Voltage Abnormalities

The Low-Voltage ECG

Criteria

Voltage is considered low in the limb leads when the average QRS amplitude is less than 5 mm and low in the precordial leads when the average QRS amplitude is less than 10 mm.

Electrical Alternans

QRS Wave Alternans

Pericardial

Effusion Alternating voltage of the QRS complex results from the pendular motion of the heart within a fluid-filled pericardial space.

SVT

Alternans can also occur at very high heart rates seen in re-entrant supraventricular tachycardias.

Left Ventricular Hypertrophy

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, V2) and taller R waves in left-sided leaves (aVL, V5, V6). Two of the most commonly used criteria are listed below:

Sokolow-Lyon Index²	Cornell Voltage Criteria³
S in V1 + R in V5 or V6 ≥ 35 mm or	Men: S in V3 + R in aVL > 28 mm
R in aVL > 11 mm	Women: S in V3 + R in aVL > 20 mm

The sensitivities associated with these criteria are very low.⁴ While 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-voltagebased abnormalities support the diagnosis of LVH:

QRS Widening

It takes longer for activation to spread from endocardium to epicardium in the thicker left ventricular myocardium. The QRS complex becomes slightly widened, and the time to the peak of the R wave is increased (>50 msec in lead V5 or V6).

ST Depression and T-Wave 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 T-wave inversion. T-wave inversion 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 with increased left ventricular mass.

ST Elevation in Leads V1-V3

Some ST elevation in leads with deep S waves represents appropriate proportional discordance.

FIGURE 9.1 Morphologic features of LVH.

Right Ventricular Hypertrophy

Due to the opposing forces of the thicker left ventricle, the sensitivity of electrocardiographic criteria for right ventricular hypertrophy (RVH) is generally low. The mass of the left ventricle is still greater than that of the right ventricle in patients with RVH. The presence of several ECG features, however, can be helpful in cases of significant RVH.

ECG Features

Right Axis Deviation

This is a consistent sign in RVH. The most common cause of right axis deviation in an adult is RVH.

QRS Voltage Criteria

FIGURE 9.2 ECG appearance of RVH in precordial leads.

S1 S2 S3 Pattern

S waves in leads I, II, and III

P Pulmonale

Peaked P Waves: Amplitude ≥ 2.5 mm in lead II

ST/T Wave Changes

ST Depression and TWI in V1-V2 are secondary repolarization abnormalities that may accompany tall R waves

Causes to Consider

Pressure Overload

Primary Pulmonary Hypertension

COPD

Mitral Stenosis

Pulmonary Embolism

Pulmonic Stenosis

Ventricular Septal Defect

Volume Overload

Tricuspid Regurgitation

Atrial Septal Defect

COPD

ECG Features

Lung Hyperinflation

Low Voltage

Air can dampen the ECG signal.

Vertical Heart Position

Lowered diaphragms cause the heart to be positioned more vertically.

Right Axis Deviation

Poor R-Wave Progression

Results from clockwise rotation of the vertical heart.

The Lead I Sign

The P-, QRS-, and T-wave vectors are all almost perpendicular to lead I. These waves in lead I have low amplitudes.

Right Atrial Abnormality

Peaked P waves in leads II, III, and aVF often accompany the above ECG changes.

RVH

Deep S waves in V5 and V6

FIGURE 9.3 Example of the lead I sign in a patient with severe COPD. P and T waves are unidentifiable. QRS complexes are 1 mm in amplitude.

Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant genetic disorder most often caused by mutations in genes that encode proteins in the cardiac sarcomere. In some cases, this cardiomyopathy is caused by other genetic disorders such as Friedrich ataxia.

Hypertrophic Patterns

Hypertrophy is frequently diffuse but can be limited to segmental areas of the left ventricle. There is no classic hypertrophic pattern.

ECG Findings

Q Waves

Deep Q waves in II, III, aVF, V5, and V6, especially in patients who are in teenage years, may be the most specific finding in HCM.

LVH

LVH and its associated repolarization abnormalities are the two most common abnormalities.⁵ The magnitude of voltage does not predict the extent of hypertrophy.⁶

Giant TWI

Giant negative T waves in the precordial leads occur when hypertrophy is localized in the apex.