Spatial vectorcardiogram in acute inferior wall myocardial infarction: its utility in identification of patients prone to complete heart block.
Spatial vectorcardiography was performed in 28 (22 males, 6 females; age 36-78 years) consecutive cases of acute inferior wall myocardial infarction during sinus rhythm within 24 hours of admission. Orthogonal leads using the corrected Frank lead system were recorded at a paper speed of 100 mm/sec. Qualitative analysis consisted of study of QRS loop inscription in all 3 orthogonal planes. Additional quantitative analysis using the spherical coordinate system was undertaken to measure the magnitude and angular direction (azimuth and elevation angle) of spatial R maximum cardiac vector. During the hospital course, 15 patients developed transient complete heart block and 13 patients did not. The direction of the QRS loop inscription in the 3 planes did not differ between the two groups. The spatial R maximum magnitude and azimuth angle did not differ between the patients who developed complete heart block and those who did not. Values for elevation angle were markedly different between the two groups. The spatial R maximum elevation angle ranged from 0 to -35 degrees and was negative (superiorly directed) in 14 of the 15 patients with complete heart block, whereas it ranged from -10 degrees to +/- 75 degrees and was negative (superiorly directed) in only 2 of the 13 patients without this complication. Thus it appears that negative elevation angle of spatial R maximum cardiac vector in patients with inferior wall myocardial infarction may indicate proneness to complete heart block.