Syncope and inducible ventricular fibrillation in a woman with hemochromatosis.

BACKGROUND: Hemochromatosis has been associated with atrial tachyarrhythmias and congestive heart failure as a consequence of dilated or restrictive cardiomyopathy. Inducible ventricular fibrillation has not been previously described. METHODS AND RESULTS: An electrophysiologic study was conducted in a woman after two episodes of syncope. Polymorphic ventricular tachycardia (PMVT) and ventricular fibrillation (VF) were induced with ventricular programmed stimulation. Magnetic resonance imaging demonstrated signal loss in the liver consistent with hemochromatosis, but normal cardiac size and function. Hematologic studies supported a diagnosis of hemochromatosis. CONCLUSION: Cardiac hemochromatosis may be associated with serious ventricular arrhythmias.

The influence of ventricular fibrillation duration on defibrillation efficacy using biphasic waveforms in humans.

OBJECTIVES: The purpose of this study was to prospectively investigate the influence of ventricular fibrillation (VF) durations of 5, 10 and 20 s on the defibrillation threshold (DFT) during implantable cardioverter-defibrillator (ICD) implantation. BACKGROUND: Although the DFT using monophasic waveforms has been shown to increase with VF duration in humans, the effect of VF duration on defibrillation efficacy using biphasic waveforms in humans is not known. METHODS: Thirty patients undergoing primary ICD implantation or pulse generator replacement were randomly assigned to have the DFT determined using biphasic shocks at two durations of VF each (5 and 10 s, 10 and 20 s or 5 and 20 s). RESULTS: There was no statistically significant difference in the mean DFT comparing VF durations of 5 s (9.5+/-6.0 J) and 10 s (10.8+/-7.0 J) (p=0.4). The mean DFT significantly increased from 10.9+/-6.1 J at 10 s of VF to 12.6+/-5.6 J (p=0.03) at 20 s of VF, and from 7.0+/-3.5 J at 5 s of VF to 10.5+/-6.3 J (p=0.04) at 20 s of VF. An increase in the DFT was observed in 14 patients as VF duration increased. There were no clinical characteristics that differentiated patients with and without an increase in the DFT. CONCLUSIONS: Defibrillation efficacy decreases with increasing VF duration using biphasic waveforms in humans. Ventricular fibrillation durations greater than 10 s may negatively affect the effectiveness of ICD therapy.

Mode switching in dual chamber pacemakers: effect of onset criteria on arrhythmia-related symptoms.

AIMS: Various mode-switching algorithms are available with different tachyarrhythmia detection criteria to be satisfied to initiate mode-switching. This study evaluated three different mode-switching algorithms in patients with paroxysmal atrial fibrillation. METHODS AND RESULTS: Seventeen patients completed the study. Three mode-switching algorithms were downloaded as software into the pacemaker, each for 1 month in a single-blind, randomized sequence. The criteria to initiate mode-switching were: mean atrial rate ('standard'), '4-of-7' or '1-of-1' atrial intervals to exceed the atrial detection rate. Symptoms for each were measured using the Symptom Checklist Frequency and Severity index. The median number of mode-switch episodes increased from 20 for 'standard' to 39 for '4-of-7' (P=0.029 vs 'standard') and 103 for '1-of-1' (P=0.0012 vs 'standard') onset criteria. Median duration of episodes decreased from 2.5 min with 'standard' to 1.4 min with '4-of-7' and 0.4 min with '1-of-1' onset criteria. Frequency of symptoms was lower using '4-of-7' (18.2 +/- 12.0 vs 23 +/- 12.0, P=0.08) or '1-of-1' (20.4 +/- 12.4 vs 23 +/- 12.0, P=0.07) than 'standard' onset criteria. Severity of arrhythmia tended to be less with either '4-of-7' (16 +/- 10.4 vs 19.1 +/- 19.4, P=0.12) or '1-of-1' (17.5 +/- 10.3 vs 19.1 +/- 9.4, P=0.18) than with 'standard' onset criteria. CONCLUSIONS: The more sensitive onset criteria for detection of atrial tachyarrhythmias were associated with lower frequency and severity of symptoms.

