myocardial disease

• Myocardial disease can be split into two groups…

  • Primary myocardial disease
  • Dilated cardiomyopathy (DCM)
  • Arrhythmogenic right ventricular cardiomyopathy (ARVC)
  • Hypertrophic cardiomyopathy (common in cats)
  • Secondary myocardial disease
  • Infective myocarditis (rarer than endocarditis)
  • Deficiency diseases (wane in occurrence)
  • Toxic causes (usually related to chemotherapy drugs such as doxorubicin)
  • Ischaemic heart disease (a clot)
  • Tachycardia-induced cardiomyopathy (most commonly seen with SVT)
• DCM is the most common muscle disease in the dog but is rare in the cat. It is characterised by impaired myocardial contractility with dilation of the left ventricle (+/- the right ventricle). Tachyarrhythmias are common and can be supraventricular and/or ventricular (sometimes the rhythm abnormality is identified first).

  • DCM is an end stage of many cardiac diseases (e.g. atrial fibrillation), primary DCM is a diagnosis of exclusion so be sure nothing else has caused it.
• The pathophysiology of DCM includes eccentric hypertrophy of the left ventricle, systolic failure (‘forward failure’), diastolic failure (‘backward failure’ –congestion) as well as left atrium dilation and increased left atrial pressure

  • Right side can also be affected

  There are breed predispositions (genetic basis) and the commonly affected breeds include the Doberman, Newfoundland, Irish wolfhounds, St Bernards, Labradors, Great Dane, Cocker spaniels, Boxers (ARVC), GSD (breeders have tried to breed this out) BUT different breeds have very different prognosis with the same disease
• DCM usually affects middle aged dogs and they are often over 12kg. Males tend to be more severely affected but there is no gender predilection.
• in DCM, the loss of systolic function results in low cardiac output (loss of contraction) which then results in forward failure. The sympathetic, hormonal and renal compensatory mechanisms are activated to maintain cardiac output by increasing HR, peripheral vasoconstriction and volume expansion. As the ventricles fail to empty, there is an increase in ventricular diastolic pressure. This results in compromised coronary perfusion, worsening myocardial function further and resulting in arrhythmias.
• DCM dogs can present in two ways…

  • Occult phase (Non-symptomatic)
  • This can be prolonged and it is the screening programmes of specific breeds that identify this phase
  • 24 hour Holter monitor (over 50 ventricular premature complexes in 24 hours is diagnostic)
  • Echocardiography
  • Symptomatic phase
  • Usually present in congestive heart failure
  • Clinical signs: weight loss, sudden death, soft murmur, atrial fibrillation, lethargy, exercise intolerance, dyspnoea (signs of left sided failure)
• • Why use a Holter monitor?

  1. To monitor heart rate control
  2. Unexplained syncope or collapse
  3. Arrhythmias
  4. Monitoring therapy
• eccentric = outwardly bigger but not thicker
• Soft murmur - blood flow is slightly sloshing which is characteristic of DCM. In comparison if there was a normal murmur then it suggests valvular disease as there is more turbulence in the blood flow
• The clinical exam with DCM is variable depending on the degree of myocardial dysfunction but signs you may pick up include…

  • Tachycardia +/-arrhythmias – atrial fibrillation, ventricular premature complexes, ventricular tachycardia
  • Variable pulses +/-pulse deficits IF dysrhythmic
  • Signs of left congestive heart failure +/- right congestive heart failure
  • Gallop sounds –IF in sinus rhythm
  • Soft MR / TR murmurs
  • If forward failure is present (often bad news) they will have pale mucous membranes, a sluggish CRT and cool extremities.
• diagnostic options for DCM are...

  • Echocardiography for a definitive diagnosis
  • Echo findings are often a large, round, poorly contractile left ventricle, poor systolic function (poor contractility), a dilated, round left atrium +/- mitral regurgitation (small/moderate due to dilation) +/-right sided changes
  • Clinical pathology to identify complications/co-existing diseases
  • Radiography to confirms the CHF
  • ECG IF dysrhythmic
  • The findings are very variable but many DCM dogs have ventricular arrhythmias
  • Blood pressure especially once on treatment
  • 24hr Holter monitor for more for screening
• arrhythmogenic right ventricular cardiomyopathy (ARVC) is a rhythm disturbance caused by the cardiac muscle in the right ventricle that usually affects Boxers

  • Myofiber atrophy, fibrosis and fatty infiltration
• There are 3 stages of ARVC

  1. Asymptomatic with ventricular arrhythmias
  2. Symptomatic –normal heart size and left ventricle function but dogs are syncopal/weak from ventricular arrhythmias
  3. The "fainting" boxer which Owners might be unsure if it’s a seizure or a syncopal episode (heart beats stop and then start again on the Holter monitor)
  4. CHF –poor myocardial function, CHF and ventricular arrhythmias
• The mean age is 8 years for ARVC but it can appear at any age. Clinical signs include…

