Clinical characteristics of patients intolerant to VVIR pacing

The incidence and clinical predictors of the development of intolerance to VVIR pacing have not been extensively studied in prospective long-term randomized trials comparing different pacing modes. The frequency and clinical factors predicting intolerance to ventricular pacing are controversial. The Pacemaker Selection in the Elderly (PASE) Trial enrolled 407 patients aged >/=65 years in a 30-month, single-blind, randomized, controlled comparison of quality of life and clinical outcomes with ventricular pacing and dual-chamber pacing in patients undergoing dual-chamber pacemaker implantation for standard clinically accepted indications. We reviewed the clinical, hemodynamic, and electrophysiologic variables at the time of pacemaker implantation in 204 patients enrolled in the PASE trial and randomized to the VVIR mode, some of whom subsequently required crossover (reprogramming) to DDDR pacing. During a median follow-up of 555 days, 53 patients (26%) crossed over from VVIR to DDDR pacing. A decrease in systolic blood pressure during ventricular pacing at the time of pacemaker implantation (p = 0.001), use of beta blockers at the time of randomization (p = 0.01), and nonischemic cardiomyopathy (p = 0.04) were the only variables that predicted crossover in the Cox multivariate regression model. After reprogramming to the dual-chamber mode, patients showed improvement in all aspects of quality of life, with significant improvements in physical and emotional role. The high incidence of crossover from VVIR to DDDR pacing along with significant improvements in quality of life after crossover to DDDR pacing strongly favors dual-chamber pacing compared with single-chamber ventricular pacing in elderly patients requiring permanent pacing.

Swelling-activated chloride current is persistently activated in ventricular myocytes from dogs with tachycardia-induced congestive heart failure

The hypothesis that cellular hypertrophy in congestive heart failure (CHF) modulates mechanosensitive (ie, swelling- or stretch-activated) anion channels was tested. Digital video microscopy and amphotericin-perforated-patch voltage clamp were used to measure cell volume and ion currents in ventricular myocytes isolated from normal dogs and dogs with rapid ventricular pacing-induced CHF. In normal myocytes, osmotic swelling in 0.9T to 0.6T solution (T, relative osmolarity; isosmotic solution, 296 mOsmol/L) was required to elicit ICl,swell, an outwardly rectifying swelling-activated Cl- current that reversed near -33 mV and was inhibited by 1 mmol/L 9-anthracene carboxylic acid (9AC), an anion channel blocker. Block of ICl,swell by 9AC simultaneously increased the volume of normal cells in hyposmotic solutions by up to 7%, but 9AC had no effect on volume in isosmotic or hyperosmotic solutions. In contrast, ICl,swell was persistently activated under isosmotic conditions in CHF myocytes, and 9AC increased cell volume by 9%. Osmotic shrinkage in 1.1T to 1.5T solution inhibited both ICl,swell and 9AC-induced cell swelling in CHF cells, whereas osmotic swelling only slightly increased ICl,swell. The current density for fully activated 9AC-sensitive ICl,swell was 40% greater in CHF than normal myocytes. In both groups, 9AC-sensitive current and 9AC-induced cell swelling were proportional with changes in osmolarity and 9AC concentration, and the effects of 9AC on current and volume were blocked by replacing bath Cl- with methanesulfonate. CHF thus altered the set point and magnitude of ICl,swell and resulted in its persistent activation. We previously observed analogous regulation of mechanosensitive cation channels in the same CHF model. Mechanosensitive anion and cation channels may contribute to the electrophysiological and contractile derangements in CHF and may be novel targets for therapy.

Persistent activation of a swelling-activated cation current in ventricular myocytes from dogs with tachycardia-induced congestive heart failure

The hypothesis that cellular hypertrophy in congestive heart failure (CHF) modulates mechanosensitive (ie, swelling- or stretch-activated) channels was tested. Digital video microscopy and amphotericin-perforated-patch voltage clamp were used to measure cell volume and ion currents in ventricular myocytes isolated from normal dogs and dogs with rapid ventricular pacing-induced CHF. In normal myocytes, osmotic swelling in 0.9x to 0.6x isosmotic solution (296 mOsm/L) was required to elicit an inwardly rectifying swelling-activated cation current (I(Cir,swell)) that reversed near -60 mV and was inhibited by 10 micromol/L Gd3+, a mechanosensitive channel blocker. Block of I(Cir,swell) by Gd3+ simultaneously reduced the volume of normal cells in hyposmotic solutions by up to approximately 10%, but Gd3+ had no effect on volume in isosmotic solution. In contrast, I(Cir,swell) was persistently activated under isosmotic conditions in CHF myocytes, and Gd3+ decreased cell volume by approximately 8%. Osmotic shrinkage in 1.1x to 1.5x isosmotic solution inhibited both I(Cir,swell) and Gd3+-induced cell shrinkage in CHF cells, whereas osmotic swelling only slightly increased I(Cir,swell). The K0.5 and Hill coefficient for Gd3+ block of I(Cir,swell) and Gd3+-induced cell shrinkage were estimated as approximately 2.0 micromol/L and approximately 1.9, respectively, for both normal and CHF cells. In both groups, the effects of Gd3+ on current and volume were blocked by replacing bath Na+ and K+ and were linearly related with varying Gd3+ concentration and the degree of cell swelling. CHF thus altered the set point for and caused persistent activation of I(Cir,swell). This current may contribute to dysrhythmias, hypertrophy, and altered contractile function in CHF and may be a novel target for therapy.

Suppression of inducible ventricular tachycardia by ibutilide in patients with coronary artery disease. Ibutilide Investigators

BACKGROUND

Recent studies suggest that class III antiarrhythmic agents may have enhanced efficacy in the treatment of ventricular tachycardia. This study describes the first clinical assessment of the new class III agent ibutilide to suppress inducible monomorphic ventricular tachycardia (VT) in human beings.

METHODS AND RESULTS

Fifty-five patients with coronary artery disease and inducible sustained monomorphic VT at baseline received either low (0.005 mg/kg + 0.001 mg/kg, load and maintenance infusion, respectively), middle (0.01 mg/kg + 0.002 mg/kg), or high dose (0.02 mg/kg + 0.004 mg/kg) infusions of ibutilide followed by repeat programmed ventricular stimulation. The mean age of the study group was 65.5 +/- 9.5 years and mean left ventricular ejection fraction was 36% +/- 11%. Of 48 evaluable patients, 21 (44%) were rendered noninducible after ibutilide, with no difference in efficacy among the three dosing groups (p = 0.83). Ventricular effective refractory periods, QTc interval, and ventricular monophasic action potential duration were prolonged over baseline at all tested cycle lengths. The QTc and action potential prolongation were dose related. Serious drug-related adverse reactions included sustained polymorphic VT in two patients (3.6%), spontaneous monomorphic VT in one patient (1.8%), heart block in one patient (1.8%), and hypotension in one patient (1.8%).

CONCLUSIONS

Ibutilide prolongs ventricular repolarization in human beings and demonstrates efficacy in suppressing inducible monomorphic VT. Significant cardiovascular side effects occurred in 12.7% of patients.

Physiology of the escape rhythm after radiofrequency atrioventricular junctional ablation

The physiology of the escape rhythm (ER) and its response to pharmacological modulation under varying autonomic conditions were studied 48 patients undergoing radiofrequency ablation of the atrioventricular junction (AVJ) for refractory atrial fibrillation. The QRS morphology and cycle length (CL) of the baseline ER were measured 15 minutes postablation. The CL of the ER was measured in response to doses of isoproterenol, atropine, adenosine, lidocaine, and verapamil. The ER QRS was narrow (QRS < 120 ms) in 20 patients and wide (QRS > 120 ms) in 28 patients. Of the 28 patients with wide QRS ER, 11 patients had a new bundle branch block (8 patients new right bundle branch block [RBBB] and 2 patients new left bundle branch block [LBBB]). The ERCL was similar in both narrow and wide ERs (1,593 +/- 376 ms and 1,516 +/- 296 ms, P = 0.44). In 23 patients receiving isoproterenol infusion, the ER CL decreased with increasing doses from 1 mcg/min to 2 mcg/min (1,378 +/- 200 to 1,240 +/- 229 ms, P < 0.001), but did not decrease further at 3 mcg/min (1,201 +/- 192 ms, P = 0.48 vs 2 mg/min). Seven patients received 0.02 mg/kg of atropine, and ER decreased significantly (1,572 +/- 408 ms to 1,319 +/- 333 ms, P = 0.028). In 30 patients who received intravenous boluses of adenosine (6-18 mg), the ER did not change significantly. In 28 patients who received 150 mg of lidocaine, the ER increased from 1,462 +/- 286 ms to 1,715 +/- 467 ms (P < 0.001), and one patient developed transient asystole. Nineteen patients received 7.5 mg of verapamil, and the ER did not change (1,488 +/- 313 ms to 1,513 +/- 666 ms, P = 0.80). There was no significant difference in response to isoproterenol, adenosine, lidocaine, or verapamil between the patients with wide and narrow QRS ERs. We conclude that patients may have stable ERs immediately following AVJ ablation even when a wide complex ER results. The ER is responsive to sympathetic stimulation and vagal blockade. The ER is prolonged after lidocaine but not after verapamil, suggesting response to sodium but not to calcium channel blockade. These data are consistent with an ER originating in the distal compact AV node or proximal His bundle.

