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PubMed1992

Cardiac arrest in Ontario: circumstances, community response, role of prehospital defibrillation and predictors of survival.

OBJECTIVES: To describe the patient characteristics, circumstances and community response in cases of out-of-hospital cardiac arrest; to evaluate the effect on survival of the introduction of prehospital defibrillation; and to identify factors that predict survival. DESIGN: Population-based before-and-after clinical trial. SETTING: Five Ontario communities: London, Sudbury, the Greater Niagara region, Kingston and Ottawa. PATIENTS: A consecutive sample of 1510 primary cardiac arrest patients who were transported to hospital by ambulance over 2 years. INTERVENTION: The use of defibrillators by ambulance attendants. MAIN OUTCOME MEASURES: Patient characteristics (sex and age), circumstances of arrest (place, whether arrest was witnessed and cardiac rhythm), citizen response (whether cardiopulmonary resuscitation [CPR] was started by a bystander, time to access to emergency medical services and time to initiation of CPR), emergency medical services response (ambulance response time, time to initiation of CPR and time to rhythm analysis with defibrillator) and survival rates. MAIN RESULTS: A total of 92.1% of the patients were 50 years of age or older, and 68.3% were men. Overall, 79.6% of the arrests occurred in the home. The average ambulance response time for witnessed cases was 7.8 minutes. The overall survival rate was 2.5%. The survival rates before and after defibrillators were introduced were similar, and the general functional outcome of the survivors did not differ significantly between the two phases. Factors predicting survival included patient's age, ambulance response time and whether CPR was started before the ambulance arrived. CONCLUSIONS: The survival rate was lower than expected. The availability of prehospital defibrillation did not affect survival. To improve survival rates after cardiac arrest ambulance response times must be reduced and the frequency of bystander-initiated CPR increased. Once these changes are in place a beneficial effect from advanced manoeuvres such as prehospital defibrillation may be seen.

Adult↗
PubMed1990

Intravenous propafenone reduces energy requirements for defibrillation in pigs.

The effect of antiarrhythmic drugs on defibrillation threshold have become an important issue with the increasing use of the automatic implantable cardioverter defibrillator (AICD). In several reports antiarrhythmic therapy has been found to affect the energy required for defibrillation; the present study examined the effects of intravenous propafenone on defibrillation threshold in open chest, anesthetized pigs. Twenty health pigs were studied; 10 pigs free from any drugs (Group 1) and 10 pigs after a constant iv infusion of 0.04 mg/kg/min of propafenone (Group 2). Defibrillation threshold was 21 +/- 5, 20 +/- 5, 21 +/- 6, 19 +/- 4 and 19 +/- 6 J in Group 1 and 20 +/- 7, 18 +/- 9, 15 +/- 5, 14 +/- 7, 9 +/- 6 J in Group 2, respectively at 20, 40, 60, 80 min (p value respectively NS, NS, less than 0.05, less than 0.01, less than 0.001). We conclude that intravenous propafenone reduces the energy requirements for defibrillation in experimental animals.

Animals↗
PubMed1990

Defibrillation: ensuring its success.

In this issue, we evaluate two alternatives to the gelled paddles traditionally used in defibrillation: disposable defibrillator pads and disposable defibrillator electrodes. These devices offer certain advantages over gel and are designed primarily to ensure adequate electrical contact for successful defibrillation. We evaluated three disposable defibrillator pads from three manufacturers and two disposable defibrillator electrodes from two manufacturers and rated them according to their suitability for three applications: general hospital use, cardiac catheterization and electrophysiology laboratory use, and prehospital use. We rated the AMI, ConMed, and 3M pads Acceptable for all three applications. Because electrodes offer advantages as well as present problems when used for different applications, we rated them accordingly. The Darox and Physio-Control electrodes are rated Conditionally Acceptable-Not Recommended, Acceptable, and Conditionally Acceptable for the three applications, respectively. Purchasing decisions should be based on a thorough understanding of the issues behind our conclusions, which can be gained only by reading this evaluation in its entirety.

Disposable Equipment↗
PubMed1989

Initial clinical experience with endocardial defibrillation using an implantable cardioverter/defibrillator with a triple-electrode system.

