Relationship between the degree of coronary artery disease and of left ventricular function and the duration of the QT-interval in ECG.

Advanced coronary artery disease (CAD), impaired left ventricular function and prolongation of the QT-interval are considered risk factors for sudden cardiac death in CAD-patients. So far, however, there are no studies investigating in detail whether there is a correlation between the QT-interval and changes in coronary anatomy or changes in left ventricular function. Therefore, coronary angiographic data were related to QT-intervals in 304 patients, who were catheterized because of suspected coronary artery disease. QT-intervals were expressed as QTc = QT/square root RR (Bazett's correction for heart rate), left ventricular function was assessed by the ejection fraction of the ventricular angiogram, and coronary angiograms were classified according to the Gensini score as well as into 1-, 2- and 3-vessel disease (stenoses greater than or equal to 50%). A multidimensional linear regression model was employed to eliminate the effects of varying mean rates still present after application of Bazett's formula. In patients with 1-, 2- and 3-vessel disease, significant changes of QTc were observed only in patients with impaired left ventricular function (EF less than 60%). In these patients the QTc-interval increased significantly from 1- to 3-vessel disease. If the critical degree of coronary stenosis was changed from greater than or equal to 50% to greater than or equal to 90% further prolongations of QTc were noted. In patients with 1-, 2- and 3-vessel disease the QTc-duration difference was further enhanced if either the proximal part of the descending branch of the left coronary artery (LAD) or the left main stem were affected (stenoses greater than or equal to 50%). The data reveal that prolongation in the duration of electrical systole correlates with known cardiac risk factors for sudden death, i.e. 3-vessel-disease, proximal LAD or left main stem stenosis and impaired left ventricular function. In the individual patient, however, the prognostic value of a single QTc-determination is limited because of a large interindividual variation of the data.