Coronary stent symmetry and vascular injury determine experimental restenosis.

OBJECTIVE: To assess the impact of stent symmetry on restenosis using the coronary overstretch sheep model. METHODS: Neointimal thickness, injury index, and percentage diameter and area stenosis were calculated by digital morphometry. The standard deviation of the angular burden was used to assess stent symmetry for each section. MATERIALS: 15 healthy Merino sheep (63-75 kg) underwent implantation of 30 slotted tube stents (7 mm). Restenosis was induced by calculated overstretch of the coronary artery. Twenty eight days after implantation, stents were excised and underwent histological examination using quantitative digital morphometry. RESULTS: The severity of vessel injury was positively correlated with neointimal thickness and with percentage diameter and area stenosis (p < 0.001). Mean neointimal thickness and mean vascular injury per cross section were strongly related to the standard deviation of angular burden, with correlation coefficients of 0.6 and 0.8, respectively (p < 0.001). CONCLUSIONS: The well known relation between vascular injury and restenosis was confirmed, and a new relation was discovered between stent asymmetry and restenosis. If these results apply to human coronary arteries, restenosis may also be dependent on the degree of asymmetric stent expansion. These results should influence the development of new stent designs to reduce asymmetric stent expansion, leading to a more homogeneous strain distribution in stented coronary segments.

Efficacy of a new balloon catheter for internal cardioversion of chronic atrial fibrillation without anaesthesia.

OBJECTIVE: To compare a new internal cardioversion system incorporated into a balloon guided catheter with a conventional two electrode system in patients with atrial fibrillation (AF). DESIGN: Prospective study. PATIENTS: 74 patients with chronic AF treated by internal cardioversion. MATERIALS: A 7.5 F balloon catheter with high energy electrode arrays each consisting of six 0.5 cm platinum rings. Brachial vein access enables one electrode array to be placed in the left pulmonary artery (distal pole) and the other at the lateral right atrial wall (proximal pole). The conventional two electrode system consists of 6 F electrodes placed in the proximal left pulmonary artery (anode) and the lower right atrium. INTERVENTIONS: Internal cardioversion was performed by shocks delivered in 40 V incremental steps from an external defibrillator. Shocks were applied by the new device to 32 patients (group A) and by the conventional system to 42 patients (group B). RESULTS: The groups differed with respect to system positioning (9.2 (7.3) upsilon 12.3 (8.1) minutes, p < 0.05) and fluoroscopy times (1.7 (1.0) v 3.3 (2.1) minutes, p < 0.01). Sinus rhythm was restored in 30 patients of group A and in 39 of group B (NS) with mean (SD) energy requirements of 8.4 (3.1) J and 7.2 (3.1) J, respectively (NS). CONCLUSIONS: This new method of internal cardioversion has comparably high primary success rates and low sedation requirements with single and two lead systems.

A comparison of treatment of atrial fibrillation with low-energy intracardiac cardioversion and conventional external cardioversion.

AIM: Low-energy (1 to 15 J), catheter-based intracardiac cardioversion was compared with transthoracic external cardioversion (360 J) in a prospective, cross-over clinical trial. METHODS AND RESULTS: In 187 consecutive patients with chronic atrial fibrillation, over a period of a mean of 10.0 +/- 7.3 (SD) months, 217 cardioversion attempts were made. Intracardiac shocks were randomly applied between two 6-F catheters located in either the right atrium and coronary sinus or between the right atrium and left pulmonary artery. When a cardioversion attempt with one method failed, the other method was implemented. After cardioversion, all patients were treated orally with sotalol with a mean daily dose of 174 +/- 54 mg. Internal cardioversion was more effective than external cardioversion (65/70 = 93% vs 92/117 = 79%, P < 0.01). The mean energy for successful cardioversion was 5.8 +/- 3.2 J for the internal and 313 +/- 71 J for the external cardioversion group. At a mean follow-up of 12.5 +/- 6.4 months, 48% (38%) of the patients treated with internal (external) cardioversion were in sinus rhythm (P < 0.05). In 22 of 25 patients in whom external cardioversion failed, sinus rhythm was restored with internal cardioversion at a mean energy of 6.5 +/- 3.0 J. Overweight patients had twice the risk of unsuccessful external cardioversion. CONCLUSIONS: Internal cardioversion is effective in restoring sinus rhythm. It might be indicated in patients in whom external cardioversion had failed or in whom external cardioversion is assumed to be difficult or even contraindicated.

