Effect of verapamil on immediate recurrence of atrial fibrillation.

INTRODUCTION: The purpose of this study was to assess the effect of verapamil on immediate recurrences of atrial fibrillation occurring after successful electrical cardioversion. METHODS AND RESULTS: The effect of verapamil on the recurrence of atrial fibrillation within 5 minutes after successful transthoracic cardioversion was assessed in 19 (5%) of 364 patients undergoing electrical cardioversion. The mean duration of atrial fibrillation was 4.44+/-3.0 months. In the 19 patients, cardioversion was successful after each of three consecutive cardioversion attempts per patient; however, atrial fibrillation recurred 0.4+/-0.3 minutes after cardioversion. Verapamil 10 mg was administered intravenously and a fourth cardioversion was performed. Cardioversion after verapamil was successful in each patient, and atrial fibrillation did not recur in 9 (47%) of 19 patients (P < 0.001 vs before verapamil). In the remaining 10 patients in whom atrial fibrillation recurred, the duration of sinus rhythm was significantly longer compared with before verapamil (3.6+/-2.4 min, P < 0.001). The density of atrial ectopy occurring after cardioversion was significantly less after verapamil (21+/-14 ectopic beats per min) compared with before verapamil (123+/-52 ectopic beats per min, P < 0.001). CONCLUSION: Among patients with immediate recurrence of atrial fibrillation after electrical cardioversion, acute calcium channel blockade by verapamil reduces recurrence of atrial fibrillation and extends the duration of sinus rhythm.

Initial clinical experience with ambulatory use of an implantable atrial defibrillator for conversion of atrial fibrillation. Metrix Investigators.

BACKGROUND: A recent study has shown that the implantable atrial defibrillator can restore sinus rhythm in patients with recurrent atrial fibrillation when therapy was delivered under physician observation. The objective of this study was to evaluate the safety and efficacy of ambulatory use of the implantable atrial defibrillator. METHODS AND RESULTS: An atrial defibrillator was implanted in 105 patients (75 men; mean age, 59+/-12 years) with recurrent, symptomatic, drug-refractory atrial fibrillation. After successful 3-month testing, patients could transition to ambulatory delivery of shock therapy. Patients completed questionnaires regarding shock therapy discomfort and therapy satisfaction using a 10-point visual-analog scale (1 represented "not at all," 10 represented "extremely") after each treated episode of atrial fibrillation. During a mean follow-up of 11.7 months, 48 of 105 patients satisfied criteria for transition and received therapy for 275 episodes of atrial fibrillation. Overall shock therapy efficacy was 90% with 1.6+/-1.2 shocks delivered per episode (median, 1). Patients rated shock discomfort as 5.2+/-2.4 for successful therapy and 4.2+/-2.2 for unsuccessful therapy (P:>0.05). The satisfaction score was higher for successful versus unsuccessful therapy (3.4+/-3. 3 versus 8.7+/-1.3, P:<0.05). There was no ventricular proarrhythmia observed throughout the course of this study. CONCLUSIONS: Ambulatory use of an implantable atrial defibrillator can safely and successfully convert most episodes of atrial fibrillation, often requiring only a single shock. Successful therapy is associated with high satisfaction and only moderate discomfort.

Randomized, double-blind trial of simultaneous right and left atrial epicardial pacing for prevention of post-open heart surgery atrial fibrillation.

