Advances in cardiac electrophysiology and pacing.

Significant advances have been made in the management of cardiac arrhythmias. New technology has enhanced the ability to understand and treat a variety of tachycardias. Excitement and caution surround ablative approaches for atrial fibrillation. The role of ICDs and class III antiarrhythmic drugs in the management of patients at risk for sudden cardiac death has been clarified. A new indication for cardiac pacing is evolving as a supplemental treatment for patients with refractory congestive heart failure. These and other advances provide numerous exciting options for management of cardiac patients.

Lethal ventricular arrhythmias following one-step pacemaker reprogramming for rapid tracking of atrial tachyarrhythmias.

An abrupt decrease in the pacing rate in patients with dual-chamber pacemakers tracking atrial tachyarrhythmias carries a high risk of malignant ventricular arrhythmia. The pacing rate should be reduced by multistep programming over several days.

Concealed accessory pathway manifesting clinically only after pacemaker implantation.

A 66-year-old man with coronary artery disease and persistent left superior vena cava received a DDDR pacemaker for symptomatic 2:1 heart block. There was no previous history of tachyarrhythmias. Endless loop tachycardia and repetitive nonreentrant ventriculoatrial synchrony occurred afterwards and were triggered by a late coupled atrial premature beat. ECGs suggested a concealed left posterior accessory pathway that was confirmed during electrophysiological study. Effective palliation was achieved with extension of the PVARP and enabling noncompetitive atrial pacing operation.

Bradyarrhythmias, temporary and permanent pacing.

Bradycardia is common in critical care units. It may be transient, asymptomatic and of little consequence, or life-threatening. Bradycardia may result from abnormalities of the sinus node, atrioventricular node, or the His-Purkinje system. It may also be precipitated by drug effects or enhanced vagal tone. Proper diagnosis is pivotal to determining prognosis and management. Temporary and permanent pacing is now readily available, markedly improving the morbidity and mortality associated with bradyarrhythmias.

Supraventricular tachycardia: implications for the intensivist.

The critical care physician must have a keen awareness of supraventricular tachycardia patterns, mechanisms, precipitants, and treatment. Although long-term management of most forms of supraventricular tachycardia lies primarily in the realm of the cardiac electrophysiologist, the intensivist must be proficient at acute arrhythmia therapy. Expertise in electrocardiography, pharmacokinetics, and pharmacodynamics is essential. Careful assessment of hemodynamics and prudent bedside clinical acumen help assure optimal patient outcomes.

Direct current cardioversion: indications, techniques, and recent advances.

Direct current cardioversion/defibrillation is an important part of the intensivist's armamentarium. Emergent application may be lifesaving. Elective cardioversion should be used cautiously, with attention to patient selection and proper techniques. Repetitive, futile attempts at direct current cardioversion should be avoided. Reducing or eliminating arrhythmia precipitants may be safer and more effective than this more dramatic intervention.

Long-term follow-up of patients requiring intravenous amiodarone to suppress hemodynamically destabilizing ventricular arrhythmias.

BACKGROUND: Intravenous amiodarone is effective for the acute suppression of recurrent hemodynamically destabilizing ventricular arrhythmias. There are no follow-up data on patients undergoing long-term therapy with intravenous amiodarone. The objective of this investigation was to evaluate long-term outcome. METHODS AND RESULTS: We reviewed the clinical courses of 245 patients given intravenous amiodarone for sustained ventricular tachyarrhythmias. Of the 107 survivors (84% men; mean age 64 years) released from the hospital taking oral amiodarone, 41 were discharged with an empiric prescription for oral amiodarone. For 64 patients a decision regarding further therapy was based on results of an electrophysiologic study. Two patients were treated empirically with oral amiodarone and an implantable cardioverter defibrillator. Clinical variables and survival curves were the same for the empirically treated group and the group whose treatment was based on electrophysiologic findings (P =.89). Survival at 6, 12, and 18 months was 88%, 81% and 71%, respectively, for empirically treated patients, and 83%, 80% and 73%, respectively, for patients whose therapy was directed with an electrophysiologic study. Of the 64 patients who underwent electrophysiologic studies, 33 received an implantable cardioverter defibrillator. The Kaplan-Meier survival curves for patients with and patients without an implantable cardioverter defibrillator were similar (P =.46). CONCLUSIONS: Patients for whom recurrent ventricular tachycardia and fibrillation are suppressed with intravenous amiodarone and who are discharged receiving oral amiodarone have an 80% 1-year survival rate. Although not randomized, our data suggested that among such patients, electrophysiologic testing, implantation of a cardioverter defibrillator, or both may not be necessary. Ascertaining the best management strategy for these patients will require a prospective randomized trial.

Interference with cardiac pacing.