Quality of life and clinical outcomes in elderly patients treated with ventricular pacing as compared with dual-chamber pacing. Pacemaker Selection in the Elderly Investigators

BACKGROUND

Standard clinical practice permits the use of either single-chamber ventricular pacemakers or dual-chamber pacemakers for most patients who require cardiac pacing. Ventricular pacemakers are less expensive, but dual-chamber pacemakers are believed to be more physiologic. However, it is not known whether either type of pacemaker results in superior clinical outcomes.

METHODS

The Pacemaker Selection in the Elderly study was a 30-month, single-blind, randomized, controlled comparison of ventricular pacing and dual-chamber pacing in 407 patients 65 years of age or older in 29 centers. Patients received a dual-chamber pacemaker that had been randomly programmed to either ventricular pacing or dual-chamber pacing. The primary end point was health-related quality of life as measured by the 36-item Medical Outcomes Study Short-Form General Health Survey.

RESULT

The average age of the patients was 76 years (range, 65 to 96), and 60 percent were men. Quality of life improved significantly after pacemaker implantation (P<0.001), but there were no differences between the two pacing modes in either the quality of life or prespecified clinical outcomes (including cardiovascular events or death). However, 53 patients assigned to ventricular pacing (26 percent) were crossed over to dual-chamber pacing because of symptoms related to the pacemaker syndrome. Patients with sinus-node dysfunction, but not those with atrioventricular block, had moderately better quality of life and cardiovascular functional status with dual-chamber pacing than with ventricular pacing. Trends of borderline statistical significance in clinical end points favoring dual-chamber pacing were observed in patients with sinus-node dysfunction, but not in those with atrioventricular block.

CONCLUSION

The implantation of a permanent pacemaker improves health-related quality of life. However, the quality-of-life benefits associated with dual-chamber pacing as compared with ventricular pacing are observed principally in the subgroup of patients with sinus-node dysfunction.

Antiarrhythmic actions of intravenous ibutilide compared with procainamide during human atrial flutter and fibrillation: electrophysiological determinants of enhanced conversion efficacy

BACKGROUND

The selective class III antiarrhythmic agent ibutilide prolongs action potential duration and terminates atrial flutter (AFL) and fibrillation (AF), but the mechanism of its antiarrhythmic efficacy in humans has not been fully characterized. This study compared the antiarrhythmic effects of ibutilide with the class IA agent procainamide in humans during AFL and AF. Antiarrhythmic drug actions and electrophysiological characteristics of AFL and AF that enhanced pharmacological termination were investigated.

METHODS AND RESULTS

Right atrial monophasic action potentials were recorded during 148 episodes of AFL (n=89) or AF (n=59) in 136 patients treated with intravenous ibutilide (n=73) or placebo (n=22) as participants in randomized, double-blinded comparative studies or intravenous procainamide (n=53) in a concurrent open-label study. The conversion rates in AFL with ibutilide, procainamide, and placebo were 64% (29 of 45 patients), 0% (0 of 33), and 0% (0 of 11), respectively, whereas in AF the rates were 32% (9 of 28), 5% (1 of 20), and 0% (0 of 11), respectively. In AFL, ibutilide increased atrial monophasic action potential duration (MAPD) more (30% versus 18%, P<.001) and prolonged atrial cycle length (CL) less (16% versus 26%, P<.001) than procainamide. Ibutilide shortened and procainamide prolonged action potential diastolic interval during AFL (-12% versus 51%, P<.001). Ibutilide increased MAPD/CL ratio, whereas procainamide tended to decrease this ratio (13% versus -6%, P<.01). In AF, ibutilide and procainamide induced similar increases in atrial CL (48% versus 45%), but ibutilide induced a greater increase in MAPD (52% versus 37%, P<.05). Independent electrophysiological predictors of pharmacological arrhythmia termination were increase in MAPD/CL ratio (P=.005) in AFL and longer baseline mean MAPD (P=.011) in AF. Termination of AFL with ibutilide was characterized by significant increases in beat-to-beat atrial CL, MAPD, and diastolic interval variability. Ibutilide was significantly more effective in converting AF when the mean atrial CL was > or = 160 ms (64% versus 0%, P<.001) or MAPD was > or = 125 ms (57% versus 0%, P=.002) at baseline.

CONCLUSIONS

Enhanced conversion efficacy of ibutilide compared with procainamide in AFL is correlated with a relatively greater prolongation of atrial MAPD than atrial CL, and termination of AFL by ibutilide is characterized by oscillations in atrial CL and MAPD. Conversion of AF by ibutilide is enhanced by a longer baseline mean atrial CL or MAPD.

Are more complex implantable cardioverter defibrillators associated with an increased mortality? Lessons learned from clinical trials

We compared 1-year survival in patients receiving implantable cardioverter defibrillators (ICDs) that provide only shock therapy with more advanced ICDs that provide antitachycardia pacing, bradycardia pacing, low-energy cardioversion, and advanced detection algorithms. Outcome in patients with advanced-generation ICD systems was similar or improved compared with outcome in patients receiving ICDs with only monophasic shock.

Effects of enhanced parasympathetic tone on atrioventricular nodal conduction during atrioventricular nodal reentrant tachycardia

The effects of various physiologic and pharmacologic stimuli on the anterograde slow pathway in patients with atrioventricular nodal reentrant tachycardia are well characterized. We sought to further characterize the nature of anterograde and retrograde conduction during tachycardia and to define the differential input of the parasympathetic nervous system to these pathways. A custom-made neck suction collar was placed to stimulate the carotid body baroreceptors during supraventricular tachycardia. Neck suction at -60 mm Hg was applied and changes in tachycardia cycle length, AH, and ventriculoatrial intervals were measured in 20 patients. These measurements were repeated after intravenous administration of 10 mg of edrophonium to enhance vagal tone. We observed a 15 +/- 6 ms increase in tachycardia cycle length from baseline (p <0.0001) and a 14 +/- 6 ms increase in AH interval (p <0.0001), but no change in the VA interval with neck suction alone. The tachycardia cycle length prolonged 26 +/- 55 ms (p <0.0001) with edrophonium and an additional 12 +/- 43 ms (p <0.001) with neck suction after edrophonium. There was no change in the VA interval before or after edrophonium during neck suction. There were 10 tachycardia terminations in 8 patients during anterograde slow pathway block during neck suction, with tachycardia cycle length prolongation and mean AH prolongation before termination of 45 +/- 37 ms (vs 15 +/- 7 ms increase in AH interval without tachycardia termination, p = 0.10). There were 12 tachycardia terminations in 4 patients with retrograde block during neck suction, only after edrophonium, without any preceding change in tachycardia cycle length during 11 episodes. We conclude that anterograde slow pathway demonstrates gradual conduction slowing with parasympathetic enhancement, whereas retrograde fast pathway responds with abrupt block.

Acute hemodynamic effects of intravenous ibutilide in patients with or without reduced left ventricular function

Many antiarrhythmic agents have adverse hemodynamic effects which limit their use in patients with impaired ventricular function or during tachyarrhythmias. Ibutilide is an intravenous, selective class III antiarrhythmic agent that is effective for conversion of atrial fibrillation or flutter. This multicenter, randomized, placebo-controlled, dose-ranging study evaluated the effects of intravenous ibutilide on hemodynamic parameters during invasive monitoring in 47 patients with or without reduced left ventricular ejection fraction (LVEF) > 35% or < or = 35%. Patients received either placebo or ibutilide as a 10-minute loading and a 30-minute maintenance infusion using 1 of the following dosing regimens: placebo then placebo (n = 12); 0.01 then 0.002 mg/kg (n = 12); 0.02 then 0.004 mg/kg (n = 12); or 0.03 then 0.006 mg/kg (n = 11). Ibutilide significantly increased QT and QTc intervals in a dose-related manner with mean increases ranging from 51 to 99 ms, but did not alter the PR interval or QRS duration. During ibutilide infusion, a few small but statistically significant changes from baseline in several hemodynamic variables were present. However, the changes in cardiac output, pulmonary artery or capillary wedge pressures, blood pressure, or heart rate in patients receiving ibutilide were not significantly different from the changes in patients receiving placebo. Thus, ibutilide did not cause clinically important adverse hemodynamic effects, even in patients with depressed ventricular function. One patient developed 2 episodes of nonsustained torsades de pointes during ibutilide. These results demonstrate that with careful monitoring for proarrhythmia, ibutilide can be used safely from a hemodynamic standpoint in the acute treatment of arrhythmias, even in patients with reduced ventricular function.

