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PubMed1994

Effects of procainamide and lidocaine on defibrillation energy requirements in patients receiving implantable cardioverter defibrillator devices.

INTRODUCTION: In acute canine studies, lidocaine, but not procainamide, increases defibrillation energy requirements. We evaluated the effects of lidocaine or procainamide on defibrillation energy requirements in 27 patients undergoing intraoperative testing for implantable cardioverter defibrillator device placement. METHODS AND RESULTS: Patients were tested off antiarrhythmic drugs and again following either lidocaine (200 to 250 mg loading and 3 mg/min maintenance infusions) or procainamide (1 gm loading and 3 to 4 mg/min maintenance infusions). The defibrillation testing protocol consisted of initial testing at 15 J, followed by higher or lower energies to determine the lowest energy producing three consecutive successful defibrillations. Overall, the mean defibrillation energy increased from 14 +/- 5 J to 18 +/- 7 J during lidocaine (plasma concentration 5.1 +/- 1.6 micrograms/mL; P < 0.02) but were similar at baseline (12 +/- 5 J) and during procainamide infusion (13 +/- 6 J) (plasma concentration: procainamide 10.7 +/- 7.2 micrograms/mL; N-acetyl procainamide 1.0 +/- 0.4 micrograms/mL). A positive linear correlation was found between lidocaine plasma concentration and percent change in defibrillation energy (lidocaine: r = 0.61; P = 0.01). Procainamide raised the defibrillation energy in three patients, two with supratherapeutic plasma concentrations. The increase in defibrillation energy equaled or exceeded 25 J in four patients after lidocaine and in one patient after procainamide. CONCLUSION: The data suggest that at high plasma concentrations, lidocaine and procainamide adversely affect defibrillation energy requirements consistent with an adverse, concentration-dependent effect of sodium channel blockade on defibrillation energy requirements in patients.

Aged↗
PubMed1995

Elevated defibrillation threshold when right-sided venous access is used for nonthoracotomy implantable defibrillator lead implantation. The Endotak Investigators.

INTRODUCTION: Although myriad factors influence the defibrillation threshold, the relation between the site of transvenous lead entry into the vascular system and the defibrillation threshold has not been reported. This study examines the influence that venous entry site has on defibrillation success for a transvenous implantable cardioverter defibrillator lead with two defibrillating coils. METHODS AND RESULTS: The study population comprised 345 patients. Their mean age was 61 +/- 13 years and, left ventricular ejection fraction was 0.33 +/- 0.13. A left-sided approach was used in 324 (93.9%) of the patients, and a right-sided approach was used in the remaining 21 (6.1%) patients. There was no difference in the gender, age, left ventricular ejection fraction, or underlying cardiac disease in the two groups. For all patients, with a transvenous lead used either alone or with a submuscular or subcutaneous patch, the biphasic defibrillation threshold was 9.9 +/- 4.8 J when a left-sided approach was used, and 14.0 +/- 7.3 J when a right-sided approach was used (P = 0.02). When a transvenous lead was used with a submuscular or subcutaneous patch (115 patients), the biphasic defibrillation threshold was 9.5 +/- 4.3 J when a left-sided approach was used, and 12.0 +/- 10.0 J when a right-sided approach was used (P = 0.98). When a transvenous lead was used without a submuscular or subcutaneous patch (230 patients), the biphasic defibrillation threshold was 10.1 +/- 5.0 J when a left-sided approach was used, and 14.6 +/- 6.6 J when a right-sided approach was used (P < 0.01). For the entire group of patients and for each specific lead arrangement, there was no significant difference in the defibrillating lead system impedance when right-sided versus left-sided approaches were compared. CONCLUSION: Left-sided approaches to implant transvenous leads with two coils for defibrillation result in lower biphasic defibrillation thresholds than when right-sided approaches are used.

Defibrillators, Implantable↗
PubMed1987

Relationship of left ventricular mass to defibrillation threshold for the implantable defibrillator: a combined clinical and animal study.

