Role of electrophysiologic testing in the diagnosis and treatment of patients with known and suspected bradycardias and tachycardias

Endomyocardial biopsy findings in patients with ventricular arrhythmias of unknown origin

To evaluate possible occult myocardial disease in patients with ventricular arrhythmias of unknown origin, over 11 years right ventricular endomyocardial biopsies (EMB) were performed on 80 consecutive such patients (29 Females, 51 Males; median age 42 years). Seventy-one (89%) had ventricular tachycardia or fibrillation, 7 (9%) had complex ventricular arrhythmias, and 2 (3%) had premature ventricular beats. None showed clinical evidence of congestive heart failure or significant coronary artery or valvular disease. Endomyocardial biopsies revealed pathologic changes in 70 out of 80 patients (88%). Of the 70 affected, 39 (56%) had nonspecific changes consistent with cardiomyopathy (e.g., myofiber hypertrophy, interstitial and perivascular fibrosis, and vascular sclerosis); 6 (9%) had active myocarditis (Myo); 7 (10%) had borderline Myo; 7 (10%) had small vessel disease; 6 (9%) had changes consistent with arrhythmogenic cardiomyopathy; 2 (3%) had amyloidosis; 2 (3%) had microfibrillar cardiomyopathy, and one (1.0%) showed intravascular organizing thrombus. Thus, EMB reveals a variety of abnormalities in the majority of patients presenting with ventricular arrhythmias without clinical evidence of structural heart disease.

Ventricular electrophysiology in congestive heart failure and its correlation with heart rate variability and baroreflex sensitivity: a canine model study

AIMS

This study investigated ventricular electrophysiological characteristics and the correlation between these parameters and heart rate variability (HRV) and baroreflex sensitivity (BRS) in a canine congestive heart failure (CHF) model.

METHODS AND RESULTS

Haemodynamics, HRV, BRS, and ventricular electrophysiological variables were measured 4-5 weeks after sham operation (control dogs) and pacemaker implantation, and rapid right ventricular pacing at 240 bpm (CHF group). In the CHF group, significant differences from the control group in ventricular effective refractory period (VERP), monophasic action potential (MAP) duration (MAPD(90)), ventricular late repolarization duration (VLRD), the ratio of VERP to MAPD(90), dispersion of ventricular recovery time (VRT-D), and ventricular fibrillation threshold (VFT) were noted. Both BRS and the time and power domain parameters of HRV were significantly decreased in the CHF group compared with the control group, and a significant, positive correlation between HRV and BRS was identified in the CHF group. Heart rate variability and BRS were negatively and significantly correlated with VLRD and VRT-D, and were positively correlated with VERP/MAPD(90) and VFT in the CHF group.

CONCLUSION

These results suggest that ventricular electrophysiological characteristics correlated with abnormal autonomic nerve function may have important effects on sudden cardiac death. Further research is warranted.

Malignant arrhythmias during strenuous work in four young men

Four young healthy men (17-25 years old) experienced life-threatening arrhythmias during physical exertion. All were successfully resuscitated. One died later. Electrophysiological studies disclosed a lack of normal conduction delay and abnormal His-Purkinje properties indicating congenital malformation of the atrioventricular (AV) node in one patient and the rare and potentially dangerous combination of an accessory AV pathway and intra-atrial conduction delay with liability to dissimilar rhythms and fibrillation in the atria in another. The conduction system functioned normally in the other two. One of the latter two patients had cerebral damage during prolonged resuscitation and experienced repeated epileptic spells until he died unexpectedly. Autopsy revealed scarring of unknown origin in the interventricular septum. The other had stress-induced ventricular ectopy, which gradually diminished and disappeared in a few weeks. The etiology of the latter two is suggested to be ischemia. It is warranted to point out the possible danger of maximal physical strain even in young people.

Atrioventricular nodal conduction during atrial fibrillation: role of atrial input modification

BACKGROUND

Posteroseptal ablation of the atrioventricular node (AVN) has been proposed as a means to slow the ventricular rate during atrial fibrillation (AF). The suggested mechanism is elimination of the AVN "slow pathway." On the basis of the unpredictable success of the procedure, we hypothesize that, in fact, the slow pathway is preserved. Therefore, the slowing of the ventricular rate results from reduced bombardment of the AVN.

