The capability ST/HR index and ST/HR hysteresis in detection of ischemia has been validated in patients undergoing standard exercise testing. Its predictive value has never been assessed in pharmacological stress tests using adenosine or dipyridamol.

The objective of our study was to compare the sensitivity and the specificity of ST/HR index and ST/HR hysteresis regarding the diagnostic capability of significant ischemia in patients undergoing stress test with dipirydamol for SPECT evaluation.

We used a cross-sectional analysis of ST/HR index myocardial perfusion stress-rest SPECT data. Two hundred eighty consecutive patients referred for SPECT evaluation and unable to perform a standard exercise test underwent a pharmacological stress test with dipirydamol. The threshold of significant ischemia was set above 10% reversibility hypoperfusion area from entire surface of left ventricle using semi-quantitative SPECT image analysis (QGS). Diagnostic performance of computerized variables was assessed by receiver operating characteristic (ROC) curve.

Area under ROC curve for ST/HR index and ST/HR hysteresis were 0.564 and 0.597. Sensitivities were 38% and 36%, respectively, when specificity was set at 73% for this parameter. The cut points for ST/HR index and ST/HR hysteresis at this same specificity were 1.05μV/(beats/min) and 0.015 mV, respectively.

Whereas ST/HR index and ST/HR hysteresis are useful to detect exercise-induced ischemia, these variables don’t have a good capability in detection of significant ischemia in a population of patients who are tested with dipirydamol despite an acceptabe specificity.