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Is it really heart failure I'm treating? (Proceedings)

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Apr 01, 2008

Differentiating between congestive heart failure and respiratory disease as the cause of acute dyspnea in dogs and cats is one of the most difficult case scenarios facing veterinary clinicians. Clinical signs of the diseases affecting these systems often overlap with very minimal distinguishing characteristics; however, the diagnostic workups and therapy differ significantly. It is the goal of this presentation to review the approach to clinical cases with suspected cardiopulmonary disease and highlight relevant points that may help differentiate the two types of diseases.

History and Signalment:

Patients with cardiac and respiratory disease often have very similar histories. Episodes of coughing, dyspnea, tachypnea and/or exercise intolerance are frequently reported by owners. Also historically, bouts of cyanosis, collapse or syncopal episodes, lethargy, and a decreased appetite may be mentioned. These clinical signs, therefore, do not help distinguish between cardiac and pulmonary etiologies. However, the combination of clinical signs and the patient's signalment may help attribute the cause to one system versus the other. For example, a cat that presents with coughing is more likely to have a disease of the respiratory system rather than the cardiovascular system. Cardiovascular related dyspnea in cats often manifests as reclusive behavior along with signs of dyspnea such as assumption of an orthopnic position and/or a significant abdominal component to breathing (a restrictive breathing pattern). Certain canine breed predispositions may help distinguish between the respiratory and cardiovascular systems. For example, older Labrador retrievers with dyspnea should be assessed for laryngeal paralysis, toy breeds may often have tracheal collapse, bracheocephalic disease is seen in bulldogs, and dilated cardiomyopathy in Dobermans.

There may be other helpful hints when comparing the history of a patient with cardiovascular versus respiratory disease. In cardiac disease, a loss of body condition (cardiac cachexia) is often noted, compared to that of many respiratory disease patients where body condition is generally maintained (and often increased). Generally, with heart disease (failure), the onset of clinical signs may appear more acute compared with that of respiratory disease. For example some owners may complain of a sudden onset in abdominal distension in their pets, which might suggest ascites associated with right sided congestive heart failure.

Physical examination:

Nothing can replace a thorough and detailed general examination when dealing with a patient with suspected cardiopulmonary disease. However, physical examination of these patients should be carried out in a staged fashion. Stressing these patients by overzealous handling may be detrimental to their health status and lead to a rapid decline. Very subtle findings may help guide the next diagnostics that may save valuable time, stress on the patient and more importantly, especially in veterinary medicine, the owner's money.

Initially, observing the patient for respiratory rate, the apparent effort being expended, the phase of respiration during which the effort occurs, as well as for paradoxical movements of the abdomen is recommended prior to proceeding with the physical exam. In many cardiopulmonary cases the need for oxygen supplementation may be noted as flaring of the nostrils, open mouth breathing or orthopnea; indicating dyspnea. Noting patterns associated with respiratory effort may help localize the level of disease. In general, patients with upper airway disease of present with inspiratory dyspnea and patients with small airway disease show effort associated with expiratory phase of respiration. A restrictive breathing pattern is often seen with disease involving the pleural space. Thoracic auscultation is obviously very important in hearing abnormal lung sounds such as crackles and wheezes, as well as for cardiac murmurs and arrhythmias. However, the mere presence of abnormal lung sounds or heart murmurs will not necessarily help you distinguish between primary heart and primary lung disease.

Signs that might clue you into heart failure when most of the above clinical signs are present include increased heart rates with loss of heart rate variability related to breathing (especially in dogs). This is secondary to increased sympathetic output and decreased vagal output due the real or perceived decrease in arterial blood pressure by the baroreceptors. Weak and rapid femoral pulses or the presence of abnormalities such as pulsus paradoxus or pulsus alternans may also suggest primary cardiac disorders. Ascites with jugular venous distension suggest right-sided heart failure or pericardial disease.

Diagnostic Evaluation:

Complete systemic evaluation of patients suspected of cardiopulmonary disease is required by assessing minimally a complete blood count, biochemical profile, and urinalysis. However, thoracic radiographs are the most important diagnostic technique in evaluating the dyspneic patient - if they can be obtained without compromising your patient. High quality inspiratory films are very helpful in discriminating cardiac versus respiratory causes of dyspnea. Comparing inspiratory and expiratory films may also be helpful. Noting the pattern and distribution of any airway and parenchymal abnormalities, evaluating the heart size, and assessing pulmonary vasculature are essential when evaluating thoracic radiographs. The findings of distended pulmonary veins associated with parenchymal densities should indicate further evaluation of the cardiovascular system, or at least diuretic trial therapy.

Once thorough evaluation of the laboratory database and thoracic radiographs has been completed the clinician should have a good idea of the underlying disorder (respiratory, cardiac or both). Additional appropriate tests may then be performed, for example electrocardiogram and echocardiography with cardiac disorders. With respiratory disorders, tests such as an arterial blood gas analysis, laryngeal examination, a transtracheal wash, bronchoscopy or fluoroscopy may be performed.