Maintenance of sinus rhythm after electrical cardioversion of persistent atrial fibrillation; sotalol vs bisoprolol.

AIMS: The purpose of the study was to compare the efficacy and safety of sotalol and bisoprolol in the maintenance of sinus rhythm after electrical cardioversion of atrial fibrillation. METHODS: Patients (n=128) were randomized to sotalol (80 mg b.i.d.) or bisoprolol (5 mg x day(-1)). Patients with contraindications to beta-blockers, class III antiarrhythmic drugs or prior treatment with use of study medication for prevention of atrial fibrillation were excluded. Follow-up clinical evaluation was performed 1 day and 1 month after cardioversion and thereafter at 3-month intervals. RESULTS: There were no group differences in baseline clinical characteristics. After a follow-up of 12 months, 59% of all patients were still in sinus rhythm. The fraction remaining in sinus rhythm was calculated for the two groups by Kaplan--Meier analysis. During follow-up, 41% of patients on sotalol and 42% on bisoprolol developed atrial fibrillation (ns). In two patients (3.1%) on sotalol, life-threatening proarrhythmias (torsade de pointes tachycardias) occurred, whereas none were found in the bisoprolol group. Symptomatic bradycardias occurred in two patients on sotalol and three on bisoprolol. CONCLUSION: This study demonstrates that sotalol (160 mg x day(-1)) and bisoprolol (5 mg x day(-1)) are equally effective in maintaining sinus rhythm. Because of the side effects of sotalol, bisoprolol seems to be advantageous for maintenance of sinus rhythm after cardioversion of atrial fibrillation.

Influence of epicardial patches on defibrillation threshold with nonthoracotomy lead configurations.

BACKGROUND: In previous studies, epicardial patch electrodes decreased transthoracic defibrillation efficacy. We studied the effects of two inactive epicardial 14-cm2 titanium mesh patches on defibrillation energy requirements with nonthoracotomy internal lead configurations. METHODS AND RESULTS: A 6/6-millisecond biphasic shock wave-form was delivered via several electrode configurations 10 seconds after ventricular fibrillation was initiated with a 60-Hz generator. In two series, a total of 16 dogs (weight, 23.3 +/- 2.4 kg) underwent an up-down defibrillation protocol. In the first series, the defibrillation threshold (DFT) was determined for each electrode configuration in the presence of two inactive epicardial patches. In the second series, DFTs were determined in the presence of an inactive right ventricular (RV) or left ventricular (LV) patch alone. For several nonthoracotomy lead configurations tested in the first 8 dogs, the mean +/- SD DFT energy increased 49% to 97% with two inactive patches on the heart compared with no patches on the heart as follows: RV to superior vena caval (SVC) electrode, from 8.9 +/- 2.6 to 18.0 +/- 14.3 J; RV to SVC plus subcutaneous array electrode, from 7.0 +/- 2.4 to 10.7 +/- 5.3 J; RV to subcutaneous pectoral plate electrode, from 6.2 +/- 1.3 to 11.4 +/- 4.0 J (P < or = .05). The lowest DFT was achieved by defibrillating between the epicardial patches (3.8 +/- 3.3 J). The second series showed that DFT voltage requirements increased significantly for all three nonthoracotomy lead configurations with the inactive LV patch alone (P < or = .05) but not with the inactive RV patch alone. CONCLUSIONS: Inactive epicardial patches can significantly increase the defibrillation energy requirements for nonthoracotomy lead configurations. This negative impact may be due to an insulating effect of the patches and to a disturbance of the potential gradient field under the patches. If the same holds true in patients, these results have clinical implications. Functioning epicardial patch leads should be incorporated in the defibrillation lead system if already present. If the LV patch is nonfunctioning, such as because of a lead fracture, the marked increase in DFT due to an inactive LV patch calls for thorough DFT testing during surgery and, in selected patients, may necessitate patch removal to produce an effective transvenous-based system.

Endocardial carbon-braid electrodes. A new concept for lower defibrillation thresholds.

BACKGROUND: In the treatment of patients with life-threatening ventricular arrhythmia, transvenous implantable cardioverter/defibrillators provide significant advantages over devices requiring a thoracotomy. This study tested the hypothesis that a new carbon-fiber electrode, designed at the Technische Universität in Munich, Germany, has a lower defibrillation threshold (DFT) than standard transvenous defibrillation electrodes. METHODS AND RESULTS: In 8 mongrel dogs (weight, 25.2 +/- 0.8 kg; heart weight, 192 +/- 19 g), we examined the efficacy and electrical characteristics of a right ventricular endocardial carbon prototype defibrillation electrode (9.5F, 4.4-cm2 surface) compared with a standard CPI 0062 Endotak electrode and a Medtronic 6966 Transvene endocardial right ventricular defibrillation electrode. The new electrode consists of 24 braided, tubular carbon filaments, each containing 1000 highly isotropic carbon fibers of 7-microns diameter, yielding a theoretical electrical surface of 480 cm2. The DFTs were determined in random order between each of the three right ventricular electrodes and a subcutaneous wire array anode placed on the left thorax. A standard step-down/up DFT protocol of 20-V shock steps was applied. Two different biphasic waveforms with a 1-ms delay between phases were tested: 3.2-ms first phase/2.0-ms second phase, and 6.0-ms first phase/6.0-ms second phase. For the 3.2/2.0-ms waveform, we found a significantly lower DFT for the carbon lead (4.96 +/- 1.58 J) compared with the CPI 0062 (6.93 +/- 1.67 J) and the Medtronic 6966 (7.49 +/- 0.99 J) leads. For the 6.0/6.0-ms waveform, the DFT for the carbon electrode (5.97 +/- 2.09 J) was significantly lower than for the Medtronic 6966 lead (8.55 +/- 1.93 J) but not for the CPI 0062 lead (6.30 +/- 1.41 J). The impedance with carbon was lower than with the other two leads for the 6.0/6.0-ms waveform but not for the 3.2/2.0-ms waveform. For the carbon electrode, the 3.2/2.0-ms waveform had a lower DFT than the 6.0/6.0-ms waveform. CONCLUSIONS: The present canine study found a lower DFT for a new carbon electrode compared with DFTs for endocardial defibrillation electrodes made of standard metal. Further long-term animal studies and clinical studies are needed to determine whether carbon materials and braided-lead technology are practical and beneficial in patients.

