Congestive heart failure

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Normal heart (left) and congestive heart failure (right)

Congestive heart failure (CHF) is a relatively common heart disease of cats.

In many cases, cardiomyopathy is the underlying cause, but chronic systemic hypertension (such as is witnessed with Conn's syndrome), endocarditis, idiopathic aortic dilation and valvular disorders such as patent ductus arteriosus can also induce this disease[1].

CHF is defined as a state of cardiac function where preload exceeds the capacity of the heart to compensate through the normal haemodynamic mechanisms of increasing the strength and speed of contractions. Elevated preload leads to pulmonary hypertension, atrial enlargement and effusion of serum into the pleural cavity. In cats, ascites is a rare finding compared with pleural effusion, which appears to be common and often consists of a modified transudate or chylothorax due to obstruction of systemic venous and lymphatic return.

In cats, the symptoms of CHF do not always correlate with audible heart murmurs, and many cats, such as those with cardiomyopathy often have normal sounding hearts on auscultation[2].

Almost any animal with heart disease leading to chamber enlargement or increased wall thickness has a failing heart, but they are usually compensated and do not manifest symptoms; therefore, they are not in heart failure or CHF. This includes probably 95% of cats with heart disease[3].

Examination of cats with CHF often reveals a systolic murmur, gallop sounds or arrhythmias with tachypnoea, pulmonary crackles and jugular distension[4]. Often times, it is difficult to ausculate cardiogenic murmurs, and ultrasonographic studies are required to elucidate a diagnosis.

In chronic cases, presenting signs may be referable to acute aortic thromboembolism, where secondary thrombotic episodes at the iliac bifurcation results in signs of acute collapse and hemiparesis.

Diagnosis is usually suggested on radiography and confirmed on echocardiography, where left atrial enlargement is characteristic of this disease[5]. These findings are supported by thoracocentesis examination of pleural effusion. Cardiac troponins may be elevated, but are not diagnostic when taken alone[6].

Other causes of pleural effusion such as FIP, trauma, parasites such as heartworm disease, and lungworm including Aelurostrongylus abstrusus.

Treatment of congestive heart failure focuses primarily on reducing preload (through use of diuretics) and reduction of pulmonary hypertension (through use of hypotensive agents). Drainage of pleural effusion is best managed by closed-tube thoracostomy or intermittent thoracocentesis.

Commonly used diuretics in cases of feline congestive heart failure include furosemide, and antihypotensive agents atenolol.

Cats that have been stabilized with congestive heart failure are best given lower long-term doses of furosemide and an ACE-inhibitor such as Benazepril. There appears to be no clear advantage amongst the different types of ACE-inhibitors when used in cats with congestive heart failure.

In a number of rare cases, low-output heart failure has also been recorded in feline CHF. In these cats, additional therapy with dobutamine appears to be effective regardless of the underlying form of cardiomyopathy. Dose recommended is 1 - 2 μg/kg/minute over several hours.

References

  1. Cote, E et al (2004) Assessment of the prevalence of heart murmurs in overtly healthy cats. J Am Vet Med Assoc 225:384
  2. Glaus T et al (2010) Cardiogenic and non cardiogenic pulmonary edema: pathomechanisms and causes. Schweiz Arch Tierheilkd 152(7):311-317
  3. Merck Veterinary Manual
  4. Fuentes, VL (2009) Management of feline myocardial disease. In Bonagura, JD & Twedt, DC (Eds): Kirk's current veterinary therapy. XIV. Saunders Elsevier, Missouri, pp:809-815
  5. Benigni L et al (2009) Radiographic appearance of cardiogenic pulmonary oedema in 23 cats. J Small Anim Pract 50(1):9-14
  6. Connolly DJ et al (2009) Assessment of the diagnostic accuracy of circulating cardiac troponin I concentration to distinguish between cats with cardiac and non-cardiac causes of respiratory distress. J Vet Cardiol 11(2):71-78