Comportamento da dispersão do intervalo QT em pacientes coronarianos e não coronarianos submetidos a teste ergométrico

Abstract

Treadmill test is one of the most common methods used for detection of coronary artery disease. However, its accuracy for significant coronary stenosis detection is quite limited, and the rate of false positive is high. The QT interval dispersion of the 12-lead measured on electrocardiogram is an index of heterogeneity of ventricular repolarization, and their relationship to malignant ventricular arrhythmias has been reported in several studies in the literature. Additionally, other authors have associated the transient myocardial ischemia during a treadmill test for coronary patients with increasing heterogeneity of ventricular repolarization, which can be quantified by increased QT dispersion. Although several studies have correlated the QT interval dispersion with ventricular repolarization heterogeneity, many criticisms in the literature have questioned the concept of QT dispersion. Even in the face of criticism, the latest Brazilian Guidelines for Effort Testing cites as promising the QT interval measure to diagnosis of obstructive coronary artery disease, and highlights that more studies that support its use are needed in the literature. Therefore, our study aims to investigate this question. Thus, we retrospectively analyzed the electrocardiographic tracing of rest and effort of 63 patients submitted to stress testing and cardiac catheterization. Patients were divided into three groups: true negative (TN), true positive (TP) and false positive (FP), where true positives were patients with coronary stenosis of at least 70%, and ST-segment depression or chest pain typical during exertion. True negatives were subjects with coronary stenosis lower than 70%, without ST segment depression or typical chest pain on exertion. False positive was composed of individuals with stenosis less than 70% in the coronary arteries, and presence of ST segment depression or typical chest pain during exertion. The QTc interval dispersion at rest was not different between the three groups. 67 ± 40 ms, 55 ± 26 ms and 49 ± 21ms respectively for the groups TN, TP and FP (p = 0.163). QTc dispersion of effort was significantly different between the groups (47 ± 17 ms TN, 72 ± 42 ms TP, and 61 ± 31ms FP, P = 0.003). Dispersion variation (delta, D) of QTc (QTc dispersion of the first minutes of the recovery minus QTc dispersion of rest) was also statistically different between the groups (-20 ± 45 ms TN, 17 ± 40 ms TP and 11 ± 30 ms FP, p = 0.013). A line graph was sketched for each one of the three groups. In the TP group, 19 patients showed a QTc dispersion increasing from rest to effort, while 7 patients showed a QTc dispersion decreasing. On the TN group, 9 patients showed a reduced QTc dispersion, and 5 patients showed a increasing of QTc dispersion. In the FP group, 14 patients showed an increased QTc dispersion, while 9 showed a decreasing of QTc dispersion. We conclude that patients with chronic coronary artery disease have an increased QTc dispersion during physical effort, and that this method can aid in the diagnosis of coronary chronic disease