Plateau Waveform Shape Allows a Much Higher Patient Shock Energy Tolerance in AF Patients
St. Jude Medical provided equipment for this study and paid Dr. Kroll a consulting fee. Dr. Mouchawar, Mr. Silvestri, and Mr. Moulder are employees of St. Jude Medical. A patent has been submitted for the plateau waveform.
Manuscript received 22 October 2006; revised manuscript received 9 February 2007; Accepted for publication 7 March 2007.
Abstract
Objectives: To evaluate the possible pain reduction of the plateau waveform in atrial fibrillation (AF) patients.
Background: Previous studies have indicated that reduced amplitude waveforms would be less painful than a conventional (65/65% tilt) biphasic waveform. Computer modeling suggested that a moderately long (10–12 msec) plateau (flat topped) shock waveform would deliver equivalent effectiveness with the lowest possible peak amplitude.
Methods: We enrolled 27 patients at two sites with persistent AF with a total of 220 shocks delivered during internal atrial cardioversion using an interleaved crossover design. Patient response was scored in three ways: (1) a verbally reported discomfort score, (2) visual analog scale (VAS), and (3) a blinded observer reporting a contraction score.
Results: All scores were significantly reduced (P < 0.0001) by the plateau waveform with impressive statistics: Verbal discomfort (3.51 ± 0.13 to 2.89 ± 0.12), VAS (7.00 ± 0.56 to 5.91 ± 0.36), and contraction scores (1.94 ± 0.12 to 1.62 ± 0.12). The average pain threshold shift (TS) for the Verbal score was 2.34, while that for the VAS score was 2.30. (This means that the patient typically could tolerate 2.34 times as much energy with the plateau waveform for the same level of verbally reported discomfort.) The contraction TS was less at 1.57. Response scores were also corrected for the shock sequence number to control for the sensitization effect from multiple shocks. This increased the TS for the Verbal score to 3.58, but the shock number was not significant for the VAS. A pulmonary artery electrode return was associated with lower pain compared with a coronary sinus position.
Conclusion: A plateau shaped biphasic waveform resulted in significantly increased shock energy pain tolerances. Controlling for session sensitization, patients tolerated over three times as much energy for the same verbally reported discomfort score.
