Aims To analyse whether heart rate may affect the efficacy of adenosine, verapamil and carotid sinus massage in terminating symptomatic episodes of paroxysmal supraventricular tachycardia (PSVT) in adults. Methods and results The study population was selected among 175 adult patients, affected by symptomatic PSVT. One hundred and six of them were considered eligible for the study. Each subject received one of the following treatments: verapamil, 5 mg intravenously (IV) in 5-10 min, followed by 1-5 lg/kg/min; adenosine, 6 mg IV, followed by 12 mg IV after 2-3 min; carotid sinus massage. Adenosine and verapamil were similarly effective in terminating PSVT (74.4% vs 81.8%, P ¼ 0:45). The efficacy of carotid sinus massage was significantly lower in comparison with the other two groups (32.4%, P ¼ 0:00032 vs adenosine and P ¼ 0:000044 vs verapamil group). At logistic regression, PSVT rate showed a positive association with the percentage of sinus rhythm restoration in the group who received adenosine (P ¼ 0:0004). The probability of success in resolving the tachycardia following treatment with adenosine was >75% for heart rates over 166 beats per minute (bpm), but rapidly decreased at lower frequencies, reducing to 25% at 138 bpm. In the verapamil group, PSVT rate was negatively related to the percentage of sinus rhythm restoration (P ¼ 0:018). The probability of success in terminating PSVT following administration of verapamil was >75% for heart rates lower than 186 bpm, but tended to decrease at faster rates, reducing to 25% at 241 bpm. No significant effects of heart rate were observed in the carotid sinus massage group (P ¼ 0:17). The probability curves obtained in the adenosine and verapamil group crossed at a point corresponding to 173 bpm, which may represent a cut-off value to predict which treatment could ensure higher rate of success. Conclusions Heart rate predicts restoration of sinus rhythm in adult subjects with symptomatic episodes of PSVT treated with adenosine and verapamil. Adenosine is highly effective in PSVT characterised by fast rates, whereas the efficacy of verapamil is increased in patients with low-frequency PSVT.

The RCP estimates, during pacing, what the spontaneous MHR would be. Ventricular stimulation at the RCP causes a high P%, stabilising cardiac cycles with a modest increase in HR.

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