Rate control in septic shock–associated atrial fibrillation: flow, not heart rate alone, should define haemodynamic success

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  Fig. 1. Heart rate–stroke-volume coupling and physiological assessment of rate control in septic shock-associated atrial fibrillation. (A) Relationship between HR reduction and the compensatory increase in SV required to preserve CO. The proportional change in CO after rate control is determined by the coupled changes in HR and SV: CO2/CO1 = (HR2/HR1) × (SV2/SV1), while preservation or increase of CO therefore requires SV2/SV1 ≥ HR1/HR2. The curve illustrates the non-linear increase in SV recruitment required as the magnitude of HR reduction increases; plotted points are illustrative. (B) Conceptual haemodynamic phenotypes following HR reduction. In patients with recruitable SV and predominantly maladaptive tachycardia, prolongation of effective filling time may permit sufficient SV recruitment, resulting in an SV compensation ratio (SVCR) ≥ 1, preserved or increased CO, and maintained or improved tissue perfusion. Conversely, when tachycardia is predominantly compensatory, HR reduction may not be accompanied by sufficient SV recruitment (SVCR < 1), resulting in reduced CO despite potentially preserved mean arterial pressure through vasoactive support. (C) Proposed physiological…