Defibrillation results when a critical mass of myocardium is depolarized. The relationship between echocardiographic determinations of left ventricular mass, volume, and cavity radius to wall thickness ratio and defibrillation threshold for the implantable defibrillator was examined. Ten patients with two large patch defibrillating lead systems were studied. Defibrillation threshold was determined intraoperatively as the lowest energy terminating ventricular fibrillation. Left ventricular mass, volume, and radius/posterior wall thickness ratio were calculated from two-dimensional echocardiograms. A significant correlation was found between left ventricular mass and defibrillation threshold (r = 0.78, p less than 0.01). The correlations between defibrillation threshold and left ventricular volume (r = 0.59) and radius/wall thickness ratio (r = 0.55) were not significant. Subsequently, 11 dogs undergoing defibrillation trials with a transvenous catheter and a chest wall patch were studied. Defibrillation threshold was defined as the lowest energy-terminating ventricular fibrillation (four separate attempts). Subsequently, the heart was dissected, and the left ventricle (including the septum) was weighed. The correlation between left ventricular weight and defibrillation threshold (r = 0.76) was significant (p less than 0.01). We conclude that noninvasive assessment of left ventricular mass and direct measurement of left ventricular weight are significantly correlated with defibrillation threshold and consistent with the critical mass hypothesis.

Animals↗
PubMed1988

Sequential pulse defibrillation in humans: orthogonal sequential pulse defibrillation with epicardial electrodes.

A newly described sequential pulse technique, using four mesh electrodes positioned to approximate a true orthogonal system around the heart, was compared with a single pulse system using two of these same electrodes, which were located in positions that would be used for an automatic implantable defibrillator. The influence of electrode size was also assessed. The minimal energy necessary for defibrillation (defibrillation threshold) was determined intraoperatively in 21 volunteer patients undergoing accessory pathway ablation of Wolff-Parkinson-White syndrome. Ventricular fibrillation was induced with alternating current. Ten seconds after fibrillation onset defibrillation shocks were begun using either the single or the sequential pulse technique with stored voltage incremented until defibrillation was accomplished (defibrillation threshold). Selection of the use of a single or sequential pulse technique for the initial attempt was randomized. Defibrillation thresholds were determined in three groups of patients: 1) those with four small mesh electrodes (6 cm2), 2) those with two small and two large (13 cm2) mesh electrodes, and 3) those with four large mesh electrodes. In all cases, the average minimal energy needed for sequential pulse defibrillation was less than that required for single pulse defibrillation in the same patients with the same electrodes (four small, 24.8 +/- 24.7 J single versus 6.7 +/- 8.3 J sequential; two small plus two large, 11.4 +/- 15.0 J single versus 2.7 +/- 1.4 J sequential; four large, 8.1 +/- 5.3 J single versus 3.9 +/- 2.6 J sequential). Using the 6 cm2 electrodes for single pulse defibrillation energies delivered at greater than 45 J in two patients failed to defibrillate the heart.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1987

Pathologic findings related to the lead system and repeated defibrillations in patients with the automatic implantable cardioverter-defibrillator.

The purpose of the present study was to examine at autopsy the effect of multiple defibrillations on the myocardium and the pathologic consequences of short- and long-term placement of the intravascular and interpericardial leads of the automatic implantable cardioverter-defibrillator. Twenty-five patients were examined at autopsy; 8 of them underwent lead implantation only and 17 received both leads and the automatic implantable cardioverter-defibrillator. Twelve patients (48%) died of ventricular tachycardia or ventricular fibrillation; seven (28%) died of other causes. Acute pericarditis occurred in all patients, resulting in a localized, progressive fibrosis around the apical patch lead without giving rise to pericardial restriction. Thrombus formation was associated with the superior vena cava spring electrode in four patients (17%) and the right ventricular rate-sensing electrode in one patient (4%). Asymptomatic pulmonary emboli occurred in two patients (8%). In one patient who underwent defibrillation 59 times, superior vena cava changes consisted of vein wall destruction, fibrosis and thrombus formation. Pathologic changes under the apical patch related to defibrillation were observed in seven patients; two of these had fewer than 5 defibrillations, one had 8 defibrillations and four had 21 to 74 defibrillations. These changes consisted of contraction band necrosis in four patients, vacuolar cytoplasmic clearing and loss of myocytes confined to the myocardium under the patch electrode in five patients who had multiple defibrillations. The observed pathologic changes were estimated to affect less than 2% of the total myocardial mass. Thus, the automatic implantable cardioverter-defibrillator lead system and multiple defibrillations result in localized myocardial injury confined to the tissue under the patch electrode.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Flecainide acetate does not alter the energy requirements for direct ventricular defibrillation using sequential pulse defibrillation in pigs.

