Comparison of dilated cardiomyopathy and coronary artery disease in patients with life-threatening ventricular arrhythmias: Differences in presentation and outcome in the AVID registry.

BACKGROUND: The etiology of structural heart disease in patients with life-threatening arrhythmias (ventricular tachycardia [VT]/ventricular fibrillation [VF]) may define clinical characteristics at presentation, may require that different therapies be administered, and may cause different mortality outcomes. METHODS: In the Antiarrhythmics Versus Implantable Defibrillators (AVID) registry, baseline clinical characteristics, treatments instituted, and ultimate mortality outcomes from the National Death Index were obtained on 3117 patients seen at participating institutions with VT/VF, irrespective of participation in the randomized trial. By use of these data, 2268 patients with coronary artery disease (CAD) were compared with 334 patients with dilated nonischemic cardiomyopathy (DCM). RESULTS: The CAD group was 7 years older and had a higher percentage of males. DCM patients were more likely to be African American, have severely compromised left ventricular function (52% vs 39%), and have a history of congestive heart failure symptoms (62% vs 44%). Patients with CAD were more likely to be treated with b-blockers and calcium channel blockers and less likely to be treated with angiotensin-converting enzyme inhibitors. Patients with DCM were more likely to be treated with diuretics, warfarin, and an implantable cardioverter defibrillator for VT/VF (54% vs 48% for CAD); the use of other antiarrhythmic therapies did not differ between the 2 groups. Two-year survival was not significantly different between the groups (76.6% [95% CI 74.6%-78.7%] vs 78.2% [95% CI 73.6%-82.9%]). CONCLUSIONS: In AVID registry patients with VT/VF, demographic and clinical characteristics were different between patients with CAD and those with DCM. Despite these differences, overall survival was similar in these 2 groups.

Resumption of driving after life-threatening ventricular tachyarrhythmia.

BACKGROUND: Although the privilege of driving must be respected, it may be necessary to restrict driving when it poses a threat to others. The risks associated with allowing patients with life-threatening ventricular tachyarrhythmias to drive have not been quantified. METHODS: The Antiarrhythmics versus Implantable Defibrillators (AVID) trial compared antiarrhythmic-drug therapy with the implantation of defibrillators in patients resuscitated from near-fatal ventricular arrhythmias. In the current study, we sent patients who participated in the AVID trial a questionnaire, to be completed anonymously, requesting information about driving habits and experiences. RESULTS: The questionnaire was returned by 758 of 909 patients (83 percent). Of these, 627 patients drove during the year before their index episode of ventricular tachyarrhythmia. A total of 57 percent of these patients resumed driving within 3 months after randomization in the AVID trial, 78 percent within 6 months, and 88 percent within 12 months. While driving, 2 percent had a syncopal episode, 11 percent had dizziness or palpitations that necessitated stopping the vehicle, 22 percent had dizziness or palpitations that did not necessitate stopping the vehicle, and 8 percent of the 295 patients with an implantable cardioverter-defibrillator received a shock. Fifty patients reported having at least 1 accident, for a total of 55 accidents during 1619 patient-years of follow-up after the resumption of driving (3.4 percent per patient-year). Only 11 percent of these accidents were preceded by symptoms of possible arrhythmia (0.4 percent per patient-year). CONCLUSIONS: Most patients with ventricular tachyarrhythmias resume driving early. Although it is common for them to have symptoms of possible arrhythmia while driving, accidents are uncommon and occur with a frequency that is lower than the annual accident rate of 7.1 percent in the general driving population of the United States.

Immediate and short-term reproducibility of the P wave signal-averaged electrocardiogram.

