Transesophageal low-energy cardioversion in an animal model of life-threatening tachyarrhythmias

Esophageal electrical cardioversion of atrial fibrillation: when esophagus gives a help to cardiologists

Atrial fibrillation is a common clinical disease especially in the elderly and in patients with organic heart disease. Electrical cardioversion is the first choice therapeutic approach for patients in which sinus rhythm could improve the quality of life and where the maintenance of sinus rhythm is considered likely. There are different techniques to perform an electrical cardioversion, each with specific indications, advantages, and limitations. The method most frequently used to restore sinus rhythm is external direct current cardioversion; however, this technique has some disadvantages, since it requires a high energy and usually general anesthesia. Esophageal cardioversion is an alternative method to obtain restoration of sinus rhythm, warranting acute and long-term results absolutely comparable with those obtained by the conventional transthoracic technique, especially in obese and COPD patients with high thoracic impedance for whom the standard technique may be less effective.

Outpatient oesophageal-precordial electrical cardioversion of atrial fibrillation: an effective and safe technique to restore sinus rhythm

OBJECTIVE

External electrical cardioversion is commonly used in the management of atrial fibrillation (AF), but usually involves general anaesthesia. We tested the efficacy, safety and tolerability of a minimally invasive cardioversion technique, not requiring general anaesthesia, performed on an outpatient basis.

METHODS

We performed outpatient oesophageal cardioversion in 87 consecutive patients (mean age: 67.5 +/- 9.6 years; weight: 77.47 +/- 12.34 kg; left atrium diameter: 46.25 +/- 6.85 mm; LVEF: 55.5 +/- 16%) with persistent AF (mean duration: 6.99 +/- 11.55 months). A biphasic shock was delivered via an oesophageal decapolar lead (cathode) and two precordial patches (anode) under a mild sedation (midazolam 2.5-5 mg). In the first 25 patients, a step-up protocol (from 10 to 100 J) was performed whereas, in the other 62, a first shock at 50 J and a second one at 100 J, were delivered.

RESULTS

Patients described the level of discomfort caused by the procedure according a five-grade scale. Cardioversion was achieved in 97.7% of patients using a mean effective energy of 51.2 +/- 15.7 J. In 88.5% of patients, sinus rhythm was restored by using 50 J or less. No complications occurred and no patient required hospital admission. Mean discomfort score was 1.56 +/- 0.74 out of 5. Sinus rhythm persisted in 62.6% of patients at the 1-month follow-up.

CONCLUSIONS

Outpatient oesophageal cardioversion is a safe, acceptable and effective way to cardiovert patients with AF. It may be a useful alternative to external cardioversion. A relatively high starting energy (50 J) was demonstrated to be superior to a low-energy step-up technique.

Electrical cardioversion of atrial fibrillation: different methods for a safe and effective technique

Atrial fibrillation is the most common cardiac arrhythmia observed in clinical practice. Many different therapeutic approaches are available at present but none may be considered the gold standard treatment. Antiarrhythmic drugs are not very effective agents to cardiovert persistent atrial fibrillation and, therefore, the technique most frequently used to restore sinus rhythm is external direct current cardioversion, which has proved to be safe and very effective. Esophageal cardioversion is an alternative method that could obviate some of the limitations of the external technique, such as the high energy required, need for anesthesia and longer hospital stay. Another technique performed during the last two decades is internal cardioversion, but at present, the advantage of this technique is limited to the small proportion of cases of unsuccessful external cardioversion.

Potential benefit of transesophageal defibrillation: an experimental evaluation

INTRODUCTION

Because of the proximity of the esophagus to the heart, transesophageal defibrillation might increase defibrillation success. We assessed the defibrillation threshold (DFT) of transesophageal defibrillation compared with standard transthoracic defibrillation.

METHODS

Defibrillation success and DFTs were determined in 22 female pigs with high (68+/-4 kg, n=12) or low body weight (39+/-1 kg, n=10). After induction of ventricular fibrillation, biphasic shocks were delivered between two cutaneous patch electrodes (sternal and apical position) or between an esophageal and two cutaneous patch electrodes in a sternal and apical position. The esophageal electrode was integrated into a latex sheath covering a standard transesophageal echocardiography probe.

RESULTS

In 5 of 12 pigs with high body weight, external defibrillation failed despite 3 consecutive 200-J shocks, whereas subsequent transesophageal defibrillation was successful with the first shock. In the remaining 7 pigs, a more than 50% reduction in DFT was obtained with transesophageal defibrillation compared with standard biphasic external defibrillation (67+/-27 vs 164+/-23 J, P<.001). Pigs with lower body weight were successfully defibrillated by both transthoracic and transesophageal shocks. The DFT in pigs with low body weight was significantly lower using transesophageal defibrillation compared with transthoracic shocks (65+/-15 vs 99+/-38 J, P<.05).

CONCLUSIONS

In this animal model, nonresponders to standard external defibrillation could successfully be defibrillated via an esophageal-cutaneous electrode configuration. Overall, an almost 50% DFT reduction was achieved by transesophageal defibrillation. Transesophageal defibrillation may provide an additional tool for terminating VF, which is refractory to external defibrillation, eg, in patients with very high body weight.

