Phyllis Holt

Biatrial pacing for paroxysmal atrial fibrillation ☆: A randomized prospective study into the suppression of paroxysmal atrial fibrillation using biatrial pacing

OBJECTIVES The purpose of this study was twofold: to assess whether biatrial pacing is superior to single-site pacing and capable of reducing the frequency of episodes of paroxysmal atrial fibrillation (PAF); and to compare pacing of the proximal coronary sinus (PCS) with the distal coronary sinus (DCS) and the effects of sequential or simultaneous biatrial pacing. BACKGROUND Interatrial conduction abnormalities have a role in the initiation of PAF. Biatrial pacing alters the site and timing of atrial depolarization and may benefit those with drug-resistant PAF. METHODS Nineteen patients with PAF who were intolerant of or refractory to medication were studied. All received right atrial (RA) and coronary sinus (CS) leads (either PCS or DCS). For three months the pacemaker was set in sensing mode only. Subsequently each patient completed three-month periods in random order in the following modes: RA pacing, CS pacing, biatrial pacing using inter-atrial delays of 15 and 70 ms. RESULTS Sixteen patients received a benefit from one or more pacing modes. The greatest reduction in PAF episodes was seen during biatrial pacing, especially with leads sited at the high right atrium (HRA) and distal CS (p = 0.0048). There was no difference for sequential or simultaneous pacing. Three patients derived no benefit. CONCLUSIONS In selected patients, biatrial pacing causes a significant decrease in atrial fibrillation episodes. Optimal lead sites were at the HRA and DCS. Simultaneous pacing conferred no benefit over sequential pacing.

An Investigation into the Electrical Ablation Technique and a Method of Electrode Assessment

Ablative techniques, using standard defibrillalors and commonly available cardiac catheters, have been applied to the His bundle and bypass tracts for the management of arrhythmias. We have done in vitro studies of the physical effects of these high energy electrical impulses delivered via different pacing electrodes. Unipolar impulses of 10 to 400 joules were delivered via three U.S.C.I. bipolar electrodes and three Vitatron Helifix electrodes immersed in Ringers solution. The effects were recorded on 35 mm still film, video tape, and high speed cine film. Pressure, voltage, and current were measured. The U.S.C.L bipolar electrodes and the Vitatron Helifix electrodes safely withstood repeated delivery of 400‐Joule impulses which produced similar flash shapes. Each took the form of an incandescent, spherical “fire‐ball” centered around the exposed electrode surface. The mean diameters of the “fire‐baH” for 10 to 400 J using the U.S.C.I. electrodes were 5–24 mm and 3–20 mm for the Helifix catheter electrodes. Peak pressure excursions of over an atmosphere were observed 3 cm from the electrode tips. Higher pressures, lower voltages, and larger currents occurred using the U.S.C.I. pacing lead. The simple. 35 mm time exposure technique showed that at low energies the flashes appeored to emerge in a retrograde manner from the U.S.C.I, catheters and more distally from the Helifrx electrode. This suggested that the latter might be more elective with lower energy impulses. It is concluded that lower energies should be used to take full advantage of the active fixation electrode.

Intravenous amiodarone in the acute termination of supraventricular arrhythmias

This study was performed to ascertain whether intravenous amiodarone would revert supraventricular tachycardias to sinus rhythm, and if so, whether this effect depended upon the underlying mechanism of the arrhythmia. Fourteen patients were studied. Seven had Wolff-Parkinson-White (WPW) syndrome, 1 had dual atrioventricular nodal pathways and 1 an ectopic atrial tachycardia. Five patients had atrial fibrillation without accessory pathways. An atrial electrode was inserted to initiate tachycardias and record the electrogram. If tachycardias were stable for more than 5 min, amiodarone (5 mg/kg) diluted with dextrose saline was infused intravenously over 5 min. Two electrocardiographic leads and the right atrial electrogram were monitored. In 7 patients with atrial fibrillation (2 with accessory pathways), 6 did not revert to sinus rhythm, 1 reverted only after 1 hr. In 5 cases without accessory pathways the ventricular rate fell 5-10 min after commencing amiodarone. Four of the 5 patients with WPW syndrome and re-entrant tachycardias returned to sinus rhythm within 6 min of commencing the infusion (atrioventricular and ventriculoatrial times increased by 0-38% and 0-14% respectively). (Tachycardias terminated in the anterograde limb.) Three patients underwent intermittent right atrial stimulation for 1 hr. No tachycardias could be initiated for 30 min post amiodarone. The ectopic atrial tachycardia and that due to dual atrioventricular nodal pathways terminated within 7 and 2 min, respectively, of commencing intravenous amiodarone. Thus the use of intravenous amiodarone would be appropriate in the acute management of sustained supraventricular tachycardias.

