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Restrictive Cardiomyopathy - Feline Cardiomyopathies (view source)
Revision as of 17:57, 17 October 2013
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==Overview==
==Overview==
Restrictive cardiomyopathy (RCM) is a series of acquired pathologies of the feline myocardium. The common element is marked diastolic dysfunction without major alteration of systolic function. In RCM, the compliance and distensibility of the ventricular walls is reduced (ventricles are stiff), such that filling of the ventricles in diastole is compromised. This ultimately reduces the amount of blood that the left ventricle (LV) can accept. During the rapid filling phase of diastole, the pressure within the LV rises abruptly, preventing the entry of additional blood from atrial contraction in late diastole. This consequently increases left atrial pressure and the diameter of the left atrium or both atria.
This is the second most common type of feline cardiomyopathy, representing ~20% of cases. Restrictive cardiomyopathy (RCM) is a series of acquired pathologies of the feline myocardium. The common element is marked '''diastolic dysfunction''' without major alteration of systolic function. In RCM, the compliance and distensibility of the ventricular walls is reduced (ventricles are stiff), such that filling of the ventricles in diastole is compromised. This ultimately reduces the amount of blood that the left ventricle (LV) can accept. During the rapid filling phase of diastole, the pressure within the LV rises abruptly, preventing the entry of additional blood from atrial contraction in late diastole. This consequently increases left atrial pressure and the diameter of the left atrium or both atria.
Grossly, RCM is characterised by a normal or near-normal appearance of the ventricles with dilation of the left atrium or both atria. The echocardiographic appearance of the cardiac chambers 2D images of cats with early RCM may be normal; however severe diastolic dysfunction may be evident from M-mode and Doppler imaging.
Grossly, RCM is characterised by a normal or near-normal appearance of the ventricles with dilation of the left atrium or both atria. The echocardiographic appearance of the cardiac chambers 2D images of cats with early RCM may be normal; however severe diastolic dysfunction may be evident from M-mode and Doppler imaging. Two forms of RCM exist, these are the '''endomyocardial form (eRCM)''' and the '''myocardial form (mRCM)'''.
==Aetiology==
==Aetiology==
==Clinical Signs==
==Clinical Signs==
The clinical presentation of cats with RCM, as with other cardiomyopathies, is extremely variable. There may be a long preclinical phase during which the cat remains asymptomatic. Early signs of cardiac dysfunction, such as exercise intolerance, often goes undetected in cats due to their sedentery nature. Cats with RCM are rarely identified in the asymptomatic phase. Cats with RCM frequently develop congestive heart failure (CHF), arterial thromboembolism (ATE) and are predisposed to arrhythmias.
The clinical presentation of cats with RCM, as with other cardiomyopathies, is extremely variable. There may be a long preclinical phase during which the cat remains asymptomatic. Early signs of cardiac dysfunction, such as exercise intolerance, often goes undetected in cats due to their sedentery nature. Cats with RCM are rarely identified in the asymptomatic phase. Cats with RCM frequently develop congestive heart failure (CHF), arterial thromboembolism (ATE) and are predisposed to arrhythmias.
===Signalment===
Most cats are middle-aged to older, but RCM has been documented in cats aged 6 months to 19 years. There may be a breed predisposition towards the endomyocardial form (eRCM) in Oriental cats, particularly Siamese, however further studies are required to confirm this.
===Physical Examination===
===Physical Examination===
* May be completely normal
* May be completely normal
* Signs of congestive heart failure
* Signs of congestive heart failure
* Arterial thromboembolism (ATE)
* Arterial thromboembolism (ATE)
====Left-sided Congestive Heart Failure====
====Left-sided Congestive Heart Failure====
*Dyspnoea, tachypnoea, crackles (pulmonary oedema)
*Dyspnoea, tachypnoea, crackles (pulmonary oedema)
*Dyspnoea, restrictive pattern (fast,shallow breathing), muffled heart and ventral lung sounds (pleural effusion)
*Dyspnoea, restrictive pattern (rapid,shallow breathing), muffled heart and ventral lung sounds (pleural effusion)
====Right-sided Congestive Heart Failure====
====Right-sided Congestive Heart Failure====
* Jugular pulse
* Jugular pulse
* Hepatojugular reflux
* Hepatojugular reflux
* Occasionally ascites
* Occasionally ascites
====Arterial Thromboembolism====
====Arterial Thromboembolism====
The enlarged left atrium, stasis of blood within the left atrium, and reduced atrial function predispose to thrombus formation, and emboli may result. Typically these cases present with paresis or paralysis of one or both rear limbs due to occlusion at the aorta-iliac trifurcation. In some cases, emboli can involve other areas and can cause complex neurological manifestations, forelimb paralysis or acute renal ischemia.
