Electrophysiology and Arrhythmias in the Elderly
In older patients without apparent cardiovascular disease, the number of cardiac myocytes declines, while residual myocytes enlarge. Concurrently, there is an increase in elastic and collagenous tissue in all parts of the interstitial matrix and conduction system with advancing age. Around the sinoatrial node, adipose tissue accumulates with age, producing a partial or complete separation of the sinoatrial node from the surrounding musculature. The number of pacemaker cells steadily decreases with age, such that by the age of 75 years, less than 10% of pacemaker cells remain functional. Calcification of the cardiac skeleton, which includes the aortic and mitral annuli, the central fibrous body, and the summit of the atrioventricular (AV) septum, also increases with age. Because of their proximity to these structures, the AV node (AVN), His-Purkinje bundle, and right and left bundle branches are frequently affected by aging. Prolongation of action potential duration and diminished autonomic response are also integral components of the aging process. Taken together, these changes provide the substrate for the age-related increase in propensity for chronotropic and dromotropic incompetence and for the development of atrial and ventricular arrhythmias.
The Baltimore Longitudinal Study on Aging demonstrated that basal heart rates in the supine position do not differ significantly among younger and older healthy subjects. Heart rate response to orthostatic challenge decreases slightly in older men and women. Heart rate variability during respiration diminishes with advancing age, reflecting changes in autonomic regulation. The PR interval increases slightly with aging, most likely owing to a delay in AVN conduction.
The prevalence of atrial premature beats on ambulatory monitoring increases with age, exceeding 80% in healthy volunteers and asymptomatic elderly subjects, particularly those older than 80 years. Brief salvos of supraventricular tachycardia occur in up to 50% of older subjects, and the prevalence doubles between the seventh and ninth decades of life. These arrhythmias have not been shown to have adverse prognostic significance. Atrial fibrillation (AF) and tachycardia–bradycardia syndrome are predominant conditions of the elderly.
Ventricular arrhythmias also increase with age. In longitudinal studies, the prevalence of ventricular arrhythmias on ambulatory monitoring is as high as 60% to 90% in asymptomatic elderly subjects. Complex forms such as pairs and triplets occur in up to 10% of such individuals. Exercise testing may induce ventricular arrhythmias in up to 60% of subjects in the ninth decade of life. The prognostic significance of these arrhythmias is dependent in large part on the presence of underlying cardiovascular disease. In patients with cardiovascular disease, frequent ventricular ectopy may adversely affect quality of life, may contribute to deterioration in myocardial function increasing susceptibility to heart failure, and may be a harbinger of symptomatic and sustained ventricular arrhythmias and cardiac arrest. Conversely, the prognostic impact of rest or exercise-induced ventricular arrhythmias is limited in the absence of cardiovascular disease. Reduced heart rate variability by fractal analysis has also been linked to the ...