The underlying heart rhythm in patients with an artificial cardiac pacemaker.

One-hundred forty-two patients with atrioventricular block (AVB) and 61 patients with sick sinus syndrome (SSS) were followed for an average of 50 months after permanent pacemaker insertion. Their underlying heart rhythms (UHR) were evaluated repeatedly by chest wall stimulation (CWS). A deficient UHR was defined as ventricular asystole lasting 4 seconds or longer. The underlying conduction disturbance increased in 14% of AVB patients, decreased in 14%, and remained constant in 68%. The occurrence of Adams-Stokes attacks before pacemaker implantation was associated with a higher incidence of deficient UHR both in AVB and SSS; a deficient UHR was seen more frequently in AVB than in SSS. Among AVB patients (1) atrial fibrillation, flutter or tachycardia and (2) sinus rhythm with incomplete AVB, especially Mobitz 1, when present before pacemaker implantation, were associated with a significantly lower incidence of deficient UHR during subsequent pacing in comparison with other AVB patients. CWS is a non-invasive method which allows the evaluation of UHR and which can contribute to the early recognition of pacemaker-dependent patients.