Most exposures to electromagnetic interference are transient and pose no threat to patients with pacemakers and implantable cardioverter defibrillators. Prolonged exposure may be catastrophic in pacemaker dependent patients. New technologies (wireless phones, electronic antitheft surveillance) are safe if proper precautions are takes. Radiofrequency ablation requires concomitant temporary pacing. MR imaging remains contraindicated in patients with these devices until further study is undertaken.

Which is the optimal testing method for identifying an AV delay that allows intrinsic conduction?

It is desirable to maintain normal, conducted ventricular activation in patients with dual-chamber pacemakers and preserved atrioventricular (AV) conduction. The shortest AV delay resulting in consistent ventricular inhibition (avoiding ventricular pseudofusion) was determined by a conventional incremental (inside-out) technique vs the alternate decremental (outside-in) technique in 20 such patients. Determinations were made in VDD mode in 20 patients and DDD mode (approximately 10 beats/min faster than the intrinsic rate) in 19. In VDD mode, the shortest AV delay avoiding ventricular pseudofusion was never found during inside-out testing. It was identical with both methods in 10 patients (50%), and shorter by 10-80 ms (mean 20 +/- 20 ms) with the outside-in method in the remaining 10 (P = 0.004). In DDD mode, the shortest AV delay resulting in consistent ventricular inhibition was found only once during inside-out testing. It was the same with both methods in 13 patients (68%), and shorter by 10-20 ms (mean 14 +/- 5 ms) with the outside-in method in the remaining 5 (26%, P = 0.18; Fisher's exact test). The shortest sensed AV delay preventing ventricular pseudofusion is most likely to be found with a decremental method (outside-in). In rare patients, it identifies AV delays resulting in inhibition, while ventricular pacing persists at longer programmable AV delays with the conventional inside-out approach.

Higher energy synchronized external direct current cardioversion for refractory atrial fibrillation.

OBJECTIVES: We sought to evaluate the safety and efficacy of higher energy synchronized cardioversion in patients with atrial fibrillation refractory to standard energy direct current (DC) cardioversion. BACKGROUND: Standard external electrical cardioversion fails to restore sinus rhythm in 5% to 30% of patients with atrial fibrillation. METHODS: Patients with atrial fibrillation who failed to achieve sinus rhythm after at least two attempts at standard external cardioversion with 360 J were included in the study. Two external defibrillators, each connected to its own pair of R-2 patches in the anteroposterior position, were used to deliver a synchronized total of 720 J. RESULTS: Fifty-five patients underwent cardioversion with 720 J. Mean weight was 117 +/- 23 kg (body mass index 48.3 +/- 4.1 kg/m2). Structural heart disease was present in 76% of patients. Mean left ventricular ejection fraction was 45 +/- 12%. Atrial fibrillation was present for over three months in 55% of the patients. Sinus rhythm was achieved in 46 (84%) of the 55 patients. No major complications were observed. No patient developed hemodynamic compromise and no documented cerebrovascular accident occurred within one month after cardioversion. Of the 46 successful cardioversions, 18 patients (39%) remained in sinus rhythm over a mean follow-up of 2.1 months. CONCLUSIONS: External higher energy cardioversion is effective in restoring sinus rhythm in patients with atrial fibrillation refractory to standard energy DC cardioversion. This method is safe and does not result in clinical evidence of myocardial impairment. It may be a useful alternative to internal cardioversion because it could be done within the same setting of the failed standard cardioversion and obviates the need to withhold protective anticoagulation for internal cardioversion.

Radiofrequency catheter ablation of atrial flutter after orthotopic heart transplantation: insights into the redefined critical isthmus.

We report a case of successful radiofrequency catheter ablation of recurrent atrial flutter in a heart transplant recipient and discuss technical aspects of the procedure. A counterclockwise flutter circuit was defined during endocardial mapping of the donor atrium. Termination of atrial flutter was achieved by creating lines of radiofrequency lesions from the tricuspid ring to the suture line between donor and recipient atria. Creation of bidirectional conduction block in the tricuspid ring-suture line isthmus resulted in abolition of atrial flutter.

Impact of rifampin on serum amiodarone concentrations in a patient with congenital heart disease.

A 33-year-old woman with congenital heart disease and atrial and ventricular arrhythmias, managed over the long term with an implantable cardioverter defibrillator, epicardial pacing system, and amiodarone, experienced an increase in palpitations and a shock from her defibrillator. Evaluation revealed decreases in amiodarone and desethylamiodarone serum concentrations from previous levels. Rifampin had been added to her therapy 5 weeks earlier. Increases in amiodarone and desethylamiodarone concentrations were observed after an increase in the amiodarone dosage and discontinuation of rifampin. The time course suggested that the addition of rifampin led to reductions in serum concentrations of both the drug and metabolite.

A comparison of 50-J versus 100-J shocks for direct-current cardioversion of atrial flutter.

