Electrocardiography
Figure 1. A lateral thoracic radiograph of a cat with CHF. Note the increased cardiac sternal contact and perihilar and caudal
edema.
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Consider performing an electrocardiographic examination in all patients with clinical signs of CHF. Most standard electrocardiographic
tracings are performed with animals in right lateral recumbency. However, if the patient is in severe respiratory distress
and unstable, the electrocardiographic tracing can be performed with the animal in sternal recumbency or standing, although
the results will need to be carefully interpreted, as standard measurements may not hold true.
Figure 2. A lateral thoracic radiograph of a dog with chronic progressive CHF. Note the loss of the caudal thoracic cardiac
waist, also known as the backpack sign.
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A lead II electrocardiogram (ECG) may reveal changes consistent with cardiomegaly or dysrhythmia, but often the ECG may simply
display a sinus tachycardia. A six-lead ECG may reveal axis deviation in cases of right-sided cardiomegaly.5 A left axis shift may be present, particularly in cats. Also, the presence of P mitrale or P pulmonale can help differentiate
between the heart vs. the lung as the cause of dyspnea. Electrical alternans, an ECG abnormality in which the complexes alternate
from large to small as the heart floats within the fluid in the pericardial sac, is most commonly associated with pericardial
effusion. However, this abnormality may also be seen, though rarely, in cases of severe pleural effusion. Supraventricular
and ventricular tachyarrhythmia and atrial fibrillation are common rhythm disturbances in cases of dilated cardiomyopathy.
Depression of the ST segment may signal myocardial ischemia.
Radiography
Figure 3. A dorsoventral thoracic radiograph of a cat with hypertrophic cardiomyopathy. Note the classic valentine shape of
the heart.
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Thoracic radiographs are one of the most important diagnostic tools in identifying CHF.6 Obtain lateral and dorsoventral radiographs once the patient is clinically stable. Increased perihilar interstitial to alveolar
infiltrates are characteristic of pulmonary edema in dogs. Cats may demonstrate caudoventral alveolar infiltrates on thoracic
radiographs (Figure 1). Left atrial enlargement may be observed as a loss of caudal cardiac waist, sometimes known as the backpack sign, on lateral thoracic projections (Figure 2). Right- or left-sided cardiomegaly may also be present in cases of valvular insufficiency. In cats, increased sternal contact
and a classic valentine-shaped heart may be observed in cases of hypertrophic cardiomyopathy (Figure 3).
Although not necessarily useful in the initial management of a patient with CHF, the vertebral heart size can be calculated
to determine the degree of cardiomegaly in dogs and cats7:
1. Measure the long axis of the heart from the apex to the carina on the lateral view, and mark the distance on a sheet of
paper. This is the long-axis heart dimension.
2. Measure the length of the long axis heart dimension in terms of vertebral bodies by placing the line below the vertebral
column on the radiograph, and count vertebral bodies caudally, starting from the cranial edge of the fourth thoracic vertebra
(T4).
3. Measure the short axis of the heart at the caudal vena cava, perpendicular to the long axis of the heart. This is the
short-axis heart dimension.
4. Measure the length of the short axis heart dimension in terms of vertebral bodies as in Step 2.
5. Add the two vertebral numbers together to yield the vertebral heart size; a vertebral heart size greater than 10.5 is
consistent with cardiomegaly.
Figure 4. A lateral thoracic radiograph of a dog with dilated cardiomyopathy and severe pulmonary edema.
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In patients with acute pericardial effusion, the cardiac silhouette may appear normal in size or may appear enlarged and globoid,
depending on the duration and volume of effusion within the pericardial sac. It may be difficult to distinguish between pericardial
effusion and dilated cardiomyopathy on thoracic radiographs. Evaluating the pulmonary vasculature is helpful in differentiating
pericardial effusion from dilated cardiomyopathy. Pericardial effusion, due to poor cardiac output and right heart incompetence,
may be associated with hypoperfused lungs and small pulmonary vessels, whereas pulmonary venous congestion is usually noted
in association with CHF due to dilated cardiomyopathy (Figure 4). Electrocardiography and echocardiography can be useful in distinguishing between the two entities.
Echocardiography
In emergent patients with CHF, an emergency echocardiogram is often not warranted, particularly if there is radiographic evidence
of left atrial enlargement, pulmonary venous distention, and perihilar edema. But echocardiography can help you distinguish
between pericardial effusion and dilated cardiomyopathy, if radiographic changes are equivocal.8 M-mode, or motion mode, echocardiography is useful in determining left ventricular chamber size dimensions during systole
and diastole, from which fractional shortening and ejection fraction can be calculated. The calculated fractional shortening
is an approximation of myocardial function in patients with CHF.
Blood pressure measurement
Physical examination findings are largely subjective and by no means should be used to gauge therapy in patients with CHF.
Knowing a patient's blood pressure is necessary to provide therapeutic intervention to improve preload, decrease afterload,
and improve cardiac contractility. Knowing the blood pressure is also important to avoid deleterious drops in blood pressure
because of certain medications used in treating CHF.
Arterial blood pressure can be measured directly or indirectly.9 The gold standard of arterial blood pressure measurement is through cannulation of an artery with a catheter connected to
a pressure transducer. It is contraindicated to restrain unstable CHF patients in order to place the arterial catheter. In
these critical patients, use indirect methods such as Doppler or oscillometric techniques to monitor blood pressure.
When using the Doppler technique, place the Doppler probe on the radial, dorsal pedal, or coccygeal artery. Place a cuff whose
width is about 40% of the circumference of the peripheral extremity proximal to the Doppler probe, and use a sphygmomanometer
to evaluate systolic blood pressure. Because of poor peripheral perfusion and peripheral vasoconstriction, using the Doppler
probe may be difficult, particularly in patients with severe respiratory distress. Alternatively, you can place a cuff attached
to an oscillometric monitor on the forelimb just above the carpus, on the hindlimb just proximal to the hock, or around the
tail to measure systolic, diastolic, and mean arterial blood pressures.
Mean arterial blood pressure (MAP) should remain above 60 mm Hg at all times, with a target goal of 80 mm Hg, whenever possible.
MAP is a function of cardiac output and systemic vascular resistance. Cardiac output is influenced by heart rate, preload,
afterload, and contractility. Depending on the type of heart failure present, cardiac output can be adversely affected for
many reasons, leading to hypotension, poor tissue perfusion, and impaired oxygen delivery. Left ventricular preload can be
decreased because of pericardial effusion, right ventricular failure, or pulmonary hypertension. Afterload can be increased
because of peripheral vasoconstriction. Dilated cardiomyopathy or chronic myocardial ischemia can cause impaired contractility.
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