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PubMed1988

Influence of ventricular fibrillation duration on defibrillation energy in dogs using bidirectional pulse discharges.

The automatic implantable defibrillator device typically discharges 5-30 seconds after detection of ventricular fibrillation. To investigate the importance of the duration of ventricular fibrillation on defibrillation, the effects of ventricular fibrillation durations of 5, 15, and 30 seconds on the energy requirements for successful internal defibrillation were compared in 15 closed chest dogs with internal electrodes. The electrode configuration utilized a transvenous right heart catheter with two electrodes and a precordial subcutaneous patch electrode, with a single bidirectional pulse discharged between the distal catheter electrode and the proximal catheter and patch electrodes. Curves of energy vs. percentage of successful defibrillation were constructed and logistic regression was used to derive 90% and 50% successful energy doses (ED90 and ED50). The mean ventricular fibrillation activation interval just prior to defibrillation was determined from discrete RV endocardial electrograms. Four dogs died during testing, all because of inability to defibrillate after 30 s of ventricular fibrillation. In the remaining 11 dogs, the ED90 increased from (mean +/- SD) 27 +/- 13J at 5 s to 41 +/- 14J at 30 s (p less than .01). The mean ventricular fibrillation activation interval decreased from 107 +/- 21 ms at 5 s to 95 +/- 18 ms at 30 s (p less than .01). In conclusion, the energy required for internal defibrillation in dogs using this electrode configuration increases with longer durations of ventricular fibrillation, and is associated with more rapid ventricular fibrillation activation intervals.

Animals↗
PubMed1988

Implanted automatic defibrillators: effects of drugs and pacemakers.

The automatic implantable cardioverter defibrillator is an effective device for prevention of sudden cardiac death. Patients who require the implantation of the device often require permanent pacing for symptomatic bradyarrhythmias and may require antiarrhythmic drug therapy. Antiarrhythmic drugs may alter the defibrillation thresholds, arrhythmia cycle length and frequency, pacing thresholds and postshock excitability. Interactions between the defibrillator and the pacemaker may result in sensing problems, leading to multiple counting and inappropriate shocks, or ventricular fibrillation nondetection, sensing or capture failure post defibrillation and pacemaker reprogramming induced by defibrillator discharge. The potential for interactions will increase as the new generation of programmable defibrillators become clinically available, combining features of permanent pacemakers, antitachycardia pacemakers and defibrillators.

Anti-Arrhythmia Agents↗
PubMed1989

Long-term internal cardiac defibrillation threshold stability.

The automatic implantable cardioverter-defibrillator is tested intraoperatively with defibrillation trials to ensure effectiveness. It is unknown if the energy requirement for internal defibrillation remains stable and that once demonstrated effective, if the device will continue to be effective in terminating lethal ventricular arrhythmias. In this study, the defibrillation energy requirement was compared in 56 patients at the time of lead implantation to that obtained at the time of generator replacement. Mean time to generator replacement was 17. +/- 6.6 months. The defibrillation threshold was stable over that time (11.9 +/- 6.7 joules compared to 12.7 +/- 8.4 joules, NS). There was no relation between transmyocardial impedance and defibrillation threshold. In addition, no effect on defibrillation threshold was demonstrated by the use of various cardiac medications, concomitant surgery or the occurrence of clinical shocks during follow-up.

Electric Countershock↗
PubMed1990

Genesis of sigmoidal dose-response curve during defibrillation by random shock: a theoretical model based on experimental evidence for a vulnerable window during ventricular fibrillation.