While abnormalities in the P wave SAECG have been associated with the occurrence of AF, its reproducibility has never been documented. The purpose of this study was to evaluate the immediate and short-term reproducibility of measurements from the P wave SAECG. P wave SAECGs were obtained using well-described techniques that utilize the QRS complex as the trigger and the P wave as template for averaging. In 28 subjects (8 controls, 11 with cardiac disease, 9 with prior AF), 3 P wave SAECGs were obtained: an initial study; on immediate reacquisition; and reacquisition after 4-5 days. Vector duration and RMS voltage of the terminal 20 ms of the P wave SAECG were measured and compared. The mean P wave duration was 152 +/- 14 ms on initial SAECG, 152 +/- 14 ms and 152 +/- 15 ms at immediate and short-term reacquisitions, respectively (both P = NS vs initial). The mean terminal RMS voltage was 6.4 +/- 6.0 mcV on initial SAECG, 6.4 +/- 5.9 mcV and 6.5 +/- 5.8 mcV at immediate and short-term reacquisitions, respectively (both P = NS vs initial). Linear regression analysis showed high reproducibility for both P wave duration (r = 0.94 for immediate and r = 0.96 for short-term reacquisition vs initial) but slightly less for terminal RMS voltage (r = 0.92 for immediate and r = 0.84 for short-term reacquisition vs initial). In subgroup analysis, P wave duration measurements were highly reproducible in controls, in subjects with cardiac disease, and in those with a history of AF. P wave duration was also reproducible for both males and females, as well as for subjects age > 65 years (r = 0.96 and 0.89 for immediate and short-term reacquisition, respectively). Terminal RMS voltage measurements were reproducible for controls, but less reproducible in other subgroups. In conclusion, P wave duration measurements on SAECG are reproducible when evaluated at immediate and short-term reacquisition regardless of age, sex, cardiac disease, or prior AF. Terminal RMS voltages were less reproducible, especially in patients with cardiac disease and/or prior AF. These findings may explain conflicting observations regarding the clinical utility of terminal P wave measurements.

Cellular and pathophysiological mechanisms of ventricular arrhythmias in acute ischemia and infarction.

Ventricular arrhythmias in the setting of acute myocardial ischemia and infarction remain a serious health problem because of their sudden and unpredictable nature and their potentially grave results. Electrophysiological changes that may be responsible for these arrhythmias have been described in cardiac cells and in ischemic tissue. Experimental models have played a major role in elucidating the diversity of potential mechanisms for these arrhythmias. Increases in extracellular K+, the presence of toxic metabolites, and the accumulation of catecholamines in ischemic tissue all appear to have a role in arrhythmogenesis. The autonomic nervous system also appears to play a major role in these arrhythmias. With increased understanding of the pathophysiology underlying these arrhythmias, prevention can be enhanced and therapy can be better targeted.

Gender-specific differences in the QT interval and the effect of autonomic tone and menstrual cycle in healthy adults.

Gender differences in the corrected QT interval have been noted since Bazett's initial description during the 1920s. The mechanism of this gender difference is unknown, and this study was undertaken to evaluate potential autonomic and menstrual cycle effects on the QT interval. The study population consisted of a healthy volunteer sample of 23 women and 20 men. Twelve-lead electrocardiographic determinations were made at rest and following double autonomic blockade (with atropine and propranolol) during the menstrual, follicular, and luteal phases of the menstrual cycle. Men were studied during 3 separate visits as controls. The corrected QT interval at baseline tended to be longer in women than men (421 +/- 16 ms vs 414 +/- 15 ms: p <0.07). Following double autonomic blockade, the corrected QT interval increased to 439 +/- 11 ms: p <0.001). However, the gender difference in corrected QT interval was unchanged (443 +/- 15 ms vs 437 +/- 12 ms). At baseline, there was no significant difference in the corrected QT interval among the 3 phases of the menstrual cycle (421 +/- 10, 423 +/- 18, and 420 +/- 18 in the menstrual, follicular, and luteal phases, respectively) and the corrected QT interval was longer in women than men at each visit. Following double autonomic blockade, the corrected QT interval in women was shorter in the luteal phase (438 +/- 16 ms) versus the menstrual (446 +/- 15 ms) or the follicular phase (444 +/- 13 ms; p <0.05). However, this difference, which was not present at baseline, does not appear to be responsible for the gender difference in the QT interval at rest. In conclusion, our results confirm that the corrected QT interval tends to be longer in women than men. Differences in autonomic tone and menstrual cycle variability in the corrected QT in women at rest do not appear to be responsible for the gender differences in the QT interval. The mechanism responsible for the longer QT interval in women remains to be defined.

Evaluation of P wave signal-averaged electrocardiographic filtering and analysis methods.