Flecainide acetate is a recently approved class 1c antiarrhythmic agent indicated for patients with serious ventricular arrhythmias. Because flecainide may be used in patients with automatic implantable defibrillators, we assessed the effect of flecainide on ventricular defibrillation energy requirements in a pig model. Different doses of flecainide maintaining plasma levels in the "subtherapeutic" (six pigs), "therapeutic" (eight pigs), and "supratherapeutic" (eight pigs) range were administered to three groups of pigs. A fourth group (six pigs) served as a time control and was given normal saline only. Episodes of ventricular fibrillation were induced and then terminated using sequential truncated trapezoidal direct current shocks delivered by a tripolar internal defibrillator system. Energy requirements for defibrillation were assessed by measuring defibrillation threshold and also by comparing shifts in the curves relating energy with percent successful defibrillation. Flecainide failed to alter defibrillation requirements at any dose. We conclude that ventricular defibrillation energy requirements are not affected by flecainide in our pig model. Both the defibrillation threshold technique and the comparison of curves relating success of defibrillation to energy yielded similar results suggesting that either can be used to assess energy requirements for defibrillation.

Animals↗
PubMed1999

Effect of general anesthesia on the defibrillation energy requirement in patients undergoing defibrillator implantation.

BACKGROUND: The effect of general anesthesia on defibrillation efficacy in humans is not known. The purpose of this study was to determine the effect of general anesthesia on the defibrillation energy requirements in patients undergoing implantation of a pectoral defibrillator. METHODS AND RESULTS: Nineteen consecutive patients who underwent defibrillator implantation under general anesthesia were prospectively compared to 16 consecutive patients who underwent defibrillator implantation by the same physicians, using similar devices, at another hospital under conscious sedation. Pre-discharge testing was performed 1.4 +/- 1.0 days after implant using sedation in both groups. The defibrillation energy requirement was determined using the same predefined step-down protocol (15, 10, 8, 5, 3, 1 J) at the time of implantation and during pre-discharge testing. The clinical characteristics of the patients were similar between groups. There was no significant difference in the mean implant defibrillation energy requirement compared to the mean pre-discharge defibrillation energy requirement in either the general anesthesia group (8.5 +/- 4.7 vs. 8.4 +/- 3.4 J; p = 0.9) or in the conscious sedation group (9.4 +/- 3.9 vs. 9.0 +/- 3.8 J; p = 0.7). CONCLUSIONS: When compared to conscious sedation, general anesthesia with mechanical ventilation has no significant effect on defibrillation efficacy in patients undergoing defibrillator implantation.

Aged↗
PubMed2003

Comparison of coronary venous defibrillation with conventional transvenous internal defibrillation in man.

OBJECTIVE: Animal studies have shown that defibrillation in coronary veins is more effective than in the right ventricle. We aimed to assess the feasibility of placing defibrillation electrodes in the middle cardiac vein (MCV) in man and its impact on defibrillation requirements. METHODS: A prospective randomised study conducted in a tertiary referral centre. 10 patients (9 male) undergoing ICD implantation (65 (12) yrs) for NASPE/BPEG indications were studied. Defibrillation thresholds (DFT) were measured, using a binary search and an external defibrillator after 10 seconds of ventricular fibrillation, for the following configurations in each patient (order of testing randomised): RV + MCV --> Can and RV --> SVC + Can. INTERVENTIONS: A dual coil defibrillation electrode was placed transvenously in the right ventricle (RV) in the conventional manner. Using a guiding catheter a 3.2 Fr (67.5 mm length) electrode was placed transvenously in MCV. A test-can was placed subcutaneously in the left pectoral region. RESULTS: Lead placement was possible in 8/10 pts. Time to perform a middle cardiac venogram and place the electrode was 21 (23) mins. No adverse events were observed. Defibrillation current was less (6.7 (2.7) A) with RV + MCV --> Can compared to the conventional RV --> SVC + Can configuration (8.9 (3.4) A, p = 0.03). There was no significant difference in defibrillation voltage or energy. However, shock impedance was higher in the former configuration (57 (10) v. 43 (6) Omega, p = 0.001). CONCLUSIONS: In the majority of cases placement of a defibrillation lead in MCV is feasible. Defibrillation current requirements are 25% less when the shock is delivered using a MCV electrode.