The sigmoidal dose-response curve (percent success vs shock energy) suggests a probabilistic nature of defibrillation. The mechanism is still largely unknown, however, random variation in the excitable state during ventricular fibrillation (VF) is suspected. A canine defibrillation study was designed to determine whether random variation in absolute VF voltage (AVFV) (a crude marker of number of excitable cells) was related to success of defibrillation, using a DC shock successful at the 50% level. The results were: (a) transmyocardial resistance (73.4 +/- 1.4 vs 73.6 +/- 1.5 ohms) and delivered energy (6.1 +/- 1.2 vs 6.2 +/- 1.2 joules) were similar; however, (b) AVFV 2 msec prior to DC shock was greater for successful as compared to unsuccessful attempts (0.5 +/- 0.1 vs 0.3 +/- 0.0 mV, P less than 0.01). A mathematical model was subsequently developed based on fluctuation in the number of excitable cells. Variation in the state of excitability resulted in a cyclic window potentially vulnerable to defibrillation. The vulnerable window occurred at a point when the number of excitable cells was low, i.e., a higher state of total depolarization, which was in agreement with the experimental finding. For a given VF pattern, duration of the vulnerable window was regulated by the shock energy. A larger shock energy generated a wider vulnerable window and, in turn, a higher success rate. Finally, the sigmoidal dose-response curve of defibrillation was theoretically constructed by calculating the variable chances of a random DC shock occurring either in a vulnerable window or elsewhere during VF. It is concluded that a vulnerable window susceptible to defibrillation can be demonstrated in the early stages (10 sec) of VF. The mathematical model provides a theoretical basis for the vulnerable window and helps elucidate the probabilistic nature of defibrillation.

Animals↗
PubMed1990

The defibrillation success rate versus energy relationship: Part II--Estimation with the "bootstrap".

Seventy or so defibrillation trials were typically attempted to determine the relationship between defibrillation success rate and energy (DSRE). Clinically, it may be desirable to estimate the DSRE relationship with fewer trials. We used the statistical resampling technique called the "bootstrap" to determine the number of defibrillation trials necessary for an accurate estimation of the DSRE relationship. The bootstrap technique assumes that the observed database is the maximum likelihood sample of the estimated population. The observed database is repeatedly resampled to produce a large bootstrap data-base and the bootstrap best estimate of a statistic is determined. DSRE data were obtained from ten dogs (20.5 +/- 1.5 kg). We bootstrapped our experimental DSRE data by two methods: (1) randomly choosing with replacement a specified number of defibrillation trials per energy; and (2) randomly choosing with replacement a specified number of defibrillation trials per bootstrap replication. For both bootstrap techniques, 100 replications were made. We performed a linear regression analysis on the bootstrap success rates and the observed success rates determined from 71.0 +/- 6.8 defibrillation attempts from each of the ten dogs. We concluded that 28 defibrillation trials are necessary to estimate the observed DSRE relationship with a correlation coefficient of 0.95.

Animals↗
PubMed1991

Comparative efficacy of subcutaneous mesh and plate electrodes for nonthoracotomy canine defibrillation.

To determine the optimal configuration for the subcutaneous placement of electrodes for the performance of ventricular defibrillation without thoracotomy, internal defibrillation using four different subcutaneous electrodes was performed in 13 anesthetized dogs (7-12 Kg, mean +/- SD: 9.2 +/- 1.5 Kg). An electrode (7 cm2) was positioned transvenously in the superior vena cava with the following electrodes randomly implanted subcutaneously on the left chest: small mesh electrode (14 cm2), large mesh electrode (28 cm2), small titanium plate electrode (14 cm2), and large plate electrode (28 cm2). Ventricular fibrillation was induced by applying alternating current; a monophasic defibrillation wave was administered between the superior vena cava and the subcutaneous electrodes 10 seconds later. The energy level associated with a 50% successful defibrillation, as predicted by logistic regression analysis, was defined as the ED50. After the completion of the defibrillation protocol using the four subcutaneous electrodes, the small mesh electrode was sutured to the epicardium and the ED50 measurements were repeated. Energy ED50s were lower when the superior vena cava electrode was used as the cathode rather than as the anode. Of the subcutaneous electrodes, the large plate electrode showed the lowest energy ED50 (3.3 +/- 0.9 joules). The plate electrodes had lower energy ED50s than the mesh electrodes, and the large electrode had a lower energy ED50 than the small electrodes. Using the epicardium electrode, transient arrhythmias and ST elevation were observed following successful defibrillation; however, no arrhythmias or ST-T changes were observed following defibrillation using the subcutaneous electrodes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Ventricular pacing threshold and time to capture postdefibrillation in patients undergoing implantable cardioverter-defibrillator implantation.