We evaluated the early clinical performance of an implantable cardioverter/defibrillator with a nonepicardial lead system in patients with refractory ventricular tachycardia or ventricular fibrillation. Ten patients, mean age 67 years, mean left ventricular ejection fraction 35%, refractory to 5 +/- 2 antiarrhythmic drugs and with a history of prior cardiac surgery (7 patients), severe lung disease (2 patients), or renal failure (1 patient) underwent device and lead system implant. A tripolar electrode catheter with one sensing electrode and two defibrillating electrodes was placed in the right ventricular apex and a left thoracic submuscular patch electrode was used in an epicostal location. Defibrillation energy threshold was determined using dual- or triple-electrode configurations. Optimal patch electrode location was determined after temporary use of a cutaneous patch electrode prior to cardioverter/defibrillator implant. Electrophysiologic studies were performed before discharge and after 2 to 3 months to assess device function. Percutaneous insertion and placement of the electrode catheter was achieved in all patients. Defibrillation energy threshold testing was done using 1 to 4 (mean, 2.7) electrode configurations per patient and required 6 to 21 (mean, 13) ventricular fibrillation inductions and 8 to 56 (mean, 22) shocks per patient. In all patients, lowest reliable defibrillation energy threshold was obtained with a triple-electrode configuration (right ventricular common cathode with right atrial and thoracic patch as dual anodes) and bidirectional shocks (mean, 18 +/- 5 J). Optimal patch electrode position could be determined in 9 of 10 patients, and these 9 patients had cardioverter/defibrillator implant. Ventricular fibrillation termination with the first delivered shock at electrophysiologic study was documented in all patients. There was no perioperative mortality in device-implanted patients. Postoperative electrophysiologic studies before discharge (9 patients) and at 3 months (8 patients) continued to demonstrate successful defibrillation by the first device shock. During follow-up (range, 2 to 10 months; mean, 6 +/- 3 months), spontaneous device discharges occurred in 4 patients with inappropriate shocks due to electrode catheter fracture being documented in 1 patient. Antiarrhythmic drug therapy was withdrawn in 6 patients and reduced in 3 patients. We conclude, based on our preliminary experience, that an implantable cardioverter/defibrillator can be successfully used with a nonepicardial lead system for endocardial defibrillation in many patients. This lead system can be used with currently available pulse generators and should be considered at cardioverter/defibrillator implantation. It can be anticipated to reduce patient risk and hospital costs associated with this procedure.

Aged↗
PubMed1987

Sequential pulse defibrillation in man: comparison of thresholds in normal subjects and those with cardiac disease.

We compared the parameters describing the defibrillation threshold in patients with normal hearts and in patients with ischemic heart disease, using a special electrode system and sequential pulses of current. Twenty-eight patients consented to the study (mean age: 36.6 +/- 10.1 years; mean mass: 80.7 +/- 13.8 kg). Twenty-one patients underwent surgery for Wolff-Parkinson-White syndrome (relatively normal hearts). Six patients had a history of previous myocardial infarction and aneurysm or coronary artery disease; and one patient had been resuscitated from an episode of sudden death, without evidence of consequent myocardial damage. For 26 patients, defibrillation thresholds were determined intraoperatively by passing sequential pulses through a catheter electrode and epicardial mesh electrode. For 2 patients defibrillation thresholds were determined during electrophysiologic study, after ventricular fibrillation was induced by programmed stimulation, by passing sequential pulses through a catheter and skin-patch electrode. Parameters for sequential pulse defibrillation thresholds between the two groups did not differ appreciably. Total energy for patients with normal hearts averaged 9.9 +/- 6.3 J compared to 8.9 +/- 4.6 J for patients with cardiac disease. No patient with cardiac disease had defibrillation parameters that exceeded the range of the normal patients. These results suggest that the presence of cardiac disease may not significantly alter the parameters necessary for successful defibrillation when using sequential pulses for delivery of energy.

Adult↗
PubMed1977

Efficacy of monophasic electrical impulses with steep leading and trailing edges in cardiac defibrillation.

Experiments on dogs were performed to investigate the efficacy of various defibrillation impulse waveforms. The results showed that the decisive factors for the effectiveness of the defibrillation impulse of certain shape are its relationship to the carciac tissue accomodation and the duration of the suprathreshold current flow. For cardiac defibrillation the most convenient impulse is therefore the impulse with the highest rate of rise of the leading edge as well as the trailing edge. The amplitude of the rear trailing edge of the defibrillation impulse should be either equal or higher than the amplitude of the front leading edge. That means that rectangular or trapezoidal impulses with an ascending slope may be most conveniently used for cardiac defibrillation. The biologically optimal duration of the trapezoidal impulse with an ascending slope proved to range from 7 to 14 msec. The authors emphasize the inevitability of additional characteristics of the defibrillation impulse by its peak current and total energy contents.