Gross and microscopic pathological changes associated with nonthoracotomy implantable defibrillator leads.

BACKGROUND: Although the effects of epicardial implantable cardioverter-defibrillator (ICD) leads on underlying cardiac tissue have been reported, the gross and microscopic changes associated with endocardial ICD leads are less well described. This study describes the gross and microscopic changes associated with endocardial ICD leads in humans. METHODS AND RESULTS: The hearts from 8 patients were examined. At the time of ICD implantation, the patients' mean age was 47+/-11 years, and the left ventricular ejection fraction was 0.24+/-0.10. Four patients had ischemic heart disease, and 4 had dilated cardiomyopathy. Five hearts were examined after transplantation; 3, after death. The electrode-myocardial interfaces were characterized by intense endocardial fibrosis and were remarkably consistent. Each lead was encased by a ring of fibroelastic tissue, and there was fibrosis of the right ventricular myocardium adjacent to the leads. Fibrosis involved the tricuspid valve in 5 patients, and 1 had perforation of the valve by the lead. Microscopically, interstitial fibrosis was adjacent to each lead in the current path of ICD shocks. Acute cell injury was present only in the hearts that had received recent shocks. CONCLUSIONS: The ICD electrode-myocardial interface is characterized by intense fibrosis. The fibrosis associated with endocardial ICD leads and the cumulative acute damage produced by defibrillation discharges may explain changes in the defibrillation and pacing thresholds and the difficulty of lead extraction that can be encountered with transvenous ICD systems.

Clenbuterol and anabolic steroids: a previously unreported cause of myocardial infarction with normal coronary arteriograms.

During the last 10 years, several cases of myocardial infarction associated with anabolic steroid use have been reported. Postulated mechanisms to explain this association have included changes in lipid levels, the fibrinolytic system, and platelet aggregation. Clenbuterol is a beta 2-agonist with anabolic properties that has not been seen previously with myocardial infarction. We report a case of myocardial infarction in an otherwise healthy 26-year-old body-builder who recently used clenbuterol and anabolic steroids. In this case, synergistic effects of the two agents seem likely to have played a role in the infarct. The normal coronary arteriograms before any anticoagulant or thrombolytic therapy strongly suggest coronary spasm as the mechanism of the infarct.

Marked reduction in internal atrial defibrillation thresholds with dual-current pathways and sequential shocks in humans.

BACKGROUND: This study tested the ability of sequential shocks delivered through dual-current pathways to lower the atrial defibrillation threshold (ADFT) compared with a biphasic shock through a standard single-current pathway. METHODS AND RESULTS: Electrodes were positioned in the right atrial appendage (RA), left subclavian vein (LSV), proximal coronary sinus (CSos), and distal coronary sinus (DCS) in 14 patients with chronic atrial fibrillation (170+/-185 days). Using a step-up protocol, we compared ADFTs for a single-current pathway (RA-->DCS) that used a single 7.5/2.5-ms biphasic shock from a 150-microF capacitor with those for a dual-current pathway system (RA-->DCS followed by CSos-->LSV) using sequential 7.5/2.5-ms biphasic shocks with capacitor discharge waveforms for 150-microF and 600-microF capacitors. Both dual-current pathway configurations (2.0+/-0.4 J for 150-microF capacitance, 2.4+/-0.5 J for 600-microF capacitance) had a significantly lower ADFT than the single-current pathway (5.1+/-1.8 J). Whereas the dual-current pathway with 150-microF capacitor shocks had a significantly lower energy threshold, there was no statistical difference in terms of leading-edge voltage compared with the dual-current pathway with 600-microF capacitance shocks. There were no ventricular arrhythmias induced with appropriately synchronized shocks. CONCLUSIONS: For internal atrial defibrillation in humans, sequential biphasic waveforms delivered over dual-current pathways resulted in a markedly reduced (>50% reduction) ADFT compared with a single shock over a single-current pathway.