Factors associated with elevated impedance with a nonthoracotomy defibrillation lead system

Peak current flow across the heart determines the success of defibrillation and is inversely dependent on impedance between defibrillation electrodes. Factors associated with elevated impedance in patients with implantable defibrillators using nonthoracotomy lead systems have not been well described. Clinical and echocardiographically derived variables were analyzed in 41 patients in whom implantation of a nonthoracotomy lead system was attempted. Lead impedance was measured at end-expiration with 5-J monophasic shocks. Successful defibrillation with or without addition of a subcutaneous patch with < or = 20 J with a monophasic waveform was required for nonthoracotomy lead placement. Patients were divided into 2 groups based on impedance: low (< or = 47 ohms, n = 30) and high (>47 ohms, n = 11). Twenty-four patients had successful defibrillator implantation using a transvenous lead alone, 13 required placement of a subcutaneous patch, and 4 required epicardial patch placement. The mean left ventricular end-diastolic and end-systolic volumes were significantly smaller (p = 0.01 for both) in patients in the low- versus high-impedance groups and were significantly correlated with impedance (r = 0.44, p <0.005 for both). Impedance was not significantly different between patients with successful defibrillation using a transvenous lead alone compared with those who required either subcutaneous or epicardial patches. Thus, impedance using a nonthoracotomy lead system with monophasic shocks is significantly correlated with both end-systolic and end-diastolic volumes, but elevated impedance does not predict increased defibrillation energy requirements.

Selective slow pathway ablation does not alter enhancement of vagal tone on sinus and atrioventricular nodal function

We studied the effects of edrophonium on sinus cycle length, atrioventricular (AV) nodal fast pathway refractoriness, and AV nodal Wenckebach cycle length in 21 patients with AV nodal reentrant tachycardia (AVNRT) who received edrophonium, and 8 patients who received phenylephrine before and after selective slow pathway ablation. Changes in sinus cycle length, fast pathway conduction, and refractoriness were not altered by radiofrequency ablation of the slow pathway, suggesting that parasympathetic denervation does not occur after slow pathway ablation of AVNRT.

Control of heart rate during transition from intravenous to oral diltiazem in atrial fibrillation or flutter

We tested whether patients presenting with atrial fibrillation (AF) or flutter (AFl) with a rapid ventricular response could maintain control of heart rate while transferring from a bolus and continuous infusion of intravenous diltiazem to oral diltiazem. Forty patients with AF or AFI and sustained ventricular rate > or = 120 beats/min received intravenous diltiazem "bolus" (20 to 25 mg for 2 minutes) and "infusion" (5 to 15 mg/hour for 6 to 20 hours). Oral long-acting diltiazem (diltiazem CD 180, 300, or 360 mg/24 hours) was administered in patients in whom stable heart rate control was attained during constant infusion. Intravenous diltiazem infusion was discontinued 4 hours after the first oral dose, and patients were monitored during 48 subsequent hours of "transition" to oral therapy. Response to diltiazem was defined as heart rate <100 beats/min, > or = 20% decrease in heart rate from baseline, or conversion to sinus rhythm. Other rate control or antiarrhythmic medications were not allowed during the study period. Thirty-seven of 40 patients maintained heart rate control during the bolus, and 35 of the remaining 37 maintained control during the infusion of intravenous diltiazem. Of the 35 patients achieving heart rate control with intravenous diltiazem who entered the transition to oral therapy, 27 maintained heart rate control (response rate of 77%/, 95% confidence interval 63% to 91%). The median infusion rate of intravenous diltiazem was 10 mg/hour, and the median dose of oral diltiazem CD was 300 mg/day. Oral long-acting diltiazem was 77% effective in controlling ventricular response over 48 hours in patients with AF or AFl in whom ventricular response was initially controlled with intravenous diltiazem.

Elucidating the mechanisms of atrial flutter cycle length variability using power spectral analysis techniques

BACKGROUND

The mechanism of the small beat-to-beat variations in cycle length of atrial flutter in humans has not been fully explained. We investigated the beat-to-beat control of atrial flutter cycle length using time and frequency analysis techniques.

METHODS AND RESULTS

Mean, SD, and power spectra of atrial cycle lengths were calculated from atrial recordings in 28 patients with type I atrial flutter. In control patients, mean and SD values of atrial cycle length were 265 +/- 37 and 4.9 +/- 1.7 ms. Power spectra contained two or three major peaks with 10.6 +/- 9.2% in band 1 (0.0 to 0.18 Hz), 26.7 +/- 15.9% in band 2 (0.18 to 0.6 Hz), and 63.1 +/- 17.7% in band 3 (0.6 to 2.2 Hz). Isoproterenol infusion (n = 8) increased percentage of total power in band 1 (7.1 +/- 5.6% to 25.7 +/- 18.9%, P < .001). Percentage of total power in band 1 was less in patients receiving (n = 5) versus not receiving (n = 18) oral beta-blockers (2.2 +/- 1.9% versus 10.6 +/- 9.2%, P = .003). Standard deviation (2.5 +/- 1.3 versus 4.9 +/- 1.7 ms, P = .009) and total power (2025 +/- 1350 versus 9768 +/- 8874 ms2, P = .005) were less in heart transplant recipients (n = 5) than control patients. Increases in respiratory rate (n = 6) shifted band 2 frequency peak to higher frequencies (0.26 +/- 0.13 to 0.38 +/- 0.18 Hz, P < .05). Atrial cycle length was longer and monophasic action potential duration was shorter during inspiration than during expiration. Band 3 frequency peak was correlated with heart rate (r = .797, P < .0001).

CONCLUSIONS

Atrial flutter cycle length variability has an underlying periodic pattern that is detected by spectral analysis. Atrial flutter is modulated on a beat-to-beat basis by an interplay between the autonomic nervous and respiratory systems and the ventricular rate.

Limitations of tachycardia confirmation and rate classification algorithms in a third-generation implantable cardioverter defibrillator

Newer ICDs provide antitachycardia (ATP) and bradycardia pacing and cardioversion and defibrillation shocks based on sensed interval criteria. The objectives of this investigation were to determine the algorithm related errors in tachycardia confirmation and rate classification that occurred in patients with a third-generation, noncommitted, tiered ICD therapy. Forty-three consecutive patients with the Guardian ATP 4210 ICD, which uses an X out of Y sensed interval counting algorithm for tachycardia detection, confirmation, and classification were studied. Surface ECGs, intracardiac electrograms, stored data logs, and sense histories were reviewed to diagnose errors due to these algorithms that resulted in delivery of inappropriate therapy or inhibition of appropriate therapy. Sixty-eight classification or confirmation algorithm errors from 7,610 tachycardia detections (< 1%) were diagnosed in 23 (53%) of 43 patients. Three types of errors not related to device or sensing lead malfunction or programming mistakes were seen. In 26 episodes, the confirmation algorithm failed to detect late tachycardia reversion of nonsustained tachyarrhythmias, on the last or next to last sensed interval, and did not inhibit ATP (n = 17) or shocks (n = 9). In 28 episodes, inaccurate classification of tachycardia rate resulted in inappropriate ATP (n = 23) or shock (n = 5) therapy. In 14 episodes, the posttherapy reconformation algorithm produced inhibition of VVI pacing and prolonged asystole following shock therapy. These errors in tachycardia confirmation and rate classification were due to the inherent limitations of the X out of Y counting algorithm.

Efficacy of ibutilide for termination of atrial fibrillation and flutter

The clinical utility of ibutilide fumarate (Corvert) for the acute conversion of atrial tachyarrhythmias to normal sinus rhythm has been demonstrated in several randomized, placebo-controlled clinical trials. The efficacy of intravenous ibutilide for rapid conversion of atrial flutter is in the range of 50-70%, whereas its efficacy for conversion of atrial fibrillation is 30-50%. Approximately 80% of atrial tachyarrhythmias that terminate do so within 30 minutes from the initiation of the intravenous infusion. Ibutilide is more effective than either intravenous procainamide or intravenous sotalol for conversion of atrial fibrillation and atrial flutter to sinus rhythm. Age, presence of structural heart disease, gender and concomitant medication do not appear to influence the efficacy of ibutilide; however, shorter duration of atrial fibrillation is a strong predictor of successful termination. Plasma concentration of ibutilide and QTc interval prolongation are not directly correlated with the success rate for conversion of atrial tachyarrhythmias. Ibutilide's greater efficacy compared with other antiarrhythmic drugs may be related to its ability to cause greater prolongation of atrial monophasic action potential duration relative to atrial cycle length. Termination of atrial flutter with ibutilide was preceded by increased atrial cycle length variability. Ibutilide rapidly and effectively converts atrial fibrillation and atrial flutter to sinus rhythm when administered as a 1-mg total dose followed by a second 1-mg dose. It should be used in conjunction with continuous electrocardiographic monitoring for at least 4 hours after the termination of the infusion, or until the QTc interval returns to baseline. Hypokalemia and hypomagnesemia should be corrected before the start of the infusion. An external cardiac defibrillator, intravenous magnesium, and an external transcutaneous cardiac pacemaker should be readily available for immediate use in the event that palymorphic ventricular tachyarrhythmias occur. Ibutilide is a new intravenous agent that safely and rapidly converts atrial fibrillation and atrial flutter to sinus rhythm.