Animals↗
PubMed1984

Energy dose and other variables possibly affecting ventricular defibrillation during cardiac surgery.

Previous studies have suggested that shocks of 5-10 J are required for direct ventricular defibrillation during open heart surgery. However, the efficacy of shocks of less than 5 J, the effects of thermal, biochemical, and temporal factors, and the influence of disease process on defibrillation have not been fully investigated, particularly with modern techniques of myocardial preservation. The purpose of this prospective study in 150 adult cardiac surgical patients was to evaluate the energy, current, and myocardial resistance with low energy DC shocks of 1, 2.5, and 5 J and to relate which biochemical, temporal, thermal, or other factors influence the outcome of a DC shock. Twenty-eight percent of shocks of 1 J and 55% of shocks of 2.5 J produced defibrillation. Above 2.5 J, the success rate reached a plateau at 55%. Other factors associated with the success of DC shocks were high normal serum potassium levels, high PaO2, high ionized calcium levels, and longer reperfusion times at mean arterial and coronary perfusion pressures above 50 mm Hg. Disease process may also play a role because patients with valvular heart disease were more difficult to defibrillate. Heart weight and thickness of ventricular myocardium, measured angiographically, appeared less important in direct defibrillation, except with 1 J shocks when thinner-walled ventricles defibrillated more easily.

Blood Chemical Analysis↗
PubMed1998

In-hospital first-responder automated external defibrillation: what critical care practitioners need to know.

Despite the development and widespread implementation of Basic Life Support and Advanced Cardiac Life Support, the percentage of patients who survive in-hospital cardiac arrest has remained stable at approximately 15%. Although survival rates may approach 90% in coronary care units, survival rates plummet outside of these units. The lower survival rates for cardiac arrest that occur outside of the coronary care unit may relate to the time elapsed between the onset of ventricular fibrillation and first defibrillation. The advent of automated external defibrillators has made it possible to decrease the time elapsed before first defibrillation in non-critical care areas of the hospital. First responders need only recognize that the patient is unresponsive, apneic, and pulseless before attaching and activating the automated external defibrillator. Our research shows that, as part of Basic Life Support training, non-critical care nurses can learn to use the device and can retain the knowledge and skill over time. Establishing an in-hospital automated external defibrillator program requires commitment from administration, physicians, and nursing personnel. Critical care practitioners should be aware of this technology and the literature that supports its safety and effectiveness when used by non-critical care first responders. Critical care nurses are in a unique position to effect changes that will decrease the time between the onset of cardiac arrest and first defibrillation.

Critical Care↗
PubMed1997

Internal atrial defibrillation: lessons learnt from experimental studies.

Following the introduction of a transvenous biatrial electrode configuration and a biphasic waveform for internal atrial defibrillation in patients in 1992, it was realized that the standard principles of efficient defibrillation derived from decades of ventricular defibrillation research would not provide painless atrial defibrillation in conscious patients. Over the last five years extensive experimental studies have addressed the risk of ventricular proarrhythmia from synchronized atrial shocks with reassuring results and the influence of the preceding R-R interval on the safety of atrial shocks has been established. Experimental atrial defibrillation research is now aimed at developing waveforms which are less painful and at exploring hybrid therapies including percutaneous right atrial compartmentalization by catheter ablation prior to atrial defibrillation and attempts at multisite pace-entrainment prior to and immediately following the delivery of perithreshold shocks.

Animals↗
PubMed1998

[Cerebral hemodynamics during implantation of cardioverter-defibrillator systems].