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.

Hemodynamic effects of an irregular sequence of ventricular cycle lengths during atrial fibrillation.

OBJECTIVES: The aim of this study was to determine the independent hemodynamic effects of an irregular sequence of ventricular cycle lengths in patients with atrial fibrillation (AF). BACKGROUND: Atrial fibrillation may reduce cardiac output by several possible mechanisms, including loss of the atrial contribution to left ventricular filling, valvular regurgitation, increased ventricular rate or irregular RR intervals. This study was designed to evaluate the effects of an irregular RR interval, independent of the average ventricular rate, on cardiac hemodynamic data during AF. METHODS: Sixteen patients with AF were studied invasively. During intrinsically conducted AF (mean rate 102 +/- 22 beats/ min), the right ventricular apex electrogram was recorded onto frequency-modulated (FM) tape. After atrioventricular node ablation, the right ventricular apex was stimulated in three pacing modes in randomized sequence: 1) VVI at 60 beats/min; 2) VVI at the same average rate as during intrinsically conducted AF (102 +/- 22 beats/min); and 3) during VVT pacing in which the pacemaker was triggered by playback of the FM tape recording of the right ventricular apex electrogram previously recorded during intrinsically conducted AF (VVT 102 +/- 22 beats/min). RESULTS: Compared with VVI pacing at the same average rate, an irregular sequence of RR intervals decreased cardiac output (4.4 +/- 1.6 vs. 5.2 +/- 2.4 liters/min, p < 0.01), increased pulmonary capillary wedge pressure (17 +/- 7 vs. 14 +/- 6 mm Hg, p < 0.002) and increased right atrial pressure (10 +/- 6 vs. 8 +/- 4 mm Hg, p < 0.05). CONCLUSIONS: An irregular sequence of RR intervals produces adverse hemodynamic consequences that are independent of heart rate.

Pacing threshold increase in nonthoracotomy implantable defibrillator leads: implications for battery longevity and margin of safety.

Just as a stable defibrillation threshold is required for implantable defibrillators to maintain efficacy and a margin of safety for the conversion of life-threatening ventricular arrhythmias, a stable pacing threshold is also required to provide bradycardia support and pacing to terminate ventricular tachycardias. This article reports the temporal course of pacing thresholds in patients treated with a tripolar, tined endocardial defibrillator lead capable of bipolar sensing and pacing, and defibrillation. Seventeen patients who underwent implantation of an implantable defibrillator system using an integrated bipolar pacing/sensing system were prospectively studied over 18 months. There were 16 males and one female, with a mean age of 69 +/- 5 years (range 61-75 years). At implantation, predischarge, and every 2 months thereafter, the pacing pulse-width threshold was tested at both 2.5 and 5.0 V stimulus amplitudes. After a mean follow-up of 363 +/- 173 days (range 34-597 days), the pacing threshold increased from 0.08 +/- 0.08 ms to 0.5 +/- 0.3 ms at the 2.5 V amplitude (p < or = 0.01, CI-0.57 to -0.27) and from 0.04 +/- 0.02 ms to 0.25 +/- 0.14 ms at the 5.0 V amplitude (p < or = 0.01, CI -0.28 to -0.14). Eight of the 17 patients (47%) received spontaneous implantable defibrillator shocks for clinically detected arrhythmias, and the total number of joules delivered via the leads did not correlate with the pacing threshold changes. We conclude that the pacing threshold for the nonthoracotomy implantable defibrillator lead system studied is not stable and increases with time. This finding has implications for defibrillator battery life in patients who use implantable defibrillators for bradycardia pacing.

Effect of radiofrequency catheter ablation on health-related quality of life and activities of daily living in patients with recurrent arrhythmias.

