Atrial fibrillation: New drugs, devices, and procedures
ABSTRACTThe way atrial fibrillation is managed has changed in recent years. Although new anticoagulants are available and more are coming, they offer only marginal benefit over warfarin (Coumadin) and have the disadvantages that their levels cannot be monitored and that their effect cannot be reversed rapidly if bleeding develops. Attempts should be made to control symptomatic atrial fibrillation, first with antiarrhythmic drugs, then with radiofrequency ablation or with a combination. Ablation can be repeated for fibrillation that persists after the first few months.
KEY POINTS
- Warfarin is as safe as—and more effective than—the combination of aspirin and clopidogrel (Plavix) if the international normalized ratio is in the therapeutic range 65% of the time or more.
- New anticoagulants are promising alternatives to warfarin, but they also pose risks. Patients who are doing well on warfarin need not change.
- Several antiarrhythmic drugs are available to control symptomatic atrial fibrillation. Dronedarone (Multaq) should only be considered for patients with paroxysmal atrial fibrillation without significant cardiovascular disease.
- Ablation is often effective in controlling atrial fibrillation, but recurrence is common. Early recurrence often subsides, but late recurrence often requires a repeat procedure.
ABLATION OF ATRIAL FIBRILLATION
Another way to try to restore sinus rhythm is to destroy or isolate the area that is generating the abnormal beats via a catheter-based procedure.
Radiofrequency ablation is generally tried in patients in whom one or two drugs have failed to control atrial fibrillation. Direct comparisons show that ablation is superior to drug therapy and is effective in about 75% of patients with paroxysmal atrial fibrillation vs 20% to 40% of patients on drug therapy. Ablation plus drug therapy is often more effective than either treatment alone.
Mechanisms of atrial fibrillation and ablation
In many cases, atrial fibrillation is stimulated by vagal and sympathetic inputs to the atrium that enter around the pulmonary veins and trigger electrical activations in the area, generating spiraling, reentering circuits. Focal atrial fibrillation also originates predominantly in the pulmonary veins. Ablation of tissue widely circumscribing the mouth of the pulmonary veins prevents the electrical signal from exiting into the atrium.
In about 11% to 37% of cases, atrial fibrillation originates elsewhere, eg, in the left atrium, in the superior vena cava, or in the vein of Marshall. Techniques have evolved to also ablate these regions.
Anticoagulation therapy is recommended before the procedure, and patients at low risk should continue it for a minimum of 2 months afterward. Patients with a higher CHADS2 score should receive anticoagulation therapy for at least 1 year. The consensus statement by the Heart Rhythm Society19 recommends that patients remain on warfarin or one of the newer anticoagulants if their CHADS2 score is 2 or higher. This is because patients have a significant risk of recurrence of atrial fibrillation after radiofrequency ablation, so if their stroke risk is high they should remain on anticoagulant therapy.
Ablation is usually effective, but it carries rare but serious risks
The efficacy of a single radiofrequency ablation procedure is in the range of 60% to 80% for paroxysmal atrial fibrillation and 40% to 60% for persistent atrial fibrillation. The Second International Ablation Registry20 shows a success rate of about 75% in patients with paroxysmal atrial fibrillation and about 65% in patients with persistent and permanent atrial fibrillation. Registry data are often more favorable because reporting is optional, but these results are consistent with those from experienced medical centers. Rates of suppression of atrial fibrillation are higher in patients who also take antiarrhythmic drugs, making a “hybrid” approach useful when ablation alone fails.
According to a worldwide survey, the risk of serious complications is 4.5%. These include stroke (0.23%), tamponade (1.3%), and pulmonary vein stenosis (< 0.29%). The esophagus lies just behind the right atrium, and burning through and creating a fistula between them occurs in about 0.04% of cases and is almost uniformly fatal.20
A second ablation procedure is sometimes indicated for the recurrence of atrial fibrillation, which is almost always caused by recovery of the pulmonary veins. Bhargava et al21 found that the success rate at Cleveland Clinic for a single procedure for paroxysmal atrial fibrillation was 77%, and that it was 92% after a repeat procedure. For persistent atrial fibrillation, success rates were 76% after the first procedure and 90% after the second. Even for long-standing persistent atrial fibrillation (ie, lasting more than 1 year), 80% success was achieved after two procedures. Patients who are less likely to have a successful ablation procedure are those with long-standing atrial fibrillation and coexisting heart disease, including severe valvular disease, although mitral regurgitation sometimes improves if sinus rhythm can be maintained.
The need for a second procedure
After ablation, patients should be closely monitored for a recurrence of atrial fibrillation. Continuous monitoring with implantable cardiac monitor loop recorders can detect unrecognized episodes of arrhythmia. Long-term follow-up is also required to track outcomes and quality of life.
According to the Heart Rhythm Society Task Force on Catheter and Surgical Ablation of Atrial Fibrillation,19 atrial fibrillation recurs after ablation in about 35% to 60% of patients in the first 3 months, with recurrence rates after 1 year ranging from 5% to 16%. The rate of success is determined by the skill of the surgeon, underlying heart disease, attention to follow-up, and how success is defined.
Freedom from recurrence early on is a good predictor that late recurrence is unlikely. Patients who only have a very early recurrence (within the first 4 weeks) are more likely to have long-term freedom from atrial fibrillation tha those who have recurrences after that time.22
In a study of 831 patients, Hussein et al23 found recurrence rates of 24% between months 3 to 13 following ablation and 9% after 12 months. At 55 months, 79% were free from atrial fibrillation without drugs, 11% were free of atrial fibrillation with medications, and 5% had refractory atrial fibrillation.
Recurrence—whether early or late—was more likely to occur in people with persistent vs paroxysmal atrial fibrillation. Other risk factors for late recurrence included older age and larger left atrial size (which is also a risk factor for recurrence on drug therapy). Although recurrent arrhythmia was most often atrial fibrillation, atrial flutter also occurred frequently (in 27% of patients with late recurrence). Three patients (4% of patients with late recurrence) developed atrial tachycardia.23
In patients with early recurrence, 81% underwent repeat ablation, all of whom had recovery of one or more pulmonary veins. After the second ablation, 21% had recurrence, 65% of whom were controlled by medications.23
Whether a patient should undergo subsequent ablation procedures depends on the severity of symptoms, the likelihood of success (based on an educated guess), and the patient’s willingness to undergo another procedure.
ATRIAL APPENDAGE OCCLUSION DEVICE UNDER INVESTIGATION
New devices are being investigated that occlude the left atrial appendage to try to prevent embolization.
The Watchman device, resembling an umbrella, is implanted via a percutaneous catheter in the left atrial appendage, closing it off to preclude a thrombus from forming in the appendage and embolizing to the body. Clinical trials showed that patients who received a device had a slightly lower risk of stroke than otherwise seen in clinical practice.24 Safety and efficacy are still being determined.
The device cannot be deployed in a patient with an existing thrombus because of the danger of dislodging the thrombus, allowing it to embolize.
