Pacemaker syndrome pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]

Overview

The loss of physiologic timing of atrial and ventricular contractions, or sometimes called AV dyssynchrony, leads to different mechanisms of symptoms production. This altered ventricular contraction will decrease cardiac output, and in turn will lead to systemic hypotensive reflex response with varying symptoms.

Pathophysiology

Loss of Atrial Contraction

Inappropriate pacing in patients with decreased ventricular compliance, which may be caused by diseases such as hypertensive cardiomyopathy, hypertrophic cardiomyopathy, restrictive cardiomyopathy, and aging, can result in loss of atrial contraction and significantly reduces cardiac output. Because in such cases the atrias are required to provide 50% of cardiac output, which normally provides only 15% - 25% of cardiac output.

Cannon A Waves

Main article: Cannon A waves

Atrial contraction against a closed tricuspid valve can cause pulsation in the neck and abdomen, headache, cough, and jaw pain.

Increased Atrial Pressure

Ventricular pacing is associated with dyssynchrony between the atria and ventricles causing an elevated right and left atrial pressures, as well as elevated pulmonary venous and pulmonary arterial pressures, which can in turn lead to symptomatic pulmonary and hepatic congestion.

Increased Production of Natriuretic Peptides

Main article: Atrial natriuretic peptide

Main article: Brain natriuretic peptide

Patients with pacemaker syndrome exhibit increased plasma levels of ANP. That's due to increase in left atrial pressure and left ventricular filling pressure, which is due to decreased cardiac output caused by dyssynchrony in atrial and ventricular contraction in ventricle paced rhythms. ANP and BNP are potent arterial and venous vasodilators that can override carotid and aortic baroreceptor reflexes attempting to compensate for decreased blood pressure. Usually patients with cannon a waves have higher plasma levels of ANP than those without cannon a waves.

VA Conduction

A major cause of AV dyssynchrony is VA conduction. VA conduction, sometimes referred to as retrograde conduction, leads to delayed, nonphysiologic timing of atrial contraction in relation to ventricular contraction. Nevertheless, many conditions other than VA conduction promote AV dyssynchrony. Ventricular paced rhythms cause a reduction in cardiac output by causing a nonphysiologic depolarization of the ventricles. Depolarization patterns and contraction are altered when pacemaker leads are placed in the apex of the right ventricle.

This will further decrease blood pressure, and secondary increase in ANP and BNP. In patients with heart failure it has been shown that institution of biventricular pacing mode has been associated with a better cardiac output.