In the past, there have been very few ways from a device-based perspective for physicians to manage pacemaker patients suffering from atrial fibrillation (AF). While the introduction of mode switching into pacemakers was a major improvement, it still left the patient and physician dealing with the resultant effects of AF (as mode switching doesn’t “treat” atrial arrhythmias per se).
More recently, the use of standard, high-rate atrial pacing to reduce AF episodes has been shown to be beneficial.1,2 However, high-rate atrial pacing has its own drawbacks as well, i.e., patient discomfort and possible ventricular dysfunction over time.
With AF affecting more than 5 million patients worldwide (2.2 million in the United States), it is the most significant cardiac arrhythmia known today. Recognizing the pervasiveness of this arrhythmia, St. Jude Medical has introduced a novel, device-based approach to persistent and paroxysmal atrial fibrillation management via its proprietary AF Suppression™ algorithm.

General Overview
In July 2001, St. Jude Medical’s proprietary AF Suppression™ algorithm was introduced in the Integrity® Model 5346 pacemaker, making it the first pacemaker commercially approved in the U.S. designed to treat patients with AF and bradycardia pacing indications. The AF suppression algorithm, which has demonstrated sound clinical performance, should prove invaluable to patients on whom AF takes its toll.
The AF Suppression algorithm (Figure 1) is designed to provide atrial stimulation that controls the atrial rate and rhythm, thereby minimizing ectopic beats, long-short cycles, and the dispersion of refractoriness. It accomplishes this by continually monitoring for intrinsic atrial rhythm and then adapting the rate slightly above the intrinsic rhythm to help ensure a high percentage of atrial pacing (typically greater than 90%) that is dynamically tailored to the patient’s rate variations. As such, the algorithm helps provide a stimulation rate that is not inappropriately rapid when the patient is at rest, yet remains sufficiently high when the patient is active.

Benefits
The goal of the AF Suppression™ algorithm is a reduction in the incidence of AF. Clinical benefits are as follows:

• Reduction in symptomatic AF episodes

• Fewer painful cardioversions required for persistent AF

• Increased patient comfort from reduced heart palpitations associated with AF

• Potentially mitigates other health complications associated with AF

How the algorithm works. Upon the detection of two P-waves within a 16-cycle window, the algorithm provides an increase in the atrial pacing rate. The atrial rate increase is dependent upon the Lower Rate Overdrive (LRO) and the Upper Rate Overdrive (URO):

• LRO (Pacing rates of 45–59 ppm): The algorithm increases the rate by 10 ppm.

• URO (Pacing rates of 151–185 ppm): The algorithm increases the rate by 5 ppm.

• For pacing rates of 60–150 ppm: The algorithm increases the rate by a value between the LRO and URO increase. The device automatically calculates this value.

The algorithm delivers atrial stimulation for a programmed number of Overdrive Pacing Cycles (programmable from 15 to 40 cycles). Upon the completion of the Number of Overdrive Pacing Cycles, the algorithm enters its Rate Recovery phase. At this point, the algorithm begins the search for the intrinsic rate by gradually extending (Rate Recovery) the atrial stimulation interval (8 ms/interval for rates >100 ppm; 12 ms/interval for rates < 100 ppm) (Table 1).

Feature in Action
As indicated in Figure 2, atrial stimulation is maintained almost continuously. Regular searching for the intrinsic atrial rhythm and automatic stimulation rate adjustments that slightly exceed the intrinsic rate prevents the patient from being subjected to constant and excessively high rates, while preserving normal circadian variation and rate-responsiveness.

Conclusion
The AF suppression algorithm represents an important new way of treating pacemaker patients who suffer from atrial fibrillation. As a device-based algorithm, it works automatically and without the side effects or compliance issues that can sometimes cause problems. Since it is part of the pacemaker itself, it can be programmed “OFF” in patients who do not currently have AF and then programmed “ON,” should that pacemaker patient develop atrial fibrillation. While AF is a complex rhythm disorder that does not necessarily respond to a single type of treatment, device-based AF suppression represents an important therapeutic alternative for patients with standard bradycardia pacing indications.

REFERENCES

1. Stabile G, Senatore G, DeSimone A, et al. Determinants of efficacy of atrial pacing in preventing atrial fibrillation recurrences. J Cardiovasc Electrophysiol 1999;10:2–9.

2. Garrigue S, Barold SS, Cazeau S, et al. Prevention of atrial arrhythmias during DDD pacing by atrial overdrive. PACE 1998;21:1751–1759.

3. Benjamin EJ, Wolf PA, D'Agostino RB, et al. Impact of atrial fibrillation on the risk of death: The Framingham Heart Study. Circulation 1998;98:946–952.