Cardiac Geometry and Function in Patients with Reflex Syncope

Abstract

Reflex syncope (RS) is the most prevalent form of syncope, yet its pathophysiology and clinical presentation are not well understood. Despite controversy, the 'ventricular theory' remains the most plausible hypothesis to explain RS in susceptible patients. Certain assumptions regarding the geometry and function of the heart are essential in supporting this theory. Given these considerations, the goal of this review was to try to integrate data on heart morphology and function in a phenotype of a patient susceptible to RS. Previous research suggests that a small left ventricle and atria, in addition to a normo- or hypercontractile myocardium, predispose to more syncopal events. These findings have been confirmed in different subsets of patients, including those with small heart and chronic fatigue syndrome, highlighting common pathophysiologic pathways in these subgroups of population. Heart geometry and function seem to play a role in different treatment strategies for RS patients, including the administration of medications, pacing, and possibly cardioneural ablation. In addition, parameters related to the geometry of the heart chambers and of the electrical activation of the heart seem to have predictive value for syncope recurrence. These parameters could be included in the future and improve the accuracy of predictive models for RS.

Keywords: left ventricle dimension and function; predictive model; reflex syncope; small left atria; ventricular theory.

Figure 1

The Bezold–Jarisch reflex as a consequence of orthostatic stress (a concept in the pathophysiology of the vasovagal syncope): orthostatic stress leads to a redistribution of the circulatory volume towards the inferior extremities of the body (‘venous pooling’), causing a decrease in venous return. The exacerbation of sympathetic tone will induce a vigorous myocardial contraction on an empty left ventricle, with further stimulation of cardiac mechanoreceptors. The C fibers’ activation can lead to a paradoxical effect, resulting in an exaggerated vagal tone, sympathetic withdrawal and syncope. ↑—increased, ↓—decreased.

Figure 2

Small heart syndrome, reflex syncope and chronic fatigue syndrome are entities that overlap partially and often have several clinical features in common.

Figure 3

The cardiac geometry reflex syncope phenotype is characterized by a small-sized left heart and variable function, which facilitate the onset and progression of a syncopal episode. RS = reflex syncope, LA = left atrium, LV = left ventricle, ↓ = decreased.

Figure 4

An ultrasound image of a parasternal long-axis view of the heart, showing small left cavities and thin ventricular walls in a patient with reflex syncope.