Plus-Hex CLINICAL
Final outcome
At recheck the patient was bright , alert and responsive , and had a resting respiratory rate ( at home ) of 20 – 24 breaths / min . He was eating well and had been very active . Systolic BP was maintained at 132 mmHg . Blood sampling was repeated to assess renal parameters , which showed a reduction in azotaemia and persistent mild hypokalaemia . These parameters were expected to improve further , in line with reduced diuretic dosage . Furosemide was reduced to 2 mg / kg ( 12 mg ) PO SID ( morning dose ) and 1 mg / kg ( 6 mg ) PO SID ( evening dose ).
Pathophysiology
Cardiomyopathies are a disorder of the heart muscle , whereby the myocardium is structurally and functionally abnormal with no underlying cause ( e . g . hyperthyroidism or hypertension ). Feline cardiomyopathies can be classified depending on phenotypic features ( Table 1 , overleaf ) [ 9 , 10 ] .
Primary HCM is the most commonly diagnosed form of feline heart disease [ 3 ] . It is characterised by concentric hypertrophy of the left ventricular free wall and / or interventricular septum without an obvious cause . Left ventricular outflow tract obstruction is a common finding in many cats with HCM , caused by either obstruction due to focal hypertrophy of the interventricular septum or systolic anterior motion of the mitral valve .
Decreased ventricular chamber volume and ventricular myocardial stiffening associated with ventricular wall hypertrophy lead to diastolic dysfunction ( impaired relaxation ). This causes an increase in ventricular pressure in diastole when the myocardium relaxes and refills , eventually causing left atrial pressure to increase , resulting in atrial enlargement and increased pulmonary venous pressure .
Preload is reduced due to the inability of the ventricle to fill effectively and , therefore , stroke volume is also decreased . Cardiac output is jeopardised and the sympathetic nervous system is activated , increasing the heart rate and causing peripheral vasoconstriction in order to maintain cardiac output and BP .
Disease progression and prognosis
Many cats can remain asymptomatic and the progression of HCM is variable . Commonly , the only clinical finding is a systolic murmur caused by turbulent blood flow due to systolic anterior motion of the mitral valve , where the mitral valve is pulled back into the outflow tract , resulting in a dynamic left ventricular outflow tract obstruction .
A gallop rhythm may also be heard , which is an extra heart sound caused by the ejection of atrial blood into a non-compliant ventricle [ 11 ] . A helpful example of a gallop rhythm can be heard at : https :// www . clinicansbrief . com / cardiac-library / heart-sound / feline-gallop-sound [ 12 ] .
As with other feline cardiomyopathies , HCM can be staged from A to D , depending on clinical findings ( Table 2 , overleaf ). Many cats with mild to moderate HCM will never progress into heart failure [ 13 ] . Negative prognostic indicators include :
• Gallop sounds or arrhythmias
• Moderate to severe left atrial enlargement ( increased risk of thrombus formation )
• Extreme left ventricular hypertrophy
• Decreased left ventricular systolic function
• Spontaneous echo contrast ( slow-moving blood in the atria , seen as ‘ smoke ’) or intracardiac thrombus
• Regional wall thinning ( myocardial infarction ).
Several other factors may also trigger the onset of CHF in patients with more advanced disease , including anaesthesia , IV fluid administration , glucocorticosteroid use and stress .
Aetiology
The underlying cause of HCM is unknown , but genetic mutations have been identified in Maine coons and ragdolls , and other breeds seem to have increased risk . The average age of cats at diagnosis of HCM is 6.5 years , but it can occur at any age . It is seen more commonly in male cats [ 14 ] .
Conclusions
Feline cardiomyopathies are a varied group of myocardial disorders . The effect of the disease on the patient can range from minimal to severe , often with few to no obvious signs unless heart failure or aortic thromboembolic events occur .
By being aware of patients that are at higher risk , VNs can deliver appropriate , tailored care to these fragile patients to improve patient outcomes .
VNs can also play a key role in improved home care for these patients by providing education and support to owners , resulting in improved patient wellbeing and quality of life .
Volume 38 ( 4 ) • August 2023
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