Objectives. We sought to investigate whether patients with syndrome X have an abnormal perception of cardiac pain. Background. Previous studies have reported an increased sensitivity to potentially painful cardiac stimuli in patients with syndrome X. However, it is not clear whether this increase is due to an increased perception of pain or to an enhanced tendency to complain. Methods. We assessed cardiac sensitivity to pain in 16 patients with syndrome X and 15 control subjects by performing right atrial and ventricular pacing with increasing stimulus intensity (1 to 10 mA) at a rate 5 to 10 beats higher than the patient's heart rate. False and true pacing were performed in random sequence, with both patients and investigators having no knowledge of the type of stimulation being administered. Results. No control subject had pacing-induced pain; conversely, 8 patients with syndrome X reported angina during atrial pacing (50%, p <0.01) and 15 during ventricular pacing (94%, p <0.001). During atrial stimulation, both true and false pacing caused chest pain in a similar proportion of patients (50% vs. 63%, p = 0.61), whereas during ventricular stimulation, true pacing caused chest pain in a higher proportion of patients (94% vs. 50%, p <0.05). Pain threshold and severity of pain (1 to 10 scale) were similar during true and false atrial pacing, whereas true ventricular pacing resulted in a lower pain threshold (mean ± SD 3.7 ± 3.0 vs. 7.9 ± 2.8 mA, p <0.001) and a higher level of pain severity (7.3 ± 2.7 vs. 3.1 ± 3.5, p <0.001) than did false pacing. Conclusions. Patients with syndrome X frequently reported chest pain even in the absence of cardiac stimulation. Yet, in addition to this increased tendency to complain, they also exhibited a selective enhancement of ventricular painful sensitivity to electrical stimulation.
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