Aged↗
PubMed2003

Prospective randomized comparison of two defibrillation safety margins in unipolar, active pectoral defibrillator therapy.

Various techniques are used to establish defibrillation efficacy and to evaluate defibrillation safety margins in patients with an ICD. In daily practice a safety margin of 10 J is generally accepted. However, this is based on old clinical data and there are no data on safety margins using current ICD technology with unipolar, active pectoral defibrillators. Therefore, a randomized study was performed to test if the likelihood of successful defibrillation at defibrillation energy requirement (DER) + 5 J and + 10 J is equivalent. Ninety-six patients (86 men; age 61.0 +/- 10.3 years; ejection fraction 0.341 +/- 0.132; coronary artery disease [n = 65], dilated cardiomyopathy [n = 18], other [n = 13]) underwent implantation of an active pectoral ICD system with unidirectional current pathway and a truncated, fixed tilt biphasic shock waveform. The defibrillation energy requirement (DER) was determined with the use of a step-down protocol (delivered energy 15, 10, 8, 6, 4, 3, 2 J). The patients were then randomized to three inductions of ventricular fibrillation at implantation and three at predischarge testing with shock strengths programmed to DER + 5 J at implantation and + 10 J at predischarge testing or vice versa. The mean DER in the total study population was 7.88 +/- 2.96 J. The number of defibrillation attempts was 288 for + 5 J and 288 for + 10 J. The rate of successful defibrillation was 94.1% (DER + 5 J) and 98.9% (DER + 10 J; P < 0.01 for equivalence). Charge times for DER + 5 J were significantly shorter than for DER + 10 J (3.65 +/- 1.14 vs 5.45 +/- 1.47 s; P < 0.001). A defibrillation safety margin of DER + 5 J is associated with a defibrillation probability equal to the standard DER + 10 J. In patients in whom short charge times are critical for avoidance of syncope, a safety margin of DER + 5 J seems clinically safe for programming of the first shock energy.

Defibrillators, Implantable↗
PubMed1993

Effects of antiarrhythmic drugs on epicardial defibrillation energy requirements and the rate of defibrillator discharges.

Antiarrhythmic drugs are commonly used with the implantable cardioverter/defibrillator to treat recurrent ventricular tachyarrhythmias. Since various antiarrhythmic drugs have been reported to alter defibrillation threshold, an important question is whether the device will provide adequate energy for defibrillation during long-term follow-up and to what extent antiarrhythmic drug treatment will affect defibrillation energy requirements. To answer these questions, the defibrillation thresholds were determined in 20 patients using an epicardial patch-patch lead configuration at the time of implantation and at the time of pulse generator replacement. During a mean follow-up period of 24 +/- 6 months, the defibrillation threshold increased significantly from 14.2 +/- 3.7 joules to 18.3 +/- 5.5 joules in the entire group (P < 0.05). This increase in defibrillation threshold was due to a marked elevation of defibrillation energy requirements in the subgroup of patients taking amiodarone compared with patients receiving mexiletine. Based on these results it is mandatory to retest defibrillation threshold at any time of pulse generator replacement to guarantee continued effectiveness. In particular, if amiodarone treatment is initiated after implantation of a defibrillator, it is recommended to reevaluate defibrillation threshold to ensure an adequate margin of safety.

Amiodarone↗
PubMed1996

Improved sensing signals after endocardial defibrillation with a redesigned integrated sense pace defibrillation lead.

