Right ventricular hypertrophy
Right ventricular hypertrophy is expressed on the ECG by diminished left ventricular forces. Right ventricular hypertrophy is often associated with a clockwise rotation of the right ventricle which becomes anterior, the left ventricle being pushed posteriorly. The right precordial leads facing the hypertrophied ventricle display a fundamental pattern. Right ventricular hypertrophy reverses the pattern of precordial leads by rendering the positive reflections predominant in right precordial leads, by decreasing the positive reflections in left precordial leads and by revealing a terminal negative reflection (S wave) in left precordial leads. Another characteristic abnormality is the presence of a more or less prominent right axis rotation of the QRS-complex. The electrical signs are inconsistent and vary with age and the degree of hypertrophy.
The detection of right ventricular hypertrophy by ECG has a poor sensitivity; indeed, mild to moderate hypertrophy may or may not change the electrical pattern, with abnormalities only becoming characteristic when the left/right ventricle weight ratio is in the vicinity of 1.
Conversely, the specificity is high only if several deformations are present; indeed, each criterion taken individually lacks specificity and can be observed in various diseases.
In the right precordial leads, one can observe:
- A predominance of the R wave in V1, V2 with an exclusive RS, Rs or R pattern; the ECG shows a large amplitude R wave (> 7 to 12 mm) in the right precordial leads (V1, V2) with a small amplitude S wave (< 2 mm) and a R/S ratio > 1; taken individually, this criterion is not very specific since one can observe an increase in the R wave in right precordial leads in patients with a clear posterior scar (typically normal axis), apical hypertrophic cardiomyopathy (characteristic pattern of giant negative T-waves), left posterior or lateral ventricular pre-excitation, substantial pleural effusion or pneumothorax;
- A Q wave in V1 with tall R wave: the qR pattern is a highly specific sign of severe right ventricular hypertrophy; this Q wave is probably the result of a hypertrophy of the right aspect of the septum that accompanies the hypertrophy of the right ventricular free wall; this pattern can also be observed in a patient with anteroseptal myocardial infarction (Q wave in V1) and right bundle branch block;
- A rsR' pattern in V1 in the absence of any conduction disorder: the ECG reveals a multiphase rSR' or rsR' complex in the right precordial leads similar to that observed in the incomplete right bundle branch block; the narrower the rsR' complex and the greater the amplitude of the R wave (R' > 5 to 10 mm and taller than the initial r wave), the greater the likelihood of a right ventricular hypertrophy; this pattern can also be observed in a patient with incomplete right bundle branch block, posterior infarction; it may also be due to a abnormal body shape (pectus excavatum) or a variant of normal;
- A delayed intrinsicoid deflection (> 30 ms) in V1 and V2; it is usually not delayed in the left precordial leads;
- QRS duration is rarely prolonged; indeed, the end of the activation of the right ventricle is usually more precocious than that of the left ventricle and only a very significant right ventricular hypertrophy induces a moderate prolongation of QRS duration;
- Abnormalities secondary to repolarization: a ST segment depression and a negative T-wave can be observed in the right precordial leads; when prominent, the ST segment depression could potentially reflect the presence of a functional myocardial ischemia demonstrating that the right ventricle adapts poorly to pressure and volume constraints;
In the left precordial leads, one can observe:
- V1 abnormalities can disappear in V2 or extend towards the left precordial leads;
- A deep reciprocal S wave in V5, V6 combined with a small amplitude R wave and therefore with a R/S ratio <1; this type of abnormality can be observed in patients with left anterior fascicular block (left axis), a left posterior fascicular block (right axis but absence of tall R waves in V1), a massive anterior infarction;
In the limb leads, one can observe:
- A right axis deviation > 100 or 110°; this is a sign of good diagnostic value in the absence of myocardial infarction, of congenital heart disease or bundle branch block; this pattern can also be observed in patients with a vertical heart (slim subjects), left posterior fascicular block or lateral extension of an infarct;
- The S wave can be increased in lead I: due to the right predominance, this can be accompanied by a deep Q wave present in lead III yielding a S1Q3 pattern;
- A lower Lewis index corresponds to: (R wave amplitude in lead I – S wave amplitude in lead I) + (R wave amplitude in lead III - S wave amplitude in lead III); a value below -14 is suggestive of right ventricular hypertrophy;
- A right atrial enlargement: this is a frequently associated indirect argument;
It is difficult to distinguish between physiological right ventricular predominance in infants and pathological right ventricular hypertrophy. Indeed, in the newborn, the electrical tracing can achieve, in a physiological manner, the pattern found in adults with right ventricular hypertrophy, the right ventricle and left ventricle mass ratio being 1/1. The amplitude of the R wave in V1 exceeds that of the R wave in V6 from birth to 6 months. From 6 months to 1 year, these two amplitudes are equal; after 1 year, the R wave in V6 exceeds the R wave in V1. The R wave in V1 gradually decreases during the first and second childhood.
The following arguments suggest a right ventricular hypertrophy in infants: 1) R wave in V1 greater than 20 mm and no S wave, 2) right axis deviation exceeding 120°, 3) repolarization disorders extending to V4, V5. The greater the number of parameters, the more likely the diagnosis.
Similarly, the distinction between dilatation and hypertrophy of the right ventricle can be difficult especially since they are often associated. Schematically, when the pressure is elevated (hypertrophy) there is essentially an increase in amplitude in the right precordial leads; when dilatation is predominant, large positive deflections can extend up to V4, V5 with presence of repolarization disorders.