BACKGROUND: Although radiofrequency catheter ablation can be used to effectively treat a variety of arrhythmias, the effects of this procedure on health-related quality of life have not been systematically studied. METHODS AND RESULTS: The SF-36 (a measure of general health status), the Symptom Checklist-Frequency and Severity Scale (an instrument specific for cardiac arrhythmias), and an Activities of Daily Living questionnaire were used to assess quality of life in 161 patients before radiofrequency catheter ablation. These same instruments were used to measure quality of life 1 and 6 months after ablation with complete data in 159 of the original 161 patients. Before ablation, SF-36 scores of the study population were low compared with the US normative data base reflecting significant impairment in physical functioning and well-being. The lowest scores were reported by patients with atrial fibrillation and atrial flutter. Catheter ablation was associated with significant improvement in quality of life that was sustained over the 6 months after ablation. Improvements were measured in both the generic SF-36 health status questionnaire and the disease-specific Symptom Checklist-Frequency and Severity Scale. Catheter ablation was followed by improved performance of activities of daily living and a marked decrease in the number of visits to physicians and emergency rooms in the 6 months after ablation compared with the 6 months before ablation. CONCLUSIONS: Radiofrequency catheter ablation improves the health-related quality of life for patients with a variety of cardiac arrhythmias.

Posterior left thoracic cardiac sympathectomy by surgical division of the sympathetic chain: an alternative approach to treatment of the long QT syndrome.

Although high thoracic left sympathectomy via an anterior surgical approach is a highly efficacious treatment for refractory ventricular arrhythmias in patients with the long QT syndrome, the degree of sympathetic denervation has been variable, success of the operation is influenced by anatomical differences between patients, and Horner's syndrome may result. We hypothesized that interruption of sympathetic input to the heart could be accomplished using a posterior thoracic approach to this variable and often complex anatomy by division of the sympathetic chain rather than by direct destruction of the stellate and superior thoracic ganglia with the more conventional anterior, supraclavicular approach. In addition, the posterior approach should decrease the risk of Horner's syndrome by avoiding the ocular sympathetic efferent nerves. This posterior approach is described in five patients with the long QT syndrome and recurrent ventricular arrhythmias. After a mean follow-up of 18 +/- 12 months, all are alive without Horner's syndrome.

PR/RR interval ratio during rapid atrial pacing: a simple method for confirming the presence of slow AV nodal pathway conduction.

INTRODUCTION: Although the AV conduction curve in patients with AV nodal reentrant tachycardia (AVNRT) is usually discontinuous, many patients with this arrhythmia do not demonstrate criteria for dual AV nodal pathways. During rapid atrial pacing, the PR interval often exceeds the pacing cycle length when there is anterograde conduction over the slow pathway and AVNRT is induced. The purpose of this prospective study was to determine the diagnostic value of the ratio of the PR interval to the RR interval during rapid atrial pacing as an indicator of anterograde slow pathway conduction in patients undergoing electrophysiologic testing. METHODS AND RESULTS: The PR and RR intervals were measured during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction in four study groups: (1) patients with inducible AV nodal reentry and the classical criterion for dual AV nodal pathways during atrial extrastimulus testing (AVNRT Group 1); (2) patients with inducible AV nodal reentry without dual AV nodal pathways (AVNRT Group 2); (3) control subjects < or = 60 years of age without inducible AV nodal reentry; and (4) control subjects > 60 years of age without inducible AV nodal reentry. For both groups of patients with inducible AV nodal reentry, AV conduction was assessed before and after radiofrequency ablation of the slow AV nodal pathway. Before slow pathway ablation, the PR/RR ratio exceeded 1.0 in 12 of 13 AVNRT Group 1 patients (mean 1.27 +/- 0.21) and 16 of 17 AVNRT Group 2 patients (mean 1.18 +/- 0.15, P = NS Group 1 vs Group 2). After slow pathway ablation, the maximum PR/RR ratio was < 1.0 in all AVNRT patients (Group 1 = 0.59 +/- 0.08, P < 0.00001 vs before ablation; Group 2 = 0.67 +/- 0.11; P < 0.00001 vs before ablation). Among both groups of control subjects, the PR/RR ratio was > 1.0 in only 3 of 27 patients with no relation to patient age. CONCLUSION: The ratio of the PR interval to the RR interval during rapid atrial pacing at the maximum rate with consistent 1:1 AV conduction provides a simple and clinically useful method for determining the presence of slow AV nodal pathway conduction. This finding may be particularly useful in patients with inducible AV nodal reentry without dual AV nodal physiology on atrial extrastimulus testing.