BACKGROUND: The purpose of this study was to assess simultaneous right and left atrial pacing as prophylaxis for postoperative atrial fibrillation. METHODS AND RESULTS: In a double-blind, randomized fashion, 118 patients who underwent open heart surgery were assigned to right atrial pacing at 45 bpm (RA-AAI; n=39), right atrial triggered pacing at a rate of >/=85 bpm (RA-AAT; n=38), or simultaneous right and left atrial triggered pacing at a rate of >/=85 bpm (Bi-AAT; n=41). Holter monitoring was performed for 4. 8+/-1.4 days after surgery to assess for episodes of atrial fibrillation lasting >5 minutes. The prevalence of postoperative atrial fibrillation was significantly less in the patients randomized to biatrial AAT pacing when compared with the other 2 pacing regimens (P=0.02). An episode of atrial fibrillation occurred in 4 (10%) of 41 patients in the Bi-AAT group compared with 11 (28%) of 39 patients in the RA-AAI group (P=0.03 versus Bi-AAT) and 12 (32%) of 38 patients in the RA-AAT group (P=0.01 versus Bi-AAT). There was no difference in the occurrence of atrial fibrillation between the right atrial AAI and AAT groups (P=0.8). There was no significant difference among the 3 groups with regard to the number of postoperative hospital days (7.3+/-4.2 days), morbidity (5.1%), or mortality rate (2.5%). CONCLUSIONS: Simultaneous right and left atrial triggered pacing is well tolerated and significantly reduces the prevalence of post-open heart surgery atrial fibrillation.

Short-term effect of atrial fibrillation on atrial contractile function in humans.

BACKGROUND: Conversion of chronic atrial fibrillation (AF) is associated with atrial stunning, but the short-term effect of a brief episode of AF on left atrial appendage (LAA) emptying velocity is unknown. The purpose of this study was to determine whether a short episode of AF affects left atrial function and whether verapamil modifies this effect. METHODS AND RESULTS: The subjects of this study were 19 patients without structural heart disease undergoing an electrophysiology procedure. In 13 patients, LAA emptying velocity was measured by transesophageal echocardiography in the setting of pharmacological autonomic blockade before, during, and after a short episode of AF. During sinus rhythm, the baseline LAA emptying velocity was measured 5 times and averaged. AF was then induced by rapid right atrial pacing. After either spontaneous or electrical conversion, LAA emptying velocity was measured immediately on resumption of sinus rhythm and every minute thereafter. The mean duration of AF was 15.3+/-3.8 minutes. The mean baseline emptying velocity was 70+/-20 cm/s. The first post-AF emptying velocity was 63+/-20 cm/s (P=0.02 versus baseline emptying velocity). The post-AF emptying velocity returned to the baseline emptying velocity value after 3.0 minutes. The mean percent reduction in post-AF emptying velocity was 9.7+/-21% (range, 15% increase to 56% decrease). A second group of 6 patients were pretreated with verapamil (0.1-mg/kg IV bolus followed by an infusion of 0.005 mg. kg-1. min-1). In these patients, the first post-AF emptying velocity, 58+/-14 cm/s, was not significantly different from the pre-AF emptying velocity, 60+/-13 cm/s (P=0.08). CONCLUSIONS: In humans, several minutes of AF may be sufficient to induce atrial contractile dysfunction after cardioversion. When atrial contractile dysfunction occurs, there is recovery of AF within several minutes. AF-induced contractile dysfunction is attenuated by verapamil and may be at least partially mediated by cellular calcium overload.

Intracardiac echocardiography to guide transseptal left heart catheterization for radiofrequency catheter ablation.

INTRODUCTION: The purpose of this study was to assess the feasibility and safety of intracardiac echocardiography to guide transseptal puncture for radiofrequency catheter ablation. METHODS AND RESULTS: Transcatheter intracardiac echocardiography (9 MHz) was utilized to guide transseptal puncture in 53 patients undergoing radiofrequency catheter ablation. The anatomy and relationship of intra- and extracardiac structures were visualized with the ultrasound transducer positioned at the fossa ovalis. The tip of the transseptal dilator and tenting of the fossa ovalis and the left atrial wall were simultaneously visualized in a single ultrasound image in all patients. With maximum tenting of the fossa ovalis, the mean distance from the fossa to the left atrial wall was 11.9 +/- 5.8 mm (range: 1.8 to 25.6 mm). In four patients (8%), the tented fossa ovalis abutted the left atrial wall and the transseptal dilator was redirected with ultrasound guidance. Puncture of the interatrial septum was achieved through the fossa ovalis in each patient and required a single attempt in 51 patients (96%). The mean number of punctures per patient was 1.1 +/- 0.4. The mean time to perform transseptal catheterization was 18.2 +/- 6.8 minutes. There were no complications. CONCLUSION: Intracardiac echocardiography delineated the anatomy of intra- and extracardiac structures not identified with fluoroscopy and simplified correct positioning of the transseptal dilator, puncture of the fossa ovalis, and cannulation of the left atrium in a timely and uncomplicated fashion.

