There are ECG criteria for all four chambers that have been established. The sensitivity of these criteria is usually poor but the specificity is better. This section will review the established criteria.
As the muscle mass of the left ventricle increases, the voltage increases as well. The R wave increases in the leads more representative of the left ventricle (V5, V6, aVL) and the S wave increases in the leads representative of the right ventricle (V1, V2 and aVR). There are also ECG diagnoses, which do not indicate LVH but are suggestive of it such as left atrial enlargement and left axis deviation. The most commonly used criteria for LVH are the Sokolow-Lyon criteria, the Cornell criteria, the Scott’s criteria and the Estes’ scoring system.
The Sokolow and Lyon criteria is straightforward. Simply add the S wave in V1 to the R wave in V5 or V6. If the total is greater than 35 mm then this suggests LVH. The criteria has a sensitivity of approximately 22% and a specificity of 100%. The Sokolow and Lyon criteria is the most commonly used and is the most obvious on ECG.
Cornell’s criteria involves the R wave in aVL and the S wave in V3. Left ventricular hypertrophy is considered present if the total is greater than 28 in males and greater than 20 in females. Reported sensitivity is 46% with a specificity of 96%.
The Estes’ scoring system is considered the most sensitive and is highly specific. The scoring system includes R and S wave voltage, left atrial enlargement, QRS widening and delay and left axis deviation. The QRS widening involves the fact that it takes longer for the electrical impulse to travel through the hypertrophied myocardium which is a similar concept with the delayed intrinsicoid deflection (the intrinsicoid deflection is the duration of the initial positive deflection of the QRS complex). Left atrial enlargement is included because the increased left ventricular end diastolic pressure will increase the left atrial size leading to enlargement. The term “strain” is commonly used when referring to ST-T wave changes consistent with LVH. Typically, the lateral leads will have a convex ST segment tapering into an inverted T wave. This pattern is downward when the R wave is predominant (V5, V6, lead I and aVL) and upward when the S wave is dominant (V1 and V2). The scoring system is listed below.
As the QRS widens and the strain pattern progresses, the complex becomes indistinguishable from left bundle branch block. There are many criteria that have been proposed all of which have both a low sensitivity and specificity. In general, if the QRS duration is greater than 0.12 seconds, left bundle branch block should be the diagnosis.
The left ventricle is what drives the QRS in the precordial leads producing a large S wave and small R wave in V1. As the leads progress across the precordium, the R wave becomes larger up to V5 and then smaller in V6. Consequently, the S wave becomes smaller as the leads cross the precordium. As the right ventricle hypertrophies, the progression of the R and S waves is altered. The increased muscle mass is represented by a larger R wave and smaller S wave in V1 changing the ratio of R:S to greater than one. The S wave in V6 also becomes more prominent. The right precordial leads are a large part of diagnosing RVH but there are other causes of a dominant R wave in V1.
A strain pattern in RVH can appear similar to LVH but is evident in the right ventricular leads of V1-V2 as well as lead II, lead III and aVF. There can also be a delay in the conduction through the right ventricle due to increased muscle mass and demonstrated on the surface ECG as incomplete RBBB or a delayed intrinsicoid deflection in V1 and V2. The complete criteria for RVH are listed.
The diagnosis of biventricular enlargement is difficult because the electrical effects of hypertrophy of one chamber can cancel the electrical evidence of hypertrophy of the other chamber. Some criteria have been proposed but the sensitivity and specificity are not very high. The criteria suggesting biventricular hypertrophy include:
Enlargement of the left atrium produces changes in both amplitude and duration of P wave in the leads II and V1. As the left atrium becomes progressively larger, the time for the electrical impulse to travel throughtout the left atrium lengthens and the P wave in lead II becomes longer. This is represented on the surface ECG as a prolonged P wave usually with notching. If the P wave in lead II is greater than 0.11 seconds, the sensitivity for LAE is 33% with a specificity of 88%. If the P wave is notched and the peak to peak interval of the notching is greater than 40 milliseconds, the sensitivity is 15% while the specificity is 100% for LAE.
As the left atrium enlarges, it also changes the electrical axis of the P wave. This is manifested in lead V1 as the terminal portion of the P wave being negative and wide on the ECG. For a negative phase of the P wave in V1 greater than 40 milliseconds, the sensitivity and specificity for LAE is 83% and 80% respectively. If the negative phase is greater than 1 mm deep, the sensitivity is 60% and the specificity is 93% for LAE.
The most sensitive criteria for LAE is a prolonged negative phase of the terminal P wave in lead V1 of greater than 40 milliseconds and the most specific criteria is the interpeak interval in lead II of greater than 40 milliseconds.
The criteria for RAE have the worst sensitivity and specificity of any of the four chambers. The most commonly used and easiest to apply involves the amplitude of the P wave in lead II of the ECG. If the amplitude is greater than 2.5 mm then this is considered consistent with RAE. It is unclear how this manifests as the right atrium is dilated rather than hypertrophied in most cases and may be due to the rotation of the heart. Another criteria involves a small QRS voltage in V1 with and abrupt increase in the QRS voltage in V2. In this case, the concept is the heart rotates and the right atrium moves forward and sits between lead V1 and the heart causing decreased voltage while V2 remains free of this interference and demonstrates what appears to be a dramatic increase in voltage.