About 200,000 Americans are diagnosed with atrial flutter each year. It starts in the atrium, which beats at 240 to 400 beats per minute. On the way down to the ventricle, the atrial-ventricular node prevents this fast beat from occurring in the ventricles by blocking a portion of the beats, usually in a 2:1 or a 3:1 ratio. Even so, the heart is racing.
Risk factors for atrial flutter include valvular heart disease, left ventricular hypertrophy, coronary artery disease, long-standing hypertension, hyperthyroidism, congestive heart failure, and diabetes.
In the long term, this rhythm is unhealthy and needs to be treated to not only control the ventricular rate but also to attempt to change the atrial rhythm to a normal sinus rhythm. Complications of atrial flutter are multiple but the most dread is the development of clots within the heart and of the resultant emboli to vital organs.
A variety of drugs can be used either to convert or to control the actual rate of beating of atrial flutter, but about half of the patients fail to respond adequately to drug therapy. Since the early 1990's, radiofrequency ablation has been used to destroy the foci causing the flutter. This therapy has a nearly 90 percent efficacy rate, but because of the nature of the radiofrequency energy, damage to nearby blood vessels and surrounding tissue is a serious complication. Radiofrequency ablation causes damage to the extracellular matrix and also leads to significant inflammatory processes in the healing phase.
Recently a totally new method has been approved by the FDA to control atrial flutter. It uses extreme cold — cryoablation. This method, approved on Aug. 1, uses the CryoCor Cryoablation System, manufactured by CryoCor. The device is indicated for use in the ablation of isthmus-dependent right atrial flutter in patients 18 or older. This method has the potential to avoid the radiofrequency side effects because it causes much less extracellular matrix damage, as well as less post-treatment inflammation, with similar efficacy.
The product consists of two components: an ablation catheter and a console. The single-use unidirectional steerable ablation catheter has a feature that locks the deflection angle. A metal tip delivers the therapy. The tissue in contact with the tip is ablated by cooling that is achieved by vaporizing refrigerant fluids inside the catheter tip assembly. The tip has the ability to collect intracardiac electrograms for mapping procedures. The catheter is connected to the console by three quick-connect receptacles — one for refrigerant gas, another for monitoring pressure, and the third for transmitting electrical signals.
Cryoablation is performed by accessing the femoral vein and feeding the catheter into the heart cavity.
The CryoCor system was evaluated in a prospective, nonrandomized, single-arm, multicenter trial conducted with 160 subjects at 24 sites in the United States. Subjects were eligible if they had a recent history of symptomatic atrial flutter proven by ECG and cavotricuspid isthmus-dependent atrial flutter proven just before ablation and were between ages 18 and 75. Primary study endpoints included measurement of all serious adverse events occurring within seven days of the procedure, and the creation of a bi-directional block to the abnormal heart rhythm. Secondary endpoints included all serious adverse events occurring seven days after the procedure as well as long-term absence of recurrences of atrial flutter.
The mean age of the enrolled patients was 63, and 65 percent had concomitant arrhythmias, with atrial fibrillation being the most common. Average temperature for each freezing attempt reached minus 81 degrees Centigrade. On average, 18 attempts were needed to complete the ablation procedure.
There were 10 acute events recorded during the trials, with four events classified as related to the device or procedure. All adverse events were resolved by the end of the study. Within seven days, there were no serious adverse events reported that were felt to be related to the procedure or to use of the device
Acute effectiveness was measured at 88 percent, with chronic effectiveness measured at 82 percent. If one included all patients who dropped out with no follow-up, the effectiveness was 70 percent.
The procedure is contraindicated in patients with an active systemic infection, in patients with intracardiac mural thrombus, in patients who have had a ventriculotomy or atriotomy within the preceding four weeks, in patients with cryoglobulinemia, a condition in which low temperatures cause side effects.
The cost of the procedure will include the cost of the single-use ablation catheter (all ablation catheters are competitively priced at about $1,000), the specialty care, the facility charges, and special imaging needed to perform the procedure. Potential cost offsets include the decreased use of antiarrythmia medications and possibly of anticoagulation therapy, and the resultant decrease in side effects from both classes of drugs.
Ablation using radiotherapy is painful and requires anesthesia; cryoablation is nearly painless, making it particularly useful for patients who have contraindications or relative contraindications to anesthesia.
Others patients may benefit from avoiding anesthesia or from having less exposure to the anesthetics.
It is unlikely that managed care will be overly concerned with this procedure. There is little argument about the need to treat atrial flutter that has failed medical therapy. Other methods of cardiac arrhythmia ablation are already accepted by managed care organizations for a variety of cardiac problems. The process and cost of the procedure is probably similar to the existing methods.
Most companies will only need to adjust their existing clinical policy and add the associated codes and instructions to their prior authorization and claim system.
Patients will benefit from a more precise and potentially less damaging procedure.
This approval did not involve a head-to-head trial with radiofrequency ablation, but the FDA is requiring a post-approval study to further evaluate the safety and effectiveness of the device. This will aid future decisions by both interventional cardiologists and health plans, again ensuring that the use of evidence will contribute to Tomorrow's Medicine.