Randomized comparison of a 90 uF capacitor three-electrode defibrillation system with a 125 uF two-electrode defibrillation system.

INTRODUCTION: A variety of factors, including the number of defibrillation electrodes and shocking capacitance, may influence the defibrillation efficacy of an implantable defibrillator system. Therefore, the purpose of this study was to compare the defibrillation energy requirement using a 125 uF two-electrode defibrillation system and a 90 uF three-electrode defibrillation system. METHODS AND RESULTS: The defibrillation energy requirements measured with both systems were compared in 26 consecutive patients. The two-electrode system used a single transvenous lead with two defibrillation coils in conjunction with a biphasic waveform from a 125 uF capacitor. The three-electrode system used the same transvenous lead, utilized a pectoral implantable defibrillator generator shell as a third electrode, and delivered the identical biphasic waveform from a 90 uF capacitor. The two-electrode system was associated with a higher defibrillation energy requirement (10.8 +/- 5.5 J) than was the three-electrode system (8.9 +/- 6.7 J, p < 0.05), however, the leading edge voltage was not significantly different between systems (361 +/- 103 V vs. 397 +/- 123 V, P = 0.07). The two-electrode system also had a higher shocking resistance (49.0 +/- 9.0 ohms vs. 41.4 +/- 7.3 ohms, p < 0.001) and a lower peak current (7.7 +/- 2.6 A vs. 10.1 +/- 3.7 A, p < 0.001) than the three-electrode system. CONCLUSIONS: A three-electrode defibrillation system that utilizes a dual coil transvenous lead and a subcutaneous pectoral electrode with lower capacitance is associated with a lower defibrillation energy requirement than is a dual coil defibrillation system with higher capacitance. This finding suggests that the utilization of a pectoral generator as a defibrillation electrode in conjunction with smaller capacitors is a more effective defibrillation system and may allow for additional miniaturization of implantable defibrillators.

Acute changes in spontaneous echo contrast and atrial function after cardioversion of persistent atrial flutter.

With use of transesophageal echocardiography, the short-term effects of transthoracic electrical cardioversion of atrial flutter (AFI) on atrial mechanical function and spontaneous echo contrast were determined. Thirty patients who had AFI for a mean of 6.4 +/- 12.2 months underwent transthoracic cardioversion. A transesophageal echocardiogram was recorded immediately before cardioversion, and left atrial appendage emptying velocity and spontaneous contrast were assessed serially at 1, 3, and 5 minutes after cardioversion in 28 patients, and also at 8, 10, and 15 minutes after cardioversion in a subgroup of 13 patients. Cardioversion was deferred in 2 patients (7%) because a thrombus was found in the left atrial appendage. Before cardioversion, spontaneous contrast was present in the left atrium in 7 of 28 patients (25%) who underwent cardioversion. The mean left atrial appendage emptying velocity of 54 +/- 22 cm/s before cardioversion fell by 26% to 40 +/- 25 cm/s at 1 minute after restoration of sinus rhythm (p <0.01). There were no significant changes in the mean left atrial appendage-emptying velocity between 1 and 15 minutes after cardioversion. Within 5 minutes after conversion to sinus rhythm, left atrial spontaneous echo contrast developed de novo or worsened in 12 of the 28 patients (43%). In conclusion, the results of this study demonstrate that persistent AFI may be associated with left atrial thrombi before cardioversion and that cardioversion of AFI is associated with a significant degree of atrial stunning and formation of spontaneous echo contrast.

Effect of isoproterenol on QRS complex morphology during ventricular pacing: implications for pace mapping.

