Cardiac Vagal Decoupling: A Conceptual Basis for Reflex-Independent Hemodynamic Management under General Anesthesia

Shotaro Nagahama^1,2*

• ¹JAVA Incorporated Association, Tokyo, Japan
• ²Gifu Daigaku, Gifu, Japan

Intraoperative hypotension is consistently associated with postoperative organ injury, and recent consensus statements emphasize maintaining mean arterial pressure above pragmatic "harm thresholds" in at-risk patients. Under balanced anesthesia, hypotension often arises in bradycardia-predominant contexts in which reflex pressure–heart rate coupling remains variably expressed. In such settings, reflex sinus slowing can complicate vasoactive titration and contribute to sequence-dependent, non-linear pressure–heart rate trajectories, particularly when vasopressors are followed by antimuscarinics. Here we present cardiac vagal decoupling as a conceptual framework for interpreting—and, when clinically appropriate, discussing—hemodynamic baselines in which subsequent pressor titration is less dominated by reflex sinus slowing, without implying abolition of reflex control or recommending a fixed drug sequence. Using atropine as a reference antimuscarinic, we outline why sinus-rate responses can appear abrupt by considering effector-level threshold-like behavior, sinoatrial node excitability near firing threshold, and non-monotonic muscarinic pharmacodynamics at low dose ranges. We then describe two broad, non-exclusive configurations in which atropine may produce little observable chronotropic change: globally reduced autonomic responsiveness versus context-limited incremental expression within the muscarinic receptor–effector pathway. Finally, we propose a four-pattern heuristic combining atropine "responsiveness" with bedside evidence of reflex pressure–heart rate coupling to organize interpretation when one signal is missing or weakly expressed, while explicitly recognizing surrogate limitations and motivating empirical evaluation.