To assess the effect of defibrillation and amiodarone on ventricular pacing threshold and time to capture in patients undergoing automatic implantable cardioverter-defibrillator (AICD) implantation, 28 patients were prospectively evaluated. The patients were entered into one of two protocols: Ia--epicardial ventricular pacing threshold measured at baseline (preventricular fibrillation induction) and 10 and 60 seconds postdefibrillation with 20 J, or Ib--two fibrillation-defibrillation sequences were performed 3 minutes apart and ventricular pacing thresholds were measured for each sequence at baseline and at 10 and 60 seconds postdefibrillation with 20 J. Ten patients also underwent asynchronous pacing at 1.1 times baseline threshold during ventricular fibrillation with measurement of time to capture postdefibrillation. All patients were randomly assigned to receive either amiodarone or no antiarrhythmic drug therapy. Ventricular fibrillation was induced with AC (applied for 1-2 seconds), and standard epicardial bipolar and epicardial patch electrodes of the AICD were used for pacing and defibrillation, respectively. Ventricular pacing threshold at baseline, 10 seconds, 60 seconds, and 3 minutes postdefibrillation did not differ significantly. There were no significant differences in patients with or without amiodarone therapy. Furthermore, there was no transient loss of ventricular capture postdefibrillation or significant difference in time to capture with amiodarone (less than or equal to 2 seconds). We conclude that following internal defibrillation with 20 J: (1) ventricular pacing threshold at 10 seconds, 60 seconds, and 3 minutes were not significantly different from baseline with one or two fibrillation-defibrillation sequences, (2) time to capture was short, and (3) there was no significant difference in no drug versus amiodarone. These findings have direct clinical importance in considering device therapy with both pacing and defibrillating capabilities.

Amiodarone↗
PubMed1997

The ventricular defibrillation and upper limit of vulnerability dose-response curves.

INTRODUCTION: A stimulus delivered in the T wave of a paced cardiac cycle can induce ventricular fibrillation (VF). If the stimulus strength is increased, the probability of inducing VF decreases. This study determines an ideal mathematical model (a dose-response curve) for the relationship between the shock strength and the probability of inducing VF or defibrillating. METHODS AND RESULTS: Defibrillating electrodes were implanted in the right ventricle and superior vena cava in 16 pigs. The electrode in the vena cava was electrically connected to a cutaneous patch. The same electrodes were used for both VF induction and defibrillation. T wave stimuli were given at the peak of the T wave according to a modified up-down protocol (40 V up, 20 V down). When a T wave stimulus induced VF, a defibrillation stimulus was delivered 10 seconds later, also according to the modified up-down protocol. Exponential, logistic, log-dose logistic, piecewise linear and Box-Tiao dose-response curves were fit to the resulting data using the maximum likelihood method. For the defibrillation data, it was found that only the logistic and Box-Tiao curves fit all of the animals (P < 0.05). For VF induction, only the Box-Tiao curve fit all of the animals (P < 0.05). Extrapolating along a dose-response curve that did not fit to a shock strength with a very low probability of inducing VF or a very high probability of defibrillating yielded errors as great as 610 V. CONCLUSION: The Box-Tiao dose-response curve is the best single choice for fitting VF induction or defibrillation datasets.

Animals↗
PubMed2005

CPR before defibrillation in out-of-hospital cardiac arrest: a randomized trial.

OBJECTIVE: Current resuscitation guidelines recommend that defibrillation be undertaken as soon as possible in patients suffering a cardiac arrest where the cardiac rhythm is either ventricular fibrillation (VF) or ventricular tachycardia (VT). Evidence from animal and clinical studies suggests that outcomes may be improved if a period of cardiopulmonary resuscitation (CPR) is given prior to defibrillation. The objective of this study was to determine if 90 seconds of CPR before defibrillation improved survival. METHODS: Patients suffering non-paramedic witnessed VF/VT cardiac arrest were randomized to receive either 90 seconds of CPR before defibrillation (treatment) or immediate defibrillation (control). The study was carried out in Perth, Western Australia between June 2000 and June 2002. The primary endpoint was survival to hospital discharge with secondary endpoints of return of spontaneous circulation (ROSC) and survival at 1 year. RESULTS: A total of 256 patients underwent randomization. Baseline characteristics including response intervals were similar in both groups. Survival to hospital discharge in the CPR first group was 4.2% (5/119) compared with 5.1% (7/137) for the immediate defibrillation group (OR 0.81; 95%CI. 0.25-2.64). No difference in those achieving ROSC was observed between the groups (OR 1.16; 95% CI 0.49-2.80). CONCLUSION: Ninety seconds of CPR before defibrillation does not improve overall survival in patients suffering VF/VT cardiac arrests. Further studies to evaluate various aspects of this treatment strategy are required as published outcomes to date are inconclusive.