METHODS AND RESULTS

In 8 rabbit heart atrial-AVN preparations, cooling of the posterior and/or the anterior AVN approaches revealed nonspecific effects on the slow and fast pathway portions of the AVN conduction curve. In 13 other preparations, simulated AF during posterior cooling (n=6) prolonged the His-His (H-H) intervals but did not reveal specific slow pathway injury. In the remaining 7 preparations, AF was applied before and after posteroseptal surgical cuts. During AF with posterior origin, the cuts resulted in longer mean H-H along with slowing of the AVN bombardment rate. However, there was no change in the minimum observed H-H, suggesting an intact slow pathway. During AF with anterior origin, the mean and the shortest H-H remained unchanged before and after the cuts in all preparations. This was associated with the maintenance of high-rate AVN bombardment.

CONCLUSIONS

Posteroseptal ablation does not eliminate the slow pathway. Ventricular rate slowing can be obtained if the ablation procedure results in a posteroanterior intra-atrial block leading to a reduction of the rate of AV nodal bombardment.

A gastroesophageal electrode for electrophysiological studies

A novel gastroesophageal electrode has been developed capable of atrial and ventricular pacing. We performed electrophysiological studies using the gastroesophageal electrode (Esothoracic) and compared the results with the standard endocardial approach. The flexible polythene gastroesophageal electrode was passed into the stomach under light sedation. Five ring electrodes, now positioned in the lower esophagus were used for bipolar atrial pacing and recording. Ventricular pacing was performed using a cathodic point source on the gastroesophageal electrode tip; the indifferent electrode (anode) was a high impedance chest pad. Parameters of sinus and AV nodal function were obtained by atrial pacing. Programmed ventricular stimulation was performed using a standard protocol. These electrophysiological parameters were subsequently determined using the endocardial approach. There was close correlation between measurements of sinus and AV node function using the two approaches in 48 subjects: sinus node recovery time (SNRT) r2 = 0.70, corrected sinus node recovery time (CSNRT) r2 = 0.87, AV Wenckebach cycle length (AVWCL) r2 = 0.97. The degree of agreement between the two approaches was estimated by the mean difference delta and standard deviation of the difference sigma (SNRT delta = 40 ms, sigma = 257 ms; CSNRT sigma = 14 ms, delta = 164 ms; AVWCL sigma = 7 ms, delta = 16 ms). Programmed ventricular stimulation was performed in 15 of 48 subjects with known or suspected ventricular tachyarrhythmias. Seven had ventricular tachycardia induced using both esothoracic and endocardial programmed ventricular stimulation. One subject was noninducible using esothoracic programmed ventricular stimulation, but inducible at endocardial electrophysiological studies. Another subject was inducible at esothoracic electrophysiological studies, but noninducible using endocardial programmed ventricular stimulation. Six subjects were noninducible using both endocardial and esothoracic programmed ventricular stimulation. The gastroesophageal electrode permits reliable atrial and ventricular pacing without transvenous catheterization or fluoroscopy. Electrophysiological parameters determined using this electrode are similar to those obtained using endocardial stimulation.

Electrophysiological testing of sinus node function: diagnostic and prognostic application-including updated information from sinus node electrograms

Sinus node function, including automaticity, conduction, and refractoriness, can be studied in the human electrophysiology laboratory. This review details the current methods used for such studies and discusses their clinical value. Of special emphasis in this article is the role of sinus node electrography in the clinical laboratory. Included also is an update of the data relating the duration of sinus node depolarization as measure on sinus node electrograms to other parameters that assess sinus node function as well as data supporting the direct relationship between the duration of the sinus node depolarization as the severity of sinus node dysfunction.

Comparison of left ventricular cryolesions created by liquid nitrogen and nitrous oxide

OBJECTIVES

This study was designed to compare the cryosurgical lesions produced by liquid nitrogen (-196 degrees C) and nitrous oxide (-76 degrees C).

BACKGROUND

Cryosurgical ablation is a useful method of arrhythmia surgery, but information on the dimensions of cardiac lesions produced by modifying cryoprobe temperature is limited.