The purpose of this study was to evaluate the signal processing and analysis methods currently in use for the P wave signal-averaged electrocardiogram and to define optimal parameters for its use. P wave signal-averaged electrocardiograms using the QRS as a trigger for alignment of the analysis window were obtained in 15 subjects with prior atrial fibrillation and 15 controls. Five methods of signal filtering (unidirectional, bidirectional, finite impulse response, least squares fit, and spectral fast-Fourier transform) and three filter frequencies (14, 29, and 60 Hz) were compared with logistic regression analysis. Analysis techniques, including P wave vector duration, individual orthogonal lead duration, and terminal root mean square voltage were also evaluated for the strength of their association with the occurrence of atrial fibrillation. The least-squares fit filter with bandwidth filtering of 29 to 250 Hz produced the strongest association with atrial fibrillation (odds ratio 26). A high correlation (r > 0.92) was noted among the individual orthogonal leads; however, neither individual leads nor total atrial activation determined from individual leads demonstrated a superior association with atrial fibrillation when compared with total vector P wave duration. Terminal P wave RMS volt ages were not significantly different between patients with prior AF and controls.

Gender differences in heart rate before and after autonomic blockade: evidence against an intrinsic gender effect.

OBJECTIVES: To document gender differences in heart rate in healthy young adult men and women, and examine the degree to which autonomic tone and other variables may be associated with the gender differences in heart rate. DESIGNS: Cohort study. SETTINGS: Clinical Research Center of a tertiary care medical center. PATIENTS: A volunteer sample of 20 healthy men and 23 healthy women between ages 21 and 39 years. INTERVENTIONS: Subjects were each studied three times: during the menstrual, follicular, and luteal phases of the menstrual cycle in women; and 5 to 10 days apart in men. Electrocardiograms (ECGs) were obtained at baseline and following double autonomic blockade with propranolol 0.2 mg/kg and atropine 0.04 mg/kg. Maximum exercise capacity was determined by bicycle ergometry. MAIN OUTCOME MEASURES: Sinus cycle length at baseline and following double autonomic blockade, before and after correction for confounding variables. RESULTS: Men had longer sinus cycle length both at baseline and after double autonomic blockade (971 +/- 88 ms versus 918 +/- 115 ms, P < 0.02, and 645 +/- 41 ms versus 594 +/- 57 ms, P < 0.0001). Sinus cycle length in women was longer than during the menstrual than luteal phase but this difference could not account for the gender difference in sinus cycle length. Men also had a greater maximum exercise capacity than women (1295 +/- 167 kpm/min versus 857 +/- 227 kpm/min; P < 0.0001). By analysis of covariance, maximum exercise capacity was the most significant predictor of sinus cycle length (P < 0.0003 at baseline, and P < 0.001 post blockade) and gender did not have a significant effect. The relationship of maximum exercise capacity to sinus cycle length was blunted but not abolished by autonomic blockade. CONCLUSIONS: Sinus cycle length is longer in men than women. This difference appears to be associated with a gender difference in exercise capacity rather than intrinsic gender related properties of the sinus node or differences in autonomic tone. In addition, exercise induced bradycardia is mediated by both autonomic and nonautonomic factors in both genders.

Diurnal pattern of QTc interval: how long is prolonged? Possible relation to circadian triggers of cardiovascular events.

OBJECTIVES: This study sought to evaluate the range and variability of the QT and corrected QT (QTc) intervals over 24 h and to assess their pattern and relation to heart rate variability. BACKGROUND: Recent Holter monitoring data have revealed a high degree of daily variability in the QTc interval. The pattern of this variability and its relation to heart rate variability remain poorly characterized. METHODS: We developed and validated a new method for continuous measurement of QT intervals from three-channel, 24-h Holter recordings. Average RR, QT, QTc and heart rate variability were measured from 5-min segments of data from 21 healthy subjects. RESULTS: Measurement of 6,048 segments showed mean (+/- SD) RR, QT and QTc intervals of 830 +/- 100, 407 +/- 23 and 445 +/- 16 ms, respectively (mean QTc interval for men 434 +/- 12 ms, 457 +/- 10 ms for women, p < 0.0001). The average maximal QTc interval was 495 +/- 21 ms and the average QTc range 95 +/- 20 ms. The maximal QTc interval was > or = 500 ms in 6 subjects and > or = 490 ms in 13. The 95% upper confidence limit for the mean 24-h QTc interval was 452 ms (men 439 ms, women 461 ms). The RR, QT and QTc intervals and the high frequency component of heart rate variability were greater during sleep. Both the QTc interval and the variability between hourly minimal and maximal QTc intervals reached their circadian peak shortly after awakening, before declining to daytime levels. CONCLUSIONS: The maximal QTc interval over 24 h in normal subjects is longer than heretofore thought. Both QT and QTc intervals are longer during sleep. The QTc interval and QTc variability reach a peak shortly after awakening, which may reflect increased autonomic instability during early waking hours, and the time of the peak value corresponds in time to the period of reported increased vulnerability to ventricular tachycardia and sudden cardiac death. These findings have implications regarding the definition of QT prolongation and its use in predicting arrhythmias and sudden death.

