Diagnostic accuracy of pace spikes in the electrocardiogram to diagnose paced rhythm

•Pace spikes can often not be detected in the ECG during pacing with CRT pacing systems.•The sensitivity of manual ECG interpretation to diagnose paced rhythm is low to moderate.•Absence of pace spikes in the ECG does not rule out paced rhythm.

ObjectiveTo determine how often cardiac resynchronization therapy (CRT) pacing systems generate visible pace spikes in the electrocardiogram (ECG).MethodsIn 46 patients treated with CRT pacing systems, we recorded ECGs during intrinsic rhythm, atrial pacing and ventricular pacing. ECGs were analysed for atrial and ventricular pace spikes by two experienced ECG readers blinded to the pacing therapy and to the study purpose.ResultsAtrial pacing generated visible pace spikes in less than 70% of the ECGs, whereas ventricular pacing generated visible pace spikes in about 90% of ECGs. The sensitivity of manual ECG interpretation for pace spikes was low for atrial pacing (Reader 1: 0.62 [95% confidence interval (CI) 0.50-0.74]; Reader 2: 0.65 [95% CI 0.53-0.77]) and moderate for ventricular pacing (Reader 1: 0.88 [95% CI 0.81-0.93]; Reader 2: 0.93 [95% CI 0.87-0.97]).ConclusionsIn patients with CRT pacing systems, the absence of visible pace spikes in the ECG does not rule out paced rhythm.