METHODS

We compared the dimensions, volumes and electrophysiologic effects of cryolesions created by a liquid nitrogen cryoprobe (Group I) and a nitrous oxide cryoprobe (Group II) on the left ventricular myocardium in the beating canine heart. Exposure time was compared at 1, 2, 3 and 4 min. In each of 18 dogs, two to four lesions were created on the left ventricle and analyzed: 35 lesions created with use of the nitrous oxide cryoprobe and 30 lesions created with the liquid nitrogen cryoprobe. Lesions were measured at the time of induced death 6 weeks postoperatively and assessed by tissue staining with the Masson trichrome technique.

RESULTS

The volumes (mm3) of the cryolesions created by the liquid nitrogen cryoprobe were significantly larger (p < 0.05) than those of lesions created by nitrous oxide: 826 +/- 163 versus 493 +/- 197 at 1 min; 1,101 +/- 327 versus 666 +/- 185 at 2 min; 1,356 +/- 318 versus 787 +/- 258 at 3 min and 1,735 +/- 534 versus 923 +/- 376 at 4 min.

CONCLUSIONS

Decreasing the temperature of the cryoprobe by using liquid nitrogen increases the volume of the lesions. Programmed electrical stimulation before and 6 weeks after cryoablation indicated no arrhythmogenicity.

A microcomputer-controlled cardiac stimulator

Detailed investigation of abnormal heart rhythms requires electrical stimulators that can deliver sophisticated sequences of stimuli to the heart under controlled laboratory conditions. A dual-channel stimulator that provides an appropriate hardware interface between a controlling microcomputer and the patient is described. The computer gives the system power and flexibility and, most importantly, provides a suitable user interface. The hardware interface is designed to have an ergonomic division between set-up and run-time tasks. Both software and hardware are discussed, and clinical examples of typical usage of the stimulator are given.

Determinants of the ventricular rate during atrial fibrillation

Determinants of the ventricular cycle length during atrial fibrillation were examined in 52 patients. Thirty-three patients had structural heart disease and none had an accessory atrioventricular (AV) connection. The AV node effective and functional refractory periods, the shortest atrial pacing cycle length associated with 1:1 conduction, the AV node conduction time and indexes of concealed conduction in the AV node were measured in the baseline state (36 patients) and after modification of sympathetic tone by infusion of isoproterenol or propranolol (8 patients each). Atrial fibrillation was then induced with rapid atrial pacing, and the mean, shortest and longest ventricular cycle lengths were measured. Variables that correlated most strongly with the mean RR interval during atrial fibrillation were the AV node effective refractory period (r = 0.93; p less than 0.001), AV node functional refractory period (r = 0.87; p less than 0.001) and shortest atrial pacing cycle length associated with 1:1 conduction (r = 0.91; p less than 0.001). The AH interval during sinus rhythm (r = 0.74; p less than 0.001) and during atrial pacing at the shortest cycle length with 1:1 conduction (r = 0.52; p less than 0.001) had weaker correlations. Measures of concealed conduction did not improve the prediction of the mean or longest ventricular cycle length during atrial fibrillation. In conclusion, the refractory periods and conductivity of the AV node are the best indicators of the potential of the node to transmit atrial impulses to the ventricles during atrial fibrillation. The degree of concealed conduction in the AV node is a less important determinant of the mean ventricular rate during atrial fibrillation.

Methodology and instrumentation for the in vitro sinus node recovery time determination

In the present work we describe a methodology and a low-cost instrument to determine the sinus node recovery time (SNRT) in the isolated rat right atrium. The instrumentation measures the SNRT using the continuous pacing method and the method of stimulation with premature pulses. When these methods were compared, we observed that the corrected SNRT (CSNRT = SNRT - the mean spontaneous cycle length, MCL) significantly (p less than 0.001) depended on the method used. The effects of norepinephrine (NE) and acetylcholine (ACh) on MCL and CSNRT were also analyzed. Although both neurotransmitters affected MCL (p less than 0.001), only in the presence of ACh a significant (p less than 0.05) correlation between CSNRT and MCL was found. In both methods, the CSNRT values were quite reproducible. The agreement between the data obtained and the predictions of the theoretical models for in vivo SNRT determination suggests that the present methodology may be useful for studies concerning physical and chemical influences on SNRT, as well as for the development of new stimulation tests.

