The Q1 deflection of the electrocardiogram in bundle branch block and axis deviation

Electrocardiographic diagnosis of myocardial infarction in the presence of complete left bundle branch block

Whether myocardial infarction (MI) can be diagnosed electrocardiographically in the presence of left bundle branch block (LBBB) is controversial. Our study sought to test the reliability of ECG criteria for diagnosing MI in patients with LBBB. Among 985 patients presenting within 18 hours of the onset of ischemic chest pain, 35 had complete LBBB. Acute MI was identified by serial MB-creatine kinase (CK) elevations and prior MI was determined by previously documented ECG and/or enzyme changes. Among those with LBBB, 24 patients had acute and/or prior MI, while 11 had neither. Eleven ECG criteria previously proposed for detecting MI in the presence of LBBB were evaluated. In patients presenting with ischemic chest pain and complete LBBB, presence of any one of the following ECG criteria was highly specific (90% to 100%) and predictive (85% to 100%) for acute or prior MI: Q waves in at least two of leads I, aVL, V5, or V6; R wave regression from V1 to V4; notching of the upstroke of the S wave in at least two of leads V3, V4, or V5, and primary ST-T wave changes in two or more adjacent leads.

Predictive accuracy of criteria for chronic myocardial infarction in pacing-induced left bundle branch block

Sensitivity, specificity and predictive accuracy of 5 electrocardiographic criteria for chronic myocardial infarction (MI) in the presence of left bundle branch block (LBBB) were evaluated in 47 patients with known (clinical and electrocardiographic Q wave) MI and 28 patients without MI. Two right ventricular sites were paced (producing LBBB with normal or left axis). The effect of infarct location on these criteria was also evaluated. In patients with LBBB: Cabrera's sign (notching of the upstroke of S wave in V3,4,5) is seen more often with MI than without (anterior more often than inferior), and the left axis increased its sensitivity. Chapman's sign (notching of upstroke of the R wave in I, L or V6) is more common in patients without MI, and its specificity and sensitivity are not altered by axis. Sensitivity of notching in 2, 3, F is too low to be clinically useful. Q 2, 3, F indicates only left axis; predictive accuracy for MI is high (100%) only for normal axis where sensitivity is low (3%). (5) Q 1, L, V6 is no more frequent with MI than without, but if MI is present it is more common in anterior than inferior infarction. Specificity and predictive accuracy are too low to be clinically useful as indicators of MI.

The pathologic correlates of the electrocardiogram: complete left bundle branch block

To assess whether gross pathologic differences exist between hearts with left bundle branch block (LBBB) and left-axis deviation (LAXD) and those with LBBB and a normal frontal plane axis, we examined 70 hearts with LBBB in a series of 1410 sequential dissections (5%). Thirty-two hearts had LAXD and 34 had normal axes on the correlative ECG. Left ventricular enlargement occurred frequently (93%). No significant differences were found in age distribution, left ventricular weight, coronary anatomy or infarct location. Quantitative analysis revealed larger inferoposterolateral and apical infarcts in hearts with LBBB and LAXD (p less than 0.01). The accuracy of various electrocardiographic signs of left ventricular enlargement and myocardial infarction in the presence of LBBB was assessed. Voltage criteria and QRS duration poorly define anatomic chamber enlargement. Anterior infarction is suggested by a q or pathological Q wave in lead I, a q wave in leads I, V5 and V6, or notched S waves in V3 or V4. Pathologic q waves or ST shifts in the inferior leads have high diagnostic specificity but low sensitivity for inferior infarction.

Studies of acute myocardial infarction with intermittent bundle branch and hemiblock

Two cases of transient hemiblock occurring during the course of acute myocardial infarction are reported. The transient manifestation permits the accurate evaluation of the diagnostic features of the hemiblocks as modified by acute infarction. One case reflects the development of left bundle branch block due to bilateral post-divisional block which inter alia permits the study of left bundle branch block in the presence of acute myocardial infarction.

High-Voltage QRS Complexes in the Absence of Left Ventricular Hypertrophy

Of an unselected group of otherwise normal electrocardiograms in which the sum of S in V 1 and R in V 5 exceeded 35 mm., 39 per cent came from patients with no clinical evidence of cardiac disease. Of electrocardiograms in which R in AV L exceeded 11 mm., 29 per cent were from patients without cardiac disease. All of the cases in which the voltage was abnormal in both lead aV L and the precordial leads had evident or possible heart disease. Thus, while the voltage indexes for left ventricular hypertrophy of Sokolow and Lyon are useful and easy to apply, the lack of specificity of voltage changes limits clinical application.

Electrocardiographic diagnosis of myocardial infarction in the presence of left bundle-branch block

It is generally accepted that most myocardial infarctions are obscured on the electrocardiogram by left bundle-branch block. The number of published cases in which this could be evaluated, however, is small, and the case reports are scattered. We have studied 30 cases of myocardial infarction with left bundle-branch block in which the location of the infarction could be determined with certainty, by autopsy, or by a previous electrocardiogram with normal intraventricular conduction. Twenty such published cases have also been collected. Electrocardiographic abnormalities have been correlated with infarctions in different locations. The possible specificity of these abnormalities is discussed.