An atrial-based pacing mode is superior to ventricular constant rate demand pacing (VVI) mode in patients with sick sinus syndrome (SSS) by providing both rate adaptation and atrioventricular (AV) synchrony. The use of a non-atrial sensor to overcome chronotropic incompetence and preserve normal intrinsic AV conduction in pacemaker therapy for SSS was investigated in 15 consecutive patients (mean age 66 +/- 2 years). All had intact AV conduction (antegrade conduction capacity > 100 beats.min-1 and an atrial paced to intrinsic R interval of < or = 220 ms). DDDR pacemakers capable of being programmed into atrial rate adaptive (AAIR), dual chamber rate adaptive (DDDR) and ventricular rate adaptive (VVIR) modes were used. Beginning with an acute study, arterial pressure was invasively assessed in each pacing mode during physiological stresses and low level exercise. In the ambulatory phase, the incidence of ventricular pacing and arrhythmias (Holter recording), diurnal blood pressure changes (ambulatory blood pressure recording), and symptom and quality of life level (questionnaires and interviews) were compared. Despite similar heart rate changes during acute physiological stresses, a higher blood pressure was recorded during AAIR or DDDR pacing compared with VVIR pacing. Systolic blood pressure over 24 h was lower in the VVIR mode (122 +/- 5 mmHg) than AAIR/DDDR pacing (129 +/- 6/128 +/- 6 mmHg, P < 0.05). VVIR pacing was associated with a higher frequency of atrial and ventricular ectopics, with two patients developing paroxysmal atrial fibrillation. Ventricular pacing was used in a higher percentage in the DDDR compared with the VVIR mode (64 +/- 11 and 39 +/- 7%, P < 0.03). VVIR pacing was associated with more palpitations, a lower level of general well being and depression. Despite the use of a sensor to overcome chronotropic incompetence, VVIR pacing is a less satisfactory pacing mode for SSS. Although AAIR/DDDR pacing may achieve similar haemodynamic and clinical status, in patients with intact AV conduction, AAIR pacing may be preferable by avoiding an abnormal ventricular activation pattern.