Adequate sensing is a basic requirement for appropriate therapy with ICDs. Integrated sense pace defibrillation leads, which facilitate ICD implantation, show a close proximity of sensing and defibrillation electrodes that might affect the sensing signal amplitude by the high currents of internal defibrillation. In 99 patients, we retrospectively examined two integrated sense pace defibrillation leads, either both with a distance of 6 mm between the tip of the lead (sensing cathode) and the right ventricular defibrillation electrode (sensing anode) or one with a distance of 12 mm. Three seconds after a shock of 20 J, mean sensing signal amplitude during sinus rhythm (SR) decreased from 10.5 +/- 4.3 mV to 5.1 +/- 3.7 mV (P < 0.001) for the 6-mm lead, but showed no significant decrease for the 12-mm lead. The degree of signal reduction was inversely related to the time passed since defibrillation. Significant differences in reduction of sensing signal amplitude concerning monophasic and biphasic shocks could not be observed. Mean sensing signal amplitude of VF after shocks that failed to terminate it decreased in the same order as during SR (from 8.3 +/- 4.1 mV to 4.1 +/- 3.2 mV), but resulted in no failure of redetection during ongoing VF. DFTs did not differ for the 6-mm and the 12-mm lead. In conclusion, close proximity of the right ventricular defibrillation coil to the sensing tip of an integrated sense pace defibrillation lead causes energy and time related reduction in sensing signal amplitude after defibrillation, and might cause undersensing in the postshock period. A new lead design with a more proximal position of the right ventricular defibrillation coil avoids these problems without impairing DFTs.

Defibrillators, Implantable↗
PubMed1996

A second defibrillator chest patch electrode will increase implantation rates for nonthoracotomy defibrillators.

Nonthoracotomy defibrillator systems can be implanted with a lower morbidity and mortality, compared to epicardial systems. However, implantation may be unsuccessful in up to 15% of patients, using a monophasic waveform. It was the purpose of this study to prospectively examine the efficacy of a second chest patch electrode in a nonthoracotomy defibrillator system. Fourteen patients (mean age 62 +/- 11 years, ejection fraction = 0.29 +/- 0.12) with elevated defibrillation thresholds, defined as > or = 24 J, were studied. The initial lead system consisted of a right ventricular electrode (cathode), a left innominate vein, and subscapular chest patch electrode (anodes). If the initial defibrillation threshold was > or = 24 J, a second chest patch electrode was added. This was placed subcutaneously in the anterior chest (8 cases), or submuscularly in the subscapular space (6 cases). This resulted in a decrease in the system impedance at the defibrillation threshold, from 72.3 +/- 13.3 omega to 52.2 +/- 8.6 omega. Additionally, the defibrillation threshold decreased from > or = 24 J, with a single patch, to 16.6 +/- 2.8 J with two patches. These changes were associated with successful implantation of a nonthoracotomy defibrillator system in all cases. In conclusion, the addition of a second chest patch electrode (using a subscapular approach) will result in lower defibrillation thresholds in patients with high defibrillation thresholds, and will subsequently increase implantation rates for nonthoracotomy defibrillators.

Adult↗
PubMed1989

Adverse effects of permanent cardiac internal defibrillator patches on external defibrillation.

At the time of left ventricular aneurysm resection, antiarrhythmic operations or other open-heart operative procedures in patients with ventricular dysrhythmia, permanent internal defibrillator patches may be inserted. Insertion of the energy source may be delayed due to its unavailability or to a desire for postoperative electrophysiologic study before its insertion. To assess the effects of permanent internal defibrillator patches on external defibrillation, 7 anesthetized calves were studied. Fibrillation-defibrillation studies were performed before and after insertion of permanent internal defibrillator patches (model L67, 27 cm2, Intec Systems), one on each ventricle. The values of percent successful defibrillation obtained before insertion of the patches, although much lower than values that would be expected in humans, are consistent with the results of an extensive earlier study involving this calf model. Similar values obtained after insertion of the patches are appreciably lower than the values obtained before implantation of the patches, and appreciably lower than the results predicted by the earlier study. A significant decrease in the percent of successful defibrillations (p less than 0.001) was observed for a shock intensity of approximately 400 J. Permanent internal cardiac defibrillator patches on the right and left ventricles reduce the probability of achieving successful defibrillation externally with unidirectional shocks. The wisdom of implanting permanent large internal cardiac defibrillator patches without the energy source is questioned.

Animals↗
PubMed1995

Atrial defibrillation using temporary epicardial defibrillation stainless steel wire electrodes: studies in the canine sterile pericarditis model.

