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 dogs.

In many cases, heartworm disease and cardiomyopathy are the underlying cause, but chronic systemic hypertension (such as is witnessed with endocarditis, idiopathic aortic dilation and valvular disorders such as mitral valve endocardiosis) can also induce this disease.

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. Pulmonary edema is commonly observed and often consists of a modified transudate or chylothorax due to obstruction of systemic venous and lymphatic return.

The symptoms of CHF do not necessarily correlate with audible heart murmurs, and many dogs, such as those with cardiomyopathy often have normal sounding hearts on auscultation[1].

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.

Examination of dogs with CHF often reveals a systolic murmur, gallop sounds or arrhythmias with tachypnoea, pulmonary crackles and jugular distension. Often times, it is difficult to ausculate cardiogenic murmurs, and ultrasonographic studies are required to elucidate a diagnosis. ECGs may reveal bundle branch block.

In chronic cases, presenting signs may be referable to acute thromboembolism.

Diagnosis is usually suggested on radiography and confirmed on echocardiography, where left atrial enlargement is characteristic of this disease. These findings are supported by thoracocentesis examination of pleural effusion. Cardiac troponins may be elevated, but are not diagnostic when taken alone[2].

Other causes of pleural effusion such as trauma, parasites such as heartworm disease and 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) with use of drugs such as diltiazem and aminophylline.

Drainage of pleural effusion is best managed by closed-tube thoracostomy or intermittent thoracocentesis.

Commonly used diuretics in cases of canine congestive heart failure include furosemide and pimobendan.

References

  1. Glaus T et al (2010) Cardiogenic and non cardiogenic pulmonary edema: pathomechanisms and causes. Schweiz Arch Tierheilkd 152(7):311-317
  2. 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