Relative importance of activation sequence compared to atrioventricular synchrony in left ventricular function

Area of Science:

• Cardiology
• Biomedical Engineering
• Physiology

Background:

• Optimizing pacemaker function is crucial for patients with cardiac conduction abnormalities.
• Understanding the hemodynamic impact of different pacing modes is essential for patient management.

Purpose of the Study:

• To compare the hemodynamic effects of normal left ventricular (LV) activation versus atrioventricular (AV) synchrony.
• To evaluate systolic and diastolic function under various pacing modes.

Main Methods:

• Radionuclide and Doppler echocardiography were used in 12 patients with pacemakers.
• Pacing modes compared included atrial demand pacing (AAI), sequential AV sensing pacing (DDD), and ventricular demand pacing (VVI).
• Studies were conducted at rest and during submaximal exercise at constant heart rates.

Main Results:

• Cardiac output and LV ejection fraction were significantly higher during AAI pacing compared to DDD and VVI.
• Ventricular pacing (VVI) induced paradoxical septal motion, impairing regional septal ejection fraction by 25%.
• Peak filling rate was higher during AAI and VVI than DDD, but time to peak filling was shorter during VVI.

Conclusions:

• A normal LV activation sequence offers superior hemodynamic performance over AV sequential and ventricular pacing.
• Pacemaker selection should consider the impact on LV activation sequence for optimal cardiac function.
• Atrial pacing (AAI) demonstrates better systolic and diastolic function compared to DDD and VVI modes.