The present role of radiofrequency catheter ablation in the management of cardiac arrhythmias.

Radiofrequency catheter ablation can be used to treat a variety of cardiac arrhythmias. Yet while the spectrum of arrhythmias amenable to catheter ablation continues to expand, the protocol for whether or not catheter ablation should be recommended for the management of an individual patient has not been firmly established. This article summarizes the experience of one medical center with radiofrequency catheter ablation. The varieties of arrhythmias that may be effectively treated with catheter ablation, the probability of success, and the attendant risks of these procedures in the series are presented. In addition, the future applications of catheter ablation to cardiac arrhythmias are discussed.

Randomized, double-blind comparison of intravenous amiodarone and bretylium in the treatment of patients with recurrent, hemodynamically destabilizing ventricular tachycardia or fibrillation. The Intravenous Amiodarone Multicenter Investigators Group.

BACKGROUND: After several days of loading, oral amiodarone, a class III antiarrhythmic, is highly effective in controlling ventricular tachyarrhythmias; however, the delay in onset of activity is not acceptable in patients with immediately life-threatening arrhythmias. Therefore, an intravenous form of therapy is advantageous. This study was designed to compare the safety and efficacy of a high and a low dose of intravenous amiodarone with bretylium, the only approved class III antiarrhythmic agent. METHODS AND RESULTS: A total of 302 patients with refractory, hemodynamically destabilizing ventricular tachycardia or ventricular fibrillation were enrolled in this double-blind trial at 82 medical centers in the United States. They were randomly assigned to therapy with intravenous bretylium (4.7 g) or intravenous amiodarone administered in a high dose (1.8 g) or a low dose (0.2 g). The primary analysis, arrhythmia event rate during the first 48 hours of therapy, showed comparable efficacy between the bretylium group and the high-dose (1000 mg/24 h) amiodarone group that was greater than that of the low-dose (125 mg/24 h) amiodarone group. Similar results were obtained in the secondary analyses of time to first event and the proportion of patients requiring supplemental infusions. Overall mortality in the 48-hour double-blind period was 13.6% and was not significantly different among the three treatment groups. Significantly more patients treated with bretylium had hypotension compared with the two amiodarone groups. More patients remained on the 1000-mg amiodarone regimen than on the other regimens. CONCLUSIONS: Bretylium and amiodarone appear to have comparable efficacies for the treatment of highly malignant ventricular arrhythmias. Bretylium use, however, may be limited by a high incidence of hypotension.

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

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

The risk of atrial fibrillation following radiofrequency catheter ablation of atrial flutter.

BACKGROUND: Although radiofrequency catheter ablation of atrial flutter is associated with a high rate of initial success, several clinical issues regarding this therapy remain to be defined. For example, the risks of recurrent atrial flutter and of developing atrial fibrillation after flutter ablation are unknown. In addition, it is not known whether elimination of atrial flutter will modify the natural history of atrial fibrillation in patients who experience both of these arrhythmias. The purpose of the present study was to determine the actuarial freedom from recurrent or new atrial arrhythmias in patients with atrial flutter undergoing catheter ablation. METHODS AND RESULTS: The study population consisted of 59 consecutive patients (mean age, 61.9 +/- 12.6 years) with typical atrial flutter who underwent catheter ablation of the reentrant circuit. Catheter ablation was not advised for patients in whom paroxysmal atrial fibrillation had been a major clinical problem. The inducibility of atrial fibrillation and atrial flutter was assessed after successful atrial flutter ablation with programmed atrial stimulation and rapid atrial pacing to a cycle length of 180 ms or 2:1 atrial capture. Atrial flutter was successfully ablated and rendered noninducible in 53 of 59 patients (90%). Over a mean follow-up period of 13.2 +/- 6.6 months, atrial flutter recurred in 5 patients (9.4%). Atrial fibrillation occurred in 14 of 53 patients after successful ablation (26.4%). Four clinical variables were associated by univariate analysis with the late occurrence of atrial fibrillation: (1) the presence of structural heart disease, (2) a history of atrial fibrillation before ablation of atrial flutter, (3) inducible sustained atrial fibrillation after ablation, and (4) a greater number of failed antiarrhythmic drugs. By multivariate analysis, only the persistent inducibility of sustained atrial fibrillation predicted the later development of atrial fibrillation. CONCLUSIONS: Although atrial flutter ablation is highly effective and associated with a low risk of recurrent atrial flutter, atrial fibrillation continues to be a long-term risk for individuals undergoing this procedure. The risk of later atrial fibrillation is especially high for patients in whom sustained atrial fibrillation remains inducible after ablation of atrial flutter.