Efficacy and safety of repeated intravenous doses of ibutilide for rapid conversion of atrial flutter or fibrillation. Ibutilide Repeat Dose Study Investigators

BACKGROUND

Currently available antiarrhythmic drugs have limited efficacy for acute termination of atrial fibrillation and flutter, especially if the arrhythmia is not of recent onset. The purpose of this multicenter study was to determine the efficacy and safety of repeated doses of intravenous ibutilide, a class III antiarrhythmic drug, in terminating atrial fibrillation or flutter.

METHODS AND RESULTS

Two hundred sixty-six patients with sustained atrial fibrillation (n = 133) or flutter (n = 133), with an arrhythmia duration of 3 hours to 45 days, were randomized to receive up to two 10-minute infusions, separated by 10 minutes, of ibutilide (1.0 and 0.5 mg or 1.0 and 1.0 mg) or placebo. The conversion rate was 47% after ibutilide and 2% after placebo (P < .0001). The two ibutilide dosing regimens did not differ in conversion efficacy (44% versus 49%). Efficacy was higher in atrial flutter than fibrillation (63% versus 31%, P < .0001). In atrial fibrillation but not flutter, conversion rates were higher in patients with a shorter arrhythmia duration or a normal left atrial size. Arrhythmia termination occurred a mean of 27 minutes after start of the infusion. Of 180 ibutilide-treated patients, 15 (8.3%) developed polymorphic ventricular tachycardia during or soon after the infusion. The arrhythmia required cardioversion in 3 patients (1.7%) and was nonsustained in 12 patients (6.7%).

CONCLUSIONS

Intravenous ibutilide given in repeated doses is effective in rapidly terminating atrial fibrillation and flutter and under monitored conditions is an alternative to current cardioversion options.

Sensing lead-related complications in patients with transvenous implantable cardioverter-defibrillators

The widespread use of the redesigned Endotak lead (CPI, St. Paul, Minnesota), which combines transvenous pacing, sensing, and defibrillation on a single transvenous lead in patients receiving transvenous implantable cardioverter-defibrillators (ICDs), has reduced morbidity and shortened length of hospital stay after ICD implantation. We describe the incidence and management of Endotak sensing lead-related failures in a series of 348 consecutive patients from 4 institutions who underwent implantation between 1990 and 1995. We retrospectively reviewed the databases for patients receiving an ICD with an Endotak lead for the incidence of lead-related sensing abnormalities. Ten patients (2.8%) with lead-related sensing abnormalities were detected at a mean of 15 +/- 11 months after ICD implantation. Sensing abnormalities were detected in 6 patients after they received inappropriate shocks. Noise or oversensing was noted in 7 patients from interrogation of the devices' data logs. Eight patients had a new transvenous sensing lead placed, 1 patient had a new Endotak lead placed, and 1 had a chronic pacemaker sensing lead converted to function as a sensing lead. No further sensing problems were noted in 8 of 10 patients during a mean follow-up of 14 +/- 8 months. The site of the sensing lead failure was localized to the subrectus pocket in 5 patients and to the clavicle-first rib area in 3 patients; it was undetermined and presumed to be in the clavicle-first rib area in the other 2 patients. One patient had late failure of the defibrillation lead. We conclude that Endotak sensing lead failure does not require insertion of a new Endotak lead, but can be managed with close follow-up and insertion of a new transvenous sensing lead. Endotak lead fractures are frequently localized to the ICD pocket.

Acute effects of radiofrequency ablation of atrial arrhythmias on implanted permanent pacing systems

We studied the safety of performing RF catheter ablation in patients with implanted permanent pacemakers by monitoring the function of implanted pacing systems before, during, and immediately after exposure to RF energy. Patients with implanted pacing systems may require RF ablation for treatment of a variety of tachyarrhythmias. High frequency electromagnetic fields, such as RF energy, may affect implanted pacing systems, causing temporary or permanent loss of output, undersensing, oversensing, asynchronous pacing, or reversion to "reset" (Recommended Replacement Time or Power On Reset) parameters. Thirty-five patients with implanted pacing systems (23 DDDR, 6 VVIR, 5 DDD, 1 VVI, 31 bipolar and 4 unipolar) underwent RF catheter ablation. Prior to ablation, each pacing system underwent measurements of pacing and sensing thresholds, telemetry of intracardiac electrograms and measurement of battery voltage and lead impedance(s). During ablation, pacemaker function was monitored by real-time telemetry, intracardiac electrograms, and surface ECG. Immediately after ablation, each pacing system was reevaluated. Telemetry during RF ablation revealed normal pacing and sensing in 14 (40%) of 35 patients. Refractory period extension with asynchronous pacing and noise mode reversion were seen in 16 (46%) of 35 patients. Rare under- and/or oversensing, reversion to reset parameters, and telemetry "lock up" with inhibition of pacing output was seen in a few patients. After ablation, there were no significant changes in atrial or ventricular pacing or sensing thresholds or measurements of atrial and ventricular lead impedances. We conclude that most permanent pacemakers are not adversely affected by exposure to RF energy during catheter ablation. A variety of pacemaker behaviors may be seen during RF ablation, and a thorough understanding of each pulse generator's potential response(s) to electromagnetic interference is important before undertaking catheter ablation in patients with permanent pacemakers. Careful reevaluation of the patient's pacing system following the procedure is mandatory.

Efficacy of intravenous ibutilide for rapid termination of atrial fibrillation and atrial flutter: a dose-response study

OBJECTIVES

Currently available antiarrhythmic drugs have limited efficacy for short-term, rapid termination of atrial fibrillation and atrial flutter.

BACKGROUND

Ibutilide fumarate is an investigational class III antiarrhythmic agent that prolongs repolarization by increasing the slow inward sodium current and by blocking the delayed rectifier current. It can be administered intravenously and has a rapid onset of electrophysiologic effects.

METHODS

The efficacy and safety of ibutilide were studied in 200 patients with atrial flutter > 3 h in duration or atrial fibrillation 3 h to 90 days in duration. Patients were randomized to receive a single intravenous dose of placebo or an infusion of ibutilide fumarate at 0.005, 0.010, 0.015 or 0.025 mg/kg body weight over 10 min. Conversion was defined as termination of the atrial arrhythmia during or within 60 min after infusion. Forty-one patients received placebo and 159 received ibutilide (0.005 mg/kg [n = 41], 0.010 mg/kg [n = 40], 0.015 mg/kg [n = 38] or 0.025 mg/kg [n = 40]).

RESULTS

The arrhythmia terminated in 34% of drug-treated patients. The rates of successful arrhythmia termination were 3% for placebo and 12%, 33%, 45% and 46%, respectively, for 0.005-, 0.010-, 0.015- and 0.025-mg/kg ibutilide. The placebo and 0.005-mg/kg ibutilide groups had lower success rates than all other dose groups (p < 0.05). The mean time to termination of the arrhythmia was 19 min (range 3 to 70) from the start of infusion. Successful arrhythmia termination was not affected by enlarged left atrial diameter, decreased ejection fraction, presence of valvular heart disease or the use of concomitant medications (beta-adrenergic blocking agents, calcium channel blocking agents or digoxin). Arrhythmia termination was not predicted by the magnitude of corrected QT interval prolongation but was associated with a shorter duration of atrial arrhythmia. The most frequent adverse events in ibutilide-treated patients were sustained and nonsustained polymorphic ventricular tachycardia (3.6%). All patients with sustained polymorphic ventricular tachycardia were successfully treated with direct current cardioversion and had no recurrence. The occurrence of proarrhythmia did not correlate with ibutilide plasma concentration.

CONCLUSIONS

These data demonstrate that ibutilide is able to rapidly terminate atrial fibrillation and atrial flutter.

