The effect of nitrite and exercise on the inverted T wave.

No unequivocal explanation has so far been found of the inverted T wave in the abnormal human electrocardiogram. It is likely that the deformed T wave associated with coronary disease is the outcome of cardiac ischaemia, but this does not appear to explain the mechanism of T-wave inversion in ventricular preponderance where a shift of the heart may play a part. The earlier papers dealing with temporary cardiographic changes in cardiac ischaemia and with the experimental evidence that nitrite increases the blood supply to the myocardium were reviewed by Evans and Hoyle (1933), who studied the effect of nitrite on the inverted T wave. In a series of 23 cases that showed deformity of the T in the form of flattening, diphasic change, or inversion, this component was wholly or partly corrected in 11 following the administration of the vasodilator. They concluded that elevation of the inverted T wave by nitrite in patients with angina pectoris was determined by the relief of myocardial ischaemia, and suggested that further observations might show that the fixed T wave and the one elevated by nitrite had a different significance, and that this might prove to be a measure of the collateral circulation around a damaged portion of heart muscle. Only nine of their cases, however, were of simple cardiac infarction without hypertension or aortic valvular disease, and in only three of these was the T wave corrected by nitrite. Exercising patients with coronary insufficiency will sometimes cause R-T depression or even inversion of the T wave; in others it may correct the deformity. Such changes were considered by Master, Friedman, and Dack (1942), as evidence of coronary abnormality. May (1939) observed that a lowering of the T wave, sometimes with S-T depression, as a result of the oxygen deficiency, gradually induced, is much more common in young athletic subjects than in older people. Levy, Alvan, and Bruenn (1938) agreed that oxygen want caused cardiographic alterations in healthy subjects as well as in patients with heart disease, but showed that the change was far greater when the coronary circulation was impaired. The effect of the administration of oxygen on the cardiogram of cyanosed patients was studied by Edson (1942), who found that the deformed T wave was not always corrected and especially in cases of recent coronary occlusion, while in some depression of the R-T segment or an increase in the degree of inversion of the T wave resulted. An understanding of T-wave changes in relation to myocardial nutrition is still far from complete. An explanation of the altered T wave of ventricular preponderance does not at first sight concern the relief of cardiac ischaemia. In practice, the similarity of the T I type of cardiac infarction and the inversion of T from hypertension or aortic valvular disease is a common problem in differential diagnosis. The chest lead CR7 of Evans and Hunter (1943) may sometimes assist this differentiation, while the administration of potassium salts (SharpeySchafer, 1943) might help if it were a safe method. The following observations on the effects of nitrite and exercise on the inverted T wave were made to evaluate the help that such tests might afford in deciding this common clinical and cardiological problem.