Catheter ablation of the accessory pathways of the Wolff-Parkinson-White syndrome and its variants.

The basis of arrhythmias in the Wolff-Parkinson-White (WPW) syndrome and its variants is the presence of accessory atrioventricular connections. Those variants include the concealed form of the WPW syndrome, the permanent form of junctional reciprocating tachycardia, and Mahaim preexcitation. In all forms of symptomatic WPW syndrome, catheter ablation of the accessory atrioventricular connections using radiofrequency current has become the treatment of choice. This review traces the development of this therapy, outlines the basics of the technique, summarizes the results reported in the largest series, indicate remaining areas of controversy, and discusses the indications and limitations of radiofrequency ablation therapy.

Differential effect of esmolol on the fast and slow AV nodal pathways in patients with AV nodal reentrant tachycardia.

INTRODUCTION: AV nodal reentrant tachycardia (AVNRT) usually involves anterograde conduction over a slowly conducting ("slow") pathway and retrograde conduction over a rapidly conducting ("fast") pathway. A variety of drugs, such as beta blockers, digitalis, and calcium channel blockers, have been reported to prolong AV nodal refractoriness in both the anterograde and retrograde limbs of the circuit. However, few data are available that address whether the fast and slow pathways respond in a quantitatively different manner to drugs such as beta-adrenergic antagonists. In addition, it is not known whether the effects of these agents on refractoriness parallel the effects on conduction in the fast and slow pathways. The present study was performed to measure the effect of the intravenous beta-adrenergic agent, esmolol, on refractoriness and conduction in both the fast and slow AV nodal pathways in patients with AVNRT. METHODS AND RESULTS: Thirteen patients with discontinuous AV nodal conduction properties and typical AVNRT were studied. Anterograde and retrograde AV nodal functional assessment was performed at baseline and following steady-state drug infusion of intravenous esmolol at a dose of 500 micrograms/kg for 1 minute, 150 micrograms/kg per minute for the next 4 minutes, followed by a continuous maintenance infusion of 50 to 100 micrograms/kg per minute. The anterograde effective refractory period of the fast pathway increased from 381 +/- 75 msec at baseline to 453 +/- 92 msec during the infusion of esmolol (P = 0.003). The anterograde effective refractory period of the slow pathway was also prolonged by esmolol, from 289 +/- 26 msec to 310 +/- 17 msec (P = 0.005). However, the absolute magnitude of the change in the anterograde effective refractory period of the fast pathway (+72 +/- 59 msec) was significantly greater than the change in anterograde effective refractory period of the slow pathway (+21 +/- 16 msec, P = 0.01). The mean retrograde effective refractory period of the fast pathway increased from 276 +/- 46 msec to 376 +/- 61 msec during esmolol infusion (P = 0.03). Retrograde slow pathway conduction that could not be demonstrated at baseline became manifest in three patients during esmolol infusion. In contrast to the effects of esmolol on refractoriness, the AH interval during anterograde slow pathway conduction prolonged to a far greater extent (+84 msec) than the HA interval associated with retrograde fast pathway conduction (+5 msec, P = 0.04). CONCLUSION: The beta-adrenergic antagonist, esmolol, has a quantitatively greater effect on anterograde refractoriness of the fast than the slow AV nodal pathway. However, the effects on conduction intervals during AVNRT are greater in the anterograde slow pathway than in the retrograde fast pathway. These observations suggest that the fast and slow pathways may have differential sensitivities to autonomic influences. This difference in the response to beta-adrenergic antagonists may be exploited as a clinically useful method for demonstrating slow pathway conduction in some individuals with AVNRT.