Comparative efficacy of intravenous ibutilide versus procainamide for enhancing termination of atrial flutter by atrial overdrive pacing

This study compares the influence of intravenous ibutilide, a class III antiarrhythmic agent, with procainamide, a class IA antiarrhythmic agent, and with placebo on its ability to terminate atrial flutter using rapid atrial pacing. Fifty-nine episodes of atrial flutter in 54 patients who failed to terminate with an intravenous infusion of ibutilide, procainamide, or placebo alone underwent attempts at pacing termination using a standard protocol of burst atrial overdrive pacing. Atrial flutter cycle length and atrial monophasic action potential duration recorded from the right atrium during atrial flutter were measured at baseline and following infusion of ibutilide, procainamide, or placebo. Both ibutilide and procainamide significantly enhanced (p <0.001) pacing-induced termination of atrial flutter compared with placebo. Pacing converted 2 of 11 patients (18%) who received placebo, 13 of 15 patients (87%) who received ibutilide, and 29 of 33 patients (88%) who received procainamide to sinus rhythm. Ibutilide and procainamide compared with placebo markedly reduced (p <0.001) the incidence of pacing-induced atrial fibrillation. The atrial flutter cycle length was prolonged significantly less (p <0.001), and the atrial monophasic action potential duration was increased significantly more (p <0.001) by ibutilide than by procainamide. Although the electrophysiologic changes induced by these antiarrhythmic agents contributed to facilitating pacing-induced termination, neither tachycardia cycle length nor action potential duration were useful predictors of the ability of pacing to terminate atrial flutter. In conclusion, despite differing electrophysiologic effects, the use of intravenous ibutilide or procainamide enhances the termination of atrial flutter by atrial overdrive pacing.

Conversion of atrial flutter by ibutilide is associated with increased atrial cycle length variability

OBJECTIVES

This study was designed to test the hypothesis that conversion of atrial flutter in humans by ibutilide, a new class III antiarrhythmic agent, is characterized by an increase in atrial cycle length variability.

BACKGROUND

Conversion of tachyarrhythmias has been associated with increased oscillations of cycle length.

METHODS

Electrograms and monophasic action potentials from the right atrium in 35 patients with spontaneous, sustained atrial flutter were recorded before, during and after intravenous ibutilide (0.005 to 0.025 mg/kg body weight, n = 25) or placebo (n = 10). Atrial cycle length, cycle length variability (coefficient of variation), diastolic interval and diastolic interval variability were measured from 10 consecutive cycles at baseline and 3 min before, 1 min before, 30 s before and immediately before conversion. Similar measurements were made in patients who received ibutilide or placebo but did not convert.

RESULTS

Ibutilide converted atrial flutter in 14 of 25 patients 25 +/- 16 min (mean +/- SD) after initiation of the infusion, whereas placebo converted no patients. Atrial cycle length was prolonged to the same extent in ibutilide converters and nonconverters (36 +/- 19 vs. 38 +/- 21 ms, p = NS) and was not affected by placebo. Beat-to-beat variability in atrial cycle length (baseline 1.2 +/- 0.7 vs. preconversion 7.3 +/- 4.9, p < 0.01) and diastolic interval (baseline 11 +/- 8 vs. preconversion 33 +/- 23, p < 0.05) increased significantly just before atrial flutter conversion and remained unchanged in ibutilide nonconverters and placebo group patients.

CONCLUSIONS

Ibutilide prolongs atrial cycle length, but conversion of atrial flutter by ibutilide is characterized by increased variability in atrial cycle length and diastolic interval.

Pharmacologic alterations in human type I atrial flutter cycle length and monophasic action potential duration. Evidence of a fully excitable gap in the reentrant circuit

OBJECTIVES

This study compared the effect of changes in action potential duration versus conduction velocity on atrial flutter cycle length to determine whether there is a fully or partially excitable gap in atrial flutter.

BACKGROUND

In an excitable gap reentrant circuit, cycle length is proportional to conduction velocity. Action potential duration is not a direct determinant of cycle length when the gap is fully excitable.

METHODS

Right atrial monophasic action potentials were recorded from 41 patients during type I atrial flutter before and during pharmacologic interventions.

RESULTS

Adenosine (17 +/- 3 mg [mean +/- SD]) shortened (p < 0.001) action potential duration but did not change cycle length. Edrophonium (10 mg) had no significant effect on action potential duration or cycle length. Isoproterenol (0.03 microgram/kg body weight per min) shortened (p < 0.05) and procainamide (15 mg/kg, then 2 mg/min) prolonged (p < 0.001) action potential duration and cycle length. Alterations in cycle length were not correlated with changes in action potential duration. Procainamide's prolongation of action potential duration was reversed by adenosine without affecting cycle length. Procainamide's prolongation of action potential duration and cycle length was partially reversed by isoproterenol. Adenosine's and isoproterenol's shortening of action potential duration and isoproterenol's shortening of cycle length were enhanced by procainamide.

CONCLUSIONS

Atrial flutter cycle length is determined primarily by conduction velocity and does not depend directly on action potential duration. Atrial flutter has a fully excitable gap, and procainamide does not convert the gap from full to partial excitability. Adenosine and isoproterenol interact with procainamide such that their effects are enhanced and procainamide's effects are diminished.

Comparison of bipolar atrial electrogram amplitude in sinus rhythm, atrial fibrillation, and atrial flutter

Automatic mode switching pacemakers revert to non-atrial tracking modes in response to sensed atrial tachyarrhythmias. It is unclear how atrial electrogram amplitudes in sinus rhythm compare to those during atrial tachyarrhythmias. In this study, peak-to-peak bipolar atrial electrogram amplitudes were measured during sinus rhythm and either atrial fibrillation or atrial flutter in 69 patients. The mean atrial electrogram amplitudes were 1.59 +/- 1.36 mV during sinus rhythm and 0.77 +/- 0.58 mV during atrial fibrillation (P < 0.0001) for 25 patients with atrial fibrillation and 1.81 +/- 2.07 mV during sinus and 1.5 +/- 1.81 mV (P < 0.0001) for 44 patients with atrial flutter. The mean electrogram amplitudes during both atrial fibrillation and flutter correlated significantly with amplitudes during sinus rhythm (R = 0.79, R = 0.94, respectively, both P < 0.0001). The coefficient of variance of individual electrogram amplitudes was greater in atrial fibrillation than sinus (P < 0.0001). By comparing 20th percentile electrogram amplitudes in atrial fibrillation and flutter to mean sinus amplitudes, intermittent very low electrogram amplitudes (< 0.3 mV) were more likely during atrial fibrillation and flutter if the mean sinus electrogram amplitudes were < 1.5 mV and < 0.5 mV, respectively (P < 0.01). Eightieth percentile electrogram amplitude values in atrial fibrillation and flutter were equally likely to exceed mean sinus amplitude values in respective patients. In conclusion, mean atrial electrogram amplitudes during atrial fibrillation and flutter are less than but correlated to sinus rhythm electrogram amplitudes. Very low amplitude individual electrograms during these atrial arrhythmias are associated with low mean sinus rhythm electrogram amplitudes. These findings may have implications for the programming of permanent dual chamber pacemakers in patients with paroxysmal atrial fibrillation and flutter.

Atrial natriuretic peptide and cardiac electrophysiology: autonomic and direct effects

Atrial natriuretic peptide (ANP) has varied effects on cardiac electrophysiologic parameters including heart rate, intraatrial conduction time, and refractory period. ANP's vagoexcitatory and sympathoinhibitory actions as well as its direct actions on cardiac ion currents may be responsible for some of these effects. This review discusses the role of ANP in cardiac electrophysiology, its interactions with the autonomic nervous system and baroreceptor reflex, and its effects on cardiac ion currents.

Reduction of antiarrhythmic drug use in patients receiving implantable cardioverter defibrillators

Widespread use of implantable cardioverter defibrillators (ICDs) for the treatment of ventricular tachycardia (VT) and ventricular fibrillation (VF) occurred in the late 1980s and early 1990s. Additionally, there has been increasing appreciation during this time for both the lack of efficacy and proarrhythmic activity of antiarrhythmic drugs to treat these cardiac arrhythmias. We evaluated the use of antiarrhythmic drugs from 1987 to 1991 (5-year period) at the time of ICD implantation in 25,450 patients. The use of all classes of antiarrhythmic agents decreased from 61% to 24% during this time period (P < 0.05). In addition, there was a significant reduction in antiarrhythmic agent use for each drug class (P < 0.05) with the exception of Class II agents (beta blockers). These changes in drug use occurred independent of any changes in age, sex, ejection fraction, prevalence of coronary artery disease, or type of ventricular arrhythmia (VT vs VF).

Hemodynamic effects of intravenous sematilide in patients with congestive heart failure: a class III antiarrhythmic agent without cardiodepressant effects

OBJECTIVES

This study sought to evaluate the hemodynamic effects of intravenous sematilide hydrochloride, a selective class III antiarrhythmic agent, in patients with heart failure and left ventricular systolic dysfunction.