Ventricular pace mapping may be used to identify the site of origin of idiopathic ventricular tachycardia. Isoproterenol is often required to induce this type of ventricular tachycardia, but its effect on QRS morphology during pace mapping is unknown. Therefore, this study was performed to evaluate the effect of isoproterenol on QRS morphology during ventricular pacing. The study population consisted of 20 patients (mean age 38 +/- 14 years) undergoing a clinically indicated electrophysiology procedure. Ventricular overdrive pacing was performed in trains of 12 stimuli at cycle lengths of 400, 350, 300, and 250 ms, first in the baseline state during an infusion of isoproterenol, and again after isoproterenol washout. Pacing was performed at the right ventricular apex in 10 patients, in the right ventricular outflow tract in 6 patients, and in the left ventricle in 4 patients. Visual evaluation revealed no apparent effects of isoproterenol on QRS morphology at any of the three pacing sites or at any of the pacing cycle lengths. It was concluded that QRS morphology during ventricular pacing is not affected by isoproterenol infusion. Therefore, in patients with idiopathic ventricular tachycardia, even if the induction of tachycardia requires infusion of isoproterenol, successful pace mapping may be performed in its absence.

Pathophysiology of atrial flutter.

Atrial flutter is a macroreentrant tachyarrhythmia most often contained within the right atrium. Typical atrial flutter is defined on an electrocardiogram by the classic "sawtooth" pattern of flutter waves with negative polarity in leads II, III, and aVF. In contrast to atrial fibrillation, which is sustained by multiple reentrant wavelets defined by anatomic and/or functional barriers, typical atrial flutter is sustained by a single reentrant circuit defined by anatomical barriers. The isthmus of atrial tissue bordered by the inferior vena cava and the tricuspid annulus forms a critical zone of slow conduction in the reentry circuit of atrial flutter. The goal of radiofrequency catheter ablation is to create a line of conduction block across this isthmus. This line of block interrupts the flutter circuit and often provides long-term freedom from recurrence.

A prospective evaluation of two defibrillation safety margin techniques in patients with low defibrillation energy requirements.

INTRODUCTION: In patients undergoing defibrillator implantation, an appropriate defibrillation safety margin has been considered to be either 10 J or an energy equal to the defibrillation energy requirement. However, a previous clinical report suggested that a larger safety margin may be required in patients with a low defibrillation energy requirement. Therefore, the purpose of this prospective study was to compare the defibrillation efficacy of the two safety margin techniques in patients with a low defibrillation energy requirement. METHODS AND RESULTS: Sixty patients who underwent implantation of a defibrillator and who had a low defibrillation energy requirement (< or = 6 J) underwent six separate inductions of ventricular fibrillation, at least 5 minutes apart. For each of the first three inductions of ventricular fibrillation, the first two shocks were equal to either the defibrillation energy requirement plus 10 J (14.6+/-1.0 J), or to twice the defibrillation energy requirement (9.9+/-2.3 J). The alternate technique was used for the subsequent three inductions of ventricular fibrillation. For each induction of ventricular fibrillation, the first shock success rate was 99.5%+/-4.3% for shocks using the defibrillation energy requirement plus 10 J, compared to 95.0%+/-17.2% for shocks at twice the defibrillation energy requirement (P = 0.02). The charge time (P < 0.0001) and the total duration of ventricular fibrillation (P < 0.0001) were each approximately 1 second longer with the defibrillation energy requirement plus 10 J technique. CONCLUSION: This study is the first to compare prospectively the defibrillation efficacy of two defibrillation safety margins. In patients with a defibrillation energy requirement < or = 6 J, a higher rate of successful defibrillation is achieved with a safety margin of 10 J than with a safety margin equal to the defibrillation energy requirement.

Preoperative amiodarone as prophylaxis against atrial fibrillation after heart surgery.

