Background-Styryl voltage-sensitive dyes (e.g. di-4-ANEPPS) have been successfully used for optical mapping in cardiac cells and tissues. However, their utility for probing electrical activity deep inside the myocardial wall and in blood-perfused myocardium has been limited because of light scattering and high absorption by endogenous chromophores and hemoglobin at blue-green excitation wavelengths.

Zaitsev AV. Three distinct phases of VF during global ischemia in the isolated blood-perfused pig heart. Am J Physiol Heart Circ Physiol 293: H1617-H1628, 2007. First published June 1, 2007; doi:10.1152/ajpheart.00130.2007.-Changes in ventricular fibrillation (VF) organization occurring after the onset of global ischemia are relevant to defibrillation and survival but remain poorly understood. We hypothesized that ischemia-specific dynamic instability of the action potential (AP) causes a loss of spatiotemporal periodicity of propagation and broadening of the electrocardiogram (ECG) frequency spectrum during VF in the ischemic myocardium. We recorded voltage-sensitive fluorescence of di-4-ANEPPS (anterior left ventricle, 35 ϫ 35 mm, 64 ϫ 64 pixels) and the volumeconducted ECG in six blood-perfused hearts during 10 min of VF and global ischemia. We used coefficient of variation (CV) to estimate variability of AP amplitude, AP duration, and diastolic interval (CV-APA, CV-APD, and CV-DI, respectively). We computed excitation median frequency (Median_F), spectral width of the AP and ECG (SpW-AP and SpW-ECG, respectively), wavebreak incidence (WBI), and recurrence of propagation direction (RPD). We found three distinct phases of local VF dynamics: "relatively periodic" (Յ1 min, high Median_F, moderate AP variability, high WBI, low RPD), "highly periodic" (1-2 min, reduced Median_F, low AP variability, low WBI, high RPD), and "aperiodic" (3-10 min, low Median_F, high AP variability, high WBI, low RPD). In one experiment, spontaneous conversion from the aperiodic to the highly periodic phase occurred after 5 min of ischemia. The SpW-ECG was correlated with SpW-AP, CV-APD, and CV-APA. We conclude that 1) at least three distinct phases of VF dynamics are present in our model, and 2) the newly described aperiodic phase is related to ischemia-specific dynamic instability of the AP shape, which underlies broadening of the ECG spectrum during VF evolution. ventricular fibrillation; action potential; electrocardiogram ONE IMPORTANT DECISION that an emergency care professional faces at the scene of cardiac arrest is whether to initiate cardiopulmonary resuscitation (CPR) before the application of a shock, or to defibrillate first. Population studies indicate that the "CPR first" strategy improves survival if the ventricular fibrillation (VF) duration exceeds 3-4 min ("circulatory phase") but not at the earlier "electrical" phase of VF (18). This observation motivated recent studies aimed at estimating VF duration based on the structure and spectral content of the electrocardiogram (ECG) waveform (6, 27, 34). Furthermore, various quantitative measures of "order" in the ECG waveform can predict the likelihood of rescue shock success, restoration of circulation, and survival to hospital discharge (4, 6). However, the relationship between the structure of the ECG waveform and the spatiotemporal dynamics of the fibrillatory waves in the myocardium remains unknown.VF organization evolves naturally after its onset as a result of glo...

Abstract-Normal "master-slave" relationship between the action potential (AP) and intracellular Ca 2ϩ transient (Ca i T) is sometimes altered during ventricular fibrillation (VF). The nature of AP/Ca i T dissociation during VF and its role in inducing wavebreaks (WBs) remain unclear. We simultaneously mapped AP (RH237) and Ca i T (Rhod-2) during VF in blood-perfused pig hearts. We computed AP and Ca i T dominant frequency (DF) and Ca i T delay in each AP cycle. We identified WBs as singularity points in AP phase movies and sites of conduction block (CB) as sites where an AP wavefront failed to propagate. We analyzed spatiotemporal relationship between abnormal AP/Ca i T sequences and CB sites. We used a calcium chelator (BAPTA-AM) to abolish Ca i T and test its involvement in WB formation. During VF, the DF difference between AP and Ca i T was Ͻ10% of the respective values in 95% of pixels, and 80% of all Ca i T upstrokes occurred during the initial 25% of the excitation cycle. Aberrant sequences of AP and Ca i T occurred almost exclusively near CB sites but could be traced to normal wavefront sequences away from CB sites. Thus, apparent AP/Ca i T dissociation was largely attributable to spatial uncertainty of the absolute position of block of each wave. BAPTA-AM reduced Ca i T amplitude to 30.5Ϯ12.9% of control and the DF of AP from 12.2Ϯ1.6 to 10.4Ϯ1.3Hz (PϽ0.01), but did not significantly alter WB incidence (0.76Ϯ0.19 versus 0.72Ϯ0.19SP/mm 2 ). These results do not support presence of spontaneous, non-voltage-gated Ca i Ts during VF and suggest that AP/Ca i T dissociation is a consequence rather than a cause of wave fragmentation. (Circ Res. 2007;101:e90-e101.) Key Words: ventricular fibrillation Ⅲ pig heart Ⅲ action potential Ⅲ calcium transient Ⅲ wavebreak R ecurrent wave fragmentation, or wavebreak (WB), is a hallmark of ventricular fibrillation (VF). 1,2 Wavebreak occurs when a propagating wavefront encounters an obstacle which may result from electrophysiological heterogeneities, [3][4][5][6] intrinsic repolarization instabilities, 7,8 anatomic structures, 9 or regional ischemia. 10 Repolarization instabilities in the form of action potential duration (APD) alternans are at least in part mediated by beat-to-beat changes in L-type Ca 2ϩ current (I Ca,L ) and Na ϩ -Ca 2ϩ exchanger (NCX). 2,11 These currents are bidirectionally coupled to intracellular Ca 2ϩ (Ca i ) cycling, so that Ca 2ϩ influx via I Ca,L triggers Ca 2ϩ release from the sarcoplasmic reticulum (SR), whereas an increase in Ca i modulates inactivation of I Ca,L and the transsarcolemmal current generated by NCX. 12 SR Ca 2ϩ cycling can exhibit intrinsic dynamics in the form of Ca i transient (Ca i T) alternans (even when the AP waveform is fixed under voltage clamp) 13 and in the form of spontaneous, non-voltage-gated Ca 2ϩ releases. 12 It was hypothesized that such intrinsic dynamics of Ca i T can promote APD fluctuations at high excitation rates and thus contribute to mechanisms of WB during VF. 2,13 To test this hypothesis, Omichi et al 14...

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