The enlarged left atrium, stasis of blood within the left atrium, and reduced atrial function predispose to thrombus formation, and emboli may result. Typically these cases present with paresis or paralysis of one or both rear limbs due to occlusion at the aorta-iliac trifurcation. In some cases, emboli can involve other areas and can cause complex neurological manifestations, forelimb paralysis or acute renal ischemia.
==Diagnosis==
==Diagnosis==
===Radiography===
===Radiography===
Radiographs are useful for the diagnosis of congestive heart failure, however they are not able to distinguish the underlying cardiomyopathy. Radiographs may reveal left atrial dilation. On the dorso-ventral projection, a classic 'Valentine heart' shape may be evident due to the marked left atrial/biatrial dilation. Pulmonary venous conjestion, interstitial/alveolar pattern or the presence of a pleural effusion may be identified. These findings are not specific for RCM.
Radiographs are useful for the diagnosis of congestive heart failure, however they are not able to distinguish the underlying cardiomyopathy. Radiographs may reveal left atrial dilation. On the dorso-ventral projection, a classic 'Valentine heart' shape may be evident due to the marked left atrial/biatrial dilation. Pulmonary venous conjestion, interstitial/alveolar pattern or the presence of a pleural effusion may be identified in cases of left-sided congestive heart failure. Dilation of the caudal vena cava may be observed if right-sided congestive heart failure is present. These findings are not specific for RCM.
===Echocardiography===
===Echocardiography===
The E/A ratio is an index used to estimate diastolic function, an E/A >2 confirms a restrictive filling pattern and diastolic dysfunction.
The E/A ratio is an index used to estimate diastolic function, an E/A >2 confirms a restrictive filling pattern and diastolic dysfunction.
=====Pulmonary Venous Inflow=====
=====Pulmonary Venous Flow=====
This is also useful to evaluate diastolic function; particularly when there is summation of the mitral E and A waves.
* During atrial systole (after the P wave of the ECG), blood flows retrograde from the left atrium to the plmonary vein. This produces the '''atrial reversal (Ar) wave'''.
* This is followed by the '''S wave''', which indicates atrial blood flow during ventricular systole (between the QRS complex and the T wave). If the heart rate is slow enough, two waves may be observed: an '''early S wave (S1)''', which represents atrial relaxation, and the main S wave '''(late S wave or S2)'''.
* During ventricular diastole, when the mitral valve is open, the left atrium allows pulmonary venous flow to reach the left ventricle, producing the '''D wave'''.
Evidence of restrictive filling pattern includes:
* Low S wave velocity
* High D wave velocity with rapid deceleration
* Ar wave velocity may be increased with adequate left atrial function, or reduced with severe atrial dysfunction.
* If the Ar wave duration exceeds the mitral A wave duration, this is evidence of increased left sided filling pressure.
====Tissue Doppler Imaging (TDI)====
This is a relatively recent technique in cats which is used to evaluate the speed of longitudinal movement of the myocardial walls during the different phases of the cardiac cycle. In normal cats, three waves can be identified:
* Positive '''systolic wave (Sm)'''
* Negative '''early diastolic wave (Em)'''
* Negative '''late diastolic wave (Am)'''
In normal cats, the Em velocity is higher than the Am velocity. In cats with diastolic dysfunction and impaired ventricular relaxation (as in the case of RCM), The Em velocity may be markedly reduced. Note that impaired ventricular relaxation is also identified as a normal aging change in cats; therefore cautious interpretation is required with elderly cats.
==Treatment==
==Treatment==
Treatment should aim to control clinical signs of congestive heart failure (CHF) and aim to prevent arterial thromboembolism (ATE).
==Prognosis==
==Prognosis==
Cats with RCM usually present with advanced disease, the long term prognosis is therefore guarded. One study of 22 cats with RCM found a median survival time of 132 days.
==References==
*Ferasin L. Feline myocardial disease. 1: Classification, pathophysiology and clinical presentation. J Feline Med Surg 2009;11:3-13.
*Fox PR. Endomyocardial fibrosis and restrictive cardiomyopathy: Pathologic and clinical features. J Vet Cardiol 2004;6:25-31.
[[Category:Cardiology Section]]