BACKGROUND: Atrial fibrillation occurs commonly after open-heart surgery and may delay hospital discharge. The purpose of this study was to assess the use of preoperative amiodarone as prophylaxis against atrial fibrillation after cardiac surgery. METHODS: In this double-blind, randomized study, 124 patients were given either oral amiodarone (64 patients) or placebo (60 patients) for a minimum of seven days before elective cardiac surgery. Therapy consisted of 600 mg of amiodarone per day for seven days, then 200 mg per day until the day of discharge from the hospital. The mean (+/-SD) preoperative total dose of amiodarone was 4.8+/-0.96 g over a period of 13+/-7 days. RESULTS: Postoperative atrial fibrillation occurred in 16 of the 64 patients in the amiodarone group (25 percent) and 32 of the 60 patients in the placebo group (53 percent) (P=0.003). Patients in the amiodarone group were hospitalized for significantly fewer days than were patients in the placebo group (6.5+/-2.6 vs. 7.9+/-4.3 days, P=0.04). Nonfatal postoperative complications occurred in eight amiodarone-treated patients (12 percent) and in six patients receiving placebo (10 percent, P=0.78). Fatal postoperative complications occurred in three patients who received amiodarone (5 percent) and in two who received placebo (3 percent, P= 1.00). Total hospitalization costs were significantly less for the amiodarone group than for the placebo group ($18,375+/-$13,863 vs. $26,491+/-$23,837, P=0.03). CONCLUSIONS: Preoperative oral amiodarone in patients undergoing complex cardiac surgery is well tolerated and significantly reduces the incidence of postoperative atrial fibrillation and the duration and cost of hospitalization.

A prospective evaluation of catheter ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an implantable cardioverter-defibrillator.

BACKGROUND: Implantable cardioverter-defibrillator (ICD) therapy is integral to current therapy for ventricular tachycardia. Patients with an ICD frequently require concomitant antiarrhythmic drug therapy. Despite this, some patients still receive frequent ICD therapies for ventricular tachycardia. Therefore, the purpose of this prospective study was to determine the utility of ablation of ventricular tachycardia in patients with an ICD who experience frequent ICD therapies. METHODS AND RESULTS: Twenty-one consecutive patients with frequent ICD therapies despite antiarrhythmic drug therapy were the subjects of this study. The mean age was 69+/-6 years, and 17 were men. The mean ejection fraction was 0.22+/-0.08, and all patients had coronary artery disease. During the 36+/-51 days (range, 4 days to 7 months) preceding the ablation procedures, the patients received 34+/-55 ICD therapies for the clinical ventricular tachycardia, or a mean of 25+/-88 ICD therapies per month. The patients underwent radiofrequency ablation of the presumed clinical ventricular tachycardia by inducing the tachycardia and mapping according to endocardial activation, continuous electrical activity, pace mapping, concealed entrainment, or mid-diastolic potentials. Ablation of the clinical arrhythmia was successful in 76% of patients during 1.4+/-0.6 (range, 1 to 3) ablation procedures and required 12.5+/-9.2 applications of energy. During 11.8+/-10.0 months of follow-up, the frequency of ICD therapies per month decreased from 60+/-80 before successful ablation to 0.1+/-0.3 ICD therapies per month after ablation (P=.01). A quality-of-life assessment demonstrated a significant improvement after successful (P=.02) but not unsuccessful ablation (P=.9). CONCLUSIONS: Radiofrequency ablation of ventricular tachycardia as adjuvant therapy in patients with coronary artery disease and an ICD has a reasonable success rate, significantly reduces ICD therapies, and appears to be associated with an improved quality of life.

Adenosine-induced atrial arrhythmia: a prospective analysis.

