Effect of electrode configuration and capacitor size on internal atrial defibrillation threshold using leads currently used for ventricular defibrillation.

BACKGROUND: Previous studies have shown that endocardial atrial defibrillation, using lead configurations specifically designed for ventricular defibrillation, is feasible but the substantial patient discomfort might prevent the widespread use of the technique unless significant improvements in shock tolerability are achieved. It has been suggested that the peak voltage or the peak current but not the total energy delivered determines the patient pain perception and therefore, lower defibrillating voltage and current achieved with modifications in lead and waveforms may increase shock tolerability. This study was undertaken to evaluate the effect, on the atrial defibrillation threshold (ADFT), of the addition of a patch electrode (mimicking the can electrode) to the right ventricle (RV)-superior vena cava (SVC) lead configuration. The influence of capacitor size on ADFT using the RV-SVC+skin patch configuration was also assessed. METHODS: In 10 patients (pts) (Group 1) cardioversion thresholds were evaluated using biphasic shocks in two different configurations: 1) right ventricle (RV) to superior vena cava (SVC); 2) RV to SVC+skin patch. In a second group of twelve patients (Group 2) atrial defibrillation thresholds of biphasic waveforms that differed with the total capacitance (90 or 170 microF) were assessed using the RV to SVC+skin patch configuration. RESULTS: In Group 1 AF was terminated in 10/10 pts (100 %) with both configurations. There was no significant difference in delivered energy at the defibrillation threshold between the two configurations (7.1 +/- 5.1 J vs 7.1 +/- 2.6 J; p < 0.05). In group 2 AF was terminated in 12/12 pts (100%) with both waveforms. The 170 microF waveform provided a significantly lower defibrillating voltage (323.7 +/- 74.6 V vs 380 +/- 70.2 V; p < 0.03) and current (8.1 +/- 2.7 A vs 10.0 +/- 2.3 A; p < 0.04) than the 90 microF waveform. All pts, in both groups, perceived the shock of the lowest energy tested (180 V) as painful or uncomfortable. CONCLUSIONS: The addition of a patch electrode to the RV-SVC lead configuration does not reduce the ADFT. Shocks from larger capacitors defibrillate with lower voltage and current but pts still perceive low energy subthreshold shocks as painful or uncomfortable.

DDD pacing with rate drop response function versus DDI with rate hysteresis pacing for cardioinhibitory vasovagal syncope.

BACKGROUND: The effectiveness of cardiac pacing in preventing vasovagal syncope remains controversial. However, DDI pacing with rate hysteresis has been reported to prevent the recurrence of cardioinhibitory vasovagal syncope in up to 35% of affected subjects and to reduce the overall incidence of syncopal episodes in the others. Recently, DDD pacing with a new promising rate drop response function (Medtronic Thera-I model 7960) has become available in clinical practice. AIM OF THE STUDY: The aim of the present open trial was to test the effectiveness of this new pacing modality in patients with cardioinhibitory vasovagal syncope. STUDY POPULATION AND METHODS: The study population included 20 patients (12 males and 8 females; mean age 61.1 +/- 14 yrs) with recurrent syncope (mean number of prior episode = 6.8, range 5-11) and cardioinhibitory responses during two head-up tilt tests: the first diagnostic and the second during drug therapy with either beta-blockade or etilephrine. The study patients were randomized to receive either DDI pacing with rate hysteresis (8 patients) or DDD pacing with rate drop response function (11 patients). The head-up tilt test performed 1 month after pacemaker implantation was positive in 3 of 12 patients (25%) with DDD pacing with rate drop response function and in 5 of 8 patients (62.5%) with DDI pacing with rate hysteresis. The mean duration of follow-up was 17.7 +/- 7.4 months. During follow-up no patients with a DDD pacemaker with rate drop response function had syncope, while 3 of 8 patients with a DDI pacemaker with rate hysteresis had recurrence of syncope (P < 0.05). CONCLUSIONS: These data suggest that DDD pacing with rate drop response function is effective in cardioinhibitory vasovagal syncope and may be preferable to DDI pacing with rate hysteresis.