Staging cardiac disease is important for choosing the appropriate therapy. Preclinical cardiac disease is managed very differently from heart disease associated with heart failure. Furthermore, the presence of heart disease does not necessarily mean that clinical signs must be related to it. Differentiating primary cardiac disease from respiratory disease can be challenging in many clinical cases. Chronic airway disease and chronic valve disease are both common in older, small breed dogs, and may exist concurrently in the same animal. In such cases, it can be difficult to determine the underlying cause of clinical signs.

If the patient is asymptomatic, then heart failure is unlikely, provided the owner has been questioned thoroughly. When heart disease results in clinical signs, this is usually (but not always) a result of congestive heart failure (CHF). Respiratory distress and coughing are typical signs associated with left-sided CHF, and ascites is associated with right-heart failure. Syncope may be caused by arrhythmias or pulmonary hypertension in the absence of CHF. It is crucial to determine whether or not CHF is present.

Respiratory Distress

Important clues about the cause of respiratory distress can be obtained from the breathing pattern. Recognition of the breathing pattern gives much valuable information about the likely cause of respiratory distress.

Physical examination can give additional information that supports a diagnosis of heart disease (murmur, gallop, arrhythmia), but CHF is usually confirmed by combining multiple findings. Heart rate is usually modestly elevated in dogs (unless a tachyarrhythmia is present). This is not true in cats. Loss of sinus arrhythmia is common in dogs (if in sinus rhythm, this rhythm is usually very regular). Respiratory rate is increased, sometimes with crackles. Other signs of low cardiac output may also be present (weak pulses, pale mucous membranes, prolonged capillary refill time) but these are not always present with CHF and are sometimes present in the absence of CHF.

Thoracic radiography is considered the gold standard for diagnosing left-sided heart failure, and may be useful for indicating other types of pulmonary parenchymal disease. Examination under anaesthesia will be useful with upper airway obstruction, and bronchoscopy may be necessary with lower airway disease.

Cardiac biomarkers may play an increasing role in the future in helping to differentiate heart disease from heart failure. Plasma NT-proBNP concentrations are elevated in dogs and cats with heart disease, and elevated still further with CHF.

Signs associated with left-sided heart failure include:

 History of labored breathing (± coughing in dogs)

  Respiratory rate (>40 breaths/min)

 Lung sounds may be normal if only interstitial edema present

 Quiet inspiratory crackles if alveolar edema present (i.e., only with severe pulmonary edema)

 Heart rate may be moderately elevated with no slowing in dogs (although note that bradycardia may develop in some terminal cases and frequently in cats with severe pulmonary oedema)

 ± Concurrent signs of heart disease (murmur, arrhythmia, gallop sounds)

 Weight loss common with severe, advanced heart failure

Radiographic features of left heart failure:

 Left atrial enlargement nearly always present with pulmonary edema (exceptions include endocarditis or ruptured chordae tendineae)--see below

 Pulmonary vessels may be wider than normal

 Pulmonary edema may be evident as hazy increase in radiodensity in hilar area

 Air bronchograms may not be obvious even with severe alveolar edema

 Cats may have patchy infiltrates, with left atrial enlargement more obvious on ventrodorsal view than lateral view

Echocardiographic features of left heart failure:

 Left atrial enlargement may be more easily documented by echocardiography than by radiographs, but is not synonymous with CHF

 Transmitral and pulmonary venous flow patterns with Doppler tissue imaging may suggest increased atrial pressures, but are still not considered proof of CHF

Coughing

The type of coughing is less useful than the type of breathing. It is not always possible to determine if coughing is productive or not. Coughing is nearly always a sign of airway disease. If coughing is associated with heart disease, severe left atrial enlargement should be noted on radiographs. Note that coughing is very rarely associated with heart disease in cats.

Additional signs associated with airway disease:

 Coughing is usually the main clinical sign

 May have marked expiratory component in respiration with small airway disease

 Inspiratory crackles often loud when associated with airway disease/ pulmonary fibrosis

 Heart rate often normal, with sinus arrhythmia in dogs

 Bodyweight usually maintained, and frequently overweight

Ascites

Ascites caused by right heart failure is usually associated with jugular distension, caused by increased right atrial pressures. Note that cats may develop increased atrial pressures secondary to pleural effusions of non-cardiac origin.

Right heart failure:

 Ascites

 Pleural effusion

 Jugular distension

Summary

 Are there signs of heart disease?

 Murmur

 Arrhythmia

 Gallop sounds

 Cardiomegaly

 If so, what are the likely causes?

 Dogs

 Mitral regurgitation

 Dilated cardiomyopathy

 Pericardial effusions

 Cats

 Hypertrophic cardiomyopathy

 Functional murmurs (asymptomatic cats only)

 Restrictive cardiomyopathy

 Dilated cardiomyopathy

 Are there any signs suggestive of congestive heart failure?

 Tachypnea

 ± Inspiratory crackles

 With coughing dogs, are there signs of left atrial enlargement on radiographs?

 If not, the coughing is probably not due to cardiac disease

 With pleural effusions in cats (modified transudates or chylothorax), are there other signs of cardiac disease?

 ECG often abnormal with cardiac disease

 Cardiomegaly generally present on radiographs

 Echo diagnostic for cardiac disease

 Is NT-proBNP elevated?

 If within normal limits, heart disease is unlikely. If markedly elevated, consider CHF.