Adolescent↗
PubMed1993

Ibutilide: enhanced defibrillation via plateau sodium current activation.

Reductions in current and energy requirements for defibrillation have previously been ascribed to type III antiarrhythmic agents that block outward potassium conductance. This study investigated the effect on defibrillation of ibutilide, a type III antiarrhythmic agent that prolongs action potential duration by activating the sodium component of the plateau inward current. Pentobarbital-anesthetized dogs were subjected to serial episodes of ventricular fibrillation lasting 10 s. In protocol I, current and energy defibrillation requirements were determined via an interactive approach after bolus injections of saline placebo and ibutilide (0.1 mg/kg i.v.). In protocol II, a current dose-response method was utilized in which four shocks each at current doses of 0.7, 0.8, 0.9, and 1.0 x an estimated defibrillation threshold were administered before and after ibutilide (0.075 mg/kg bolus; 0.00125 mg.kg-1 x min-1 i.v.). In protocol I, current and energy values associated with defibrillation measured 10.9 +/- 4.5 A and 16.0 +/- 11.9 J for ibutilide compared with 14.1 +/- 5.6 A and 27.7 +/- 17.7 J for placebo, respectively (n = 9, P < 0.005). In protocol II, ibutilide significantly shifted the current doses associated with 50% successful defibrillation from 14.8 +/- 3.7 to 8.9 +/- 2.0 A (n = 6, P < 0.05). Eight of 15 animals given ibutilide exhibited one or more episodes of spontaneous defibrillation. Ibutilide significantly (P < 0.05) increased ventricular effective refractory period (+23.4%), and both preventricular fibrillation and postdefibrillation monophasic action potential duration at 90% repolarization (+21.7% and +23.3%, n = 9, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1994

Transmyocardial impedance during single and multiple internal ventricular defibrillation shocks.

Little is known about the transmyocardial impedance during internal ventricular defibrillation. In a canine model, using high rate on-line digitization, random shock delivery, and titanium electrodes, we determined the relationship among voltage, current, and impedance, delivered energy, and defibrillation success within the individual and within successive defibrillation shocks. Impedance decreased with repeated defibrillation in 10 of 11 dogs. Impedance always increased during trapezoidal discharges, whereas voltage decreased. Impedance was lower with high energy-voltage shocks in all dogs. Visually, voltage and current waveform did not show a phase shift. There was no difference in the total energy delivered and the energy converted into heat by the resistive part of the impedance. With a formula valid only for resistive loads, the capacitance of the defibrillator was calculated to be within the measurement accuracy and tolerance of the factory-provided value of 132 microF. Polarization voltage was consistently observed. Thus the transmyocardial impedance during defibrillation is primarily resistive, nonlinear voltage dependent, and declines with successive shocks. Defibrillation success was not influenced by these phenomena.

Animals↗
PubMed2000

Ventricular defibrillation with triphasic waveforms.

