INTRODUCTION

Cardiac or systemic diseases may have electrocardiographic manifestations that do not fit into standard categories.

LOW VOLTAGE

Low voltage of the limb leads is present when the amplitude of the QRS complex in each of the three standard limb leads (I, II, and III) is <5 mm (waveform 1). Low voltage of all leads is diagnosed when the average voltage in the limb leads is <5 mm and the average voltage in the chest leads is <10 mm. This may be due to underlying myocardial disease (particularly amyloidosis), pericardial effusion, lung disease, severe hypothyroidism, obesity, or anasarca, in which the low voltage correlates with weight gain [1].

EARLY REPOLARIZATION

The term early repolarization (ER), also known as "J-waves" or "J-point elevation," has long been used to characterize a QRS-T variant on the electrocardiogram (ECG). Most literature defines ER as being present on the ECG when there is J-point elevation of ≥0.1 mV in two adjacent leads with either a slurred or notched morphology. Historically, ER has been considered a marker of good health because it is more prevalent in athletes, younger persons, and at slower heart rates. However, newer reports have suggested a small association between ER and an increased risk for arrhythmic death and idiopathic ventricular fibrillation. Early repolarization is discussed in greater detail separately. (See "Early repolarization".)

ELECTRICAL ALTERNANS

Electrical alternans is recognized by alternating amplitude of the QRS complexes in any or all leads (waveform 2). Every other QRS complex has reduced amplitude alternating with increased amplitude. Most often it is observed in the precordial leads where the QRS amplitude is greater.

The most frequent cause of electrical alternans is a pericardial effusion; it is thought that the alternating amplitude is the result of a pendulum motion of the heart as it "swings" from beat to beat within the fluid contained in the pericardial sac; there is a change in electrical axis as the heart swings. (See "Diagnosis and treatment of pericardial effusion", section on 'ECG findings'.) Frequently, there is also sinus tachycardia when there is electrical alternans from pericardial effusion. Electrical alternans may also be seen when there is severe cardiomegaly and left ventricular dysfunction or with aortic regurgitation.

                   

Literature review current through: Jun 2017. | This topic last updated: May 31, 2016.

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