OBJECTIVES: This study sought to determine whether temporary epicardial wire electrodes can be used safely and effectively to defibrillate the atria with low energy shocks in the absence of anesthesia. BACKGROUND: Atrial fibrillation after open heart surgery is a significant clinical problem. METHODS: Twelve dogs with sterile pericarditis were studied. In the first group (6 dogs, bilateral thoracotomy group), a wire electrode, insulated except for the distal 6 cm, was placed on the epicardial free wall of each atrium. Each end of the bare wire was then sutured to the parietal pericardium. In the second group (6 dogs, median sternotomy group), the wire electrodes were kept in place by a double loop of Prolene placed around the distal tip of the bare wire and sewn to the overlying parietal pericardium. In the bilateral thoracotomy group, atrial defibrillation thresholds (defined as < 90% and > 10% successful defibrillation of 20 shocks at a given delivered energy) were obtained in anesthetized dogs using the wire electrodes with the chest closed and open and using two transvenously placed catheters with coil electrodes in the distal 6 cm (one in the coronary sinus and the other in the right atrial appendage) with the chest open. In the median sternotomy group, thresholds were obtained in minimally sedated animals without reopening the chest. A 25% increase above threshold shock was also used to determine a new percent success. After 4 days, the wire electrodes were removed by pulling on the external ends. At the time of removal, blood pressure and heart rate were monitored for 30 min, after which dogs were killed and their hearts sent for histopathologic study. For all dogs, chest radiographs were obtained postoperatively and on study days. RESULTS: Atrial defibrillation using the wire electrodes was successful in all dogs at a mean (+/- SE) voltage of 112 +/- 9 V, with an energy level of 0.46 +/- 0.07 J and an impedance of 59.3 +/- 5 ohms. The mean percent success at the atrial defibrillation threshold was 36 +/- 5%. The 25% increase in defibrillation voltage improved the mean percent success to 73% (mean energy 0.66 +/- 0.19 J). No clinical or hemodynamic complications were observed during shock delivery, and no ventricular arrhythmias were induced during the shocks. No complications followed wire electrode removal. Histopathologic analysis showed no structural damage. CONCLUSIONS: The atrial defibrillation threshold obtained using temporary epicardial wire electrodes for atrial defibrillation is < 1 J in dogs. Atrial defibrillation using temporary epicardial wire electrodes can be performed safely, quickly and reliably without the need for anesthesia or antiarrhythmic agents. The wire electrodes can be removed without adverse hemodynamic or structural consequences. These data provide a basis for testing atrial defibrillation using epicardial wire electrodes in patients after open heart surgery.

Algorithms↗
PubMed1993

An evaluation of automated defibrillation and manual defibrillation by emergency medical technicians in a rural setting.

We show that automated external defibrillation training of emergency medical technicians (EMTs) is less time consuming than manual defibrillation training, and hypothesize that both improve survival from sudden cardiac death. Data on 91 cardiac arrests over 27 months among five basic life support services was collected before EMT-defibrillation (EMT-D) training. Subsequently, seven BLS services were trained in EMT-D using either manual difibrillation or automated external defibrillation technology, and 55 sudden cardiac death patients were entered after training. Manual defibrillation required 11 more hours per student in initial training. Survival to hospital discharge improved from two of 91 patients (2.2%) in the series before EMT-D training to nine of 55 patients (16.4%) after EMT-D training (P = .001). Improved survival was correlated with shorter prehospital defibrillation times, 8.84 minutes, when EMTs performed defibrillation versus 16.3 minutes before training when EMTs awaited advanced life support defibrillation (P < .001). To enhance equipment familiarity we allowed EMTs to apply three-lead electrode monitors to all medical/cardiac patients during transport (surveillance). There were six emergency medical service-witnessed "surveillance" arrests and three arrests survived to hospital discharge (50% survival). This group represented 33% of all survivors in the series. We recommend automated external defibrillation training for EMTs. Improved survival in sudden cardiac death cases in well-run emergency medical service systems should result from EMT-D training. Finally, we recommend that routine "surveillance" of high-risk patients during transport by defibrillation-capable EMTs be considered in EMT-D programs, rather than limiting EMT-D only to units capable of rapid "man-down" response.

Aged↗
PubMedDate not supplied

Do pulse checks delay semiautomatic defibrillation by EMT-defibrillators?