BACKGROUND: It has been reported that triphasic defibrillation waveforms cause less myocardial injury than biphasic waveforms. This study compared the defibrillation thresholds (DFTs) of triphasic and biphasic waveforms. METHODS AND RESULTS: ++DFTs were determined for a transvenous lead system and a 300-microF-capacitor defibrillator. In 8 pigs (group 1), DFTs were determined for 5 triphasic waveforms with tilts of 80%, 83%, and 86% and for 1 biphasic waveform. DFTs were determined in another 8 pigs (group 2) for 2 triphasic and 4 biphasic waveforms with tilts of 43%, 49%, and 56%. In both groups, a biphasic waveform from a 140-microF-capacitor defibrillator was also evaluated, and both shock polarities were tested for each waveform. In group 1, with the 300-microF-capacitor defibrillator, the leading-edge voltage and energy stored at DFT were significantly lower for triphasic waveforms with phase-duration ratios of 50/33/17 and an anode at the right ventricular electrode for phase 1 than for biphasic waveforms (P<0.001). In group 2, the stored energy of triphasic waveforms with 56% and 49% tilt was significantly lower than that of biphasic waveforms with the same tilts for anodal but not cathodal phase 1 at the right ventricular electrode. Electrode polarity significantly affected the DFT of triphasic waveforms for both studies. CONCLUSIONS: Some 80% tilt triphasic waveforms defibrillate more efficiently than biphasic waveforms with a 300-microF-capacitor defibrillator. The triphasic waveforms for both groups were not superior to 140-microF-capacitor biphasic waveforms. The efficacy of triphasic waveforms depends on phase durations and electrode polarity.

Animals↗
PubMed1987

Improved defibrillation thresholds with large contoured epicardial electrodes and biphasic waveforms.

A reduction in the shock strength required for defibrillation would allow use of a smaller automatic implantable cardioverter-defibrillator and would reduce the possibility of myocardial damage by the shock. Most internal defibrillation electrodes require 5 to 25 J for successful defibrillation in human beings and in dogs. In an attempt to lower the shock strength needed for defibrillation, we designed two large titanium defibrillation patch electrodes that were contoured to fit over the right and left ventricles of the dog heart, covering areas of approximately 33 and 39 cm2, respectively. In six anesthetized open-chest dogs, the electrodes were secured directly to the epicardium and ventricular fibrillation was induced by 60 Hz alternating current. Truncated exponential monophasic and biphasic shocks were given 10 sec later and defibrillation thresholds (DFTs) were determined. The DFT was 159 +/- 48 V, 3.2 +/- 1.9 J (mean +/- SD) for 10 msec monophasic shocks and 106 +/- 22 V, 1.3 +/- 0.4 J, for biphasic shocks with both phase durations equal to 5 msec (5-5 msec). The experiment was repeated in another six dogs in which the electrodes were secured to the pericardium. The mean DFT was not significantly higher than that for the electrodes on the epicardium: 165 +/- 27 V, 3.1 +/- 1.2 J for 10 msec monophasic shocks and 116 +/- 19 V, 1.6 +/- 0.5 J for 5-5 msec biphasic shocks. Low DFTs were also obtained with biphasic shocks in which the duration of the first phase was longer than that of the second.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Cardiac potential and potential gradient fields generated by single, combined, and sequential shocks during ventricular defibrillation.

BACKGROUND: Potential gradient field determination may be a helpful means of describing the effects of defibrillation shocks; however, potential gradient field requirements for defibrillation with different electrode configurations have not been established. METHODS AND RESULTS: To evaluate the field requirements for defibrillation, potential fields during defibrillation shocks and the following ventricular activations were recorded with 74 epicardial electrodes in 12 open-chest dogs with the use of a computerized mapping system. Shock electrodes (2.64 cm2) were attached to the lateral right atrium (R), lateral left ventricular base (L), and left ventricular apex (V). Four electrode configurations were tested: single shocks of 14-msec duration given to two single anode-single cathode configurations, R:V and L:V, and to one dual anode-single cathode configuration, (R+L):V; and sequential 7-msec shocks separated by 1 msec given to R:V and L:V (R:V----L:V). Defibrillation threshold (DFT) current was significantly lower for R:V----L:V than for the other configurations and markedly higher for L:V. Despite these differences, the minimum potential gradients measured at DFT were not significantly different (approximately 6-7 V/cm for each electrode configuration). Potential gradient fields generated by the electrode configurations were markedly uneven, with a 15-27-fold change from lowest to highest gradient, with the greatest decrease in gradient occurring near the shock electrodes. Although gradient fields varied with the electrode configuration, all configurations produced weak fields along the right ventricular base. Early sites of epicardial activation after all unsuccessful shocks occurred in areas in which the field was weak; 87% occurred at sites with gradients less than 15 V/cm. Ventricular tachycardia originating in high gradient areas near shock electrodes followed 11 of 67 successful shocks. CONCLUSIONS: These data suggest that 1) defibrillation fields created by small epicardial electrodes are very uneven; 2) achievement of a certain minimum potential gradient over both ventricles is necessary for ventricular defibrillation; 3) the difference in shock strengths required to achieve this minimum gradient over both ventricles may explain the differences in DFTs for various electrode configurations; and 4) high gradient areas in the uneven fields can induce ectopic activation after successful shocks.