OBJECTIVE: During ICD-implantation it is necessary to prove the function and to determine the optimal threshold by means of induced ventricular fibrillation (VF). Provoked cardiac arrests cause a circulator stop of the cerebral perfusion. Our aim was to examine the changes of cerebral blood flow velocity (CBFV(MCA)) after induced VF depending on the duration of fibrillation and prior values of CBFV(MCA). PATIENTS AND METHODS: Sixty induced episodes of VF in 9 patients (mean age +/- SD 53.5 +/- 8 years) were examined during ICD-implantation. Beside the standardized anaesthesiological monitoring, transcranial Doppler sonography was used to record the cerebral blood flow velocity in the middle cerebri artery CBFV(MCA). The duration of the fibrillation-period and the range and duration of the CBFV increase during the post defibrillation-period were correlated. Additionally, we examined whether systematic differences existed between the episodes of each patient (time-trend) by means of 5 following episodes of a patient. RESULTS: During all episodes of VF and hyperperfusion was present, that means a time interval showing increased values of CBFV(MCA), compared to the values present before VF. The duration of hyperperfusion depended significantly on the fibrillation time (r = 0.57; p < 0.001). The equation of regression is: hyperperfusion time = 11.1 + 1.22 x fibrillation time. The amount of hyperperfusion, that means the maximal CBFV after defibrillation, increase significantly with CBFV(MCA) before VF (correlation = 0.88; p < 0.001). The equations of regression is hyperperfusion height = 6.11 + 1.22 x CBFV(MCA) before VF. The duration of hyperperfusion is not influenced by the maximal CBFV(MCA) after defibrillation (r = 0.08; p = 0.52). In the examined patients no significant differences in the hyperperfusion time maximal CBFV(MCA) after defibrillation between the episodes were found. CONCLUSION: After induced VF you always have to expect a reactive cerebral hyperperfusion. The amount of increase of CBFV after defibrillation depends on the prior values of CBFV before fibrillation and shows a nearly proportional relation to these. The duration of hyperperfusion shows a linear dependency on VF-times. This may show that we had VF-times, in which the cerebral autoregulation and other cerebral physiological reactions compensate the drop of the CBFV(MCA) during VF in the postfibrillation time. In further studies will be examined if there are similar changes in the cerebral metabolism as in CBFV(MCA).

Adult↗
PubMed1994

Implantable cardioverter defibrillator compared with antiarrhythmic drug treatment in cardiac arrest survivors (the Cardiac Arrest Study Hamburg).

In 1987, the Cardiac Arrest Study Hamburg (CASH), a prospective, multicenter, randomized controlled study, was started in survivors of sudden cardiac death resulting from documented ventricular tachyarrhythmias. Through December 1991, 230 survivors (46 women, 184 men; mean age 57 +/- 11 years) of cardiac arrest caused by ventricular tachyarrhythmias were randomly assigned to receive either oral propafenone (56 patients), amiodarone (56 patients), or metoprolol (59 patients) or to have an implantable defibrillator (59 patients) without concomitant antiarrhythmic drugs. The primary endpoint of the study was total mortality. In March 1992, the propafenone arm of CASH was stopped because of excess mortality compared with the implantable defibrillator group. This article presents preliminary results of the comparison of implantable defibrillator therapy with propafenone therapy. A significantly higher incidence of total mortality, sudden death (12%), and cardiac arrest recurrence or sudden death (23%) was found in the propafenone group compared with the implantable defibrillator-treated patients (0%, p < 0.05). It was concluded that, in survivors of cardiac arrest, propafenone treatment is less effective than implantable defibrillator treatment.

Amiodarone↗
PubMed1993

Comparison of biphasic and monophasic shocks for defibrillation using a nonthoracotomy system.

A comparison of defibrillation thresholds was made using biphasic and monophasic shocks delivered by a nonthoracotomy lead system in 2 clinically distinct groups of patients. The first group were patients receiving an implantable cardioverter-defibrillator who were studied before surgery with their chests closed. The second group were patients undergoing coronary artery bypass grafting (CABG) who were studied before surgery with their chests open but reapproximated. Biphasic defibrillation thresholds (stored energy) were significantly (p < 0.001) less than monophasic ones in subjects with the implantable cardioverter-defibrillator (12.3 +/- 5.3 vs 21.1 +/- 9.3 J) or CABG (14.6 +/- 7.1 vs 24.2 +/- 12.6 J). These values are less than were previously reported with a similar nonthoracotomy lead configuration. There were no significant differences between the 2 groups in all measurements derived from corresponding shock waveforms, although impedance tended to be greater in patients with CABG. However, subjects with CABG had greater left ventricular ejection fractions and did not have history of potentially lethal ventricular arrhythmias. Despite these differences, the conclusion that biphasic shocks are more effective would have been made in a study of either group alone. It is concluded that patients with CABG who have not had preceding potentially lethal ventricular arrhythmias may be a potential source of surrogate subjects for defibrillation research such as epicardial mapping, which requires that the chest be open.

Coronary Artery Bypass↗
PubMed1994

Defibrillator twiddler's syndrome.

Long-term complications of internal cardioverter defibrillators have generally involved inappropriate shocks or hardware malfunctions. The present case documents a new problem of internal cardioverter defibrillator lead disruption resulting from patient-induced rotation of the generator in its pocket, similar to the previously reported pacemaker twiddler's syndrome. However, unlike the usual early symptoms of pacemaker nonfunction, the first symptomatic manifestation of the defibrillator twiddler's syndrome may be an inappropriate internal cardioverter defibrillator discharge or more importantly, unrescued sudden death. Careful attention to patient complaints about the internal cardioverter defibrillator generator and being alert to subtle lead changes on chest radiographs may allow the clinician to recognize this syndrome before a major, possibly fatal event.