Time dependence of ventricular refractory periods: implications for electrophysiologic protocols

Cardiac refractory periods are routinely measured during electrophysiologic testing. Informal observations suggested that the effective refractory period lengthened with a prolongation of the time in sinus rhythm (basic cycle length time) between successive runs of drive stimuli (S1S1s). If this were true, failure to control the basic cycle length time could affect the results and interpretation of electrophysiologic testing. To study this phenomenon, the effective refractory period was studied in 20 patients during sinus rhythm and two ventricular paced rates with up to three extrastimuli, while varying the basic cycle length time from 2 to 3, to 10 to 20 s. With each of the stimulation sequences used, the effective refractory period lengthened as the basic cycle length time increased ("basic cycle length time-effective refractory period effect"). The effect was most pronounced when extrastimuli were used during the two ventricular paced rates. As the basic cycle length time increased from 2 to 3 to 20 s, the mean effective refractory period determined during sinus rhythm increased from 296 to 300 ms; with the first ventricular paced rate, the effective refractory period increased from 259 to 272 ms (p less than 0.0003) and with the second ventricular paced rate, the effective refractory period increased from 250 to 263 ms (p less than 0.01). The basic cycle length time-effective refractory period effect became more pronounced as the number of extrastimuli increased. With the second ventricular paced rate, as basic cycle length was increased from 2 to 3 to 20 s, the mean prolongation in the cumulative effective refractory period (S1 to final extrastimulus) as the number of extrastimuli increased from 1 to 2 to 3, was 13 (p less than 0.01), 42 (p less than 0.0003) and 82 ms (p less than 0.001), respectively. Results were confirmed in 17 instances by redetermining the effective refractory period at the 2 to 3 s basic cycle length time after the final 20 s basic cycle length time determination, and demonstrating that it was similar to the effective refractory period after the initial 2 to 3 s basic cycle length time. No further prolongation of the effective refractory period could be demonstrated by increasing basic cycle length time from 20 to 60 s, and no significant effect of medications on the basic cycle length time-effective refractory period effect could be demonstrated.

Tachycardia control with cardiac pacemakers

Techniques used to treat tachyarrhythmias with brief electrical impulses are described. The disease process is described, identifying the prevention of one of the three conditions required for reentry (which provides the mechanism for most electrically convertible rhythms) as the basis for therapy. The risk of inducing fibrillation is discussed. The four major pacing techniques used to treat tachycardia are described. The first technique involves using additional pacemaker pulses to establish the appropriate conditions permitting interruption of the tachycardia. The second technique, which permits adaptation to the variations in tachycardia characteristics, is scanning. Scanning changes the intervals on successive bursts in an interactive process, allowing a series of paced intervals to be tested. The third technique is usually called an adaptive or automatic technique. The final technique is ramp pacing, which allows extrastimuli to be introduced at progressively premature intervals within a burst of stimuli.

Comparison of endocardial and epicardial programmed stimulation for the induction of ventricular tachycardia

Twenty-seven patients who had pairs of stainless steel wire electrodes placed on the right and the left ventricle during cardiac surgery underwent both epicardial and endocardial programmed ventricular stimulation to assess the inducibility of ventricular tachycardia. Twenty-six of the patients had coronary artery disease and were studied to evaluate map-guided surgery for treatment of ventricular arrhythmias. Burst ventricular pacing and up to three ventricular extrastimuli coupled to two drive train cycle lengths were delivered from the right and left ventricular epicardial wire electrodes and from endocardial catheter electrodes placed at the apex and outflow tract of the right ventricle. Ventricular tachycardia was reproducibly induced in three patients by both endocardial and epicardial stimulation. In one patient ventricular tachycardia was reproducibly induced by epicardial stimulation, but nonreproducible, nonsustained ventricular tachycardia was induced by endocardial stimulation. Ventricular tachycardia remained inducible by both endocardial and epicardial stimulation in three instances (two patients) during drug therapy. A negative study (less than 10 consecutive ventricular beats induced) was obtained in 23 patients by both endocardial and epicardial stimulation. The patients were followed up for 12 to 43 months (average 31). Sudden death or documented ventricular tachycardia occurred in two of the three patients with a positive study by both endocardial and epicardial stimulation. Nineteen (83%) of the 23 patients with concordantly negative studies remained free of arrhythmias. On the basis of concordant results of endocardial and epicardial stimulation (p = 0.001) these results suggest that epicardial stimulation of the right and the left ventricle is an acceptable method to assess the postoperative inducibility of ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

