RHYTHMOLOGICAL PITFALLS IN CARDIAC PACING

Some electrocardiographic appearances in cardiac pacing may suggest pa cemaker dysfunction but in fact the unit may be functioning normally o r have a minor fault which is easy to correct by reprogramming. A paci ng rate different to that programmed may be due to the rate-response h ysteresis or rate smoothing functions. Irregular pacing is often due t o phenomena of inappropriate sensing. A pacemaker in the bipolar AAI m ode may seem to have no output if the spike is not visible: function i n AAI mode should not be interpreted as pacing catheter displacement. The practician may wrongly interpret faulty ventricular sensing in pat ients with AAI pacemakers and atrial fibrillation when irregular pacin g is observed or when ventricular extrasystoles do not inhibit the pac emaker. In dual chamber pacing, the blanking per;od may result in inad equate ventricular stimulation. The phenomenon of crossed detection or cross-talk is a cause of inappropriate inhibition. Applications of th e magnet blocks the sensing function: the magnet pacemaker rate is an indicator of pacemaker end of life. In fact, the magnet induces differ ent behaviours depending on the model of pacemaker which makes ii: ess ential to know the special characteristics of each pacemaker. The appl ication of the magnet may trigger arrhythmias or no output of pacemake rs at the end of life. The A-V interval may vary with respect to its r esponse to the heart rate, when there is a hysteresis function of the A-V interval, sensing in the safety gap or when anti-atrial trachycard ia algorithms are activated. The acceleration of a dual-chamber pacema ker may be related to electronic reentrant tachycardia or to an atrial tachycardia: a fault or delayed activation of various anti-arrhythmic algorithms may also cause difficulties in the interpretation of the e lectrocardiogram.