summated EA has higher flow velocity than isolated E flow velocity in the same cat. The sum of individual E and A velocities in cats with slow heart rates is similar to the summated EA flow velocity in normal cats (54). As discussed in Chapter 4, diastolic dysfunction is a continuum of events, and flow profiles will transition through a pseudonormal phase into a pattern of restrictive physiology typical of decreased compliance (Table 4.3).
Diastolic Failure in HCM
Impaired relaxation
Increased IVRT
Decreased MV E peak
Pulmonary vein Ar flow
Increased duration
Increased velocity
Figure 7.19 A reversed E : A ratio on Doppler examination of mitral inflow suggests impaired ventricular relaxation in this cat with hypertrophic cardiomyopathy.
Figure 7.20 Dramatically reduced E wave velocity, slow E wave deceleration, and an E : A ratio less than 1 imply diastolic dysfunction and abnormal relaxation in this cat with hypertrophic cardiomyopathy. This pattern of flow may be seen with other forms of cardiomyopathy also.
Acceleration and deceleration times of systolic pulmonary venous flow into the left atrium is also evaluated. Whereas parameters assessing left ventricular filling patterns are similar in human patients with HCM and hypertrophic heart disease secondary to aortic stenosis and systemic hypertension, pulmonary venous flow differs between idiopathic HCM and secondary forms of hypertrophy. Patients with HCM have decreased systolic acceleration times, increased deceleration times and reduced rate of systolic declaration. Patients with secondary forms of hypertrophy had parameters similar to normal controls (52). There is no difference in the pulmonary venous flow velocities, acceleration or deceleration times, or rates between human patients with obstructive versus non-obstructive HCM, nor between the varying patterns of hypertrophy (asymmetric, symmetric, and apical) (52).
Pulmonary venous flow is used to differentiate normal from psuedonormal transmitral flow and isovolumic relaxation times. In the presence of elevated left ventricular filling pressure secondary to impaired relaxation, despite normal IVRT and normal transmitral flow, there will be enhanced reverse flow into the pulmonary vein during the atrial contraction. This includes both duration of reverse flow and velocity of reverse flow. Systolic pulmonary venous flow may be decreased in the presence of elevated left atrial pressure, and diastolic flow will be greater than systolic flow as the atrial component of filling plays a more dominant role (Figure 7.21) (21).
Pseudonormal diastolic function
MV flow appears normal
IVRT normal
Use pulmonary vein flow to identify pseudonormal diastolic function.
Ar flow increased in duration and velocity
Figure 7.21 (A) Increased velocity and duration of pulmonary venous atrial reversal flow is consistent with elevated left atrial pressure and left ventricular filling pressure. (B) This cat has increased duration of atrial reversal flow and diminished systolic forward flow (S) velocity consistent with high left atrial pressure.
Tissue Doppler Evaluation of Diastolic Function
Tissue Doppler imaging is able to define abnormalities of systolic and diastolic function in the myocardium. Hypertrophic cardiomyopathy has abnormal longitudinal systolic shortening (reduced systolic annular velocity) and abnormal diastolic lengthening (reduced early diastolic annular velocity), which can be documented with tissue Doppler (55). It has the ability to identify subclinical HCM in asymptomatic patients and provide a measure of left ventricular filling pressure in man (46,56–59). Annular systolic and diastolic velocities are lower in human patients with subclinical hypertrophic cardiomyopathy even before the development of any left ventricular hypertrophy (59). Some of these parameters have been studied in the cat, and the differences in PW tissue Doppler parameters between cats with HCM and normal cats are listed in Tables 7.1, 7.2, and 7.3) (48,55,60). Cats with HCM have lower E′ at all apical four-chamber locations and lower E′ : A′ at all myocardial locations, lower Se′ at the free wall annulus on the apical four-chamber view, lower S′ at both sides of the mitral annulus and at the chordal level in the ventricular septum on the apical four-chamber view, lower E′ acceleration and deceleration rates at all locations on the apical view and in the left ventricular free wall at the chordal level on the right parasternal four-chamber plane, lower Se′ acceleration rate on both side of the mitral annulus and in the left ventricular free wall on the apical
four-chamber view (Figure 7.22) (48,55). Asymptomatic cats with HCM have increased A′ velocity in the ventricular septum on both apical and parasternal four-chamber views. This probably reflects preserved or increased atrial contractility in the setting of high left atrial pressure (55,61).