Animals↗
PubMed1998

Effects of postshock atrial pacing on atrial defibrillation outcome in the isolated sheep heart.

BACKGROUND: Failed atrial defibrillation shocks are associated with organization of postshock activity and a substantial postshock electrical quiescence. We investigated the ability of a train of pacing stimuli to capture or locally entrain atrial myocardium during the quiescent period after low-energy shocks and to alter defibrillation outcome. METHODS AND RESULTS: High-resolution video imaging of near-defibrillation-threshold atrial shocks was performed in 12 Langendorff-perfused sheep hearts. A train of 10 pacing stimuli (10-ms pulse width, 200-ms cycle length) was coupled to the shock at various delays in 7 hearts. Coupling intervals of 40 to 130 ms were investigated for feasibility of capture of the first pacing stimulus. The success rate of capture was 0, 0.08+/-0.08, 0.43+/-0.13, 0.73+/-0.13, and 0.11+/-0.1 for 40-, 60-, 80-, 100-, and 120-ms coupling intervals, respectively (P<0.001). In 5 experiments, the coupling interval was fixed at 100 ms (highest success, see above), and the pacing stimulus amplitude was varied between 1.0, 2.0, and 4.0 V. Successful capture rates were 0.38+/-0.08, 0.75+/-0.08, and 0.64+/-0.08, respectively (P<0.003 for 1.0 versus 2.0 V, P=0.2 for 2.0 versus 4.0 V). Rates of successful defibrillation for the groups without and with pacing were 0.56+/-0.07 and 0.64+/-0.04, respectively (P=0.3). With capture of the first pacing stimulus, the rate of successful defibrillation rose to 0.75+/-0.05 (P<0.01); it remained unchanged without capture (0.48+/-0.07 versus 0.56+/-0.07 for no pacing). CONCLUSIONS: Pacing during the quiescent period that follows defibrillation shocks is feasible. A pacing train whose first pacing stimulus successfully captures during the quiescent period of near-defibrillation-threshold shocks appears to alter the outcome.

Animals↗
PubMed2006

Predictors of sudden cardiac death and appropriate shock in the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Trial.

BACKGROUND: The factors that determine the risk for sudden death or implantable cardioverter defibrillator therapy in patients receiving cardiac resynchronization therapy (CRT) therapies are largely unknown. METHODS AND RESULTS: We hypothesized that clinical measures of heart failure severity and the presence of comorbid conditions would predict the risk of malignant arrhythmias in the 1520 patients enrolled in the Comparison of Medical Therapy, Pacing, and Defibrillation in Heart Failure (COMPANION) Trial. Outcomes in the CRT group after implantable cardioverter defibrillator therapy were also evaluated. The CRT-defibrillator device reduced the risk of sudden death by 56% compared with drug therapy (17 of 595 [2.9%] versus 18 of 308 [5.8%], P<0.02). CRT therapy was not associated with sudden death risk reduction (48 of 617 [7.8%]). Other factors associated with reduced sudden death risk were left ventricular ejection fraction >20% (HR, 0.55 [95% CI, 0.35 to 0.87]; P=0.01), QRS duration >160 ms (HR, 0.63 [95% CI, 0.40 to 0.997]; P=0.05), and female gender (HR, 0.56 [95% CI, 0.34 to 0.94]; P=0.003). The risk for sudden death was increased by advanced New York Heart Association class IV heart failure (HR, 2.62 [95% CI, 1.61 to 4.26]; P<0.011) and renal dysfunction (HR, 1.69 [95% CI, 1.06 to 2.69]; P=0.03). An appropriate shock was experienced in 88 (15%) of the 595 CTR-D patients. In the CRT-defibrillator patients, female gender (HR, 0.54 [95 % CI, 0.31 to 0.94]; P=0.03) and use of neurohormonal antagonists were associated with reduced risk. Class IV heart failure status increased risk. Appropriate implantable cardioverter defibrillator therapy was positively associated with risk of death or all-cause hospitalization (HR, 1.57; P<0.002), pump failure death or hospitalization (HR, 2.35; P<0.001), and sudden death (HR, 2.99; P=0.03), but not total mortality (HR, 1.3; P=0.28). CONCLUSIONS: In CRT candidates, sudden cardiac death risk is associated with higher New York Heart Association class and renal dysfunction. In CRT-defibrillator recipients, reduction in the risk of an appropriate shock is associated with medical therapy with neurohormonal antagonists, female gender, and New York Heart Association functional class III versus IV clinical status. Shock therapy was associated with worse outcome.