Radiofrequency catheter ablation of atrial flutter: procedural success and long-term outcome.

The objective of this study was to describe the procedural success and clinical recurrences after radiofrequency catheter ablation of atrial flutter. A deflectable catheter with a 4 or 5 mm tip was positioned in the posterior right atrium. Radiofrequency energy was delivered sequentially from the tricuspid annulus to the inferior vena cava. Catheter ablation during 18 sessions for 16 patients resulted in abrupt atrial flutter termination and noninducibility in all patients. Successful sites were near the os of the coronary sinus but had no distinguishing electrographic features. During a follow-up period of 8 +/- 5 months, 4 (25%) patients had recurrence of atrial flutter; 3 of 4 underwent successful repeat ablation. By actuarial analysis, 87% of patients remained in normal sinus rhythm 6 months after the initial procedure. The only distinguishing feature of those with recurrence compared with those whose sinus rhythm was maintained was the induction of nonclinical atrial arrhythmia (50% vs 0%, respectively; p < 0.05). One patient had resolution of presumed tachycardia-related cardiomyopathy. Catheter ablation by an anatomic approach was highly successful in terminating type 1 atrial flutter and was associated with good long-term response. This technique may represent a meaningful alternative for restoration and maintenance of normal sinus rhythm. However, further investigation is warranted to define its clinical role fully.

The P wave signal-averaged ECG.

The P wave signal-averaged electrocardiogram is designed to predict the development of atrial fibrillation. This review will discuss the methodology and summarize the published experience with the P wave signal-averaged electrocardiogram.

Effect of stimulus intensity on atrial refractoriness and sinus node recovery.

INTRODUCTION: Prior studies of sinus node function in man stated that the stimulus intensity of overdrive pacing has no effect on the response of the sinus node to overdrive suppression; however, data documenting these statements were lacking. Previous studies have also suggested that drive train stimulus intensity can alter ventricular refractoriness, but similar studies have not been performed on the human atrium. The purpose of this study was to evaluate the effects of drive train stimulus intensity on atrial effective refractory period and sinus node recovery time. METHODS AND RESULTS: The effect of drive train stimulus intensity on atrial effective refractory period and sinus node recovery time was studied in 42 patients undergoing clinical electrophysiologic tests. The atrial effective refractory period was shorter at 10 mA (221 +/- 20 msec) and 5 mA (232 +/- 25 msec) than at a drive train stimulus intensity of 1.5 times late diastolic threshold (248 +/- 24 msec, P < 0.05 for pairwise comparison). The sinus node recovery time did not demonstrate a similar effect in the baseline state, following beta-adrenergic blockade, or following combined parasympathetic and beta-adrenergic blockade. However, following isolated parasympathetic blockade with atropine, the corrected sinus node recovery time shortened from 88 +/- 51 msec at 1.5 times late diastolic threshold to 48 +/- 55 msec at 10 mA (P < 0.05). Significant variability was present in sinus node recovery time measurements at baseline and following beta blockade; this variability decreased following parasympathetic blockade. CONCLUSION: These data suggest that drive train stimulus intensity can affect the electrophysiologic properties of sinus node and atrial tissue. This effect appears to be mediated by local catecholamine and acetylcholine release and provides further evidence that the interaction between pacing stimuli and the cardiac autonomic system may need to be considered in evaluating electrophysiologic effects.

Atrial and accessory pathway activation direction in patients with orthodromic supraventricular tachycardia: insights from vector mapping.

