Effects of combination of sotalol and verapamil on initiation, maintenance, and termination of ventricular fibrillation in swine hearts.

Introduction: Sotalol and verapamil alone reduce reentry incidence during ventricular fibrillation (VF). We tested whether the combination of these two drugs had a synergistic effect on initiation, maintenance, and termination of VF.

Methods: Six open-chest pigs received intravenous sotalol (1.

Endocardial Activation Drives Activation Patterns During Long-Duration Ventricular Fibrillation and Defibrillation.

Background: Understanding the mechanisms that drive ventricular fibrillation is essential for developing improved defibrillation techniques to terminate ventricular fibrillation (VF). Distinct organization patterns of chaotic, regular, and synchronized activity were previously demonstrated in VF that persisted over 1 to 2 minutes (long-duration VF [LDVF]). We hypothesized that activity on the endocardium may be driving these activation patterns in LDVF and that unsuccessful defibrillation shocks may alter activation patterns.

Mechanisms of Long-Duration Ventricular Fibrillation in Human Hearts and Experimental Validation in Canine Purkinje Fibers.

Objectives: This study sought to determine the characteristics of human LDVF, particularly as it contrasts with short-duration VF (SDVF), and evaluate the role of Purkinje fibers in its maintenance.

Background: The electrophysiological mechanisms of long-duration ventricular fibrillation (LDVF) have not been studied in the human heart.

Methods: VF was induced in 12 human Langendorff hearts, and the hearts were examined from initiation to LDVF (10 min).

Ventricular fibrillation: are swine a sensitive species?

Purpose: Legislation and sentiment have pushed large-animal electrophysiological research from the canine to the swine model. Anecdotal experience suggests that the swine is particularly sensitive to ventricular fibrillation (VF) induction, and radiofrequency ablation studies are consistent with this. Currently, no data exist directly comparing the VF threshold (VFT) in humans to swine.

Verapamil reduces incidence of reentry during ventricular fibrillation in pigs.

The characteristics of reentrant circuits during short duration ventricular fibrillation (SDVF; 20 s in duration) and the role of Ca(++) and rapid-activating delayed rectifier potassium currents during long duration ventricular fibrillation (LDVF; up to 10 min in duration) were investigated using verapamil and sotalol. Activation mapping of the LV epicardium with a 21 × 24 electrode plaque was performed in 12 open-chest pigs. Pigs were given either verapamil (0.

The importance of Purkinje activation in long duration ventricular fibrillation.

Background: The mechanisms that maintain long duration ventricular fibrillation (LDVF) are unclear. The difference in distribution of the Purkinje system in dogs and pigs was explored to determine if Purkinje activation propagates to stimulate working myocardium (WM) during LDVF and WM pacing.

Methods And Results: In-vivo extracellular recordings were made from 1044 intramural plunge and epicardial plaque electrodes in 6 pig and 6 dog hearts.

Long-duration ventricular fibrillation exhibits 2 distinct organized states.

Background: Previous studies showed that endocardial activation during long-duration ventricular fibrillation (VF) exhibits organized activity. We identified and quantified the different types of organized activity.

Methods And Results: Two 64-electrode basket catheters were inserted, respectively, into the left ventricle and right ventricle of dogs to record endocardial activation from the endocardium during 7 minutes of VF (controls, n=6).

Evaluation of acute cardiac and chest wall damage after shocks with a subcutaneous implantable cardioverter defibrillator in Swine.

Background: A subcutaneous implantable cardioverter defibrillator (S-ICD) could ease placement and reduce complications of transvenous ICDs, but requires more energy than transvenous ICDs. Therefore we assessed cardiac and chest wall damage caused by the maximum energy shocks delivered by both types of clinical devices.

Methods: During sinus rhythm, anesthetized pigs (38 ± 6 kg) received an S-ICD (n = 4) and five 80-Joule (J) shocks, or a transvenous ICD (control, n = 4) and five 35-J shocks.

The stability of electrically induced ventricular fibrillation.

The first recorded heart rhythm for cardiac arrest patients can either be ventricular fibrillation (VF) which is treatable with a defibrillator, or asystole or pulseless electrical activity (PEA) which are not. The time course for the deterioration of VF to either asystole or PEA is not well understood. Knowing the time course of this deterioration may allow for improvements in emergency service delivery.

Different types of long-duration ventricular fibrillation: can they be identified by electrocardiography.

We tested the hypothesis that after 2 minutes of ventricular fibrillation (VF), periods of highly organized activations occur on the endocardium, arising from an intramural mother rotor or triggered activity originating in the Purkinje fibers. In 6 anesthetized dogs, we recorded electrically induced VF from two-thirds of the endocardium with a 64-electrode basket catheter. In another 12 dogs, the study was repeated with the addition of the early afterdepolarization blocker pinacidil in 6 animals and the delayed afterdepolarization blocker flunarizine in the other 6 animals.

Ascending-ramp biphasic waveform has a lower defibrillation threshold and releases less troponin I than a truncated exponential biphasic waveform.

Background: We tested the hypothesis that the shape of the shock waveform affects not only the defibrillation threshold but also the amount of cardiac damage.

Methods And Results: Defibrillation thresholds were determined for 11 waveforms-3 ascending-ramp waveforms, 3 descending-ramp waveforms, 3 rectilinear first-phase biphasic waveforms, a Gurvich waveform, and a truncated exponential biphasic waveform-in 6 pigs with electrodes in the right ventricular apex and superior vena cava. The ascending, descending, and rectilinear waveforms had 4-, 8-, and 16-millisecond first phases and a 3.