Aged↗
PubMed1994

Frequency of ventricular fibrillation as a predictor of defibrillation success during cardiac surgery.

The purpose of this study was to record median frequency of ventricular fibrillation (VF) in patients undergoing cardiopulmonary bypass for cardiac surgery, and to assess whether defibrillation success depends upon median VF frequency. Data were collected from 20 patients undergoing aortocoronary bypass grafting. Using computerized fast Fourier transformation of the signal from the electrogram, median VF frequency was assessed from onset of VF until aortic cross-clamping and during the 4-s period immediately before each defibrillation during the reperfusion phase. During VF, when an adequate coronary perfusion was maintained by cardiopulmonary bypass prior to aortic cross-clamping, median VF frequency (5.8 +/- 0.1 Hz to 6.2 +/- 0.1 Hz) remained constant for the entire observation interval (96 +/- 25 s; mean +/- SEM). A total of 42 defibrillations were performed: 22 resulted in supraventricular rhythm, 10 in VF, 6 in asystole, and 4 in electromechanical dissociation (EMD). Median VF frequency before defibrillation resulting in supraventricular rhythm was 4.7 +/- 0.17 Hz. In contrast, median VF frequencies before unsuccessful defibrillation resulting in persistent VF (3.5 +/- 0.28 Hz; P < 0.05), EMD (2.9 +/- 0.15 Hz; P < 0.01), or asystole (2.8 +/- 0.28 Hz; P < 0.01) were significantly lower. Above a threshold of 3.0 Hz, the probability of successful defibrillation increased as median VF frequency increased. The probability of success was 100% at a frequency of > or = 5.5 Hz. We conclude that median VF frequency is a reliable noninvasive variable which can be used to predict defibrillation success during the reperfusion phase after cardiac surgery.

Cardiopulmonary Bypass↗
PubMed1986

The effect of lidocaine and bretylium on the defibrillation threshold during cardiac arrest and cardiopulmonary resuscitation.

The effect of intravenous lidocaine, 2 mg/kg, and bretylium, 5 mg/kg, on defibrillation threshold (DFT) was investigated in alpha-chloralose anesthetized dogs undergoing conventional closed chest cardiopulmonary resuscitation (CPR) following induced ventricular fibrillation. Ventricular fibrillation was induced electrically and CPR was performed by a pneumatic device set to compress the chest 60 times and inflate the lung 12 times a minute. Defibrillation was achieved using underdamped sinusoidal current shocks from a special defibrillator which allowed determination of delivered energy. The DFT was defined as the peak current which defibrillated, but no more than 20% higher than a current which did not defibrillate. All DFTs were obtained within 5 min of CPR. The mean +/- SD current and energy thresholds required for defibrillation during lidocaine-CPR (seven dogs) were 17.0 +/- 8.9 A and 53.0 +/- 40.7 J as compared to 12.5 +/- 6.2 A and 34.3 +/- 30.7 J, respectively during control-CPR (P less than 0.05). The mean +/- SD current and energy thresholds during bretylium-CPR were 11.0 +/- 3.4 A and 24.1 +/- 1.3 J as compared to 11.8 +/- 1.7 A and 29.4 +/- 9.6 J, respectively, during control-CPR (NS). These results show that lidocaine acutely elevated defibrillation threshold whereas bretylium did not produce such an effect. The effect on DFT along with other pharmacologic properties should be considered when lidocaine or bretylium is used in the setting of cardiac arrest and CPR.

Animals↗