We postulated that reducing peak leading edge shock voltage and its rate of rise (waveform rounding) would reduce energy requirements for cardioversion of AF and AFl, and may therefore reduce patient discomfort. Transvenous defibrillating catheters (In-Control Inc.) were placed in the RAA (active fixation) and the CS of six anesthetized sheep. AF or AFl was induced by electrical stimulation (100 Hz, 2 V; Grass stimulator). A standard trapezoidal biphasic (S) waveform (3-ms duration each phase) was compared with a similar waveform that had the first phase rounded (R). Cardioversion was attempted after 30 seconds of arrhythmia, using a Ventritex HVS-O2 defibrillator modified to allow waveform rounding. Each waveform was randomly tested several times at 100-, 150-, and 200-V leading edges, and percentage cardioversion success calculated. Shock energy was calculated from delivered current and voltage using Flukeview (Fluke, Inc.) software. At 100-V leading edge R (64% success) and S (59%), shocks were similarly efficacious (P = 0.37). However, R delivered less current, voltage, and energy than the comparable S shock (means 1.30 A, 65.0 V, 0.33 J R vs 1.92 A, 94.2 V, 0.47 J S; P = 0.0001). Both waveforms were equally successful at 150 V (88% vs 100%; P = NS) and 200 V (100% vs 100%), but again R delivered less current, voltage, and energy (2.05 A, 102.5 V, 0.82 J R vs 2.78 A, 142.3 V, 1.11 J S at 150 V; 2.76 A, 141.2 V, 1.58 J R vs 3.77 A, 189.4 V, 2.03 J S at 200 V; both P = 0.0001). No arrhythmic or other complications occurred in the 174 shocks delivered. Waveform rounding reduces delivered peak voltage, current, and energy without reducing defibrillation efficacy. To determine if these changes are associated with a reduction in discomfort, patients with AF are currently being cardioverted with these waveforms during electrophysiological studies.
The aim of this study was to compare the efficacy of internal atrial defibrillation by conventional truncated exponential biphasic waveforms with and without waveform rounding (1-2 phases) and to determine optimal duration for this novel double rounded waveform. Atrial fibrillation, induced by rapid electrical stimulation, was converted by internal shocks through defibrillation catheters (lateral right atrium and coronary sinus) in anesthetised sheep. Rounding the leading edges of the conventional biphasic waveform (Ventritex HVS-02; settings 100/-50 V, 150/-70 V, and 200/-100 V; n = 8) reduced delivered peak and trough voltages, currents, and energy (by > or = 21 %, P < 0.001; for double (both phases) rounded) without decreasing cardioversion success. At 100/-50 V the efficacy of single (first phase) rounded (53 +/- 13%; mean +/- SEM) and double rounded (59 +/- 11%) shocks was similar to the conventional waveform (56 +/- 14%). Double rounded waveform (phase durations 1-20 ms) efficacy was optimum at 6-10 ms phase duration (100% success at 10-ms phase duration; 1.52 +/- 0.04 J delivered energy; n = 6). Successful cardioversion by conventional, single rounded, and double rounded biphasic waveforms (duration 6 ms each phase), conventional monophasic, rounded monophasic (duration 12 ms), and a damped sine waveform correlated strongly with peak-to-trough voltage swing within the waveform (r = 0.882; P < 0.01; n = 8). For internal atrial defibrillation, rounding both phases of the conventional biphasic waveforms, the double rounded waveform, permits similar efficacy to the conventional truncated exponential biphasic waveform at reduced peak voltage, current, and delivered energy. Optimum phase duration is 6-10 ms (tested range 1-20 ms).
Since the introduction of percutaneous transluminal coronary angioplasty (PTCA), percutaneous intervention with balloon catheters, stents, and atherectomy devices has become a widely accepted practice. The persistent complication of non-Q-wave myocardial infarction (MI), as evidenced by increased cardiac enzyme levels after intervention, has aroused only moderate concern because its incidence was perceived to be small and not clinically relevant. With more systematic assessments of cardiac enzymes--specifically, creatine kinase (CK) and its MB isoform--evidence has begun to clarify both the incidence and the prognosis of periprocedural non-Q-wave MI: It appears to occur nearly three times more often than is clinically evident across all device types (8 to 9% of all interventions) and is directly and continuously associated with adverse outcomes, including late death. Although directional and rotational atherectomy improve angiographic outcome compared with PTCA, periprocedural infarction occurs at least twice as often with these newer technologies; the incidence associated with stent placement is comparable to and possibly higher than that of PTCA. Factors that may cause elevated CK-MB levels include distal embolization, side branch occlusion, thrombus, and coronary spasm. Analyses of the major trials of platelet glycoprotein (GP) IIb/IIIa receptor inhibitors, a class of potent antiplatelet agents, show striking effectiveness of these drugs in reducing the incidence of "enzyme-only" or "silent" MI and in improving long-term clinical outcomes. The findings implicate platelet mediation in the occurrence of periprocedural infarction and suggest an important role for antiplatelet therapy, particularly GP IIb/IIIa receptor inhibition, in protecting patients undergoing percutaneous intervention.
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