Patient characteristics and underlying heart disease as predictors of recurrent atrial fibrillation after internal and external cardioversion in patients treated with oral sotalol.

The aim of this study was to identify predictors for recurrent atrial fibrillation after internal and external cardioversion in 157 patients. After cardioversion, patients were treated orally with sotalol (174 +/- 54 mg/day). Univariate predictors for recurrence included coronary artery disease (p < 0.05) and advanced age (p < 0.05). Multivariate adjusted risk for relapse increased with the presence of coronary artery disease (odds ratio [OR] 3.4, 95% confidence interval [CI] 1.6 to 8.0), presence of atrial fibrillation > 2 months before cardioversion (OR 2.3; 95% CI 1.4 to 4.5), left atrial diameter > 60 mm (OR 2.1; 95% CI 1.2 to 3.1), and age > 65 years (OR 1.6; 95% CI 1.3 to 3.3). In 26% of patients with lone atrial fibrillation, recurrence was observed compared with 51% of patients with underlying structural heart disease (p < 0.05). The mode of conversion, internal or external, had no impact on the recurrence rate. These findings might be useful for selection of the most appropriate therapy for the individual patient.

Does reducing capacitance have potential for further miniaturisation of implantable defibrillators?

OBJECTIVE: To determine whether considerably smaller capacitors could replace 125 microF capacitors as the standard for use in implantable defibrillators. METHODS: Measured energy, impedance, voltage, and current delivered were compared at defibrillation threshold in 10 mongrel dogs for defibrillation using 75 microF and 125 microF capacitors alternated randomly. Defibrillation was attempted with biphasic shocks of comparable tilt between an endocardial lead in the right ventricular apex and a "dummy" active can of an experimental implantable device placed in the subpectoral position. RESULTS: A reduction of capacitor size of 40% was associated with an increase in voltage of 21% and in current of 22%. With a 65% tilt, no significant differences were found between the two capacitances with respect to the impedance or energy required for defibrillation. CONCLUSIONS: Multiple advances in electrode material, electrode configuration, shock morphology, and shock polarity have reduced defibrillation energy requirements. Smaller capacitors could be used in implantable cardioverter/defibrillators without a major decrease in effectiveness.

Effect of electrode position on outcome of low-energy intracardiac cardioversion of atrial fibrillation.

The aim of this study was to evaluate the new method of low-energy, catheter-based intracardiac cardioversion in patients with chronic atrial fibrillation (AF) and to compare 2 different lead positions. Accordingly, we prospectively studied 80 consecutive patients with chronic AF (9.8 +/- 7.9 months) who were randomly assigned to undergo internal cardioversion either via defibrillation electrodes placed in the right atrium and coronary sinus (coronary sinus group) or via defibrillation electrodes placed in the right atrium and left pulmonary artery (pulmonary artery group). Intracardiac shocks were delivered by an external defibrillator synchronized to the QRS complex. After conversion, all patients were treated orally with sotalol (mean daily dose, 189 +/- 63 mg/day). For conversion to sinus rhythm, the overall mean energy requirement was 5.6 +/- 3.1 J. In the coronary sinus group, cardioversion was achieved in 35 of 38 patients at a mean energy level of 4.1 +/- 2.3 J (range 1.0 to 9.9), and in the pulmonary artery group in 39 of 42 patients with 7.2 +/- 3.1 J (range 2.5 to 14.8). Although there was no difference with regard to success rate, the energy differed significantly between the 2 groups (p < 0.01). Mean lead impedance was 56.4 +/- 7.0 omega and 54.6 +/- 8.5 omega, respectively (p = NS). No serious complications were observed in either lead group. At a mean follow-up of 14.2 +/- 7.0 months, 54% and 56%, respectively, of patients who had been converted successfully remained in sinus rhythm. Thus, low-energy biphasic shocks delivered between the right atrium and coronary sinus or pulmonary artery are equally effective for cardioversion of patients with chronic AF. The energy requirements for conversion from a pulmonary artery electrode position are higher than for the coronary sinus position.

