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Arrhythmias in PMK/ICD patients:

Atrial fibrillation is the most frequent arrhythmia in PMK/ICD patients. The diagnosis from surface ECG generally is not difficult, with rare exceptions. It is of interest, somewhat, analysis of some specific functions of pacemakers that should be known to correctly explain ECG patterns. These algorithms have been introduced whether to prevent AF (Atrial Preference Pacing, Atrial Rate Stabilization, Post Mode Switching Overdrive Pacing (PMOP)) or to interrupt it (ATP - AntiTachycardic Pacing - burst, ramp, shock). For example, PMOP function is aimed to decrease the incidence of premature relapse of AF. This algorithm assures an atrial stimulation at high rate (f.e. 100 bpm) for several minutes, when sinus rhythm is restored after episodes of AF, that is when for mode switch function the PMK stimulates in DDD/R modality from DDI/R. Atrial Rate Stabilization function allows the PMK to stimu-late after a premature ectopic atrial beat to prevent potentially proarrhythmic long pauses. It gradually extends stimulation inter-val until a normal and organized intrinsic rhythm could emerge or to the achievement of the lower rate. Atrial Preference Pacing is a function that supports a continuous atrial stimulation instead of a spontaneous atrial rhythm within a programmable maximum heart rate to prevent supraventricular tachyarrhythmias inhibiting the dispersion of atrial refractory period.

The interruption therapies for atrial and ventricular tachyarrhythmias are burst, ramp and shock. Burst stimulation consists of supplying of a determined number of sequences in AOO (for atrial tachyarrhythmia - modality or VOO modality (for ventricular tachy). During ramp stimulation the device supplies impulses with intervals gradually shortening with a programmable decrement. The first impulse of each sequence attends during the tachycardia at a programmable percentage of its duration. Antitachycardia pacing is not painful. Shocks can be synchronized (for AF or VT) or not (for VF) and with different energy. They are painful. In ICD patients, AF often causes inappropriate interventions of device when ventricular rate is so fast that falls in the range of ventricular tachyarrhythmias. In this case, we should modify pharmacological therapy or device programming to obtain beneficial effects. Surface ECG sometimes can show AF onset mechanism. For example after nonsustained atrial tachycardia on paced rhythm). An example of interest could be the possibility (however rare) that an appropriate intervention for a VT as a shock can turn VT into normal rhythm

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