CLINICAL FEATURES AND DIAGNOSIS Symptoms are nonspecific, and patients most commonly complain of dyspnea and profound exertional intolerance. Additional complaints may be present due to the underlying disease (e.g., uremia) or if the pericardial effusion has developed gradually (e.g., tuberculous pericarditis). Such symptoms may include weight loss, pedal edema, ascites, and so on.
Physical examination most commonly reveals tachycardia and low systolic arterial blood pressure with a narrow pulse pressure. Pulsus paradoxus may also be present. A paradoxical arterial pulse is said to be present when the cardiac rhythm is regular and there are apparent dropped beats in peripheral pulse during inspiration. There is usually a greater than 10-mmHg decrease in systolic blood pressure during inspiration in the supine position. A value greater than 25 mmHg usually separates true tamponade from lesser degrees of restricted cardiac filling. 24 Pulsus paradoxus occurs because there is an inspiratory decrease in LV filling secondary to the dominance of inspiratory right heart filling within the confined intrapericardial space. Pulsus paradoxus is not diagnostic of cardiac tamponade and may be noted in other cardiopulmonary processes, as listed in Ta.ble 51:6.. The neck veins are usually distended with an absent y descent. The apical impulse is indistinct or tapping in quality. Cardiac auscultation may reveal "distant" or soft heart sounds. Pulmonary rales are usually absent, and there may be right upper quadrant tenderness due to hepatic venous congestion.
The chest x-ray may or may not reveal an enlarged cardiac silhouette, and this finding is dependent on the amount of intrapericardial fluid accumulation. The pulmonary vasculature typically appears normal. An epicardial fat-pad line, or sign, may occasionally be seen within the cardiac silhouette.
The ECG usually shows low-voltage QRS complexes (less than 0.7 mV) and ST-segment elevation (due to the inflammation of the epicardium) with PR-segment depression, as in pericarditis. Electrical alternans (beat-to-beat variation in the amplitude of the P and R waves unrelated to the respiratory cycles) is a classic but uncommon finding (about 20 percent of cases). Electrical alternans is demonstrated in Fig, 51-2..
FIG. 51-2. This rhythm strip (lead II, top tracing) and plethysmograph (bottom tracing) were recorded in a patient who presented with dyspnea, hypotension, and clinical and echocardiographic evidence of cardiac tamponade. A paradoxical pulse was noted on palpation of the radial artery. The amplitude of the R waves varies from beat to beat (electrical alternans). Similar changes are seen in P-wave amplitude. These ECG changes are not related to the respiratory cycle.
The diagnosis should be suspected based on the clinical examination and chest x-ray findings. Echocardiographic assessment is the diagnostic test of choice. In addition to a large pericardial fluid volume, typical echocardiographic findings described in cardiac tamponade are listed in Table51:9,25
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