Three distinct phases of VF during global ischemia in the isolated blood-perfused pig heart

Abstract

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...

Influence of the skeletal muscle activity on time and frequency domain properties of the body surface ECG during evolving ventricular fibrillation in the pig

“…In our study, the MF and F lim (99) of UEGs were highly correlated with those of RECG, with MF and F lim (99) not exceeding 15 and 40 Hz, respectively. This agrees with previous findings of compactness and good correlation between the spectral content of optical action potentials and volume-conducted ECG in isolated, globally ischemic porcine hearts [13]. Since the excitation frequency in human VF is lower than in porcine VF [22], the upper limit of frequency content of cardiac activity during VF in patients is expected to be lower than that in pigs.…”

“…UEGs were recorded using a sock electrode with 247 unipolar leads uniformly distributed over the epicardial surface of the ventricles [12]. In one open-chest pig the heart was isolated and perfused with blood in the Langendorff apparatus [13]. A volumeconductor ECG was recorded using two silver electrodes and a ground electrode immersed in the superfusion chamber [13].…”

“…In one open-chest pig the heart was isolated and perfused with blood in the Langendorff apparatus [13]. A volumeconductor ECG was recorded using two silver electrodes and a ground electrode immersed in the superfusion chamber [13]. In 2 closed chest pigs, only Lead II ECG and 3 EMGs were recorded.…”

Spatiotemporal Relationship Between Intracellular Ca 2+ Dynamics and Wave Fragmentation During Ventricular Fibrillation in Isolated Blood-Perfused Pig Hearts

“…Measurements were performed at least 5 minutes after VF induction to allow steady state conditions to be attained. 10,18 Other experimental procedures and measurements were different among experiments and are summarized in the Table. We recorded dual AP and Ca i T movies during baseline VF in 7 hearts. After defibrillation, BAPTA-AM was delivered to 4 of these hearts, and in 2 additional hearts where we imaged Di-4-ANEPPS fluorescence.…”

“…18 In each pulse, the amplitude was defined as the difference between the respective local maximum and minimum. The pulses with amplitudes less than 10% of the difference between the global maximum and global minimum in the same pixel were discarded from this analysis.…”