Efficacy of Biphasic Shock for Transthoracic Cardioversion of Persistent Atrial Fibrillation:. Can We Predict Energy Requirements?

Esophageal electric fields are predictive of atrial cardioversion success-a finite element analysis

BACKGROUND

Atrial fibrillation (AF) is a debilitating cardiac arrhythmia, one potential treatment of which is external cardioversion. Studies have shown external cardioversion success is affected by electrode placement and that esophageal electric fields (EEFs) during low strength shocks have the potential to be used in determining patient-specific optimal electrode placements during animal experiments. The objective of this study was to determine the relationship between EEFs and atrial defibrillation thresholds (ADFTs) during computer simulations using an anatomically realistic computer model of a human torso.

METHODS

Over 600 electrode placements were simulated during which EEFs were compared to ADFTs.

RESULTS

There was no single optimal electrode placement with multiple electrode placements resulting in similarly low ADFTs. There was over 40% difference in the ADFTs between the most and least optimal electrode configurations. There was no correlation between EEFs and ADFTs for all electrode placements, but a strong negative correlation when small shifts from clinically relevant electrode placements were performed.

CONCLUSIONS

These results suggest a small shifts protocol from clinically relevant electrode placements has the potential to increase the probability of successful cardioversion on the first shock and reduce the cumulative number of shocks and energy to which patients are exposed.

Novel Pharmacological Interventions to Maintain Sinus Rhythm after DC Cardioversion

Despite the availability of potentially curative interventions for atrial fibrillation, there remains an important role for conventional anti-arrhythmic therapy and anti-coagulation combined with direct current cardioversion. Unfortunately, the latter approach is disturbed by high recurrence rates of atrial fibrillation. In recent years, several adjunctive therapies have emerged which may facilitate the maintenance of sinus rhythm. These novel therapies and their potential mechanisms of action are reviewed in this article.

Esophageal electric fields are predictive of atrial defibrillation thresholds

BACKGROUND

Atrial fibrillation (AF) is a common cardiac arrhythmia characterized by disorganized cardiac electrical activity. Defibrillation electrode placement has been shown to affect the amount of energy and number of shocks required to defibrillate. The objective of this study was to investigate the relationship between esophageal electric fields (EEFs) and atrial defibrillation thresholds (ADFTs) to determine the feasibility of using EEFs during a low-strength shock to predict patient-specific defibrillation electrode placements.

METHODS

AF was induced and defibrillated according to a Bayesian four-shock protocol for 12-electrode placements in six pigs. EEFs were measured during each of the four shocks of the protocol and during a 1-J shock for each electrode placement. Squared EEFs (EEF(2) s) during all shocks were compared to the ADFTs using a linear regression.

RESULTS

There was a negative relationship between EEF(2) s during the 1-J shocks and ADFTs, with median R(2) values of 0.863 and 0.840 for anterior-anterior (AA) and anterior-posterior (AP) electrode placements, respectively. There was a strong, positive relationship between applied energy and EEF(2) s, with median R(2) values of at least 0.866 for all animals. The placement with the highest EEF(2) resulted in the lowest ADFT for both AA and AP placements in four of six pigs. In the other two animals, this held for one electrode set but not both.

CONCLUSIONS

There was a strong negative relationship between EEF(2) s during 1-J shocks and ADFTs for both AA and AP electrode placements. These preliminary results suggest that using EEF(2) s to predict patient-specific electrode placements is feasible.

Atrial fibrillation in the elderly

Atrial fibrillation (AF) remains the most common form of cardiac arrhythmia seen in man, and often requires acute intervention. This article provides an overview of the incidence, prevalence, etiology, and pathophysiology of AF in elderly patients, with special emphasis on the perioperative period. The pharmacologic and nonpharmacologic management strategies available to the anesthesiologist are described. The anesthesiologist must be aware of the causes, consequences, and treatment of elderly patients developing AF during the perioperative period, as well as patients presenting to the operating room with chronic AF.

Postoperative atrial fibrillation

Atrial fibrillation is a common arrhythmia that occurs after cardiac surgery. It is associated with an increase in morbidity, length of hospital stay and mortality. Patients who are at higher risk of postoperative atrial fibrillation should receive prophylactic treatment. Atrial fibrillation usually resolves spontaneously after heart rate is controlled; however, if patients are highly symptomatic or hemodynamically unstable, sinus rhythm should be restored by electrical or pharmacologic cardioversion.

Postoperative atrial fibrillation

Atrial fibrillation is a common arrhythmia after cardiac surgery. It is associated with an increase in morbidity, length of hospital stay, and mortality. Patients who are at higher risk of postoperative atrial fibrillation should receive prophylactic treatment. Atrial fibrillation usually resolves spontaneously after heart rate is controlled; however, if patients are highly symptomatic or hemodynamically unstable, sinus rhythm should be restored by electrical or pharmacologic cardioversion. Patients with atrial fibrillation of more than 48 hours should receive antithrombotic therapy for thromboembolism prevention.

A simple point score system for predicting the efficacy of external rectilinear biphasic cardioversion for persistent atrial fibrillation

AIMS

To develop a simple point score system that can accurately predict the optimal energy of initial rectilinear biphasic (RLB) waveform shock for cardioversion (DC) of persistent atrial fibrillation (AF).

METHODS AND RESULTS

Data from 302 consecutive patients with AF who underwent a step-up protocol of sequential shocks of 50 J-from 1 up to 2 J/kg-200 J of RLB waveform DC were prospectively examined. Using a logistic regression model, three variables independently predicted the need for 2 J/kg shocks: AF duration > 7 months, previous DC, and increased left atrial (LA) diameter > 4.5 cm. A simplified point score system (REBICAF score) that spans from 0 to 4 was developed. The score gives two points for AF duration > 7 months and one point for previous DC or LA diameter > 4.5 cm. The area under the receiver operator curve (ROC) of the proposed score for predicting the need for 2 J/kg shock was 0.84. There was a progressive increase in the need for 1 J/kg, 2 J/kg, and 200 J as the point score increased (P < 0.001, chi2 test for trend). More than 90% cumulative success rate was achieved in the low- (0-1), intermediate- (2), and high-REBICAF (3-4) score subgroups with 1 J/kg, 2 J/kg, and 200 J RLB shocks, respectively.

CONCLUSION

A simple point score system is useful in prediction of successful initial RLB energy for DC of AF.

Esophageal electric fields are correlated to atrial defibrillation thresholds: towards patient-specific optimization of external atrial defibrillation

Studies have investigated the effect of defibrillator paddle position on the efficacy of external electrocardioversion of atrial fibrillation, without agreeing upon an optimal placement. We wish to investigate using esophageal electric fields (EEFs) to predict atrial defibrillation thresholds (ADFTs) on a patient-specific basis. We propose to (1) investigate the relationship between EEFs and ADFTs using computer simulations, (2) develop an esophageal probe that can accurately measure three-dimensional electric fields and (3) investigate the relationship between EEFs and ADFTs values in-vivo. Sixteen anterior-anterior and eleven anterior-posterior placements were simulated yielding a negative relationship between EEFs and ADFTs (R2=0.91 and 0.93, respectively). An esophageal probe was developed that accurately measures EEFs. Animal studies showed a negative relationship between EEFs and ADFTs. This data suggests using EEFs to predict ADFTs on a patient-specific basis is plausible.