OBJECTIVES: The purpose of this study was to utilize vector mapping to investigate atrial and accessory pathway activation direction during orthodromic supraventricular tachycardia. BACKGROUND: Although advances have been made in the electrophysiologic evaluation and management of accessory pathways, our understanding of accessory pathway anatomy and physiology remains incomplete. Vector mapping has been validated as a method of studying local myocardial activation. METHODS: In 28 patients with a left-sided or posteroseptal accessory atrioventricular (AV) pathway referred for ablation, atrial and accessory AV pathway activation direction was determined during ventricular pacing or orthodromic supraventricular tachycardia, or both, by summing three orthogonally oriented bipolar electrograms recorded from the coronary sinus to create three-dimensional vector loops. Atrial and accessory AV pathway activation direction was determined in all patients from the maximal amplitude vectors of the vector loops. Because of beat to beat variability in the directions of the vector loops, data from 8 of 28 patients could not be analyzed. RESULTS: At 81 of 83 sites, atrial activation direction along the long axis of the coronary sinus corresponded with the direction suggested by activation time mapping. Activation direction along the anteroposterior and inferosuperior axes was variable, potentially due to variations in the level of the atrial insertion of the accessory AV pathway and in the depth or angling of pathway fibers in the AV fat pad. In eight patients, at least one recording was obtained at the site of an accessory AV pathway potential. Accessory AV pathway activation proceeded superiorly and to the right in seven of eight patients; in one patient with a posteroseptal pathway, accessory AV pathway activation proceeded superiorly and to the left. CONCLUSIONS: 1) Vector mapping is a useful technique for localizing accessory AV pathways; 2) left-sided accessory AV pathways angle from left to right as they traverse the AV groove; and 3) variable activation directions of the atrial myocardium adjacent to the coronary sinus suggest that accessory AV pathway insertion into the atrium differs from patient to patient.

Successful radiofrequency energy ablation of automatic junctional tachycardia preserving normal atrioventricular nodal conduction.

Automatic junctional tachycardia is frequently refractory to medical management and difficult to treat with nonpharmacological methods. A 12-year-old female with symptomatic, refractory automatic junctional tachycardia is reported. Earliest atrial activation during supraventricular tachycardia was in the posterior portion of the intraatrial septum. The patient underwent electrophysiological study and successful radiofrequency current ablation of the ectopic automatic focus within the atrioventricular junction. Normal atrioventricular junctional conduction was maintained, and at 7-month follow-up the patient has been free of tachycardia.

Relation between QT and RR intervals during exercise testing in atrial fibrillation.

The ability to predict the RR-QT relation over a range of heart rates was evaluated in 10 patients with atrial fibrillation (AF) and in 10 control subjects in sinus rhythm. The data from each subject were fitted by regression into 3 QT prediction formulas (the square root formula of Bazett, the cube root formula of Fridericia and the exponential formula of Sarma) applied in standard form and modified with a weighted average of the preceding 5 RR intervals. The goodness-of-fit of each formula was evaluated using mean square residual and Akaike information criterion. For AF, the mean square residuals did not differ among the 3 standard QT prediction formulas (Bazett 624 +/- 274, Fridericia 625 +/- 274 and Sarma 611 +/- 267) and among the 3 modified QT prediction formulas (Bazett 507 +/- 325, Fridericia 496 +/- 255 and Sarma 495 +/- 328). The weighted average modification produced a significant decrease in mean square residuals for all 3 equations (p less than 0.05) in all patients. These findings were confirmed by Akaike information criterion. Goodness-of-fit in sinus rhythm was similar to previously published reports, and significantly better than the fit for AF (p less than 0.0001). For 9 of the 10 patients with AF, sinus rhythm electrocardiograms were obtained and the above regression equations were used to predict QT intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence of hibernating myocardium by a new transesophageal echocardiographic technique.

Reversal of resting wall motion abnormalities after successful coronary angioplasty were documented in a patient with the use of a novel approach to stress testing. Transesophageal stress echocardiography utilizes transesophageal atrial pacing to provoke myocardial ischemia while the left ventricular contractility is being monitored by means of transesophageal echocardiography. The potential use of this technique is illustrated in this report.