BACKGROUND

Class I antiarrhythmic agents, which primarily slow conduction, can depress ventricular function, particularly in patients with heart failure. In contrast, pure class III agents, which selectively prolong repolarization, do not adversely affect hemodynamic variables in animal models, but there are no data evaluating their hemodynamic effects in humans.

METHODS

In 39 patients with congestive heart failure and a left ventricular ejection fraction < 40%, hemodynamic and electrocardiographic measurements were obtained at baseline, after a loading dose and during a maintenance infusion of intravenous sematilide using either a low (0.75 then 0.3 mg/min) or high dose (1.5 then 0.6 mg/min) regimen. The study had an 80% power to detect clinically meaningful differences in hemodynamic variables.

RESULTS

Both low (n = 20) and high (n = 19) dose sematilide infusions produced dose-dependent increases in QT interval (5 +/- 8% [mean +/- SD] and 18 +/- 10%, respectively) and corrected QT interval (4 +/- 8% and 14 +/- 10%), and high dose sematilide decreased heart rate by 7 +/- 10% (all p < 0.025 vs. baseline). Neither dose regimen had a statistically significant effect on any other hemodynamic variable, including mean arterial, right atrial, pulmonary artery and pulmonary capillary wedge pressures; cardiac index, stroke volume, systemic and pulmonary vascular resistances; and left ventricular stroke work index. Sematilide showed no adverse hemodynamic effects in patients with left ventricular ejection fraction < or = 25% or > 25% and in patients with cardiac index < 2 or > or = 2 liters/min per m2. Sustained polymorphic ventricular tachycardia (n = 1) and excessive QT prolongation (n = 4) were seen during the high dose.

CONCLUSIONS

Sematilide, in the doses administered, prolonged repolarization but did not alter hemodynamic variables in patients with heart failure. These data suggest that class III antiarrhythmic agents, which selectively prolong repolarization, are not cardiodepressant but may be proarrhythmic in humans, especially at high doses.

Examination of mechano-electrical feedback in the transplanted human heart

Several investigators have demonstrated that changes in atrial or ventricular pressure and size may modulate changes in electrophysiologic properties. The coupling of mechanical and electrical changes in the heart has been termed mechano-electrical feedback and is believed to play a role in arrhythmias observed with mitral valve disease, congestive heart failure, and left ventricular hypertrophy. To avoid confounding influences of the autonomic nervous system on electrophysiologic measurements, we measured right atrial and ventricular pacing thresholds with temporary epicardial pacing wires, right ventricular monophasic action potential duration at 90% repolarization during right ventricular pacing at 600 and 400 ms, donor heart rate, systolic, diastolic, and mean arterial and central venous pressures in 22 patients after orthotopic heart transplantation. Each variable was measured at baseline, in the resting supine state, and during graded lower body negative pressure of -10, -20, and -30 mm Hg. All levels of lower body negative pressure resulted in a significant decrease in mean right atrial pressure up to 5 +/- 6 mm Hg at maximal lower body negative pressure, and a significant decrease in mean arterial pressure occurred only at -20 and -30 mm Hg. Lower body negative pressure did not result in a significant change in any electrophysiologic variable despite significant changes in right atrial pressure. Thus, in the denervated transplanted human heart, unloading of the right heart results in no or small changes in atrial or ventricular pacing thresholds and ventricular monophasic action potential duration.

Long-term temporal patterns of ventricular tachyarrhythmias

BACKGROUND

Technological limitations have precluded investigation of long-term temporal patterns of ventricular tachyarrhythmia recurrences. Newer implantable cardioverter-defibrillators permit such analyses by accurately recording the time and date of tachycardia detections during long-term follow-up. This study tests the hypothesis that ventricular tachycardia occurrences are randomly distributed over time in individual patients.

METHODS AND RESULTS

The time and date of 727 episodes of ventricular tachyarrhythmias were recorded from the data logs of 31 patients with implantable cardioverter-defibrillators followed for a median of 177 days (range, 7 to 782 days). All patients had three or more ventricular tachycardia detections and no detections from causes other than ventricular arrhythmias. In 28 of 31 patients, the distribution of the interdetection time intervals during follow-up differed significantly (all P < .01) from an exponential model distribution of interdetection intervals that assumed that detections were equally likely to occur at any time during follow-up (random). The Kolmogorov-Smirnov goodness-of-fit test was used to compare sample and model distributions. In each patient, the nonrandom distributions resulted from a preponderance of interdetection time intervals that were shorter than predicted by the random model, resulting in a temporal clustering of arrhythmic events. The interdetection interval was < or = 1 hour and < or = 91 hours for 55% and 78% of all intervals, respectively. When only those episodes receiving shock or antitachycardia pacing therapy were analyzed, 25 of 29 patients still manifested nonrandom distributions (all P < .01). When only episodes with tachycardia rates > 240 beats per minute were analyzed, 11 of 13 patients manifested non-random distributions (all P < .01).

CONCLUSIONS

Ventricular tachycardia detections and delivered antitachycardia therapies by implantable cardioverter-defibrillators are nonrandomly distributed throughout long-term follow-up in the majority of patients. The temporal clustering of these arrhythmic events may allow preemptive antiarrhythmic therapy and should be considered in the design of therapy based on suppression of spontaneous ventricular arrhythmias to statistically derived end points.

Clinical experience with nonthoracotomy cardioverter defibrillators

A new generation of defibrillators has been introduced that do not require a thoracotomy. The purpose of this report was to examine 100 consecutive nonthoracotomy implantations at our institution and compare them with a series of 102 patients undergoing thoracotomy implantations by the same surgeon over a 4-year period between August 1989 and September 1994. The two groups were comparable for age, sex, comorbidity, cardiac disease status, ejection fraction, and electrophysiologic presentation. Nonthoracotomy systems were implanted successfully in 94% of patients. Patients undergoing a nonthoracotomy implantation had significantly shorter intensive care unit (1.7 +/- 1.7 versus 3.3 +/- 3.9 days; p < 0.005) and postoperative stays (5.0 +/- 2.8 versus 9.5 +/- 5.6 days; p < 0.001) than patients undergoing a thoracotomy approach. This was due to a significant decrease in the incidence of postoperative complications from 29% in the thoracotomy group to 11% in the nonthoracotomy group (p < 0.001). There was no significant difference in overall mortality rates. Nonthoracotomy systems are implantable in the majority of patients and are associated with less morbidity and shorter hospital stays than traditional thoracotomy approaches.

Circadian pattern of ventricular tachyarrhythmias in patients with implantable cardioverter-defibrillators

OBJECTIVES

This study examined the temporal patterns of ventricular tachycardia detections by implantable cardioverter-defibrillators for circadian variability.

BACKGROUND

Previous studies of circadian arrhythmia patterns have been methodologically limited by very brief observational periods. Late-generation implantable cardioverter-defibrillators accurately record the times of arrhythmia detections during unlimited follow-up.

METHODS

Forty-three patients with late-generation implantable cardioverter-defibrillators were followed up for 226 +/- 179 days (mean +/- SD). The times of all recorded episodes of ventricular tachyarrhythmias were retrieved from the data log of each device during follow-up.

RESULTS

The weighted distribution of 830 ventricular tachyarrhythmia episodes from the 43 patients fit a single harmonic sine curve model with a peak between 2 and 3 P.M. (95% confidence interval 1:13 to 4:13 P.M., R = 0.75, p < 0.05). The distributions of spontaneously terminating episodes, episodes receiving device therapy, episodes receiving shocks and episodes in the absence of antiarrhythmic therapy also fit the sine curve model (all R = 0.53 and 0.73, all p < 0.05), all with peak frequencies between 2:08 and 3:09 P.M. and 95% confidence intervals for peak frequencies between 11:38 A.M. and 5:07 P.M. Episodes recorded during continuous antiarrhythmic drug therapy did not fit the model (p > 0.05).

CONCLUSIONS

The distribution of ventricular tachyarrhythmias detected by late-generation implantable cardioverter-defibrillators follows a circadian pattern, with a peak tachycardia frequency between noon and 5 P.M. This pattern was not observed in patients receiving antiarrhythmic drug therapy. Knowledge of circadian periodicity for these events has implications for patient management.

Late occurrence of incessant atrial tachycardia following the maze procedure

We report a patient with incessant atrial tachycardia and AV nodal reentrant tachycardia tachycardia and AV nodal reentrant tachycardia beginning almost 18 months following a successful maze procedure. Both tachycardias were cured by radiofrequency ablation. We speculate that the right atrial tachycardia may have been related to the maze procedure. Finally, we believe this report should emphasize the importance of careful and long-term follow-up of all patients undergoing the maze procedure. Proper evaluation of the place of this therapy greatly depends on reporting of all short- and long-term complications of this new procedure.

