Significance of Rightward Axis Shift in Anterior Acute Myocardial Infarction

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The purpose of this study was to assess the significance of two types of rightward axis shift appearing during anterior acute myocardial infarction. Of 731 consecutive patients admitted with evidence of anterior acute myocardial infarction, 72 (10%) developed acute rightward axis shift and were divided into two groups according to electrocardiographic criteria: group A consisted of 27 patients with rightward axis shift and an electrocardiographic pattern characteristic of left posterior hemiblock, and group B consisted of 45 patients with rightward axis shift without the electrocardiographic pattern of left posterior hemiblock. A comparison between their electrocardiographic patterns, clinical course, prognosis, and échocardiographie findings was made. There was no significant difference in the average shift of the axis to the right between the groups (60 vs. 62°). The average mean axes of the first (<0.04 ms) and second (>0.04 ms) vector in group A were 2 and 107°, respectively, as compared with 68 and 52° in group B (p < 0.001). The Killip class on admission was worse in group A (26 vs. 2% for Killip III and IV). The patients in group A had a significantly higher incidence of in-hospital morbidity such as congestive heart failure (63 vs. 24%) and cardiogenic shock (74 vs. 7%). The in-hospital mortality rate in group A was very high (70%) as compared with group B (9%; p < 0.001). The echocardiogram of group A patients showed severe general hypokinesia as compared with group B patients in whom there was a better left ventricular function with normal inferior wall motion and lateral base wall compensatory hyperkinesia. The right axis deviation in group A is attributed to different degrees of left posterior hemiblock, while in group B the rightward axis shift is attributed to the cancellation of electrical forces from the anterolateral wall as a result of the infarction and the upsurge of the right electrical forces from the posterior wall. In conclusion, it is very important to differentiate between patients with these two electrocardiographic patterns of rightward axis shift during anterior acute myocardial infarction because they are completely different in their electrocardiographic characteristics, clinical course, and prognosis.