Intramural optical mapping of V(m) and Ca(i)2+ during long-duration ventricular fibrillation in canine hearts.

Intramural gradients of intracellular Ca(2+) (Ca(i)(2+)) Ca(i)(2+) handling, Ca(i)(2+) oscillations, and Ca(i)(2+) transient (CaT) alternans may be important in long-duration ventricular fibrillation (LDVF). However, previous studies of Ca(i)(2+) handling have been limited to recordings from the heart surface during short-duration ventricular fibrillation. To examine whether abnormalities of intramural Ca(i)(2+) handling contribute to LDVF, we measured membrane voltage (V(m)) and Ca(i)(2+) during pacing and LDVF in six perfused canine hearts using five eight-fiber optrodes.

Ventricular fibrillation threshold of rapid short pulses.

The risk of VF (ventricular fibrillation) from continuous AC utility (50/60 Hz) power has been well quantified and is reflected in accepted standards. Similarly, the required charge for a single pulse delivered during the T-wave of the ECG is also quantified. However, there are no studies that deal with the VF risk of a train of multiple short pulses such as those used in electric fences and conducted electrical weapons (CEWs).

Evolution of activation patterns during long-duration ventricular fibrillation in pigs.

Quantitative analysis has demonstrated five temporal stages of activation during the first 10 min of ventricular fibrillation (VF) in dogs. To determine whether these stages exist in another species, we applied the same analysis to the first 10 min of VF recorded in vivo from two 504-electrode arrays, one each on left anterior and posterior ventricular epicardium in six anesthetized pigs. The following descriptors were continuously quantified: 1) number of wavefronts, 2) wavefront fractionations, 3) wavefront collisions, 4) repeatability, 5) multiplicity index, 6) wavefront conduction velocity, 7) activation rate, 8) mean area activated by the wavefronts, 9) negative peak rate of voltage change, 10) incidence of breakthrough/foci, 11) incidence of block, and 12) incidence of reentry.

Effect of chest compressions on ventricular activation.

External mechanical forces can cause ventricular capture and fibrillation (i.e., commotio cordis).

Intramural activation during early human ventricular fibrillation.

Background: We investigated patterns of intramural activation in early human ventricular fibrillation (VF) and hypothesized that intramural reentry colocalizes to sites with increased intramural fibrosis.

Methods And Results: Thirteen human Langendorff hearts were used for this study. Twenty-five plunge needles (4 unipoles/needle) were used to map 100 intramural sites.

Vernakalant selectively prolongs atrial refractoriness with no effect on ventricular refractoriness or defibrillation threshold in pigs.

Vernakalant is a novel antiarrhythmic agent that has demonstrated clinical efficacy for the treatment of atrial fibrillation. Vernakalant blocks, to various degrees, cardiac sodium and potassium channels with a pattern that suggests atrial selectivity. We hypothesized, therefore, that vernakalant would affect atrial more than ventricular effective refractory period (ERP) and have little or no effect on ventricular defibrillation threshold (DFT).

Implantable intravascular defibrillator: evaluation of defibrillation waveforms with inferior vena cava electrode system.

Background: A percutaneously placed, totally intravascular defibrillator has been developed that shocks via a right ventricular (RV) single-coil and titanium electrodes in the superior vena cava (SVC) and the inferior vena cava (IVC). This study evaluated the defibrillation threshold (DFT) with this electrode configuration to determine the effect of different biphasic waveform tilts and second-phase durations as well as the contribution of the IVC electrode.

Methods: Eight Bluetick hounds (wt = 30-40 kg) were anesthetized and the RV coil (first-phase anode) was placed in the RV apex.

Novel intravascular defibrillator: defibrillation thresholds of intravascular cardioverter-defibrillator compared to conventional implantable cardioverter-defibrillator in a canine model.

Background: An intravascular, percutaneously placed implantable defibrillator (InnerPulse percutaneous intravascular cardioverter-defibrillator [PICD]) with a right ventricular (RV) single-coil lead and titanium electrodes in the superior vena cava (SVC) and the inferior vena cava (IVC) has been developed.

Objective: The purpose of this study was to compare defibrillation thresholds (DFTs) of the PICD to those of a conventional implantable cardioverter-defibrillator (ICD) in canines.

Methods: Eight Bluetick hounds were randomized to initial placement of either a PICD or a conventional ICD.

Periods of highly synchronous, non-reentrant endocardial activation cycles occur during long-duration ventricular fibrillation.

Unlabelled: Periods of Highly Organized Activation During VF.

Background: Little is known about long-duration ventricular fibrillation (LDVF), lasting 1-10 minutes when resuscitation is still possible.

Methods And Results: To determine global left ventricle (LV) endocardial activation during LDVF, 6 canines (9.

Mechanisms of defibrillation.

Electrical shock has been the one effective treatment for ventricular fibrillation for several decades. With the advancement of electrical and optical mapping techniques, histology, and computer modeling, the mechanisms responsible for defibrillation are now coming to light. In this review, we discuss recent work that demonstrates the various mechanisms responsible for defibrillation.

Activation becomes highly organized during long-duration ventricular fibrillation in canine hearts.

Little is known about the three-dimensional (3-D) intramural activation sequences during long-duration ventricular fibrillation (VF), including the role of the subendocardium and its Purkinje fibers (PFs) in long-duration VF maintenance. Our aim was to explore the mechanism of long-duration VF maintenance with 3-D electrical mapping. We recorded 10 min of electrically induced VF in the left ventricular anterior free wall of six 10-kg, open-chest dogs using a 3-D transmural unipolar electrode matrix (9 x 9 x 6, 2-mm spacing) that allowed us to map intramural activation sequences.