Mechanosensitivity of the Heart

Atrial flutter (AFL) is a supraventricular arrhythmia, based on a reentrant mechanism, which presents small fluctuations in cycle length. We report on studies in humans and animals which disclosed the nature of these variations and supported their mechanical origin. The sources of the spontaneous variability of atrial flutter cycle length have been identified in ventricular contraction and respiration, which cause phasic variations in atrial interval. The phase-response curves have been shown to be closely related to atrial volume changes during ventricular and respiratory activities and oscillations in cycle length have been reported to be independent of autonomic tone. All this evidence has led to the formulation of the mechano-electrical feedback (MEF) paradigm, which suggests that changes in atrial volume directly affect atrial flutter cycle length variability via direct alteration of the reentrant circuit size and mechano-electrical modulation of conduction velocity. Theoretical predictions of experimental variability patterns by a closed-loop mathematical model of AFL variability, including a MEF branch, provided additional evidence in favour of a mechanically-mediated mechanism at the basis of atrial flutter cycle length variability.