Intracellular calcium dynamics at the core of endocardial stationary spiral waves in Langendorff-perfused rabbit hearts

In vitro models of sustained monomorphic ventricular tachycardia (MVT) are rare and do not usually show spiral reentry on the epicardium. We hypothesized that MVT is associated with the spiral wave in the endocardium and that this stable reentrant propagation is supported by a persistently elevated intracellular calcium (Ca_i) transient at the core of the spiral wave. We performed dual optical mapping of transmembrane potential (V_m) and Ca_i dynamics of the right ventricular (RV) endocardium in Langendorff-perfused rabbit hearts (n = 12). Among 64 induced arrhythmias, 55% were sustained MVT (>10 min). Eighty percent of MVT showed stationary spiral waves (>10 cycles, cycle length: 128 ± 14.6 ms) in the endocardial mapped region, anchoring to the anatomic discontinuities. No reentry activity was observed in the epicardium. During reentry, the amplitudes of V_m and Ca_i signals were higher in the periphery and gradually decreased toward the core. At the core, maximal V_m and Ca_i amplitudes were 42.95 ± 5.89% and 43.95 ± 9.46%, respectively, of the control (P < 0.001). However, the trough of the V_m and Ca _i signals at the core were higher than those in the periphery, indicating persistent V_m and Ca_i elevations during reentry. BAPTA-AM, a calcium chelator, significantly reduced the maximal Ca _i transient amplitude and prevented sustained MVT and spiral wave formation in the mapped region. These findings indicate that endocardial spiral waves often anchor to anatomic discontinuities causing stable MVT in normal rabbit ventricles. The spiral core is characterized by diminished V_m and Ca_i amplitudes and persistent V_m and Ca_i elevations during reentry.