Left ventricular hypertrophy

ECG: Left ventricular hypertrophy with major increase in voltages which no longer fit into the grid; very distinct increase in R wave amplitude in V4, V5, V6 but also in leads I, II and aVF; increase in S wave in V1, V2; positive Sokolow index (S_V1 + R_V5 = 60); positive Lewis index ([R_I – S_I] + [R_III – S_III] = 35); repolarization disorders in leads I, II, aVF, V4-V6 with ST segment depression and negative T-waves;

Comments: Left ventricular hypertrophy corresponds to an increase in the size of left myocardial ventricular fibers most often in response to pressure overload (essential hypertension and aortic stenosis) or volume overload (aortic or mitral regurgitation) with the exception of hypertrophic cardiomyopathy which occurs in the absence of obvious modifications in hemodynamics. The typical pattern of left ventricular hypertrophy is a concentric hypertrophy with an equally increased thickness of the septum and the free wall and accentuation of a physiological and anatomical preponderance of the left ventricle, which is normally present. In rare instances, wall thickening can be uneven, predominant in the basal regions and eccentric. Contrary to right ventricular hypertrophy, left ventricular hypertrophy does not reverse the electrical potentials but rather exaggerate the normal patterns. Various electrical signs can be observed:

• An increase in amplitude in limb leads: the activation vector of the left ventricular free wall is increased which explains the exaggeration of R wave voltage in the left precordial leads (V5, V6) and of S waves in the right precordial leads ( V1, V2); in V1, there is hence a preserved rS pattern, but with a deep S wave and a decreased r/S ratio; in contrast, in V5, V6, in the leads facing the hypertrophied ventricle, an increase in R wave amplitude is observed with a increased R/S ratio; it should be noted that the Gaussian normality tables are particularly useful in children because a tall R wave in V6 is not uncommon ; the R wave measurements in V5, V6 and S wave measurements in V1, V2 constitute the basis for the  calculation of indices defining left ventricular hypertrophy in clinical practice;
• The amplitude of the initial q waves is most often normal or decreased with the exception of familial hypertrophic cardiomyopathies where it is common to observe deep pseudo-necrois q waves;
• A delayed onset of intrinsicoid deflection (pathological beyond 50 ms) in the left precordial leads (V5, V6) can be observed in severe cases; it is generally less prominent than for a left bundle branch block (remains below 80 ms); on the other hand, it remains normal in right precordial leads;
• The duration of the QRS-complex can be prolonged; indeed, the increase in left ventricular mass causes a moderate prolongation (of the order of 10 to 15 ms) of the time required for depolarization; this prolongation is most often discrete and does not exceed 110 ms in the absence of bundle branch block;
• The transition zone in precordial leads is usually displaced to the left-sided precordial leads; it may therefore be useful to record posterior leads (V7, V8); the transition zone is often abrupt (very negative QRS in right precordial leads followed by very positive QRS in left precordial leads) with variation in polarity from one complex to another;
• Weakly specific repolarization disorders can be observed: in the majority of cases, a dichotomy between the direction of the T-wave and that of the R wave is observed (if tall R wave in V5, V6, negative and asymmetrical T-wave in these leads with a possible moderate ST segment depression); in contrast, in the presence of a “diastolic” overload, the T-wave can maintain a normal direction with a large amplitude and a peaked and symmetrical pattern;
• In frontal leads, it is common to observe an increase in voltages mainly in leads I and aVL;
•  A rotation of the mean vector toward the actual seat of the hypertrophy (to the left, backward and upward) can be observed; a left axis deviation is relatively common in adults, slightly less in children and in slim patients where the axis is often vertical; this axis deviation often remains moderate and even within the limits of normal (between +30° and -30°); a clearly deviated left axis should prompt the search for the presence of an associated conduction disorder (left anterior fascicular block);

The sensitivity of the electrical signs of ventricular hypertrophy is not very good, albeit better than for right ventricular hypertrophy. Indeed, certain patients maintain a normal electrical pattern, a nascent left ventricular hypertrophy can lead to an increase in voltages but without reaching the limits deemed pathological. The specificity is somewhat better with regard to the increase in voltages provided that the observed physiological variations are taken into consideration, according to age (increased voltages in young patients) and gender (higher voltages in men compared to women). It should be noted that depending on the type of hypertrophy and patient morphology, certain patients exclusively present increased voltages in frontal leads, while others have an elective increase in precordial voltages.

There are multiple criteria for diagnosing left ventricular hypertrophy:

In a first instance, it is common to search for increased voltages in each lead; left ventricular hypertrophy is suspected when detecting an R wave greater than 25 mm in V5 or V6, an S wave greater than 20 mm in V1, an S wave greater than 25 mm in V2 or an R wave greater than 13 mm in aVL.

As explained previously, the increase in voltages in right precordial (S waves) or left precordial (R waves) leads is a good sign of left ventricular hypertrophy although sensitivity remains average (values may remain within the norm); this is why various indices were created by adding the voltages in different leads to optimize the ability to detect a hypertrophy:

• The most commonly-used index in clinical practice is the Sokolow-Lyon index which adds the S wave voltage in right precordial leads and the R wave voltage in the left precordial leads; this index is equal to the sum of the amplitude of the S wave in V1 and the R wave in V5 or V6 (the highest of these two values being chosen); a value greater than 35 mm is suggestive of a left ventricular hypertrophy although it may be useful to index the measurement according to age and gender;
• The Blondeau Heller index is very similar to the Sokolow index with identical threshold values and diagnostic value; this index is equal to the sum of the amplitude of the S wave in V2 and the R wave in V7 (posterior lead); it is especially useful when there is a leftward shift in the transition zone;
• A left ventricular hypertrophy is suspected if the sum of the largest R wave and the largest S wave in precordial leads exceeds 45 mm;
• The Lewis index is based on the voltages in frontal leads; it is equal 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 above 17 is suggestive of left ventricular hypertrophy;
• The Gubner index (R wave amplitude in lead I + S wave amplitude in lead III) is positive if the value exceeds 25 mm;
• The Cornell index (R wave amplitude in aVL + S wave amplitude in lead II) is positive if the value exceeds 28 mm in men and 20 mm in women;

Take-home message: Left ventricular hypertrophy does not reverse the electrical potentials but rather exaggerates the normal patterns. Diagnosis is based on the increase in voltages corresponding to the activation of the left ventricle. In clinical practice, the Sokolow index is the most commonly used.