We postulated that ventilatory assistance during exercise would improve cardiopulmonary function, relieve exertional symptoms, and increase exercise endurance (T(lim)) in patients with chronic congestive heart failure (CHF). After baseline pulmonary function tests, 12 stable patients with advanced CHF (ejection fraction, 24 +/- 3% [mean +/- SEM]) performed constant-load exercise tests at approximately 60% of their predicted maximal oxygen consumption (V O(2)max) while breathing each of control (1 cm H(2)O), continuous positive airway pressure optimized to the maximal tolerable level (CPAP = 4.8 +/- 0.2 cm H(2)O) or inspiratory pressure support (PS = 4.8 +/- 0.2 cm H(2)O), in randomized order. Measurements during exercise included cardioventilatory responses, esophageal pressure (Pes), and Borg ratings of dyspnea and leg discomfort (LD). At a standardized time near end-exercise, PS and CPAP reduced the work of breathing per minute by 39 +/- 8 and 25 +/- 4%, respectively (p < 0. 01). In response to PS: T(lim) increased by 2.8 +/- 0.8 min or 43 +/- 14% (p < 0.01); slopes of LD-time, V O(2)-time, V CO(2)-time, and tidal Pes-time decreased by 24 +/- 10, 20 +/- 11, 28 +/- 8, and 44 +/- 9%, respectively (p < 0.05); dyspnea and other cardioventilatory parameters did not change. CPAP did not significantly alter measured exercise responses. The increase in T(lim) was explained primarily by the decrease in LD- time slopes (r = -0.71, p < 0.001) which, in turn, correlated with the reductions in V O(2)-time (r = 0.61, p < 0.01) and tidal Pes-time (r = 0.52, p < 0.01). in conclusion, ventilatory muscle unloading with PS reduced exertional leg discomfort and increased exercise endurance in patients with stable advanced CHF.

This study demonstrated that UHR at first follow-up has an important influence on how pacing mode selection affects cardiovascular death and total mortality. Pacemaker-dependent patients with low UHR will probably be paced frequently and will likely benefit from physiological pacing. In contrast, non-pacemaker-dependent patients will likely be paced infrequently and may not benefit from physiological pacing.

An increasing number of premature ventricular stimuli are being used during programmed stimulation of the heart in the investigation of patients with documented or suspected ventricular arrhythmias. To analyze the significance of the different types of ventricular arrhythmias that are initiated, we evaluated in a prospective study the effect of from one to four ventricular premature stimuli in 52 patients without (non-VT group) and 50 patients with (prior-VT group) documented ventricular tachycardia or ventricular fibrillation. More than half of the patients in the prior-VT group had coronary heart disease. In the majority of patients of the non-VT group the heart was normal. In 44 of the 50 patients in the prior-VT group the clinically documented ventricular arrhythmia was initiated by programmed ventricular stimulation of the heart. In 88% of these 44 patients, one or two ventricular premature beats were required to initiate the clinical arrhythmia. A ventricular arrhythmia could be initiated in 31 of the 52 patients in the non-VT group. The ventricular arrhythmias included nonsustained monomorphic ventricular tachycardia (two patients), six to 25 complexes of sustained polymorphic ventricular tachycardia (24 patients), and ventricular fibrillation (five patients). In 70% of patients in the non-VT group three or four ventricular premature beats were required to initiate the ventricular arrhythmia. Our results indicate that not only the number of extrastimuli required to initiate ventricular arrhythmias but also the type of ventricular arrhythmia initiated differed between the two groups of patients. Nonsustained polymorphic ventricular tachycardia and ventricular fibrillation are nonspecific responses to aggressive stimulation protocols.Circulation 69, No. 1, 87-92, 1984. IN PATIENTS with ventricular tachycardia, programmed stimulation of the heart was initially introduced to study mechanisms of the arrhythmia. IA Subsequently it was realized that the method was of value to select the best mode of treatment -drugs, surgery, or pacemakers.5 13 Recently attention has been focused on the use of programmed electrical stimulation of the heart in patients resuscitated out of hospital'"'6 and those with unexplained syncope,'7 18 and for the identification of high-risk patients who have had myocardial infarction. [19][20] Over the past 10 years we have witnessed a gradual increase in the number of premature stimuli and stimu-

