Introduction: Exercise stress testing (EST) is used to detect exercise-induced myocardial ischemia but has limited diagnostic value because of its known low sensitivity. The analysis of high-frequency QRS segments (HFQRS-analysis) may provide additional information during EST. The aim of this study was to assess the incremental diagnostic value of HFQRS-analysis on top of conventional ST-segment analysis.
Methods: In this prospective observational study, we enrolled consecutive patients referred for nuclear myocardial perfusion imaging (MPI) using bicycle EST to detect stress-induced myocardial ischemia. Patients with atrial fibrillation or QRS duration of more than 120ms in the baseline ECG were excluded. The results of MPI (SDS ≥2) were used as the diagnostic gold standard for the presence of a myocardial ischemia. Manual ECG interpretation based on ST-segment changes was performed by a cardiologist according to current guidelines. Automated HFQRS analysis was performed as described in the Figure in a blinded fashion.
Results: 873 patients were enrolled. The HFQRS result was non-diagnostic, mostly due to insufficient signal quality, in 235 patients (27%), and standard ST-segments could not be assessed in 7 patients (1%) due to noise, leaving 634 patients for analysis. Of those, 140 patients (22%) had an ischemia as final diagnosis. The sensitivity was similar with HFQRS-analysis compared to conventional ST-segment analysis (45% vs 42%, p=0.67) and the specificity was lower (74% vs 87%, p<0.001). If HFQRS was used on top of manual ST-analysis, the sensitivity improved to 61% (p<0.001 vs ST-segment analysis alone). In the multivariable logistic regression analysis, the HFQRS analysis provided independent information on top of age, gender, clinical pre-test probability and conventional ST-segment analysis and was associated with an odds ratio of 1.9 (1.2–3.0, p=0.003). For the detection of a prognostically relevant ischemia (SDS ≥8), the additional use of HFQRS on top of manual ST-analysis improved the sensitivity from 68% to 88% (p=0.008).
Conclusion: In patients with suspected exercise induced ischemia, the use of HFQRS-analysis on top of conventional ST-segment analysis during bicycle EST significantly improves the sensitivity of the test from 42% to 61% and adds independent diagnostic information on top of age, gender and clinical pre-test probability. Further technical improvement however is needed to reduce the proportion of non-diagnostic tests.