Inferior myocardial infarction as a cause of asymmetric septal hypertrophy. An echocardiographic study.

The diastolic thickness of the septum and posterior left ventricular wall were measured with M mode echocardiography in 68 patients 2 or more months after a single transmural myocardial infarction. In 42 patients with inferior wall infarction, the septal thickness of 12.4 +/- 0.6 mm (mean +/- standard error of the mean) was larger than the mean measurement in 26 patients with anterior wall infarction (9.6 +/- 0.6 mm, P less than 0.01). Twenty-five of these 42 patients (59 percent) had increased septal thickness (greater than 11 mm), including 12 (48 percent) who had hypertension and 11 (26 percent) who had decreased posterior wall thickness. The ratio of septal to posterior wall thickness was greater in the patients with inferior infarction than in those with anterior infarction (1.36 +/- 0.06 versus 0.89 +/- 0.06, P less than 0.001). This ratio exceeded 1.3 in 22 patients with an inferior infarction (52 percent) but was increased in only 1 patient with an anterior infarction. Hypertension did not predict the presence or absence of an abnormal ratio. Increased septal thickness on echocardiography may occur after interior infarction and result in an abnormal septal to posterior wall thickness ratio that meets current echocardiographic criteria for asymmetric septal hypertrophy.