Defibrillators, Implantable↗
PubMed1994

Single-incision implantation of cardioverter defibrillators using nonthoracotomy lead systems.

This study describes the placement of a newly designed implantable cardioverter defibrillator in a subpectoral device pocket using the incision for venous access in 16 patients undergoing implantation of an implantable cardioverter defibrillator with a nonthoracotomy lead system. The endocardial lead system consisted of a right atrial/superior vena cava defibrillation spring electrode and a right ventricular bipolar sensing/defibrillation electrode, inserted by cephalic venotomy or by puncturing of the subclavian vein. As a result of intraoperative testing using biphasic shocks the defibrillation threshold (DFT) had to be less than 24 J, otherwise an additional subcutaneous patch electrode was placed in the lateral chest wall near the cardiac apex through another incision. All patients received a nonthoracotomy lead system in combination with a subpectoral device placement. In 11 of 16 patients the endocardial leads alone were sufficient (DFT, 13.4 +/- 7.0 J), 5 of 16 patients (31%) required an additional subcutaneous patch electrode to achieve proper device function (DFT, 14.6 +/- 9.0 J). The operation lasted 93 +/- 20 minutes. This was a significant (p < 0.05) lower time consumption than standard nonthoracotomy approach combined with abdominal device placement (120 +/- 50 minutes). There were no postoperative complications. During follow-up period (average, 4 months), none of the patients reported major local symptoms, especially no device migration occurred. This approach, in contrast to an abdominal device placement, avoids another incision and subcutaneous tunneling of leads. In 11 of 16 patients defibrillator implantation by a single incision in the deltoideopectoral groove was possible.

Aged↗
PubMed1995

Assessment of the ventricular fibrillation detection algorithm in the semi-automatic Cardio-Aid defibrillator.

The sensitivity and specificity of ventricular fibrillation (VF) detection in the semi-automatic Cardio-Aid defibrillator was assessed with 25 ECG recordings, each of length 40 s. Of the 25 ECG recordings, 12 contained VF requiring defibrillation, 3 contained a tachyarrhythmia with a waveform similar to VF but which self-terminated, and 10 were selected from abnormal rhythms and artefacts which contained some features similar to VF. Sensitivity was assessed from the VF data. Specificity was assessed from both the rhythm preceding VF or the tachyarrhythmias, and from the VF-like data. The response to a changing rhythm was assessed from the self-terminating tachyarrhythmias. Each recording was replayed to the defibrillators at 3 signal amplitudes (normal, half and double). Request to analyse the ECG because of possible VF and advice to shock were noted separately. The sensitivity for recommending a shock when a shock was required was 92%. The sensitivity for drawing attention to VF, through requesting analysis was 97%. There were no false detections in the rhythms preceding VF or the tachyarrhythmias (specificity with good quality signals 100%). The specificity with the VF-like data ws 90%. There was significant difference between this defibrillator and other semi-automated defibrillators previously assessed.

Algorithms↗
PubMed1993

Use of a regional wall motion score to enhance risk stratification of patients receiving an implantable cardioverter-defibrillator.

OBJECTIVES: We postulated that preoperative assessment of both regional wall motion and left ventricular ejection fraction would serve as an accurate prognostic indicator of long-term cardiac mortality and functional outcome in patients treated with an implantable cardioverter-defibrillator. BACKGROUND: Long-term cardiac mortality has remained high in patients receiving an implantable cardioverter-defibrillator. The ability to risk stratify patients before defibrillator implantation is becoming increasingly important from a medical and economic standpoint. METHODS: The hypothesis was retrospectively tested in 74 patients who had received an implantable cardioverter-defibrillator. Left ventricular ejection fraction and regional wall motion score, derived from centerline chord motion analysis, were calculated for each patient from the preoperative right anterior oblique contrast ventriculogram. Wall motion score was the only significant independent predictor of long-term cardiac mortality and functional status by multivariate analysis because of its enhanced prognostic capability in patients with an ejection fraction in the critical range of 30% to 40%. RESULTS: Patients with an ejection fraction > 40% had a 3-year cardiac mortality rate of 0% compared with 25% for those with an ejection fraction of 30% to 40% and 48% for those with an ejection fraction < 30% (p < 0.05). Similarly, 75% of patients with an ejection fraction > 40% were in New York Heart Association functional class I or II during long-term follow-up compared with 59% of those with an ejection fraction 30% to 40% and 29% of those with an ejection fraction < 30%. Among patients with an ejection fraction of 30% to 40%, those with a wall motion score > 16% had a 3-year cardiac mortality rate of 0% compared with 71% of those with a wall motion score < or = 16% (p = 0.002). In addition, 86% of patients with a wall motion score > 16% were in functional class I or II during long-term follow-up compared with 13% of those with a wall motion score < or = 16% (p = 0.001). CONCLUSIONS: Long-term cardiac mortality and functional outcome in patients receiving an implantable cardioverter-defibrillator can be predicted if the left ventricular ejection fraction and regional wall motion score are measured preoperatively.