Table 7.1
Differences in Tissue Doppler Parameters Obtained from the Right Parasternal Four-Chamber View in Cats with Hypertrophic Cardiomyopathy Compared to Cats with Normal Hearts
E′ = early diastolic motion, A′ = late diastolic motion, Se′ = early systolic motion, Sl′ = late systolic motion, acc rate = acceleration rate, acc time = acceleration time, dec rate = deceleration rate, dec time = deceleration time, dur = duration, IVRT = isovolumic relaxation time, IVCT = isovolumic contraction time, N = 23, body weight = 5.2 ± 1 kg, age = 6.9 ± 3 years, heart rate = 158 ± 35.
Adapted from: Koffas H, Dukes-McEwan J, Corcoran M, et al. Pulsed Tissue Doppler Imaging in Normal Cats and Cats with Hypertrophic Cardiomyopathy. Journal of Veterinary Internal Medicine 2006;20:65–77.
Table 7.2
Differences in Tissue Doppler Parameters Obtained from the Apical Four-Chamber View at the Mitral Annulus in Cats with Hypertrophic Cardiomyopathy Compared to Cats with Normal Hearts
E′ = early diastolic motion, A′ = late diastolic motion, Se′ = early systolic motion, Sl′ = late systolic motion, acc rate = acceleration rate, acc time = acceleration time, dec rate = deceleration rate, dec time = deceleration time, dur = duration, IVRT = isovolumic relaxation time, IVCT = isovolumic contraction time, N = 23, body weight = 5.2 ± 1 kg, age = 6.9 ± 3 years, heart rate = 158 ± 35.
Adapted from: Koffas H, Dukes-McEwan J, Corcoran M, et al. Pulsed Tissue Doppler Imaging in Normal Cats and Cats with Hypertrophic Cardiomyopathy. Journal of Veterinary Internal Medicine 2006;20:65–77.
Table 7.3
Differences in Tissue Doppler Parameters Obtained from the Apical Four-Chamber View at the Chordae Level in Cats with Hypertrophic Cardiomyopathy Compared to Cats with Normal Hearts
E′ = early diastolic motion, A′ = late diastolic motion, Se′ = early systolic motion, Sl′ = late systolic motion, acc rate = acceleration rate, acc time = acceleration time, dec rate = deceleration rate, dec time = deceleration time, dur = duration, IVRT = isovolumic relaxation time, IVCT = isovolumic contraction time, N = 23, body weight = 5.2 ± 1 kg, age = 6.9 ± 3 years, heart rate = 158 ± 35.
Adapted from: Koffas H, Dukes-McEwan J, Corcoran M, et al. Pulsed Tissue Doppler Imaging in Normal Cats and Cats with Hypertrophic Cardiomyopathy. Journal of Veterinary Internal Medicine 2006;20:65–77.
Figure 7.22 Cats with HCM have lower E′ at all apical four-chamber locations and lower E′ : A′ at all myocardial locations. This cat has an E′ : A′ ratio less than 1.
Several systolic and diastolic time intervals are also significantly different in HCM cats when compared to normal cats. These parameters show that peak early pulsed-wave diastolic myocardial velocity is both decreased and occurs later in the diastolic time period, and that isovolumic relaxation times are prolonged in cats with HCM. Specific differences in cats with HCM from normal cats are as follows: there is longer E′ acceleration time at both sides of the mitral annulus on the apical view and the left ventricular free wall at the chordal level on both apical and right parasternal four-chamber views, longer E′ deceleration time at the free wall mitral annulus on the apical four-chamber and on the right parasternal four-chamber imaging plane at the level of the chordae in the free wall, longer early systolic (Se′) acceleration time at all locations on apical four-chamber views except at the septal annulus, longer E′ duration at the free wall mitral annulus and free wall chordal level on both imaging planes, and a longer time interval between the start of Se′ to start of late systolic motion (Sl′) at the free wall annulus on the apical view and at the chordal level of the septum on the right parasternal four-chamber plane. Isovolumic relaxation time at all locations on the apical four-chamber view using pulsed-wave tissue Doppler is also longer in cats with HCM (48,55).
Tissue Doppler changes from normal are also evident in subclinical dystrophic-deficient HCM even before the presence of any documented hypertrophic changes (60). Early evidence of impaired diastolic function included decreased radial and longitudinal lateral wall annular E′, increased longitudinal lateral wall annular A′, and lengthened longitudinal lateral wall and radial isovolumic relaxation times. The E′ : A′ relationship in these cats was less than 1 in most cats for radial motion and all cats for longitudinal motion of the lateral wall. These changes were more prominent at the base than the apex and in the endocardium than the epicardium. This may indicate that longitudinal fibers are affected earlier in the course of the disease than radial fibers.
