SafeR 2: switch for first degree atrioventricular block during exercise
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Rate responsive (>120/mn) atrial pacing (Ap) and ventricular (Vs) sensing; switching to DDD mode after 6 consecutive Ap-Vs intervals exceeding the programmed value of the long PR;
The presence of a very long PR interval may be associated with the occurrence of symptoms, if the response to exercise is not physiological. Indeed, in the absence of reduction of the PR interval concomitant with the increase in exercise rate, atrial systole following atrial depolarization occurs too early during ventricular diastole. Atrial systole may even occur at the end of ventricular systole resulting in a loss of active atrial contribution to cardiac ejection, a shortening of left ventricular filling time, diastolic mitral regurgitation and, in most cases, atrial contraction against closed AV valves. This can be accompanied by a more or less marked symptomatology (exertional dyspnea, retrograde flow sensation in the jugular veins, palpitations, malaise) similar to that observed in paced patients in VVI mode with retrograde conduction (pacemaker syndrome). A certain number of uncontrolled studies suggest that pacemaker implantation can reduce symptoms and improve functional status in this setting. In the latest European recommendations, there is a hemodynamic indication (Class IIA) for pacemaker implantation for this type of presentation: “implantation of a pacemaker should be considered in patients with first-stage AV block (PR> 300 ms) and symptoms compatible with pacemaker syndrome “.
As explained previously, it is possible to program the AVB I criterion on rest + exercise or exercise only.
When the minimum rate is programmed at 70 bpm or less, rest corresponds to the zone between the minimum rate and 100 bpm (non-programmable) during acceleration. Exercise corresponds to the zone between 100 bpm and the programmed maximum rate. During deceleration, exercise corresponds to the zone between the maximum rate and 90 bpm.
When the minimum rate is programmed to greater than 70 bpm, rest corresponds to the zone between minimum rate and minimum rate + 30 bpm during acceleration. Exercise corresponds to the zone between minimum rate + 30 bpm and the programmed maximum rate. During deceleration, exercise corresponds to the zone between maximum rate and minimum rate + 20 bpm.
For this patient (minimum rate at 55 bpm), if the parameter is programmed to exercise only, switching on a long PR only occurs for a rate > 100 bpm during acceleration then > 90 bpm during deceleration.
When the parameter is programmed to rest + exercise, the limit value defining a long PR varies linearly between the maximum value at the basic rate and the minimum value at the maximum rate.
When for a same exercise, the device diagnoses 3 DDD mode switches for atrioventricular conduction impairment, the device remains in DDD mode until the end of the exercise (no return thereafter to ADI mode until the end of this exercise defined by a rate < 90 bpm).
When the PR interval is extremely prolonged, the physiological activation/contraction sequence between atria and ventricles is no longer preserved leading to contraction of the atria while the AV valves are closed, the latter of which can be associated with the presence of symptoms. In this setting, the SafeR algorithm allows switching to DDD mode in order to restore a physiological atrioventricular activation sequence. The nominal value of 250 ms for the minimum PR corresponding to the maximum rate, and therefore to the maximum capacities of the patient, appears as a good compromise to limit the occurrence of symptoms while avoiding iterative switching.
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68-year-old man with a Microport™ Kora 100 DR dual-chamber pacemaker for sinus node dysfunction; programming: SafeR-R mode, base rate 60 bpm, maximum rate 130 bpm, BAV I switch rest+exercise, long PR max 350 ms, long PR min 250 ms, max pause 3 s; recording of episodes AVB I switch episodes during (exertion, exercise) in pacemaker memory;
Which are the correct answers regarding the SafeR mode?CorrectIncorrect