Author Affiliation: Johns Hopkins Medical Institutions, Baltimore, Md.
The implantable cardiac pacemaker was first introduced in 1960, with
a primary goal of maintaining adequate heart rates in individuals with symptomatic
bradycardia. In such patients, single-ventricle stimulation was effective
even though it was suboptimal from a physiologic standpoint. However, with
sustained bradyarrhythmia requiring frequent ventricular activation, problems
with this approach became apparent. Ventricular pacing disrupted the normal
temporal sequence of atrial-ventricular systole, resulting in AV-dissociation,
mitral and tricuspid valvular regurgitation, and cardiac cycles with variable
filling and thus systolic dysfunction. For patients in whom cardiac performance
was compromised, loss of effective atrial contraction and elevated filling
pressures worsened symptoms.
Kass DA. Pathophysiology of Physiologic Cardiac PacingAdvantages of Leaving Well Enough Alone. JAMA. 2002;288(24):3159-3161. doi:10.1001/jama.288.24.3159