A Visual Guide to ECG Interpretation

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A VISUAL GUIDE TO ECG INTERPRETATION

Left Ventricular Hypertrophy (Fig. 9.1) Left ventricular hypertrophy (LVH) is independently associated with increased morbidity in patients with hypertension. 1 The diagnosis of LVH requires advanced imaging. Increased Voltage The most commonly used diagnostic criteria for LVH are based on measurements of QRS voltages. In LVH, leftward ventricular forces largely outweigh rightward forces and become unopposed briefly after right ventricular activation is completed. The resultant QRS complexes are exaggerated forms of those in a normal ECG with deeper S waves in right-sided leads (V1 and V2) and taller R waves in left-sided leaves (aVL, V5, and V6). Two of the most commonly used criteria are listed in Table 9.1.

TABLE 9.1 Two Most Commonly Used Diagnostic Criteria for LVH Sokolow-Lyon Index 2 Cornell Voltage Criteria 3 S in V1 + R in V5 or V6 ≥ 35 mm or

Men: S in V3 + R in aVL > 28 mm Women: S in V3 + R in aVL > 20 mm

R in aVL > 11 mm

The sensitivities associated with these criteria are very low. 4 Although QRS voltage increases with left ventricular mass, there are a number of other factors including age, gender, lung disease, and body habitus that affect voltage. The ECG cannot be used as a screening tool for LVH. Fulfillment of voltage criteria alone does not make an ECG diagnostic for LVH. Increased voltage can be seen in young, thin adults. The following non–voltage-based abnormalities support the diagnosis of LVH.

V1

QRS Widening It takes longer for activation to spread from endocardium to epicardium in the thicker left ventricular myocar dium. The QRS complex becomes slightly widened, and the time to the peak of the R wave is increased (>50 ms in lead V5 or V6). ST Depression and TW Inversion Repolarization can occur before the entire left ventricular myocardium has depolarized. This can result in a downward shift of the ST segment in leads with tall R waves. Earlier repolarization of the endocardium allows repolarization to proceed from endocardium to epicardium, resulting in asymmetric TW inversion. TW inver sion may also result from subendocardial ischemia. In leads with tall R waves, downsloping ST depression next to inverted T waves is a secondary repolarization abnormality commonly referred to as the “LV strain pattern.” Left Atrial Abnormality Changes in left ventricular pressure and volume commonly result in left atrial enlargement. Left Axis Deviation A more horizontal axis of the QRS complex may result in increased left ventricular mass. ST Elevation in Leads V1 to V3 Some ST elevations in leads with deep S waves represent appropriate proportional discordance.

Left atrial enlargement

ST elevation

Deep S wave

Tall R wave

V6

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ST depression

Asymmetric TW inversion

Left atrial enlargement

QRS widening

FIGURE 9.1 Morphologic features of LVH.