Safety and efficacy of intravenous diltiazem in atrial fibrillation or atrial flutter

This study examines the efficacy of various doses of intravenous diltiazem to control the ventricular response during atrial fibrillation or atrial flutter. Control of the ventricular response of patients with atrial fibrillation and a rapid ventricular response can provide patients with relief of symptoms and improve hemodynamics. Eighty-four consecutive patients with atrial fibrillation or atrial flutter, or both, received an intravenous bolus dose of diltiazem followed by a continuous infusion of diltiazem at 5, 10, and 15 mg/hour. The mean ventricular response and blood pressure were monitored. Overall, 94% of patients (79 of 84) responded to the bolus dose with a > 20% reduction in heart rate from baseline, a conversion to sinus rhythm, or a heart rate < 100 beats/min. Seventy-eight patients received the continuous infusion. After 10 hours of infusion, 47% of patients (confidence interval [CI]: 36%, 59%) had maintained response with the 5 mg/hour infusion, 68% (CI: 57%, 79%) maintained response after the infusion was titrated to 10 mg/hour, and 76% (CI: 66%, 85%) after titration from the 5 and 10 mg/hour infusion to the 15 mg/hour dose. For the 3 diltiazem infusions studied, mean (+/- SD) heart rate was reduced from a baseline value of 144 +/- 14 beats/min to 98 +/- 19, 107 +/- 25, 107 +/- 22, 101 +/- 22, 91 +/- 17, and 88 +/- 18 beats/min at infusion times 0, 1, 2, 4, 8, and 10 hours, respectively. By the end of the infusion, 18% of patients (14 of 78) had conversion to sinus rhythm.(ABSTRACT TRUNCATED AT 250 WORDS)

Safety of pacemaker implantation in patients with transvenous (nonthoracotomy) implantable cardioverter defibrillators

While several reports have documented the safety of implantation of transvenous pacemakers in patients with epicardial patch-based implantable cardioverter defibrillators (ICDs), the implantation of transvenous pacemakers in patients with transvenous (nonthoracotomy) ICDs has not been well-described. We present three patients with transvenous ICDs who subsequently underwent implantation of transvenous pacemakers without complication. Technical considerations and a testing, protocol for detection of pacemaker-ICD interactions are discussed.

Lessons learned from data logging in a multicenter clinical trial using a late-generation implantable cardioverter-defibrillator. The Guardian ATP 4210 Multicenter Investigators Group

OBJECTIVES

This study examined patterns of implantable cardioverter-defibrillator use as documented by data logging.

BACKGROUND

Implantable cardioverter-defibrillators are accepted therapy for malignant ventricular tachyarrhythmias; however, relatively little is known about their patterns of use. Incorporation of data-storage capacities into these devices provides insight into long-term defibrillator function.

METHODS

Stored data-logging information was retrieved from 401 implanted cardioverter-defibrillators in 393 patients over an average of 303 days of follow-up.

RESULTS

A total of 91,443 detections were recorded in 299 patients. One hundred-six patients (26%) had detections due to supraventricular tachycardias, electrical noise or other causes, resulting in inappropriate therapy delivery to 92 patients (23%). Two hundred eighty-one patients recorded 66,276 episodes of ventricular tachycardia or ventricular fibrillation. Of these, 74.4% episodes terminated spontaneously without any delivered therapy, 22.1% terminated after antitachycardia pacing, and 1.7% terminated after shock therapy. Antitachycardia pacing was activated without formal testing in 47% of all patients receiving this therapy and was successful in 96% of all episodes receiving this therapy. Acceleration of tachycardia to shock therapy occurred in 1.3% of all episodes and in 30.5% of patients receiving antitachycardia pacing. Thirty-four patients (8.7%) died during follow-up. Mortality was associated with patient age, heart failure functional class at implantation and frequency of shocks received during follow-up (all p < or = 0.05).

CONCLUSIONS

Most ventricular tachyarrhythmia detections by this noncommitted implantable cardioverter-defibrillator resolve spontaneously, whereas the majority receiving therapy can be treated with antitachycardia pacing. Mortality after implantable cardioverter-defibrillator implantation is associated with age, heart failure class and frequency of shocks received during follow-up. Data-logging capabilities provide valuable insights into the patterns of defibrillator use.

Uniformity of calcium channel number and isometric contraction in human right and left ventricular myocardium

We compared contractile performance in trabeculae carneae (n = 25) from non-failing right and left ventricles (n = 25) of brain dead organ donors without known cardiovascular disease and measured connective tissue content in trabeculae carneae from both non-failing and failing human hearts. Peak twitch force and time-course of contraction were not different between muscles taken from right or left ventricles. Peak twitch force was 13.9 +/- 3 vs. 13.7 +/- 2.7 mN/mm2 for right and left ventricular trabeculae carneae, respectively in 2.5 mM [Ca2+]0 at a 0.33 Hz stimulation frequency. Time to peak tension (405 +/- 21 vs. 405 +/- 12 ms), time to 50% relaxation from peak contractile response (277 +/- 21 vs. 278 +/- 14.6 ms) and time to 80% relaxation (428 +/- 29 vs. 433 +/- 22) were not different between right and left ventricular trabeculae carneae. Calcium channel number determined by [3H]PN200-100 dihydropyridine-radioligand binding assay was also not different (56.2 +/- 6.5 fmol/mg protein vs. 58.6 +/- 8.4 fmol/mg protein for right and left heart preparations, respectively). However, in myocardium obtained from ischemic hearts the left ventricle showed a reduced number of calcium channels compared to the right ventricle (55.3 +/- 3.8 vs. 36.6 +/- 3.9 fmol/mg protein for right and left ventricle, respectively p = 0.027). No differences were noted in the number of DHP receptor binding sites between right and left ventricular myocardium from patients with idiopathic dilated cardiomyopathy (51.4 +/- 7.6 fmol/mg protein vs. 61.8 +/- 6.5 fmol/mg protein respectively). Our data indicate that calcium channel number is similar for non-failing left and right human ventricle. Contractile response to changes in [Ca2+]0 and frequency were similar for trabeculae carneae from the left and right ventricles of non-failing human hearts. Studies involving calcium channel activation or inhibition in ischemic human myocardium, where there may be differences in calcium channel number and/or function are warranted. Whether changes in calcium channel number have biological consequences on contractile function remains to be determined. Importantly, careful studies of calcium channel function under in vivo conditions are warranted.

Flecainide: its value and danger

Flecainide is an important addition to the therapeutic armamentarium because it is a potent agent for the treatment of paroxysmal supraventricular tachycardia in patients without structural heart disease. Flecainide also may be useful in patients with debilitating nonsustained ventricular arrhythmias in the absence of structural heart disease. It is rarely useful in the management of life-threatening sustained ventricular arrhythmias.

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.

Can amiodarone pulmonary toxicity be predicted in patients undergoing implantable cardioverter defibrillator implantation?

Implantable cardioverter defibrillator (ICD) implantation is rapidly becoming accepted as primary therapy for malignant ventricular arrhythmias. Many patients undergoing ICD implantation are on concomitant antiarrhythmic drugs to decrease shock frequency, slow tachycardia rate, and suppress supraventricular arrhythmias. Amiodarone is a potent antiarrhythmic agent that is also frequently used in the treatment of patients with refractory ventricular arrhythmias. Ten to forty percent of patients undergoing ICD implantation will also be taking amiodarone. It has been reported to cause pulmonary toxicity in about 5% of patients per year. Acute amiodarone toxicity presenting as adult respiratory distress syndrome has been reported much less frequently. Although perioperative morbidity due to amiodarone has been described, the risk, predictability, and consequences of acute pulmonary toxicity from amiodarone in patients undergoing ICD implantation have not been previously described. We reviewed the records of 99 consecutive patients undergoing ICD implantation at our institution from October 1987 to April 1992. Thirty-nine patients were taking 480 +/- 230 mg of amiodarone (median 400 mg, lower 20th percentile 400 mg, upper 80th percentile 800 mg) for 291 +/- 554 days prior to ICD implantation. Ten patients taking amiodarone developed acute pulmonary toxicity clinically manifesting as diffuse pulmonary infiltrates on chest radiography and adult respiratory distress syndrome with hypoxia (arterial pO2 < 60 mmHg) without evidence of pneumonia or elevated pulmonary capillary wedge pressure (PCW < or = 15 mmHg). Of the 60 patients not taking amiodarone none developed adult respiratory distress syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Procainamide: a perspective on its value and danger

Procainamide remains one of the most widely used antiarrhythmic agents in clinical practice. Currently, it is widely used alone or in combination with class I agents (eg, mexiletine or tocainide) to prevent recurrent ventricular tachycardia or symptomatic nonsustained ventricular tachycardia. Procainamide is also used for short-term treatment of ventricular tachycardia and a variety of supraventricular tachycardias, primarily atrial flutter and atrial fibrillation. Long-term procainamide therapy is limited by a number of systemic side effects, primarily lupus-like syndrome, gastrointestinal disturbances, and autoimmune blood dyscrasias. Procainamide levels can be useful in initial dose titrations; however, QRS and QT interval measurements help prevent drug toxicity. It is recommended that patients being started on antiarrhythmic therapy with procainamide be admitted to the hospital for monitoring to ensure that their QT interval is not excessively prolonged.

