Stress-induced pacemaker desynchronization in the sinoatrial node.

The sinoatrial node (SAN) functions as a heterogeneous population of electrically coupled pacemaker cells rather than as a single dominant oscillator. We propose a SAN-centered hypothesis in which stress-related arrhythmogenic vulnerability may arise from transient loss of synchronization within this pacemaker population. Sustained autonomic stress, recurrent orthostatic autonomic loading associated with human upright posture, inflammatory remodeling, fibrosis, or structural SAN remodeling may amplify intrinsic-frequency dispersion and reduce effective coupling, thereby lowering synchronization reserve. Abrupt autonomic, respiratory, or thermal transitions, including stress-recovery sympathovagal transitions, sleep-related respiratory events, fever-associated thermal acceleration, and rapid defervescence, may then expose this vulnerable substrate. In this framework, arrhythmogenesis reflects not only abnormal impulse generation, conduction disturbance, reentry, or afterdepolarization-mediated triggered activity, but also perturbation-induced loss of pacemaker-network coherence and transient competition among pacemaker domains. The model remains a reduced phenomenological framework rather than a calibrated anatomical simulation, but it yields testable predictions, including transition-linked sinus cycle-length instability, supraventricular ectopy, P-wave morphology variability, and reduced coherence in heterogeneous SAN models. This hypothesis suggests that attention should also be directed to dynamic synchronization reserve during physiological challenge, rather than resting rate alone.