Atrial fibrillation: Epidemiology, mechanisms, and management

Stretch-activated currents in cardiomyocytes isolated from rabbit pulmonary veins

Evidence is growing of a relationship between atrial dilation and atrial fibrillation (AF), the most prevalent type of arrhythmia. Pulmonary veins, which are important ectopic foci for provoking AF, are of increasing interest in relation to the early development of AF. Here, using single cardiomyocytes isolated from rabbit pulmonary veins, we characterised the stretch-activated currents induced by swelling and axial mechanical stretching. Swelling induced both a stretch-activated nonselective cationic current (NSC) and a Cl(-) current. The swelling-induced Cl(-) current (I Cl,swell) was inhibited by DIDS, whereas the swelling-induced NSC (I NSC,swell) was inhibited by Gd3+. The cationic selectivity of the I NSC,swell was K+ >Cs+ >Na+ >Li+, whilst the PK/PNa, PCs/PNa, and PLi/PNa permeability ratios were 2.84, 1.86, and 0.85, respectively. Activation of the I NSC,swell was faster than that of the I Cl,swell. Given a high K+ concentration in the bath solution, the I NSC,swell showed limited amplitude (<-70 mV). Mechanical stretching induced an immediate Gd3+- and streptomycin-sensitive NSC (I NSC,stretch) that was permeable to Na+, K+, Cs+ and NMDG. Persistent stretching activated a DIDS-sensitive current (I Cl,stretch). The I NSC,stretch, but not the I NSC,swell, was completely blocked by 400 microM streptomycin; therefore, the two currents may not be associated with the same channel. In addition, the type of current induced may depend on the type of stretching. Thus, stretch-induced anionic and cationic currents are functionally present in the cardiomyocytes of the main pulmonary veins of rabbits, and they may have pathophysiological roles in the development of AF under stretched conditions.

Totally Endoscopic Ablation of Lone Atrial Fibrillation: Initial Clinical Experience

BACKGROUND

Atrial fibrillation is the most common form of arrhythmia leading to hospital admission. Over 2.2 million Americans are affected by atrial fibrillation and approximately 160,000 new cases are identified annually. As the population continues to age, the number of patients will increase. AF is an incremental risk factor for death and stroke, and consumes billions of dollars in health care expenditures.

METHODS

Between August 2003 and October 2004, 50 drug-resistant, symptomatic atrial fibrillation patients underwent thoracoscopic or robotic-assisted off-pump epicardial microwave ablation with the FLEX 10 device (Guidant, Indianapolis, IN). There were 35 men (70.0%) and 15 women (30.0%), mean age 59.1 years +/- 10.0 (range, 37-75 years). Mean duration of atrial fibrillation was 73.5 months +/- 82.3 (range, 5-480 months). Thirty-three patients (66.0%) had intermittent atrial fibrillation and 17 (34.0%) continuous. Intermittent patients had pulmonary vein isolation whereas continuous patients had additional right and left atrial lesions performed. Forty-six patients (92.0%) had endoscopic stapling of the left atrial appendage.

RESULTS

There were no hospital deaths. Postoperative in-hospital complications were minimal with 2 patients (4.0%) experiencing diaphragmatic dysfunction. No patient required a permanent pacemaker implant. Mean postoperative length of stay was 3.7 +/- 2.2 days. Cumulative follow-up was 335.8 patient months, mean 7.6 months (range, 2.0-15.9 months). There was 1 late death (2.0%). In 5 patients (10.0%) the MicroMaze operation and subsequent electrophysiology intervention failed and a Cox-Maze III operation was performed. Follow-up was 100% complete with 79.5% (35 of 44) patients in normal sinus rhythm.

CONCLUSIONS

Totally endoscopic closed-chest microwave ablation for treatment of intermittent and continuous atrial fibrillation is technically feasible and presents minimal risk to the patient. Initial results are impressive and demonstrate an enhanced quality of life and freedom from atrial fibrillation in drug-resistant symptomatic patients.

Atrial Flutter After Surgical Radiofrequency Ablation of the Left Atrium for Atrial Fibrillation

BACKGROUND

Left atrial radiofrequency ablation is the most common technique for the treatment of atrial fibrillation during mitral valve surgery. Reported failure rates range between 15% and 30%, with some patients remaining in atrial fibrillation and others experiencing atrial flutter. The incidence and nature of the postoperative atrial flutter is not yet well defined.

METHODS

The study group consisted of 50 patients with atrial fibrillation who underwent mitral valve surgery combined with left atrial radiofrequency ablation, and were followed for a mean period of 15 +/- 7 months. The majority of patients (39; 78%) had persistent or permanent atrial fibrillation. Placement of the ablation lines was as follows: encircling the pulmonary veins, isolating the base of the left atrial appendage, and bridging the lateral or posterior mitral annulus and the margin of the pulmonary vein or the appendage-encircling ablation lines.

RESULTS

There were three hospital deaths (6%). Thirty-four (72%) patients were free of any atrial tachyarrhythmia events, and 37 (79%) patients were in sinus rhythm by the end of the study's follow-up. During the follow-up, 6 patients (12.7%) experienced atrial flutter and 1 patient had atrial tachycardia. Electrophysiologic study was performed in 5 of 6 patients with postoperative atrial flutter. In 4 of them, the study findings were consistent with left atrial flutter. One patient with typical isthmus-dependent right atrial flutter underwent successful ablation.

CONCLUSIONS

Left atrial surgical radiofrequency ablation is associated with a high rate of postoperative atrial flutters that appear to be predominantly of left-sided origin.

Atrial fibrillation and cardiac surgery

PURPOSE OF REVIEW

To discuss the pathophysiology, risk factors, and treatments for atrial fibrillation occurring after cardiac surgery.

RECENT FINDINGS

Atrial fibrillation occurs frequently after cardiac surgery and it may lead to patient morbidity. Many variables have been suggested to be associated with this arrhythmia, but only advanced patient age can consistently identify risk for this complication. Immediate electrical cardioversion is indicated when the arrhythmia leads to hemodynamic instability or myocardial ischemia. Otherwise treatment is aimed at heart rate control, elective cardioversion with drugs or electrical means, and anticoagulation when the arrhythmia persists. Multiple investigations have evaluated methods for preventing postoperative atrial fibrillation, but only beta-adrenergic receptor blocking drugs have been consistently shown to be effective, and then not in all patients. Surgical treatments are increasingly being considered as a therapeutic means for ameliorating chronic atrial fibrillation. The use of these procedures has been simplified with the development of devices that can generate linear scars in the atrium and around the pulmonary vein orifices. These simplifications will allow for broader application of these techniques to patients undergoing other cardiac surgery (e.g. mitral valvular surgery).

SUMMARY

Atrial fibrillation is one of the most common complications of cardiac surgery. There are three major aims for treating atrial fibrillation: conversion to sinus rhythm, heart rate control, and anticoagulation. Only beta-blockers can be recommended for prophylaxis against postoperative atrial fibrillation. Further refinements in surgical treatments for atrial fibrillation may allow for wider applications of this therapy with lower rates of complications.

Atrial fibrillation: current surgical options and their assessment

Atrial fibrillation (AF) is the most common cardiac arrhythmia and is associated with morbidity and mortality. Traditional surgical treatment of AF is the Cox-Maze III procedure, a complicated operation. New surgical approaches include alternate energy sources (radiofrequency, microwave, cryothermy) and simplified left atrial lesion sets. These operations cure AF in 70% to 80% of patients. This review describes contemporary and emerging surgical approaches to AF, synthesizes results of these operations, and proposes new standards for reporting results of AF treatment.