BACKGROUND: Adenosine is considered safe and effective for paroxysmal supraventricular tachycardia (PSVT), but anecdotal experience suggests that adenosine can precipitate atrial arrhythmias. OBJECTIVES: To determine the frequency and mechanisms of adenosine-induced atrial arrhythmias. SETTING: Clinical electrophysiology laboratory at a university medical center. DESIGN: Prospective observational study. PATIENTS: 200 consecutive patients with PSVT undergoing an electrophysiology procedure. INTERVENTION: During PSVT, 12 mg of adenosine was administered centrally through the femoral vein. MEASUREMENTS: Frequency of adenosine-induced atrial fibrillation. RESULTS: Paroxysmal supraventricular tachycardia terminated after adenosine administration in 198 patients (99% [95% CI, 96% to 100%]). Adenosine led to atrial fibrillation (n = 22) or atrial fibrillation and atrial flutter (n = 2) in 24 patients (12% [CI, 7.5% to 16.5%]). An atrial premature complex occurred in all 24 patients who developed atrial fibrillation, atrial flutter, or both and in 102 of the 176 patients (58%) who did not (P < 0.001). The mean (+/-SD) time from the preceding atrial complex to the atrial premature complex was shorter when an atrial arrhythmia occurred, and the mean ratio of this interval to the preceding atrial cycle length was also lower when atrial fibrillation developed (0.37 +/- 0.16 compared with 0.49 +/- 0.16; P = 0.002). CONCLUSIONS: The incidence of atrial fibrillation induced by 12 mg of adenosine administered through the femoral vein was 12%. Fibrillation seems to be associated with a "long-short" atrial sequence. If the mechanism of PSVT is unknown and the Wolff-Parkinson-White syndrome is possible, administration of adenosine should be limited to medical facilities that have emergency resuscitation equipment.

Effect of verapamil and procainamide on atrial fibrillation-induced electrical remodeling in humans.

BACKGROUND: Atrial fibrillation (AF) shortens the atrial effective refractory period (ERP) and predisposes to further episodes of AF. The purpose of this study was to determine the effect of verapamil and procainamide on these manifestations of AF-induced electrical remodeling. METHODS AND RESULTS: In adult patients without structural heart disease, the atrial ERP was measured before and after AF after pharmacological autonomic blockade and administration of verapamil (17 patients), procainamide (10 patients), or saline (20 patients). AF was then induced by rapid pacing. Immediately on AF conversion, the post-AF ERP was measured at alternating drive cycle lengths of 350 and 500 ms. In the saline group, the pre-AF and first post-AF ERPs at the 350-ms drive cycle length were 206+/-19 and 179+/-27 ms (P<.0001), respectively, and at the 500-ms drive cycle length, the values were 217+/-16 and 183+/-23 ms, respectively (P<.0001). There was a similar significant shortening of the first post-AF ERP in the procainamide group. In the verapamil group, however, there was no difference between the pre-AF and the first post-AF ERP at the 350-ms (226+/-15 versus 227+/-22 ms, P=.8) or 500-ms (230+/-17 versus 232+/-20 ms, P=.6) drive cycle length. During determinations of the post-AF ERP, 105 secondary episodes of AF were unintentionally induced in 12% of verapamil patients compared with 90% and 80% of saline and procainamide patients (P<.01 versus verapamil). CONCLUSIONS: Pretreatment with the calcium channel antagonist verapamil, but not the sodium channel antagonist procainamide, markedly attenuates acute, AF-induced changes in atrial electrophysiological properties. These data suggest that calcium loading during AF may be at least partially responsible for AF-induced electrical remodeling.

Accuracy of the unipolar electrogram for identification of the site of origin of ventricular activation.

INTRODUCTION: The purpose of this study was to determine the accuracy of the unipolar electrogram for identifying the earliest site of ventricular activation. The earliest site of ventricular activation may be identified with the unipolar electrogram by the absence of an R wave. However, the accuracy of this technique is unknown. METHODS AND RESULTS: A single ventricular premature complex was induced mechanically at the tip of an electrode catheter to simulate a ventricular premature depolarization site of origin. Unipolar electrograms were recorded from the right ventricular septum at the tip electrode and at 2, 5, 8, and 11 mm from the electrode tip in 20 patients. No R waves were detected at the ventricular premature depolarization site of origin. R waves were detected in 4 of 20 patients (20%) at 2 mm from the tip electrode and 7 of 20 patients (35%) at 5, 8, and 11 mm from the tip electrode. An R wave was not observed at distances < or = 11 mm from the site of tachycardia origin in 13 of 20 patients (65%). CONCLUSIONS: While an R wave in the unipolar electrogram can be seen as close as 2 mm from the site of impulse origin, the absence of an R wave as an indicator of the site of impulse origin in the right ventricle is highly inaccurate. Therefore, the absence of an R wave in the unipolar electrogram is unlikely to be an adequate guide for identification of an effective target site for ablation of right ventricular tachycardia.