Pain threshold for low energy intracardiac cardioversion of atrial fibrillation with low or no sedation.

UNLABELLED: Recent studies have shown that internal cardioversion of atrial fibrillation is safe and effective. In this randomized prospective study, we have tried to evaluate the influence of different waveforms on the perception of pain during internal cardioversion in patients with chronic atrial fibrillation. METHODS: Internal cardioversion was performed with minimal or no sedation in 31 consecutive patients. R wave triggered, biphasic shocks of 6 ms/6 ms or 3 ms/3 ms duration (randomly selected) and approximately 65% tilt were used starting with a 50-V test shock. The shock intensity was increased in 40-V steps up to a maximum voltage of 520 V Shocks were applied via two custom-made catheters (Elecath, Rahway, NJ). In 16 patients (3 females, age 61 +/- 11 years, left atrium diameter 58 +/- 5 mm, duration of atrial fibrillation 4 +/- 4 months), 6/6 waveforms were used, and in 15 patients (1 female, age 62 +/- 5 years, left atrium diameter 59 +/- 4 mm, duration of atrial fibrillation 5 +/- 2 months), 3/3 waveforms were used. After cardioversion, each patient was asked to quantify their pain on a scale from 0-10 (0 = no pain, 10 = intolerable). Fourteen of the 15 patients in the 3/3 ms and 15 of the 16 patients in the 6/6 ms group were successfully cardioverted. Patients from the 6/6 waveform group were cardioverted with a lower mean voltage of 254/92 versus 355/127 V (P < 0.02), at lower pain score 1.8 +/- 1.3 versus 4.2 +/- 2.2 (P < 0.05) with equivalent energy (6.8 +/- 2.8 versus 6.2 +/- 1.5 J, n.s.) and required lower doses of midazolam of 2.2 +/- 1.9 versus 4.0 +/- 1.8 mg IV (P < 0.02). The waveform used in internal cardioversion seems to have a major impact on the patients' perception of pain. These results imply that energy determines the success of a shock, but voltage determines the pain perceived by the patient. The use of waveforms that deliver greater energy at lower peak voltages offers the possibility of internal cardioversion with less sedation and greater patient tolerance.

Improving accelerometer-based rate adaptive pacing by means of second-generation signal processing.

Accelerometer-based rate adaptive pacing has gained widespread clinical use. Limitations exist for the distinction between walking upstairs and downstairs. It was the aim of this study to evaluate a new signal processing algorithm for more physiological rate adaptation. A custom-made pacemaker incorporating an accelerometer was randomly fixed to the left or right chest of 16 pacemaker patients (7 females, age: 64 +/- 11 years), 18 elderly study participants (6 females, age: 62 +/- 11 years), and 15 students (7 females age: 23 +/- 2 years). Study participants walked on level ground, upstairs and downstairs at five different step rates (72, 84, 96, 108, and 120 steps/min) controlled by an acoustic quartz metronome. The accelerometer signals, recorded on a portable data recorder, were analyzed with respect to frequency content, peak average of the mean acceleration, and morphology characteristics of the acceleration signal above and below zero baseline. By calculating the quotient of the signal's duration above and below zero baseline, a reliable discrimination between walking upstairs and downstairs was possible. A correction of the Leaky integrator signal by the new quotient yielded a more adequate rate adaptation to walking up and downstairs to represent at the patient's daily life activities. A more physiological rate adaptation can be achieved when using not only the accelerometer signal's amplitude, but applying additionally the morphology criterium of the acceleration signal's content in the positive and negative direction.