On-line interval measurement during invasive cardiac electrophysiologic testing

A microprocessor-based timer has been developed for routine and research use in cardiac electrophysiologic studies. The cycle length (A-A) and the conduction times through the right atrium (A(HRA)-A(HIS], the AV node (A-H) and the His-Purkinje system (H-V) can be automatically measured beat-to-beat in real-time both during sinus rhythm and during atrial pacing. The design has been refined during three years of use in over 80 clinical studies. A comparison between manual and automatic measurements has been executed for randomly chosen portions of 10 studies. With the manual measurements as reference procedures the sensitivities of the automatic measurements of the A, H and V waves were 0.98, 0.88 and 0.92, respectively, while the specificities were 0.93, 0.92 and 0.93, respectively. For the true positive measurements the correlation coefficients of the intervals were r(A-A) = 0.9998, r(A-H) = 0.987 and r(H-V) = 0.988. The statistical analysis of the differences between manual and automatic readings for the intervals A-A, A-H and H-V yielded mean values of -1 ms, -0.8 ms and 0.6 ms and standard deviations of 3 ms, 4 ms and 4 ms which are smaller than the accuracy of the common manual measurements.

Long-term efficacy of antitachycardia pacing for supraventricular and ventricular tachycardias

Over a 14-year period, 53 patients received implanted pacemakers to assist in the control of recurrent tachycardias. Indications were: prevention of tachycardia in 2 patients with supraventricular tachycardia (SVT), and 4 with ventricular tachycardia (VT); termination of tachycardia (15 SVT, 20 VT); and long-term periodic programmed electrical stimulation with potential for tachycardia termination (12 VT). Pacemakers for prevention of VT were implanted in 3 patients with prolonged QT interval syndromes and 1 in whom Holter monitoring showed a significant reduction in ectopic activity during pacing. Pacers were implanted for tachycardia termination only after patients underwent a rigorous protocol aimed at achieving 100 trials of the proposed modality. Patients with tachycardia also requiring antibradycardia pacemakers received pacemakers capable of noninvasive programmed stimulation for use during follow-up. There were no tachycardia recurrences among those patients in whom pacemakers were implanted for prevention. Pacers capable of outpatient programmed stimulation were useful, and it may be desirable to expand their use. The 15 patients with pacers designed for termination of SVT were followed for a mean of 68 months. Among these, actuarial continuation of pacing efficacy was 93% at 1 year, and 78% at 5 years. The 20 patients with pacers for termination of VT were followed for a mean of 37 months. Actuarial efficacy was 78% at 1 year, and 55% at 5 years. Sudden death occurred in 4 of these patients, none clearly pacer related. Pacemakers can play a major therapeutic role in some patients with recurrent tachycardias. The role of such pacemakers in patients with VT may be expanded with the advent of combined pacer-defibrillators.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnostic and prognostic implications of recurrences in patients with syncope

The incidence and the diagnostic and prognostic implications of recurrences in 433 patients enrolled in a prospective syncope study are reported. Over a mean follow-up of 30 months, 146 patients had recurrent syncope. Patients with an initial diagnosis of a cardiovascular cause of syncope had a recurrence rate of 31 percent, patients with a noncardiovascular cause had a recurrence rate of 36 percent, and patients with syncope of unknown origin had a recurrence rate of 43 percent at three years (these differences were not significant; the minimum for any two-way comparison was p greater than or equal to 0.11). In eight of the 191 patients in whom a cause of syncope could not be found on initial evaluation, a diagnosis was assigned in follow-up after recurrent syncope. Recurrences led to major morbidity in eight of 146 patients (5 percent) and minor trauma in 10 patients (7 percent). Using recurrence as a time-dependent variable in the Cox models, it was found that this variable was not a significant predictor of overall mortality or sudden death. It is concluded that recurrences are common in patients with syncope, but new diagnosis are rarely established on the basis of evaluation of recurrences. Recurrences are not predictors of mortality or sudden death.

