Table 2.

Electrophysiological differences between the elderly and young that can predispose to AF (summarised from human and animal studies in Table 1).

Features	Elderly	Young
Impulse initiation
(i) Sinus node function	Impaired (leading to longer sinus node recovery times), contributing to abnormal impulse initiation	Generally preserved
(ii) Pulmonary vein ectopic activity	Also contributes to AF pathogenesis although substrate abnormalities have a dominant role in initiation and maintenance	Predominant trigger for AF initiation
Impulse conduction
(i) P wave morphology and duration (usually signifying interatrial conduction)	Abnormal P wave morphology and prolonged interatrial conduction	Usually normal
(ii) Wavefront propagation	Abnormalities noted such as conduction slowing (particularly of premature impulses) thereby contributing to reentrant waves	Usually normal
Substrate abnormalities
(i) Complex fractionated atrial electrograms	Greater number	Lesser than in elderly
(ii) Atrial refractoriness—effective Refractory Period (ERP)	ERP prolonged in the right atrium and could contribute to dispersion in refractoriness	Usually not prolonged
(iii) Action potential duration (APD)	Prolonged in the right atrium	Generally within normal limits
(iv) Regional atrial voltage differences	Larger atrial volumes with more number of low voltage areas	Atria usually of normal size and mean voltage within normal limits