Antitachycardia pacing: a comparison of burst overdrive, self-searching and adaptive table scanning programs.

Eight patients with the Siemens Elema “Tachylog” genera for implanted for management of paroxysmal reentrant tachycardia were studied to assess the safety and efficiency of three antitachycardia programs. The programs investigated were burst overdrive, self‐searching, and adaptive table scanning. There were five males and three females aged 19–62 years. Seven had Wolff‐Parkinson‐White syndrome, and one had dual atrioventricular nodal pathways. Four had right atrial electrodes and four had right ventricular electrodes. Patients were studied lying, standing, and exercising in all three modes, and the appropriate long‐term programs were chosen. The generator remained in a program for 1 month, if was interrogated and the memory was read, and then it was reprogrammed to a different antitachycardia mode. Burst overdrive was unsuitable for long‐term use in four patients, producing atrial fibrillation in one and ventricular arrhythmias in three. In this group, self‐searching and adaptive table scanning were safe and equally effective (mean number of attempts/tachycardia 6.97 and 6.3, respectively). In the four patients in whom all three programs could be used, burst overdrive proved to be most efficient, the mean number of attempts/tachycardia were 2.4 (cf 9.6 and 9.0 for self‐searching and adaptive table scanning). Thus, burst overdrive was only suitable for long‐term use in 50% of our patients, but when safe it was more efficient than the other two programs, especially in those with narrow termination windows on exercise.

Right ventricular outflow tract tachycardias in patients without apparent structural heart disease

We have investigated 13 patients with monomorphic ventricular tachycardia which originated from the right ventricular outflow tract. No patient had evidence of organic heart disease. There were 3 males and 10 females, aged 13-53 years. All had non-invasive investigations including an exercise electrocardiogram, chest radiography, echocardiograms and gated blood pool scintigraphy. Ten patients underwent cardiac catheterisation. Five patients had a prolonged QTc on their resting electrocardiogram. The remaining investigations showed no evidence of organic heart disease. Ten patients had ventricular arrhythmias which were completely suppressed during maximal exercise but which recurred in the immediate post-exercise period. A further 2 patients with no arrhythmias before exercise had ventricular tachycardia in the post-exercise period. Electrophysiology studies were performed in 5 patients with syncopal episodes, suggesting an automatic focus in 4. Four patients required specific antiarrhythmic surgery for symptoms refractory to medical therapy. Pace-mapping at operation confirmed the origin to be within the right ventricular outflow tract in all. Thus, we have identified a group of patients who have ventricular tachycardia originating from the right ventricular outflow tract in whom there is no apparent structural heart disease. Their arrhythmias are influenced by exercise and are probably due to an automatic focus. Four patients required surgery for ventricular tachycardias and recurrent syncopal episodes refractory to medical therapy.

Low energies and Helifix electrodes in the successful ablation of atrioventricular conduction.

High energies delivered via standard pacing catheter electrodes produce permanent atrioventricular conduction block and generate high pressures. We investigated the use of lower energies and an active fixation electrode. Ten patients with refractory supraventricular tachycardias (six with paroxysmal atrial fibrillation, three with dual AV nodal pathways, and one with a concealed accessory atrioventricular pathway) were treated. A 6F Vitatron Helifix electrode was positioned to give the maximum His bundle deflection. Four shocks of only 50 joules each were delivered at 1‐minute intervals. Long‐term follow‐up showed that seven patients (70%) had persistent complete heart block and two had atrial fibrillation with slower ventricular rates. Nine patients (90%) were symptom‐free without antiarrhythmic therapy. Permanent pacemakers were implanted in eight patients. There were no complications resulting from the procedure. Transvenous ablation of atrioventricular conduction can be safely achieved using a Vitatron Helifix eleclrode and much lower energy values than have been previously employed.

Reversion and Maintenance of Sinus Rhythm in Patients with Permanent Atrial Fibrillation by Internal Cardioversion Followed by Biatrial Pacing

