A Visual Guide to ECG Interpretation



ECG 9.4B A 48-year-old woman complains of dyspnea on exertion.

Electrical Alternans

The voltage in the precordial leads is low (<10 mm). As the heart swings to and fro within the pericardial fluid, its electrical axis changes. This is inscribed on the ECG as alternating levels of QRS amplitude. The transthoracic echocardiogram of this patient is shown to the right. Almost 3 cm of pericardial fluid was measured anterior to the right ventricle. This image demonstrates scalloping of the right ventricle (indentation of the right ventricular wall) in diastole as the hydrostatic pressure of the pericardial fluid exceeds the end-diastolic pressure of the right ventricle. This patient had 610 mL of fluid drained from the pericardial space (Fig. 9.5).

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FIGURE 9.5 Image from this patient’s echocardiogram.

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