Postsystolic contraction can be seen in man with myocardial ischemia and was seen in several of the dystrophic cats. It is thought to represent impairment of systolic function, but its mechanism is not fully understood. This systolic motion is present late in systole or early in diastole rather than during early systole. This contraction often occurs during the time when early diastolic motion should occur resulting in the absence of an E′ wave (55,60). Depressed systolic function despite normal systolic dimension and normal fractional shortening was also verified by decreased S′ motion on longitudinal but not radial myocardial fibers (55,60). One study reports that decreased S′ in the longitudinal fibers of cats with HCM is seen only in symptomatic cats with HCM (55).
The differences in longitudinal early diastolic wall motion between segments of the septum and the free wall seen in normal feline hearts is no longer present in most portions of the myocardium in cats with HCM (55). This heterogeneity in myocardial motion along the longitudinal axis is thought to be an important component for optimal myocardial function (55). Nonuniformity in myocardial motion that is lost in cats with HCM include the E′ acceleration rate of the interventricular septum at the chordae level is greater than the acceleration rate at the septal mitral annulus on apical four-chamber imaging planes and the E′ acceleration time was decreased at the chordal level when compared to the level of the mitral annulus of the septum. Cats with HCM have greater E′ : A′ ratios at the left ventricular free wall when compared to the septum on right parasternal long-axis four-chamber views.
Tissue Doppler in HCM
Lower E′ at all apical locations
Lower E′ : A at all apical locations
Lower S′ at all apical locations
Summation of early and late diastolic motion is seen at rapid heart rates. Summated EA′ has higher velocity than when they are separate. One study shows that this does not affect the interpretation of myocardial velocity when compared to cats without heart disease and rapid heart rates (48). Another found that if the summated EA′ was compared to the sum of E′ and A′ when existing separately in cats with slower heart rates, there was no significant difference (54). Therefore summated EA′ myocardial velocity and summated EA transmitral flow may potentially be used to assess diastolic function in cats with hypertrophic cardiomyopathy. It is important to use different reference ranges in order to interpret summated and nonsummated diastolic tissue Doppler variables. When early diastolic motion is decreased and summated with a potentially increased late diastolic velocity, the interpretation of events can become difficult (48,55). There is up to 30% variation in these variables from study to study, and small changes in tissue velocity should not be overinterpreted as a significant change unless a trend is established (55).
Pulsed-wave tissue Doppler of the right side of the heart exhibits some differences from normal in cats with HCM. The E′ velocity is decreased at the tricuspid valve annulus and the A′ velocity is increased in cats with HCM when compared to normal cats (55).
Early diastolic myocardial velocity is preload dependent and can be used to identify diastolic failure in cats with psuedonormal transmitral flow profiles (55,62). An E′ value of >7.2 cm/sec separates normal feline hearts from hearts with HCM (Figures 7.22, 7.23) (55). This value has a specificity of 87% and a sensitivity of 92%. Diastolic pressure in the left atrium affects the PW Doppler transmitral flow profile and velocity. Early diastolic longitudinal myocardial velocity is affected by left ventricular filling pressure. The relationship of E : E′ is strongly correlated to left ventricular filling pressure in man and in cats (21,55,56). Normal E′ is greater than 7.2 cm/sec, and normal E : E′ is less than 8.07.
Tissue Doppler
E′ <7.2 cm/sec longitudinal velocity identifies HCM cats.
Figure 7.23 An E′ value of >7.2 cm/sec separates normal feline hearts from hearts with HCM. This cat has an E′ less than 5 cm/sec that is consistent with the diagnosis of HCM.
Recently tissue Doppler imaging of the base of the interventricular septum in human patients with outflow obstruction showed characteristic systolic motion. A sudden midsystolic deceleration in myocardial velocity was seen in patients with clinically significant outflow obstruction. A midsystolic notch is displayed on the tissue Doppler flow profile (63). This may be a useful in cats when a reliable outflow gradient cannot be obtained. In man the degree of left ventricular outflow obstruction is significantly correlated with poorer systolic and early diastolic myocardial motion and a higher E : E′ (46).
Overall Assessment of Diastolic Dysfunction
Grades of diastolic dysfunction have been established in man (Table 4.3). The parameters used to assign a grade include transmitral flow, pulmonary venous flow, tissue Doppler, and size of the left atrium. These parameters allow indirect evaluation of relaxation, compliance, atrial function, and left ventricular filling pressure (64).
