Unexpected and undesired side-effects of pacing algorithms during exercise

Cardiac implantable devices during exercise: Normal function and troubleshooting

“…Most pacemakers have algorithms that progressively shorten the AV interval, according to the level of exercise of the individual, as well as the PVARP and the ventricular refractory period—the equivalent of the QT interval in the electrocardiogram, such as it happens under physiological conditions. Patients with paroxysmal or intermittent AV block, during exercise can achieve a fast sinus rate with adequate AV conduction; in these cases, it must be verified that a “mismatch” has not occurred due to any of these excessively long intervals 11,14‐16 or, as it has already been mentioned, a false atrial tachyarrhythmia is misdiagnosed (Figure 4) or the automatic mode switch algorithm kicked in; or, in devices capable of treating atrial tachyarrhythmias, antitachycadia pacing is performed inappropriately 16,18 . Attention should be paid to these intervals, especially when the MTR has been already adjusted to the level of exercise the patient is capable of.…”

“…In patients who have a partially preserved AV conduction, different degrees of fusion with the patient's intrinsic beats can be observed (Figure 3A); if the patient has intrinsic Wenckebach‐type AV block, the progressive prolongation of the AV interval can cause the subsequent atrial contraction to occur during the post‐ventricular atrial refractory period (PVARP); 14,15 in these cases, errors can occur, such as a false diagnosis of a supraventricular tachyarrhythmias (Figure 3B), followed by inappropriate automatic mode switch function 16,17 and the subsequent loss of AV synchrony (Figure 4). In some patients with AV block, sinus node dysfunction occasionally may coexist and symptoms secondary to chronotropic incompetence are not recognized after pacemaker implantation; in them, is also necessary to turn on a rate response algorithm and a maximum stimulation rate limit, according to the physical performance of the patient.…”

“… 22,23 It is necessary to carry out a stress test in order to evaluate the physical condition of the individual, the maximum heart rate reached, and eventually, the appearance of arrhythmias, given that they must be taken into account as criteria for individualized programming; since young patients reach sinus rates around 160‐180 bpm, so the first diagnostic zone is usually programmed above this value; the risk of inappropriate delivery of exercise‐induced shocks in young patients is frequently associated with sinus tachycardia; 24 while in older patients with heart failure, it is more common to observe atrial fibrillation or other mechanisms not related to physical exercise. In patients who also have a biventricular stimulation device, the greatest challenge is avoiding loss of resynchronization, in the context of an elevated heart rate related to physical exercise 16,25 …”