Ventricular fibrillation induced by low-energy shocks from programmable implantable cardioverter-defibrillators in patients with coronary artery disease

Many of the newest implantable cardioverter-defibrillators (ICDs) provide the option of programmable low-energy cardioversion for monomorphic ventricular tachycardia (VT). Whereas these devices may provide less myocardial damage and increased comfort in patients receiving frequent shocks for VT, the proarrhythmic effects of low-energy cardioversion from ICDs in patients with structural heart disease are not clear. The purpose of this study was to determine prospectively the per-patient incidence of ventricular fibrillation (VF) induction after low-energy cardioversion of VT by ICDs in patients with coronary artery disease. The estimated cardioversion energy requirement was determined during the course of routine predischarge ICD testing in 40 patients with newly implanted ICDs. Two groups of patients were identified during determination of the cardioversion energy requirement: (1) a non-VF group consisting of 26 of 40 patients (65%) without VF induced by low-energy shock and, (2) a VF group consisting of 14 of 40 patients (35%) who developed VF during low-energy cardioversion. There was no difference between the 2 groups in terms of patient age, sex, concurrent antiarrhythmic drug therapy, VT cycle length, or type of ICD system implanted. Compared with the non-VF group, the VF group was more likely to have both a lower ejection fraction (25 +/- 5% vs 33 +/- 8%; p = 0.005) and a cardioversion energy requirement > 2 J (79 vs 27%; p = 0.005). Our results suggest that low-energy cardioversion is associated with a high per-patient risk of VF induction, and the risk is higher in patients with poorer left ventricular function and, possibly, higher cardioversion energy requirement.(ABSTRACT TRUNCATED AT 250 WORDS)

Transesophageal defibrillation: animal studies and preliminary clinical observations

Ventricular fibrillation (VF) that fails to respond to transthoracic defibrillation leaves the clinician with few alternatives. The purpose of this study was to develop a technique of rescue defibrillation by use of transesophageal electrodes. Fourteen anesthetized dogs (20-30 kg) were investigated in this study. Two electrodes (300 mm2) were mounted 8 cm apart on an esophageal probe and inserted approximately 40 cm from the mouth. VF was induced using AC current delivered to the myocardium. Defibrillation was then performed between the distal electrode (anode) and anterior skin patch (cathode). After 15 seconds of induced VF, transesophageal and transthoracic defibrillation thresholds (DFTs) were determined in random order. The esophageal DFT (90 +/- 15 joules) tended to be lower than the transthoracic DFT (115 +/- 35 joules), though this difference was not statistically significant. One dog could not be defibrillated by transthoracic defibrillation but responded to transesophageal defibrillation. Esophageal electrodes were also useful for arrhythmia discrimination and ventricular pacing (pacing threshold of 38 +/- 5 mA at a pulse duration of 2.5 msec). Following transesophageal DFT determination, in ten dogs (total energy of 600 +/- 150 joules), acute esophageal histopathology demonstrated mild to severe focal injury to the mucosa and/or muscular layers. However, esophagi in four chronic dogs (total energy of 470 +/- 110 joules) showed no gross evidence of mucosal damage, perforation, or stricture 4 weeks following defibrillation. Histopathology showed only focal myocyte atrophy and repair. As a last resort, transesophageal defibrillation was performed in the emergency room on four patients with out-of-hospital refractory VF who failed > 6 high energy transthoracic shocks.(ABSTRACT TRUNCATED AT 250 WORDS)

High and low strength nonsynchronized shocks given during canine ventricular tachycardia

Cardioversion shocks given during ventricular tachycardia may cause ventricular fibrillation or acceleration of ventricular tachycardia, or arrest the tachycardia. A recently proposed theory may explain why the former two phenomena may occur. Briefly, this theory states that potential gradient shock fields of a critical strength delivered to tissue with a critical degree of refractoriness will cause circulating wave fronts of ventricular activation ("rotors") manifest as ventricular arrhythmia. We tested this theory by delivering nonsynchronized shocks 50% higher than defibrillation threshold or 50% lower than defibrillation threshold during 275 episodes of ventricular tachycardia in eight dogs with 5- to 7-day-old myocardial infarcts. Shocks stronger than the defibrillation threshold are likely to create shock fields in the ventricles everywhere stronger than this critical value, and therefore would not generate rotors. Shocks less strong than the defibrillation threshold may create shock fields within the ventricles that include the critical value, and therefore cause rotors if given when critically refractory tissue is present. Nonsynchronized shocks were used to increase the likelihood of encountering tissue with a critical degree of refractoriness. Ventricular fibrillation or acceleration of ventricular tachycardia occurred following 83 of 138 (60%) low strength shocks and following 20 of 137 (14.6%) high strength shocks. The pooled odds ratio for induction of ventricular fibrillation or accelerated ventricular tachycardia after low strength shocks as compared to high strength shocks was 8.9.

CONCLUSION

when given during ventricular tachycardia, low strength shocks are much more likely to cause ventricular fibrillation or accelerated ventricular tachycardia than are high strength shocks (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Transesophageal low-energy synchronous cardioversion of atrial flutter/fibrillation in the dog

The purpose of this study was to determine the feasibility and efficacy of terminating atrial flutter/fibrillation using low-energy synchronous shocks delivered through a transesophageal catheter in dogs with talc-induced pericarditis. Atrial flutter/fibrillation was induced by employing the pulse train method. The minimum effective cardioversion energy level was compared for three different methods--method A, delivery between a distal esophageal electrode and a proximal esophageal electrode; method B, delivery of shocks through a distal esophageal electrode and a plate placed on the chest; method C, transthoracic cardioversion. The minimum effective cardioversion energy level did not differ significantly between methods A and B (1.30 +/- 0.46 joules versus 1.29 +/- 0.35 joules). Transesophageal cardioversion decreased the defibrillation threshold three- to fourfold from that of conventional transthoracic cardioversion. There were no complications of heart block, ventricular fibrillation, or any pathologic evidence of esophageal injury. Thus transesophageal low-energy synchronous cardioversion is considered a feasible and effective method for the treatment of atrial flutter/fibrillation.