Aims: The aim of this Italian multicentre study was to evaluate the haemodynamic and antiarrhythmic effects of DDIR versus DDI pacing mode in sick sinus syndrome with chronotropic incompetence.
Methods: Seventy-nine patients were implanted with a dual chamber rate-responsive pacemaker (Medtronic 7075) and centrally randomised to DDI or DDIR pacing mode. After six months, the pacing modality was crossed over. Follow-up included clinical data, rest ECG, echocardiography, Holter monitoring and exercise testing in DDIR.
Results: a) Haemodynamic effects. Comparing postimplant exercise testing in DDIR mode with preimplant tests, peak heart rate increased from 96 +/- 17 to 115 +/- 17 bpm (+20%, p < 0.0001), total work capacity from 7.0 +/- 3.5 to 8.8 +/- 4.3 minutes (+26%, p < 0.0001), peak oxygen uptake from 1238 +/- 406 to 1453 +/- 423 ml/min (+17%, p < 0.001) and oxygen uptake at anaerobic threshold from 977 +/- 343 to 1222 +/- 415 ml/min (+25%, p < 0.001). These benefits persisted unchanged during one-year follow-up. b) Antiarrhythmic effects. After six months, paroxysmal atrial fibrillation recurrence significantly decreased in the whole population: group I (DDI) 20.7 vs 48.3%, p < 0.02; group II (DDIR) 21.2 vs 36.4%, p < 0.05; group I + II (DDI + DDIR) 21.0 vs 41.9%, p < 0.001. After one year no significant differences were found between DDI and DDIR. Group I: DDI 23.8 vs DDIR 28.6%, ns; group II: DDI 22.7 vs DDIR 18.2%, ns.
Conclusion: DDIR vs DDI significantly improves short- and long-term haemodynamic performance. Dual chamber pacing shows a significant reduction of paroxysmal atrial fibrillation recurrence, regardless of rate responsiveness.