ST-segment deviations during pacing-induced increased heart rate in patients without coronary artery disease

Introduction: In order to interpret ST-segment changes as an indicator of ischemia in patients with higher heart rates (HRs), the relation between ST-segment levels and HR needs to be well defined in subjects without coronary artery disease. Methods: Eighteen patients with normal ECGs in the catheterization laboratory, after radiofrequency ablation of AV nodal re-entry tachycardia or an accessory pathway were included. Computerized online vectorcardiography (VCG) was performed during step-wise atrial pacing-induced increases in HR up to 150 beats min(-1) (bpm). The ST-vector magnitude (ST-VM) and the relative ST change vector magnitude (STC-VM) were analysed at the J point, J + 20 and J + 60 ms. Results: There was no divergence in the course of ST-VM or STC-VM based on J point + 0, 20, or 60 ms during increasing HR. The STC-VM mean values increased progressively during increases in HR above 100 bpm, with an average increase in STC-VM of 15-20 mu V per 10 bpm increases in HR. The ST-VM response during HR increases showed a heterogeneous and unpredictable pattern. Conclusion: The STC-VM increases linearly with rising HRs above 100 bpm. The STC-VM can exceed widely recognized ischemic thresholds during higher HRs in the absence of ischemia. The choice of J point time to ST-VM measurements as tested here is not important for the STC-VM relation to HR at these HR levels. Further clinical testing is needed to improve the diagnostic specificity of STC-VM measurements during increased HRs.