Rate modulated pacing based on right ventricular dP/dt: quantitative analysis of chronotropic response.

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase with exercise workload. Thus, the maximum systolic dP/dt may be a potentially useful sensor to control the pacing rate of a permanent pacing system. The present study was designed to test the long-term performance of a permanent pacemaker that modulates pacing rate based on right ventricular dP/dt and to quantitatively analyze the chronotropic response characteristics of this sensor in a group of patients with widely varying structural heart diseases and degrees of hemodynamic impairment. A permanent pacing system incorporating a high fidelity pressure sensor in the lead for measurement of right ventricular dP/dt was implanted in 13 patients with atrial arrhythmias and AV block, including individuals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septal defect, dilated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VVIR pacing modes with measurement of expired gas exchange and quantitative analysis of chronotropic response using the concept of metabolic reserve. The peak right ventricular dP/dt ranged from 238-891 mmHg/sec with a pulse pressure that ranged from 19-41 mmHg. There was a positive correlation between the right ventricular dP/dt and pulse pressure (r = 0.70, P = 0.012). The maximum pacing rate and VO2max were 72 +/- 6 beats/min and 12.61 +/- 4.0 cc O2/kg per minute during VVI pacing and increased to 124 +/- 18 beats/min and 15.89 +/- 5.9 cc O2/kg per minute in the VVIR pacing mode (P < 0.0003 and P < 0.002, respectively). The integrated area under the normalized rate response curve was 96.7 +/- 45.7% of expected during exercise and 100.1 +/- 43.4% of expected during recovery. One patient demonstrated an anomalous increase in pacing rate in response to a change in posture to the left lateral decubitus position. Thus, the peak positive right ventricular dP/dt is an effective rate control parameter for permanent pacing systems. The chronotropic response was proportional to metabolic workload during treadmill exercise in this study population with widely varying forms of structural heart disease.

Predictors of recurrent atrioventricular nodal reentry after selective slow pathway ablation.

Although radiofrequency catheter ablation of the slow atrioventricular (AV) nodal pathway is highly effective for the management of AV nodal reentrant tachycardia (AVNRT), this arrhythmia may recur in some patients after an ablation procedure that initially renders AVNRT noninducible. A retrospective study examined the factors that are associated with the recurrence of AVNRT after selective radiofrequency catheter ablation of the slow pathway. Patients were included in the study if they had initially inducible, typical slow-fast AVNRT that was noninducible at the end of the ablation session. Selective ablation of the slow pathway was performed using radiofrequency energy applied along the tricuspid annulus near the coronary sinus ostium. AVNRT recurred after initially successful slow pathway ablation in 10 of 136 patients (7.4%) over a mean follow-up period of 20.1 +/- 5.0 months; the time to recurrence ranged from 1 to 411 days. Despite the absence of inducible AVNRT, dual anterograde AV nodal conduction properties persisted after slow pathway ablation in 10 patients. AVNRT recurred in 4 of 10 patients who had evidence of residual slow pathway conduction compared with only 6 of 126 who had no residual slow pathway conduction (p = 0.003). All patients with persistent slow pathway conduction and recurrent AVNRT also had residual AV nodal echo beats. AVNRT recurred in 3 of 6 patients without accelerated junctional tachycardia during radiofrequency application compared with only 7 of 109 with accelerated junctional tachycardia (p = 0.003). Thus, AVNRT infrequently recurs after successful selective radiofrequency ablation of the slow pathway.(ABSTRACT TRUNCATED AT 250 WORDS)