BACKGROUND: Direct-current cardioversion remains the gold standard for restoration of sinus rhythm in patients with atrial flutter. Although an initial energy of 50 J is recommended, the optimal energy settings have not been evaluated in a large series of contemporary patients. METHODS: We compared the outcome of cardioversion with 50 J versus 100 J in 330 consecutive patients with atrial flutter. Initial energy was based on attending physician preference. One hundred sixty patients received 50 J and 170 patients received 100 J. RESULTS: Patients in both groups did not differ significantly in age, sex, weight, body mass index, duration of the arrhythmia, postoperative status, presence and type of structural heart disease, or use of antiarrhythmic drugs. Patients in the 100-J group had more first shock conversion (85% vs 70%; P =. 001), fewer total shocks (1.2 +/- 0.5 vs 1.4 +/- 0.7; P =.001), and less induction of atrial fibrillation (2% vs 11%; P =.002). There were no significant differences in overall restoration of sinus rhythm, cumulative energy delivered, anesthetic dose, and procedure room time. On multivariate analysis, delivery of 100 J was the strongest predictor of first shock success (odds ratio 2.6, 95% confidence interval 2.13 to 3.16; P <.001). CONCLUSION: An initial energy of 100 J is more efficient for restoration of sinus rhythm in patients with atrial flutter.

Characteristics of the signal-averaged P wave in orthotopic heart transplant recipients.

UNLABELLED: Rejection remains the Achilles heel of orthotopic cardiac transplantation (OHT). Reliable noninvasive markers of rejection are desirable for timely therapy and to reduce risks and costs. Changes in atrial electrophysiology may precede ventricular changes during acute rejection. Although P wave duration in the signal-averaged ECG reflects atrial conduction, the feasibility of such measurement and the range of its values in OHT patients in absence of rejection is uncertain. This study compared the filtered P wave duration in 15 hypertensive OHT patients free of rejection with that in 15 age-matched hypertensive controls. All OHT patients had biatrial anastomoses. Two electrophysiologists interpreted the tracings independently. Three tracings (2 OHT, 1 control) could not be interpreted by either reader. An adequate P wave signal-averaged ECG was obtained in the remaining patients, despite the frequent presence of dissociated P waves (recipient and donor atria) on standard ECG in OHT patients. There was good interobserver agreement in the measurement of filtered P wave duration (r = 0.91; P < 0.0001). CONCLUSIONS: The filtered P wave duration was significantly shorter in the OHT patients (112 +/- 15 ms versus 128 +/- 14 ms; P = 0.008). Filtered P wave duration can be measured in most OHT. Filtered P wave duration is shorter in OHT patients than in hypertensive controls, possibly as a result of the reduced mass of the truncated donor atria. Further studies are needed to determine whether the signal-averaged P wave can be useful to predict acute cardiac rejection.

Is hospital admission for initiation of antiarrhythmic therapy with sotalol for atrial arrhythmias required? Yield of in-hospital monitoring and prediction of risk for significant arrhythmia complications.

OBJECTIVES: We sought to determine the yield of in-hospital monitoring for detection of significant arrhythmia complications in patients starting sotalol therapy for atrial arrhythmias and to identify factors that might predict safe outpatient initiation. BACKGROUND: The need for hospital admission during initiation of antiarrhythmic therapy has been questioned, particularly for sotalol, with which proarrhythmia may be dose related. METHODS: The records of 120 patients admitted to the hospital for initiation of sotalol therapy were retrospectively reviewed to determine the incidence of significant arrhythmia complications, defined as new or increased ventricular arrhythmias, significant bradycardia or excessive corrected QT (QTc) interval prolongation. RESULTS: Twenty-five patients (20.8%) experienced 35 complications, triggering therapy changes during the hospital period in 21 (17.5%). New or increased ventricular arrhythmias developed in 7 patients (5.8%) (torsade de pointes in 2), significant bradycardia in 20 (16.7%) (rate <40 beats/min in 13, pause >3.0 s in 4, third-degree atrioventricular block in 1, permanent pacemaker implantation in 3) and excessively prolonged QTc intervals in 8 (6.7%) (dosage reduced or discontinued in 6). Time to the earliest detection of complications was 2.1 +/- 2.5 (mean +/- SD) days after initiation of sotalol, with 22 of 25 patients meeting criteria for complications within 3 days of monitoring. Baseline electrocardiographic intervals or absence of heart disease failed to distinguish a low risk group. Multivariate analysis identified absence of a pacemaker as the only significant predictor of arrhythmia complications (p = 0.022). CONCLUSIONS: Because clinically significant complications can be detected with in-hospital monitoring in one of five patients starting sotalol therapy, hospital admission is warranted for initiation of sotalol. Patients without pacemakers are at higher risk for these complications.