[Bradycardic arrhythmias and changes in the bradycardia-induced hemodynamics by electrical and drug treatment]

Cardiac output depends at first on heart rate and second on contractility. Chronotropic incompetence means inappropriate adaptation of rate to metabolic demands and in this condition increase of cardiac output is only made possible by increase of contractility and stroke volume. The old, insufficient, or ischemic heart cannot control cardiac output appropriately by increasing contractility. This explains the different importance of bradycardia at rest or under exercise. Drug treatment is only possible if a bradycardia is vagus induced. The prevention of asystole is the first aim of pacemaker treatment and can be achieved by conventional ventricular stimulation. If long stimulation sequences are to be expected, or if there is chronotropic incompetence, a more physiologic correction of the arrhythmia has to be considered. A competent sinus node reestablishing normal AV sequence and rate control by atrial-triggered ventricular pacing results in optimal long-term hemodynamic improvement. However, in choosing the AV interval, intramyocardial conduction delay has to be considered and therefore, AV delay has to be individually adapted. With chronotropic incompetence and normal AV conduction rate, adaptive atrial stimulation will best imitate physiologic conditions while binodal disease will be treated best by rate adaptive dual chamber pacemaker.