Concentric and eccentric hypertrophy result from systolic and diastolic overloading of the left ventricle. The ECG patterns are often similar, although aortic regurgitation (diastolic overload) is more often associated with prominent septal Q waves than aortic stenosis (systolic overload). Asymmetric septal hypertrophy as noted in hypertrophic subaortic aortic stenosis (hypertrophic obstructive cardiomyopathy) is generally indistinguishable by ECG changes, although an approximately 20 percent incidence of large prominent Q waves ("pseudo-infarction") is noted. The various ECG criteria for recognition of left ventricular hypertrophy include voltage and repolarization changes. The voltage criteria tend to be more sensitive, but less specific. ST and T wave abnormalities are less sensitive but more specific. All the classic indices of hypertrophy may be absent in more than 20 percent of patients with severe aortic valve disease or hypertrophic subaortic stenosis. In some instances, ECG signs of left atrial enlargement may provide additional clues to the presence of left ventricular dysfunction. It is generally not possible to quantitate the actual severity of aortic valve lesions from the ECG changes with any degree of accuracy. Although vectorcardiographic criteria have been examined, these are not significantly more useful in the evaluation of a patient with aortic valve disease, they provide but one more clue in the total clinical picture.