Advanced cardiac life support (ACLS) guidelines from the American Heart Association (AHA) now recommend not checking for a pulse between the initial three defibrillations for pulseless patients in ventricular tachycardia or fibrillation. The AHA asserts that checking for a pulse needlessly delays defibrillation. This study was undertaken to determine if pulse checks delay defibrillation by EMT-Defibrillators (EMT-Ds) using a semiautomatic defibrillator (SAED). Twenty-seven EMT-Ds demonstrated delivery of three successive defibrillations during two test scenarios: once with and once without pulse checks after the first and second defibrillations. The time from the first to third defibrillation was recorded. The mean time to deliver the defibrillations was 60.2 +/- 6.2 seconds with pulse checks and 57.5 +/- 4.6 seconds without pulse checks. The difference, 2.7 +/- 5.9 seconds, was statistically significant (P = 0.026). Pulse checks by EMT-Ds do delay administration of defibrillations, but consideration should be given to reinstating pulse checks as a part of the AHA guidelines, since this delay is of questionable clinical significance.

Electric Countershock↗
PubMed2001

Out-of-hospital defibrillation with automated external defibrillators: postshock analysis should be delayed.

STUDY OBJECTIVE: The American Heart Association protocols for use of automated external defibrillators (AEDs) recommend that a rhythm analysis be done immediately after each defibrillation attempt. However, shock is often followed by electrical silence or marginally organized electrical activity before ventricular fibrillation (VF) or ventricular tachycardia (VT) recurs. The optimal timing of postshock analysis for identification of recurrent VF/VT is unknown. This study examines the time to recurrence of VF/VT after a defibrillation attempt with AED. METHODS: Over an 18-month period, all tapes from patients with out-of-hospital cardiac arrest who received shocks at least once with an AED were screened for recurrent VF/VT. All cases come from a single emergency medical services system providing basic life support, defibrillation with AED, and intubation with an esophageal-tracheal twin-lumen airway device (Combitube) for a population of 633,511 individuals. Pediatric and traumatic cases were excluded. When VF/VT recurred within 3 minutes of the defibrillation attempt, rhythm strips were printed and included in the study. Two cardiology fellows, blinded to the study objectives, measured the time from defibrillation to recurrent VF/VT for each strip. RESULTS: Over the study period, 222 tapes from 96 patients met the inclusion criteria. Only 44 (20%) occurrences of VF/VT had recurred within 6 seconds of defibrillation, 162 (73%) at 60 seconds, and 200 (90%) at 90 seconds. CONCLUSION: Eighty percent of VF/VT recurred more than 6 seconds after defibrillation and were missed when using current American Heart Association AED protocols. Subsequent analysis should be postponed until at least 30 seconds after defibrillation. Performing 30 seconds of chest compressions after defibrillation before subsequent AED rhythm analysis would increase AED identification of VF/VT to 52%.

Adult↗
PubMed1997

A comparison of transvenous atrial defibrillation of acute and chronic atrial fibrillation and the effect of intravenous sotalol on human atrial defibrillation threshold.

The comparative efficacy and safety of transvenous defibrillation for acute and chronic AF and the effect of antiarrhythmic agents on this therapy have not been evaluated. Transvenous atrial defibrillation was performed in 25 patients with chronic AF and 13 patients with acute AF by delivering R wave synchronized, biphasic shocks between the right atrium and coronary sinus. The lowest energy and voltage resulting in successful defibrillation were considered to be atrial defibrillation threshold (ADFT). Intravenous sotalol (1.5 mg/kg) was then given over 15 minutes and ADFT was determined again. The mean ADFT was 1.5 J and 3.6 J for acute and chronic AF, respectively, and the threshold was highly reproducible. Sotalol reduced ADFT in patients with acute AF while the reduction in chronic AF group was not significant. There was no significant increase in creatinine kinase nor reduction in blood pressure, but prolonged pause after successful defibrillation required ventricular supporting pacing. We conclude that transvenous atrial defibrillation is a safe and effective means for defibrillating both acute and chronic AF. ADFT was lower in acute AF than in chronic AF. ADFT was highly reproducible during repeated defibrillation. Sotalol reduced ADFT in acute AF and to a lesser extent in chronic AF, and increased the defibrillation success rate. Ventricular pacing will often be required because of prolonged pause after successful defibrillation.

Acute Disease↗