Usefulness of Diastolic Time Measured on Electrocardiogram to Improve Sensitivity and Specificity of Exercise Tolerance Tests

Abstract

The current exercise tolerance test (ETT) criteria predominantly assess changes in ST-segment deviation (i.e., a systolic component of the cardiac cycle). Because diastolic dysfunction precedes that of systolic dysfunction during myocardial ischemia and most coronary flow is diastolic, the addition of electrocardiographic markers of diastolic time might improve the ETT sensitivity and specificity for detecting significant coronary artery disease. Among consecutive patients who had an ETT and subsequently underwent coronary angiography, we evaluated the diastolic time by assessing the TP and TQ segments and TP/RR and TQ/RR ratios in each ETT stage. Coronary artery disease was defined angiographically as significant (≥70% lumen occlusion), intermediate (>50% but <70% lumen occlusion), or nonsignificant (≤50% lumen occlusion). Of the 48 study patients, hypertension and hyperlipidemia appeared highly prevalent. TP, TQ, TP/RR, and TQ/RR correlated significantly with RR and changed with each ETT stage. Although TP and TQ were not significantly associated with significant coronary artery disease, TP/RR and TQ/RR proved to be, particularly beyond stage 2. When TQ/RR of ≤0.39 and TP/RR of ≤0.13 were used, their individual sensitivities and specificities were reasonably comparable to that of traditional ETT criteria (79% sensitivity and 44% specificity at our institution). Adding TQ/RR of ≤0.39 and/or TP/RR of ≤0.13 to existing ETT criteria improved its sensitivity to 100% and specificity to 86%. In conclusion, the addition of diastolic time indexes of TP/RR and TQ/RR significantly improved the overall ETT diagnostic value above the guideline-oriented, perhaps "traditional," criteria for the diagnosis of myocardial ischemia. Such parameters should be widely investigated further for clinical accuracy and compatibility.