The effect of the Q wave infarct on left ventricular electromechanical function.

Objective: To assess the nature of left ventricular (LV) electrical and mechanical dysfunction in Q compared to non-Q anterior myocardial infarction (MI).

Subjects: We used ECG and echocardiography to study 54 unselected patients, age 57+/-15 years, 32 male, with old (>6 months after) anterior MI (39 Q and 15 non-Q), confirmed by enzyme rise and regional wall motion abnormality, and compared them with 21 normals of similar age.

Methods: Analysis of resting LV minor and long axis function and 12-lead surface electrocardiogram.

Results: Only 10% of normals did not have a normal septal Q wave compared with 46% of non-Q wave MI and 84% Q wave MI (P<0.001). All patients with Q wave MI had a scarred anteroseptal wall but none of the non-Q wave MI. LV minor axis dimensions were increased only with Q wave MI: 6.0 +/- 0.9 vs. 4.9 +/- 0.5 cm at end-diastole and 4.5 +/- 1.1 vs. 3.3 +/- 0.5 cm at end-systole and fractional shortening was reduced 27 +/- 8 vs. 33 +/- 3% (P<0.001 for all). Total left ventricular long axis amplitude of motion was reduced at the left, septal and posterior sites only in Q wave MI but was not different from controls in non-Q wave MI. The onset of long axis shortening was delayed by 20 ms at the left and septal sites in non-Q wave MI and by an additional 20 ms at the three sites in Q wave MI. Peak long axis shortening rate was reduced in the two patient groups, with the same distribution as post-ejection shortening (greater than 1 mm), which occurred in 21% of patients with non-Q wave MI and 76% of patients with Q wave MI (P<0.001). In diastole, the onset of long axis lengthening was delayed by 20 ms at the left and septal sites in non-Q wave MI and at the three sites in Q wave MI (P<0.001). Peak long axis lengthening rate was reduced with a similar distribution in the two patient groups.

Conclusion: Patients with Q wave MI have an increased LV dimension and reduced FS, whereas patients with non-Q wave MI appear to have morphologically normal LV minor axis dimensions and fractional shortening apart from the anterior wall hypokinesis. In the latter, however, long axis function shows significant systolic and diastolic disturbances affecting the anteroseptal and lateral walls. The absence of conduction disturbances in non-Q wave MI suggests intrinsic myocardial dysfunction that may be reversible.