  • Ventricular arrhythmias
  • Supra-ventricular arrhythmias
  • More than 500 ventricular premature complexes in 24hrs
  • But spontaneous variation of up to 80%
  • Syncope
  • Sudden death
• Treatment of AVRC is the same as any heart failure as well as anti-arrhythmic medication (soltalol).
• Myocardial disease is the most common in cats and there are multiple types…

  • HCM (hypertrophic cardiomyopathy) –most common via literature
  • RCM (restrictive cardiomyopathy)
  • DCM (dilated cardiomyopathy)
  • ARVC (arrhythmogenic right ventricular cardiomyopathy)
  • FUCM (Feline unclassified cardiomyopathy)
• Concentric = gets bigger on the inside decreasing the lumen size
• In RCM the walls it becomes fibrotic and stops being function (whereas in HCM it becomes thick)
• HCM is the inappropriate myocardial hypertrophy of a non-dilated left ventricle, occurring in the absence of an identifiable stimulus. With these cases, you need to do a diagnosis of exclusion to ensure there is no other cause. Other things that can result in concentric hypertrophy such as…

  • Aortic stenosis –ventricles struggle to inject blood
  • Systemic hypertension (Primary, Diabetes Mellitus, Cushing’s disease)
  • Metabolic disorders capable of inducing hypertrophy (Hyperthyroidism and acromegaly)
  • Renal disease and associated hypertension.
• there are two clinical forms of HCM

  • Obstructive (42% of cats)
  • It also affects a great majority of dogs. In this disease, the ventricular walls become so thick affecting the systolic anterior motion of the mitral valve leading to a dynamic left ventricular outflow tract obstruction. This causes turbulent flow in the left ventricular outflow tract (aorta) and the concurrent eccentric jet of mitral regurgitation along the posterior wall of the left atrium
  • Non-obstructive
• the pathology of HCM goes as follows, the excessive left ventricular wall / septum hypertrophies without dilation. The extent and distribution of left ventricular hypertrophy is variable and the left atrial enlargement varies depending on the severity of diastolic dysfunction.
• RCM (restrictive cardiomyopathy) usually presents in the same way as HCM but they have an unknown aetiology (probably multifactorial as there is a range of pathological findings). This could be the end stage of other disease processes. There are 2 Forms

  • Endomyocardial
  • Myocardial
• In RCM, extensive endocardial, subendocardial or myocardial fibrosis occurs and then there is atrial enlargement (usually very large!) due to poor ventricular filling and regurgitation. Mild LV hypertrophy can also happen leading to diastolic failure (poor filling) (backwards failure)
• taurine deficiency can cause what heart disease in cats?

  DCM
• DCM is often end stage of another myocardial abnormality – toxic, drug induced, CM or infection. This has similar features similar to dogs such as poor contractility, has dilation of all 4 chambers especially LV and LA, arrhythmias are common and pleural effusions (common). It presents in older cats and they frequently present in heart failure (some present in output failure)

  • Bradyarrhythmia's can also occur
  • Treatment as HCM when in CHF plus pimobendan (not licensed, but need to improve contractility)
• The presentation of HCM/RCM cases are very variable but they often present in heart failure (good at hiding disease so owners may say this has come out of nowhere). Range from asymptomatic cat with a heart murmur to recumbent, cold dyspnoeic cat via congestive cardiac failure.

  • Often increased respiratory rate at rest
  • If stressed then can lead to severe dyspnoea
  • Frequently present after fluid tx/GA/steroid use!!
  • Acute onset lameness / paralysis - arterial thromboembolism
  • Sudden death
• If you cant compress a cats chest then its a key sign that there is HCM as it indicates there is something large preventing you from performing this
• an echocardiogram is very important in making the definitive diagnosis of any cardiomyopathy
• on ultrasound with HCM / RCM you often see…

  • Left ventricular hypertrophy often asymmetrical (Left ventricular hypertrophy greater than 6mm (5.5mm, 5mm) in diastole)
  • Basal septum frequently affected
  • Hypertrophied, hyperechoic, irregular papillary muscles
  • 2DE measurements as well as MM
  • Left ventricle lumen is usually small
  • Left atrial enlargement is variable -mild to severe
  • Can have obstructive component
  • Systolic anterior motion of the mitral valve (SAM)
• Pimobendan is not first line treatment in HCM as pimobendan increases contractility and these hearts are already quite contracted. Instead use vasodilators and diuretics.
• what shaped heart is classic for HCM on radiography?

  valentine