Significance of the QX-QT ratio and the QT ratio (QTr) in the exercise electrocardiogram.

mHE exercise electrocardiogram is a fairly well established and frequently used procedure as an adjunct in the diagnosis of symptomatic or latent coronary insufficiency. Many authors have confirmed its value.'-" The criteria for a positive test, however, still remain somewhat controversial. The value of "ischemic" type ST-segment depression is well documented, but the problem of the significance of various degrees of junctional-type depression is still controversial. Recently, Master and Rosenfeld3-6 introduced among their criteria the QX/QT ratio and QT ratio (QTr). They state that a J depression of less than 2 mm., but with a QX/QT ratio of 50 per cent or more, represents a positive or an equivocal test.4,6 The possible value of the QX/QT ratio was first advanced by Lepeschkin and Surawicz.7 8 X represents the point where the depressed ST segment returns to the baseline. In order to express the ST-segment depression in a quantitative manner independent of the heart rate, these authors studied the ratio QX/QT in an attempt to distinguish a "true-positive" from a "false-positive" ST-segment depression. It was assumed that the duration of the ST depression due to a current of injury produced by subendocardial ischemia should persist longer than the depression associated with simple tachycardia or with changes in the ventricular gradient. These authors proposed a QX/QT ratio of 50 per cent or more as a