FRAGAKIS, N., et al.: Reversion and Maintenance of Sinus Rhythm in Patients with Permanent Atrial Fibrillation by Internal Cardioversion Followed by Biatrial Pacing. Patients in atrial fibrillation (AF) who fail external cardioversion are usually regarded as in permanent AF. Internal cardioversion may revert many such patients into sinus rhythm (SR) but the majority relapse rapidly into AF. We investigated whether internal cardioversion followed by biatrial pacing is an effective to restore and subsequently maintain SR in patients with permanent AF. Patients in permanent AF underwent internal cardioversion that was followed by biatrial temporary pacing for 48 hours. Those who remained in SR received a permanent biatrial pacemaker programmed to a rate responsive mode with a lower rate 90 beats/min. Primary end point of the study included maintenance in SR 3 months after internal cardioversion. Sixteen patients (14 men, 57 ± 11 years) were cardioverted. The median duration of AF was 24 months (quartiles, Q1= 8.5 and Q3= 102) and mean left atrium diameter was 48 ± 04 mm. A permanent biatrial pacemaker was implanted in 11 patients. At a mean follow‐up of 15 months (range 4 to 24), 8 patients remained in SR for more than 3 months. AF was eliminated in 5 patients, while in two a second internal cardioversion on amiodarone was required. Antiarrhythmic therapy was used in half of our population and did not predict the long‐term maintenance of SR. Following internal cardioversion with continuous biatrial pacing, 50% of patients with permanent AF were maintained for prolonged periods in SR. This is a new modality of treatment of permanent AF directed to the maintenance of SR that provides a further therapeutic option in end‐stage AF.

Developments in the high energy endocardial ablation technique: towards low energies

Until recently the therapeutic choices available for the management of patients with paroxysmal tachyarrhythmias refractory to drug therapy were antitachycardia pacemakers, which are unsuitable for some patients, or surgery, with its attendant hazards. Gonzales et al. [l] first demonstrated in animal experiments that permanent complete heart block could be achieved by delivering high energy direct current shocks to the His Bundle from a standard defibrillator via a catheter electrode. Such impulses produced localised and permanent tissue damage [2]. Following this, Gallagher et al. [3] and Scheinman et al. [4] reported the successful use of this technique in the production of atrioventricular block in patients with paroxysmal supraventricular tachycardias refractory to drug treatment. The technique of both groups was very similar. Under local anaesthesia two temporary catheter electrodes were inserted. One was positioned in the right ventricle to provide pacing cover and the second was accurately positioned against the His bundle. Under general anaesthesia unipolar cathodal shocks were delivered via the His bundle electrode from a standard defibrillator. Permanent pacemakers were subsequently implanted in those patients with persistent complete heart block. The clinical use of His bundle ablation expanded rapidly, with most groups employing the method described above. The energies used by different workers have varied considerably. Shocks have been delivered ranging in amplitude from 50 J by McComb et al. [5], 150-300 J by Manz et al. [6], 200-300 J by Gallagher et al. [3], 300-400 J by Nathan et al. [7] and 300-500 J by Scheinman et al. [4]. Frequently multiple shocks are required, therefore the total energy delivered to a patient can be considerably higher than these figures would suggest.

Permanent Left Atrial Pacing

Left atrial pacing is feasible via the coronary sinus. However, long‐term characteristics of coronary sinus pacing parameters are largely undefined as yet. This study assessed the feasibility and long‐term pacing parameters of coronary sinus pacing. Twenty four patients (13 men, 11 women) with a history of paroxysmal AF refractory to drug therapy underwent biatrial pacemaker implantation. Leads were sited in the high right atrium or right atrial appendage and in either proximal (PCS) or distal coronary sinus (DCS). Pacemaker parameters were measured at implant, 24 hours postimplant, 1 month, 3 months, and at 3 monthly intervals over a period of 2 years. Threshold, impedance, and energy requirements (E = Threshold2/impedance x pulse width) were measured. There was one lead displacement from the PCS within 24 hours postimplant. There were no other acute or chronic complications. The energy values at implant and at 2 years were 0.49 ± 0.47 and 2.18 ± 1.69 mJ for the PCS leads and 0.94 ± 1.47 and 1.27 ± 0.75 mJ for the DCS leads. P values were >0.05 at all points and suggested no significant difference between the two sites over the long‐term. Chronic coronary sinus pacing is a safe and feasible technique. There was no significant difference in energy parameters for leads positioned in the proximal or distal coronary sites. The trends seen at both sites for chronic changes in pacing characteristics are analogous to those described for endocardial leads at other sites. (PACE 2004; 27:314–317)

Inappropriate Discharges by the Implantable Cardioverter Defibrillator During Postoperative Testing: Implications for Intraoperative Assessment

Inappropriate shocks were delivered to a patient while in sinus rhythm by an implantable Cardioverter defibrillator (ICD) during routine prehospitai discharge testing. This was induced by the standard programmer when the “read” telemetry sequence was initiated. The ICD was removed and found to suffer from electrical artifact that was sensed as ventricular tachycardia during telemetry. To avoid inadvertent telemetry‐induced shocks during routine testing, all ICDs should be interrogated, using a standard programmer, intraoperatively, with the unit in “defibrillation on” mode.