Electrocardiographic detection of left ventricular hypertrophy in the presence of left anterior fascicular block.

The hitherto available electrocardiographic indexes for the detection of left ventricular hypertrophy in the presence of left anterior fascicular block do not provide a reliable diagnosis. Consequently, a new index based on the behavior of the QRS complex in left anterior fascicular block in the frontal and horizontal plane was constructed and its value assessed by echocardiographic measurements. The new index SIII + (R + S) maximal precordial greater than or equal to 30 mm was applied to the electrocardiograms of 50 patients without myocardial infarction and without right bundle branch block, showing a specificity of 87%, a sensitivity of 96%, a positive predictive value of 89% and a negative predictive value of 95%. Echocardiographic measurements were used as reference. Compared with the electrocardiographic indexes used so far (which were also applied to the 50 electrocardiograms), the new index showed a comparable high specificity and a distinctly superior sensitivity. The apparent paradox--why the electrocardiographic diagnosis of left ventricular hypertrophy is easier in the presence rather than in the absence of left anterior fascicular block--is discussed.