Complications
Thrombus
Thrombus may form within the left atrium (Figures 7.24, 7.25, 7.26). Left atrial dilation seems to be a risk factor for the development of arterial thromboembolism although statistically this is not supported (13,65,66). Thrombus formation in the left atrium is reported in 13 to 17% of cats with clinically diagnosed hypertrophic cardiomyopathy and 41% of cats at postmortem. Thrombus forms within the left auricular appendage in cats with dilated left atrial chambers secondary to stasis of blood. Cats with left atrial size greater than 20 mm are thought to be predisposed to the development of arterial thromboembolism, but a recent study found that the atrial size in many cats with thromboembolic disease was as small as 14 mm. Pulsed-wave Doppler analysis of left auricular flow can provide evidence for the potential formation of spontaneous echo contrast or thrombus formation in man and in cats (67–69). Flow velocity lower than .25 m/sec is correlated with stasis of blood flow and a high possibility of thrombus formation (69). Low to nonexistent auricular flow velocities are a sign of significant left auricular dysfunction (67,69).
Figure 7.24 A thrombus may form within the left atrial chamber of cats with hypertrophic cardiomyopathy. The thrombus (arrow) may be attached to the wall and immobile or freely move within the chamber. RV = right ventricle, LV = left ventricle, LA = left atrium, AO = aorta, plane = right parasternal left ventricular outflow view.
Figure 7.25 This thrombus moved back and forth through the mitral valve in this cat with hypertrophic cardiomyopathy (arrow). LV = left ventricle, LA = left atrium, AO = aorta.
Figure 7.26 The left auricle is the most common site for thrombus formation. (A) This is a normal left auricular appendage. Plane = left cranial transverse view. (B) The left auricle in this cat has a soft tissue density in the tip of the auricle (large arrow) consistent with a thrombus, and there is spontaneous echo contrast (smoke, small arrows). (C) This dog has a free-floating thrombus within its large left atrial and auricular chamber. RA = right atrium, RV = right ventricle, AO = aorta, LA = left atrium, LAA = left auricular appendage.
Ischemia and Effusion
Myocardial ischemia may be seen on occasion in cats with HCM. Initially only depressed systolic thickening of either the septum or left ventricular free wall is seen (Figure 7.27). Chronic ischemia
may lead to infarction, and a regional area of hypokinesis with thin walls and potentially an aneurysmal dilatation may be seen. Fractional shortening may be reduced in these cats if the M-mode measurement incorporated this portion of the ventricle. This is typically seen as a sequela to severe long-standing disease (12).
Severe long-standing HCM disease may result in depressed function and areas of myocardial ischemia and infarction.
Figure 7.27 Depressed systolic thickening of the free wall is suggestive of myocardial ischemia in this heart with hypertrophic cardiomyopathy. RV = right ventricle, VS = ventricular septum, LV = left ventricle, LVW = left ventricular wall.
Pericardial effusion may be seen in cats with severe hypertrophic cardiomyopathy and clinical signs of heart failure (12). Pleural effusion and dyspnea are also often seen as a presenting compliant in cats with HCM (Figures 7.28, 7.29) (11,12).
Figure 7.28 Pericardial effusion may be seen in cats with congestive heart failure secondary to hypertrophic cardiomyopathy. Notice that the effusion is not seen behind the left atrium but only around the right ventricular wall. This helps differentiate pleural from pericardial effusion. This image also shows a very large left atrial chamber. PE = pericardial effusion, RV = right ventricle, AO = aorta, LA = left atrium, LAU = left auricle, plane = right parasternal transverse heart base.
Figure 7.29 Severe pericardial effusion and some pleural effusion are seen around this cat’s heart. Left ventricular hypertrophy appears severe, but this amount of fluid may restrict ventricular filling creating the appearance of more significant hypertrophy than would be present without the effusion. (A) Transverse two-dimensional image of the left ventricle showing the effusions. (B) M-mode of the same heart showing tamponade with total collapse of the ventricular chambers. PE = pericardial effusion, P = pericardial sac, RV = right ventricle, LV = left ventricle, PLE = pleural effusion.
Other Causes of Hypertrophy
True HCM is idiopathic, and the presence of other diseases that may lead to potentially reversible left ventricular hypertrophy should be ruled out. These include systemic hypertension, a common sequela of chronic renal failure seen so often in older cats, and hyperthyroidism (70–72). Hyperthyroidism