Atrial Electrophysiologic Characteristics In The Elderly And Its Relationship With Atrial Fibrillation

Background and objectives: Atrial fibrillation (AF) is the mostcommon cardiac arrhythmia affecting about 2-3 million adults in theUnited States and at least 8 million adoults. It has been well recognized thatAF is a disease of the elderly. The data from the Framingham Heart Studyshowed that the risk factor-adjusted odds ratio for developing AFapproximately doubled with each decade. Although it is quite clear thatatrial fibrillation is a disease of the elderly, age-related changes in thearrhythmogenic substrate is not known. It has been well recognized that Atrial effective refractory period(AERP) and Atrial conduction velocity (ACV) are two key components toany reentry circuit. The minimum wave length (WL) of a given waveletmust be greater than or equal to the product of the AERP and ACV. The aim of this study is to acquire preliminary data on age-associatedelectrophysiologic properties in the human atrium and how these changesmay foster arrhythmogenic substrates for atrial fibrillation. Methods: 30 patients (44.5 ± 18.6 years) who had not organic orstructural heart disease were divided into 3 groups. 10 patients aged ≤30years (group A), 10 patients aged 31 to 59 years (group B), and 10 patientsaged ≥60 years (group C). After the diagnostic electrophysiologic studyand radiofrequency ablation procedure, one 10-polar electrode catheterwith 2 mm intra-pair, one 20-polar electrode catheter with 1 mm intra-pairand one 4-polar electrode catheter with 10 mm intra-pair distances will bepositioned, respectively in the coronary sinus, one along the right atriallateral wall parallel to the crista terminalis and at the His bundle. The distalpair of the 10 and 20-polar electrodes will be used for pacing while theanother proximal pairs will be used for recording. Pacing will be performedat twice the diastolic threshold. autonomic blockades were administered(atropine 0.04 mg/kg and Metoprolol 15 mg in less then 5 min) beforecommencement of the research protocol. We measured P-wave duration insinus rhythm; AERP at the distal coronary sinus (CS) and high lateral rightatrium (LRA) at cycle length of 600, 500, 400 and 300 ms; conduction time(CT) along the CS and LRA; and CT between high LRA and distal CS ,then observed inducibility of AF. Results: ACV at premature atrial complex is much slower than basalpacing(p<0.001). Aging was associated with an increase inP-wave-duration and AERP, decreased ACV and WL along theLRA(p<0.05). increased shortened ratio of AERP. There are no significantchanges in ACV and WL along the CS. In the patients who could induceAF, iaCT are much higher than the others. The inducibility of AF in theelderly is 60%, much higher the youth (0%). Conclusions: Aging is associated with AERP prolongation, butregional conduction slowing, increased shortened ratio of AERP anddecreased WL might create the substrate of AF. These changes may, in part,be responsible for the increased propensity to atrial arrhythmias observedwith increasing age.