Activities of Daily Living↗
PubMed1994

Sensing/pacing lead complications with a newer generation implantable cardioverter-defibrillator: worldwide experience from the Guardian ATP 4210 clinical trial.

OBJECTIVES: This report describes the sensing/pacing lead complications that developed during a worldwide clinical trial of a new implantable cardioverter-defibrillator. BACKGROUND: The reliability of the leads used for sensing and pacing with the implantable cardioverter-defibrillator has not been adequately studied. METHODS: The Guardian ATP 4210 was implanted in 302 patients. The sensing/pacing leads consisted of either two unipolar epicardial electrodes or a bipolar endocardial electrode from a variety of manufacturers. RESULTS: During a mean follow-up period of 380 days, 39 patients (12.9%) required reoperation because their device developed sensing/pacing lead system complications. The most common clinical presentation was device oversensing (multiple tachycardia or noise detections or inappropriate shocks), which was observed in 27 patients, whereas elevated pacing thresholds were seen in 10 patients. Forty-one (11.8%) of 347 implanted lead systems required revision. The mean time to revision was 156 +/- 145 days. Actuarial lead survival rate at 1 and 3 years was 89% and 79%, respectively. Epicardial lead systems required significantly (p < 0.05) more revision than did endocardial systems, but when adapter problems were excluded, the revision rates of epicardial and endocardial leads were similar. Causes of lead system failures included adapter connection problems, lead dislodgement and insulation disruption. Predictors of lead revision were use of an epicardial lead system or an adapter. CONCLUSIONS: A high rate of sensing/pacing lead complications was found with this newer generation implantable cardioverter-defibrillator. The enhanced diagnostic and data storage capabilities of this implantable cardioverter-defibrillator facilitated the recognition and troubleshooting of these complications. These findings emphasize the need for careful surveillance and testing of implantable cardioverter-defibrillator sensing/pacing leads during follow-up.

Aged↗
PubMed1994

Comparison of biphasic and monophasic waveforms in epicardial atrial defibrillation.

OBJECTIVES: Because biphasic waveforms have previously been shown to be more efficient than monophasic waveforms in defibrillation of the ventricle, we compared the efficiency of the two waveforms in defibrillation of the atria. BACKGROUND: The development of an implantable atrial defibrillator would offer significant advantages over current approaches to the management of atrial fibrillation. Patient tolerance of atrial shocks from such a device, however, would depend critically on the deployment of an efficient waveform. METHODS: Both the monophasic and biphasic shocks were of 8-ms duration, and the biphasic was a dual-capacitor waveform with equal first- and second-phase duration and leading-edge voltage. One hundred randomized atrial shocks were evaluated in 21 patients during cardiopulmonary bypass. Atrial fibrillation was induced by the application of alternating current. Atrial shocks were delivered through customized, contoured epicardial paddles applied to the posterior left atrial wall (surface area 11 cm2) and to the anterior right atrial wall (surface area 26 cm2). RESULTS: For the monophasic waveform the delivered energy (joules) associated with 50% success (E50) was 1.44 J (95% confidence interval [CI] 0 to 11.2) and with 80% (E80) success 3.9 J (95% CI 2.42 to 109.8); for the biphasic waveform 50% success was achieved with 0.37 J (95% CI 0.36 to 0.38) (p = NS) and 80% success with 0.57 J (95% CI 0.56 to 0.58) (p < 0.05). CONCLUSIONS: A biphasic waveform is more efficient than a monophasic waveform in atrial defibrillation. This may have implications for the development of an implantable atrial defibrillator for paroxysmal atrial fibrillation in addition to improvement of elective transthoracic and endocardial cardioversion of chronic atrial fibrillation.

Aged↗