A Randomized Controlled Trial of Prophylactic Pulmonary Vein Isolation as Adjunct to Coronary Artery Bypass Grafting

Atrial fibrillation (AF) is a well recognized postoperative complication associated with cardiac surgery occurring in approximately 30% to 40% of patients. AF occurs most frequently within 24 to 72 hours after surgery. Even though postoperative AF is often a short-lived, self-limiting complication, it is associated with a two-fold increase in cardiovascular mortality and morbidity. Patients are often symptomatic due to irregular and/or rapid ventricular rates and complain of palpitations, anxiety, and diminished physical capacity. Postoperative AF is associated with increased incidence of other complications and increased hospital length of stay and overall costs. Patients may also develop congestive heart failure and hemodynamic instability as a result of this complication. As a result of stasis in the left atrium, the risk of thromboembolic complications is increased and the incidence of postoperative stroke is increased. Patients with persistent AF have a 13-fold higher hospital stroke rate than patients without persistent AF. Further morbidity is added in patients requiring anticoagulation if AF lasts greater than 48 hours. Elderly patients requiring anticoagulation have a significantly increased risk of hemorrhagic complications. The incidence of ventricular arrhythmias is also increased in patients in whom AF develops after cardiac operations.

Postoperative AF has an immense impact on both the cardiac surgery patient and hospital resources. One study determined that patients developing AF after cardiac surgery spend about twice as many days in the Intensive Care Unit as patients without AF, and their hospital stay is extended by 3-4 days.Strategies aimed at preventing postoperative AF are necessary to optimize the postoperative care of patients undergoing open heart operations. A large number of clinical trials have evaluated the effectiveness of various pharmacologic modalities in decreasing rates of AF following cardiac surgery. A recent meta-analysis demonstrated that beta blockers, sotalol and amiodarone all reduce the risk of postoperative AF with no marked difference between them. However, neither agent completely eliminated the occurrence of postoperative AF. In the largest available beta blocker prevention trial, metoprolol decreased the prevalence of postoperative AF from 39% to 31%.

The mechanism of AF following cardiac surgery is not well understood, but possible etiologies include rapid firing from an ectopic focus and multiple reentrant circuits within the atria to propagate this rhythm. It has been discovered that in chronic and paroxysmal AF, the pulmonary veins and the surrounding ostial areas frequently contain focal triggers or re-entrant circuits critical to the initiation of AF. In a study of 45 patients with frequent episodes of AF refractory to drug therapy, 94% of ectopic beats responsible for instigating AF were located in the pulmonary veins. Studies have shown that these foci are responsive to radiofrequency ablation. Although it has never been used in the prevention of postoperative AF, circumferential pulmonary vein ablation (CPVA) is a technique that has shown much success in the treatment of AF. In CPVA, radiofrequency lesions are created around the ostia of each pulmonary vein, with the aim to electrically isolate these veins from the left atrium. In one study, 26 patients with resistant AF were treated with CPVA and 64% had sinus rhythm restoration during ablation. In addition, 85% of patients were free of AF at 9 months, with 62% no longer requiring antiarrhythmic drugs and 23% taking drugs that had been ineffective before ablation. Radiofrequency pulmonary vein isolation with electro-anatomic guidance is a safe and effective treatment of AF.

Recently, Medtronic has developed the Cardioblate® BP and BP 2 Surgical Ablation System devices (Minneapolis, MN) to perform pulmonary vein isolation to treat AF. Vichol et al have demonstrated a mean ablation time of 15.2 seconds per lesion with the use of this device.

It is clearly evident that postoperative AF increases morbidity, length of hospital stay, and costs associated with surgical coronary artery revascularization. The current prophylactic agents are not completely effective at eliminating the occurrence of postoperative AF. It has been shown that pulmonary vein isolation is an effective method of treating patients with chronic AF. We propose a study to determine if performing pulmonary vein isolation with the Cardioblate® BP 2 as an adjunct in those patients undergoing routine coronary artery bypass surgery, who are at increased risk of developing postoperative AF, will significantly reduce the occurrence of this complication.