Intrinsic heart rate response as a predictor of rate-adaptive pacing benefit.

OBJECTIVE: More than half of the pacemaker systems now being implanted can be rate adaptively paced. Our objective was to determine which patients benefit from rate-adaptive pacing in terms of improvement in maximum performance and aerobic capacity. METHODS: Thirty patients with implanted accelerometer-driven, rate-adaptive pacemakers underwent a standardized, ergospirometrically and maximally symptoms = limited cardiopulmonary exercise (CPX) stress test with both rate-adaptive and fixed-rate stimulation in a randomized order. The patients were divided into three groups depending on the intrinsic heart rate achieved during maximum workload: group 1 achieved < or = 90 beats per minute (bpm), group 2 achieved 90 to < or = 110 bpm, and group 3 achieved > 110 bpm. RESULTS: Group 1 demonstrated a significant increase (p < or = 0.01) in maximum oxygen uptake from 16.4 +/- 5.6 mL/kg/min with fixed-rate pacing to 23.2 +/- 11.1 mL/kg/min (+ 41.5%) with rate-adaptive pacing. At the anaerobic threshold, oxygen uptake significantly increased (p < or = 0.01) from 11.8 +/- 2.7 mL/kg/min to 15.7 +/- 5 mL/kg/min (+33.1%). Group 2 patients showed an increase in maximum oxygen uptake from 23.3 +/- 5.4 mL/kg/min to 25.3 +/- 4.9 mL/kg/min (+8.5%, p < or = 0.05) as well as an increase in oxygen uptake at the anaerobic threshold from 15.9 +/- 2.6 mL/kg/min to 18.1 +/- 2.9 mL/kg/min (+13.8%, p < or = 0.05) with rate-adaptive pacing. Group 3 demonstrated no significant difference between the two pacing methods (from 25.6 +/- 9.4 mL/kg/min to 25.9 +/- 9.3 mL/kg/min and from 15.8 +/- 5.5 mL/kg/min to 16.3 +/- 6 mL/kg/min). No difference in maximum oxygen uptake and in oxygen uptake at the anaerobic threshold was evident among the three groups when paced rate adaptively (not significant). CONCLUSION: The second-generation, accelerometer controlled rate-adaptive pacemakers used in testing enabled a stress-oriented heart rate increase and an age- and gender-dependent adequate matching of maximum performance. The benefit from a rate-adaptive system to the patient increases as his or her chronotropic reserve limitation became more pronounced.

Improved defibrillation threshold with a new epicardial carbon electrode compared with a standard epicardial titanium patch.

BACKGROUND: Recent studies show that depending on the type of shock morphology used, 5% to 15% of patients requiring implantable defibrillators cannot be treated with a nonthoracotomy system. In these cases, an epicardial patch-based system becomes necessary. In this study, we investigated a newly developed epicardial carbon electrode as an alternative to a standard epicardial titanium patch. METHODS AND RESULTS: A tubular epicardial braided carbon electrode of 7F diameter and 14-cm length applied in a U-shape to the epicardium was compared with a standard left ventricular epicardial 15-cm2 titanium mesh patch (CPI Inc). As cathode, a CPI endocardial lead, a Medtronic lead, or a carbon-platinum-iridium prototype electrode was used. Ventricular fibrillation was induced with a 60-Hz generator and allowed to continue for 10 seconds before a shock was given. Two different biphasic shock waveforms (3.2/2- and 6/6-millisecond) were delivered by the six electrode configurations. Eight dogs (weight, 24.5 +/- 1.3 kg) underwent an up-down defibrillation protocol. The order of testing the epicardial electrodes, the endocardial cathodes, and the waveform was randomized. With the epicardial carbon electrode, the mean defibrillation threshold (DFT) energy decreased 39% to 56% and the voltage decreased 24% to 35% compared with the titanium patch: from 8.3 +/- 2.5 to 4.9 +/- 3.6 J with the CPI lead and the 3.2/2-millisecond waveform, from 6.2 +/- 2.5 to 2.9 +/- 2.1 J with the carbon-platinum-iridium prototype, and from 6.4 +/- 3.4 J to 3.5 +/- 2.6 J with the Medtronic lead (P < or = .05). The DFT determinations with the 6/6-millisecond biphasic waveform showed a similar trend with slightly higher values. CONCLUSIONS: Compared with a titanium patch, the new braided epicardial electrode significantly decreases the defibrillation energy requirements. This effect can be maximized by using an endocardial carbon-platinum-iridium prototype as cathode and a short duration biphasic waveform.