Probability of successful defibrillation at multiples of the defibrillation energy requirement in patients with an implantable defibrillator.

BACKGROUND: The probability of successful defibrillation has been determined in normal animals but not in patients undergoing defibrillator implantation. Therefore, the purpose of this prospective study was to determine the probability of successful defibrillation in humans on the basis of a step-down defibrillation energy requirement. METHODS AND RESULTS: Fifty-three consecutive patients underwent five separate inductions of ventricular fibrillation after the defibrillation energy requirement was determined with the use of small decrements and a step-down protocol (20, 15, 12, 10, 8, 6, 5, 4, 3, 2, 1, and 0.8 J). The first shock energy for defibrillation was either 1.0, 1.3, 1.5, 1.7, or 2.0 times the defibrillation energy requirement, and the likelihoods of successful defibrillation were 70+/-27%, 84+/-12%, 86+/-25%, 80+/-29%, and 88+/-32%, respectively (P=.03). The frequencies of uniformly successful defibrillation (5 of 5 defibrillation attempts) were 30%, 27%, 60%, 64%, and 73%, respectively (P=.01). Seven patients in whom the defibrillation energy requirement was <4 J had an overall rate of successful defibrillation of 54+/-20% compared with 86+/-20% in the remaining 47 patients (P=.002). The likelihood of successful defibrillation at twice the defibrillation energy requirement was 98% in the 46 patients with a defibrillation energy requirement of >4 J and 67% in the 7 patients with a defibrillation energy requirement of <4 J (P=.17). An absolute safety margin of 7 J was associated with a 96% probability of successful defibrillation. CONCLUSIONS: The probability of successful defibrillation is 70% at the defibrillation energy requirement. The probability plateaus at 88%, at twice the defibrillation energy requirement. A 96% probability of successful defibrillation is achieved at an absolute safety margin of 7 J, and a 98% success rate is achieved at energies that are twice the defibrillation energy requirement if the defibrillation energy requirement is >4 J. If the defibrillation energy requirement is <4 J, larger multiples of the defibrillation energy requirement are needed to achieve a high probability of successful defibrillation.

Rise in chronic defibrillation energy requirements necessitating implantable defibrillator lead system revision.

The chronic defibrillation energy requirement (DER) is believed to remain clinically stable in patients with defibrillators. Six patients (two with an epicardial and four with a nonthoracotomy system) were identified with a rise in their chronic DER, which eliminated a 10-J safety margin, thus necessitating a defibrillator lead system revision. The mean increase in DER was 14.7 +/- 4 J and was discovered at a mean of 16.0 +/- 18 months (range 2-41) following implantation. Management included placement of a defibrillator with a biphasic waveform, placement of an additional defibrillation electrode, or both. At 2 months following revision of the defibrillation system, a 10-J DER safety margin was present in each patient. In some patients, there is a progressive increase in the chronic DER with elimination of a 10-J safety margin necessitating revision of the defibrillation system. Routine reevaluation of the chronic DER, therefore, is necessary to identify these patients.

Relation between amiodarone and desethylamiodarone plasma concentrations and ventricular defibrillation energy requirements.

The main finding of this prospective, controlled study is that amiodarone and desethylamiodarone plasma concentrations < 1 mg/L are associated with a 23% increase in the acute defibrillation energy requirement and with a 31% increase in the requirement for a subcutaneous patch or array. The defibrillation energy requirement does not correlate with the plasma concentrations of amiodarone, desethylamiodarone, amiodarone plus desethylamiodarone, or with the duration or daily dosage of amiodarone therapy.