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Background Lyme carditis (LC), an early manifestation of Lyme disease that most commonly presents as high‐degree atrioventricular block (AVB), usually resolves with antibiotic treatment. When LC is not identified as the cause of AVB, a permanent pacemaker may be inappropriately implanted in a reversible cardiac conduction disorder. Hypothesis The likelihood that a patient's high‐degree AVB is caused by LC can be evaluated by clinical characteristics incorporated into a risk stratification tool. Methods A systematic review of all published cases of LC with high‐degree AVB, and five cases from the authors' experience, was conducted. The results informed the development of a new risk stratification tool, the Suspicious Index in LC (SILC) score. The SILC score was then applied to each case included in the review. Results Of the 88 cases included, 51 (58%) were high‐risk, 31 (35.2%) intermediate‐risk, and 6 (6.8%) low‐risk for LC according to the SILC score (sensitivity 93.2%). For the subset of 32 cases that reported on all SILC variables, 24 (75%) cases were classified as high‐risk, 8 (25%) intermediate‐risk, and 0 low‐risk (sensitivity 100%). Specificity could not be assessed (no control group). Notably, 6 of the 11 patients who received permanent pacemakers had reversal of AVB with antibiotic treatment. Conclusion The SILC risk score and COSTAR mnemonic (constitutional symptoms; outdoor activity; sex = male; tick bite; age < 50; rash = erythema migrans) may help to identify LC in patients presenting with high‐degree AVB, and ultimately, minimize the implantation of unnecessary permanent pacemakers.

In 12 patients (nine with Wolff-Parkinson-White syndrome and three with ventricular tachycardia) the electrophysiologic effects of intravenous (5 mg/kg body weight in 1 min) and oral (total dose 9800 to 11,200 mg) amiodarone were studied with programmed stimulation of the heart. Intravenous and oral amiodarone had a similar (p < .05) effect of lengthening on the effective refractory period of the atrioventricular node. Only intravenous amiodarone prolonged (p < .05) the AH interval. Oral amiodarone was more effective than intravenous amiodarone in lengthening the anterograde effective refractory period of the accessory atrioventricular pathway. Only oral amiodarone prolonged the effective refractory period of atrium and ventricle and the HV interval, all significantly (p < .05). Intravenous amiodarone slowed (p < .05) the rate of circus-movement tachycardia in patients with Wolff-Parkinson-White syndrome, and further slowing was observed after oral amiodarone. Termination of tachycardia by intravenous amiodarone predicted prevention of reinitiation of tachycardia during oral amiodarone. These data indicate that intravenous and oral amiodarone do not have the same electrophysiologic effects. It is not clear whether cumulative effects, active metabolites, or both are responsible for these differences.Circulation 69, No. 1, 120-124, 1984. IT HAS BEEN established that amiodarone administered orally is a very powerful drug for the treatment of arrhythmias occurring at the supraventricular and ventricular level.1`8 Although its mechanism of action at the cellular level is not quite clear, the electrophysiologic effects of oral amiodarone have been well studied.2', 915 A major problem in using oral amiodarone is the necessity of giving the drug for several days to weeks before it can reach its maximal effect. This limits its use in patients in whom an immediate antiarrhythmic effect is required. The introduction of intravenous amiodarone'6 was therefore received with great interest.In this article we report on the comparison between the electrophysiologic effects of intravenous and oral amiodarone. During programmed stimulation of the heart, we studied the effects of intravenous amiodarone in 12 patients. In the same patients the same stimu- 120 lation program was repeated 5 to 6 weeks after administration of oral amiodarone. Materials and methodsTwelve patients were studied, and their clinical data are given in table 1. After informed consent was obtained, a study of programmed stimulation was performed. Our methods of stimulation and recording and our definitions of the different electrophysiologic parameters have been reported previously.'7The following measurements were made: (1) heart rate during sinus rhythm, (2) the effective refractory period of the right atrium, (3) the effective refractory period of the right ventricle, (4) the effective refractory period of the atrioventricular (AV) node, (5) the refractory period of the accessory AV pathway (in the nine patients with Wolff-Parkinson-White synd...

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Background— The Canadian Trial of Physiological Pacing (CTOPP) reported that the risk of stroke or cardiovascular death was similar between patients receiving ventricular versus physiological pacemakers at the end of the original follow-up period of 3 years. However, the occurrence of atrial fibrillation was significantly less frequent with physiological pacemakers. To assess a potential delayed benefit of physiological pacing, follow-up of patients in this study was extended to 6 years. Methods and Results— A total of 1474 patients requiring a pacemaker for symptomatic bradycardia were randomized to receive ventricular and 1094 to physiological pacemakers. The primary outcome was stroke or cardiovascular death. The study was completed in July 1998, and follow-up was extended to July 2001. At a mean follow-up of 6.4 years, there was no difference between treatment groups in the primary outcome of cardiovascular death or stroke. There was no significant difference in total mortality or stroke between groups. There was a significantly lower rate of development of atrial fibrillation in the physiological group, with a relative risk reduction of 20.1% (CI, 5.4 to 32.5; P =0.009). Conclusions— The CTOPP extended study does not show a difference in cardiovascular death or stroke, or in total mortality, or in stroke between patients implanted with ventricular or physiological pacemakers over a mean follow-up of >6 years. However, there is a persistent significant reduction in the development of atrial fibrillation with physiological pacing.