Radiofrequency catheter ablation of sinus node reentrant tachycardia

Sinus node reentrant tachycardia is a relatively uncommon (5%-15%) form of recurrent paroxysmal supraventricular tachycardia (SVT). We describe a case of symptomatic sinus node reentrant tachycardia in a 67-year-old male with ischemic heart disease, congestive heart failure, and depressed ventricular function. Adenosine administered during an electrophysiology study caused prolongation of the tachycardia cycle length due to atrial cycle length prolongation (without atrio-His prolongation) prior to tachycardia termination. Right atrial mapping revealed the earliest site of atrial activation in the high lateral right atrium just below the superior vena cava. Low energy (10 and 20 W) radiofrequency lesions were applied at this site with termination of the tachycardia within 3 seconds of radiofrequency energy delivery. Tachycardia could not be reinduced after delivery of the radiofrequency lesions. The sinus node function immediately and 6 weeks after radiofrequency catheter ablation remained normal and the patient was without clinical recurrence of SVT. Mapping of sinus node reentrant tachycardia and elimination of the reentrant circuit with radiofrequency catheter ablation is possible without causing sinus node dysfunction. Adenosine causes prolongation of the atrial cycle length followed by termination of sinus node reentrant tachycardia.

Acute intravenous cocaine causes transient depression followed by enhanced left ventricular function in conscious dogs

BACKGROUND

Prior studies in experimental canine models have demonstrated that intravenous cocaine administration causes myocardial depression. The purpose of the present study was to establish the mechanisms of cocaine's actions on myocardial and left ventricular performance after single intravenous bolus doses in conscious, chronically instrumented dogs, in which the full autonomic influences of cocaine would be manifest.

METHODS AND RESULTS

In the intact state, cocaine (1 mg/kg) caused a transient decrease in left ventricular dP/dt (baseline; 3,086 +/- 107 mm Hg/sec; 2.5 minutes, 2,649 +/- 114 mm Hg; p < 0.05) followed by a 25 +/- 4% increase in left ventricular dP/dt that peaked at 15 minutes (left ventricular dP/dt, 3,751 +/- 127 mm Hg/sec, p < 0.01) and remained elevated during the 30-minute period of observation. Both the initial depression and the sustained increase in left ventricular contractile response were dose related. The increase in left ventricular dP/dt persisted under circumstances in which the responses were normalized for changes in heart rate and preload that accompanied cocaine administration. The positive inotropic effects were abolished by full autonomic or selective beta-adrenergic blockades. Finally, both cardiac output (baseline, 2,461 +/- 142 min/mL; peak [5 minutes], 3,434 +/- 218 mL/min; p < 0.05) and left ventricular stroke work (baseline, 39 +/- 5 g.m; peak, 49 +/- 6 g.m; p < 0.05) were increased at all times after cocaine administration, suggesting that pump performance was enhanced, despite early reductions in myocardial contractility. Similarly, indexes of early diastolic filling were enhanced despite transient early prolongation in isovolumic relaxation.

CONCLUSIONS

Acute intravenous cocaine administration (0.1-2 mg/kg) has a biphasic effect on myocardial and left ventricular function with a transient depression followed by significant sustained increases in left ventricular contractility. The results are in keeping with an early local effect followed by significant adrenergic stimulation, which may be obscured by anesthesia or masked by changes in loading conditions.

Cholinergic modulation of the coronary vasoconstriction induced by cocaine in conscious dogs

BACKGROUND

The effects of cocaine on the coronary circulation were examined in conscious dogs chronically instrumented to measure arterial and left ventricular pressures, coronary blood flow, and arterial and coronary sinus oxygen content.

METHODS AND RESULTS

With heart rate held constant, the peak effects of cocaine (1 mg/kg i.v.) occurred within 2 minutes, when mean arterial pressure increased by 42 +/- 5 mm Hg, coronary blood flow increased by 13 +/- 3%, and coronary vascular resistance increased by 24 +/- 3%. The arterial oxygen content increased significantly (by 2.8 +/- 0.3 vol%), the arterial-coronary sinus oxygen difference increased by 2.5 +/- 0.6 vol%, and myocardial oxygen consumption increased by 41 +/- 9%. The increase in coronary vascular resistance induced by cocaine was attenuated (p < 0.05) in the presence of cholinergic blockade (12 +/- 3%) despite a similar increase in MVO2 (49 +/- 8%). The increase in coronary vascular resistance was enhanced (p < 0.05) in the presence of beta-adrenergic receptor blockade (46 +/- 8%), whereas the MVO2 response was less (28 +/- 3%). Again, the addition of cholinergic blockade to beta-blockade attenuated the increase in coronary vascular resistance (23 +/- 6%) without affecting the increase in MVO2 (25 +/- 4%). Combined alpha-, beta-, and cholinergic blockades abolished the systemic hemodynamic and coronary vasoconstrictor response to cocaine.

CONCLUSIONS

In conscious dogs, cocaine induces coronary vasoconstriction, which competes with coronary vasodilator responses to increases in myocardial oxygen consumption. The mechanisms of cocaine's coronary vascular effects are mediated via adrenergic stimulation, and the intensity of the vasoconstrictor effects was reduced significantly by cholinergic blockade, in both the presence and absence of beta-adrenergic receptor blockade.

Measurement of ventricular electrogram amplitude during intraoperative induction of ventricular tachyarrhythmias

Adequate sensing of ventricular tachycardia (VT) and ventricular fibrillation (VF) is necessary for proper functioning of an implantable cardioverter defibrillator (ICD). Several ICDs currently undergoing investigation have programmable fixed gain sensitivity for tachycardia detection. If intracardiac electrogram amplitude decreases below the programmed sensitivity during VT or VF, detection of a ventricular arrhythmia may be delayed or missed. The mean amplitude of intracardiac electrograms (ICEGM) recorded with bipolar epicardial or transvenous sensing leads was measured in 63 patients during induced VT and VF recorded in the operating room at the time of ICD implantation. The mean amplitude of the ICEGM during 41 episodes of VF in 15 patients decreased from 14.9 +/- 0.9 mV during sinus rhythm to 8.8 +/- 0.7 mV at 1 second, 9.7 +/- 0.7 mV at 5 seconds, and 9.4 +/- 0.7 mV at 10 seconds (p < 0.0001 vs sinus rhythm ICEGM) with endocardial leads. The mean amplitude of the ICEGM recorded during 173 episodes of VF in 43 patients with epicardial leads decreased from 10.4 +/- 0.3 mV in sinus rhythm to 7.8 +/- 0.3 mV at 1 second, 8.3 +/- 0.3 mV at 5 seconds and 8 mV at 10 seconds (p <0.0001 vs sinus rhythm ICEGM). The mean amplitude of epicardial and transvenous ICEGMs recorded during 34 episodes of monomorphic VT decreased from 18.5 +/- 1.8 mV (epicardial) and 14.4 +/- 2.0 mV (transvenous) during sinus rhythm (p = 0.15, epicardial vs transvenous) to 16.0 +/- 1.7 mV (epicardial) and 13.7 +/- 1.9 mV (transvenous) at 10 seconds (< 10% of baseline amplitude).(ABSTRACT TRUNCATED AT 250 WORDS)

Implantation of cardioverter defibrillators in the post-sternotomy patient

In an attempt to minimize the hazards of redo sternotomy or thoracotomy in patients who have undergone previous cardiac procedures, a technique has been developed for cardioverter defibrillator implantation that involves dissection through a left subcostal incision and placement of extrapericardial defibrillation patches. This approach was used in 22 consecutive patients who required an implantable cardioverter defibrillator 4 to 156 months after previous median sternotomy. Defibrillation threshold energy was less than or equal to 20 J in every patient. Ninety-one percent of patients were extubated during the first 24 hours and were transferred out of the intensive care unit by the second postoperative day. One patient died of an acute myocardial infarction 3 days postoperatively (1/22, 4.5%). It was necessary to replace one lead for mechanical failure of an adapter, one patch required repositioning, and 1 patient needed drainage of a persistent pleural effusion (3/22, 13.6%). No further complications occurred during 3 to 27 months of follow-up. Advantages of the subcostal approach included prompt extubation, a single incision, and minimal morbidity. This approach is safe and effective, and is the method of choice for implantation of a cardioverter defibrillator in patients who have undergone prior sternotomy.