Disopyramide-pyridostigmine interaction: selective reversal of anticholinergic symptoms with preservation of antiarrhythmic effect

This double-blind, randomized, placebo crossover study was used to evaluate the effects of a cholinesterase inhibitor--slow-release pyridostigmine (180 mg orally every 12 hours)--on the anticholinergic and antiarrhythmic properties of disopyramide. Quantitative side effects questionnaire scores were used to guide disopyramide administration in 20 men with ventricular tachycardia. Disopyramide was given to each patient both with placebo and with active pyridostigmine. The maximal administered dose for each regimen was used in conjunction with corresponding questionnaire scores to calculate an index or estimate of the maximal tolerable dose of disopyramide. Additional evaluations performed at baseline and at each maximal administered dose regimen included tear and saliva quantitation, 24 hour electrocardiogram (ECG), exercise testing and programmed ventricular stimulation. Results showed that the maximal administered dose of disopyramide was greater with active pyridostigmine than with placebo: 295 +/- 75 versus 245 +/- 100 mg every 6 hours (p less than 0.05). The calculated maximal tolerable dose was substantially greater in the presence of pyridostigmine: 355 +/- 90 versus 260 +/- 115 mg every 6 hours (p less than 0.001). Maximal side effects questionnaire scores also reflected decreased anticholinergic activity in the presence of pyridostigmine compared with placebo: 101.9 +/- 2.2 versus 104.6 +/- 2.8, respectively (p less than 0.005). Baseline tear and saliva production was significantly reduced during disopyramide therapy, but was restored toward normal by the addition of pyridostigmine.(ABSTRACT TRUNCATED AT 250 WORDS)

Antiarrhythmic effects of VVI pacing at physiologic rates: a crossover controlled evaluation

Ventricular pacing can prevent bradycardia-dependent ventricular ectopic activity (VEA) and is helpful in some cases of drug-refractory ventricular tachycardia (VT). This study is a prospective evaluation of VVI pacing for the control of VEA not related to underlying bradycardia, drug side-effects, or prolonged QT interval syndromes. Twenty-nine patients undergoing serial electrophysiologic-pharmacologic testing for VT control were studied. Eighteen of these patients (12 men; mean age = 60.1) both completed the protocol and had sufficient VEA for analysis. Coronary disease was present in 13 patients, cardiomyopathy in two patients, and one patient each had myocarditis, mitral valve prolapse, and no structural heart disease. Ambulatory (Holter) monitor recordings during VVI pacing were compared with control recordings made in the absence of pacing. VVI pacing rates were 10-15 bpm above the mean daily heart rate (mean = 92 bpm; range = 63-110). Hours from paced recordings were paired with hours from control (prior to analysis) according to time of day to reduce the effects of spontaneous variability in VEA frequency. Overall, VVI pacing reduced ventricular premature complexes (VPCs) 26% from 331 to 245/hour (p less than 0.001). During pacing, couplets (pairs, successive VPCs) were reduced from 6.95 to 1.03/hour (p less than 0.000001) and VT (greater than or equal to 3 successive VPCs) from 0.89 to 0.045 episodes/hour (p less than 0.003). Of 13 patients with couplets, 11 had greater than or equal to 50% reduction and five had greater than or equal to 90% reduction. Baseline VT was eliminated in four out of nine patients during pacing. Pacing did not increase VEA significantly in any patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Susceptibility to atrial fibrillation and ventricular tachyarrhythmia in the Wolff-Parkinson-White syndrome: role of the accessory pathway

Clinical and electrophysiologic characteristics associated with spontaneous and inducible atrial fibrillation and ventricular tachyarrhythmia were assessed in 20 consecutive patients with Wolff-Parkinson-White (WPW) syndrome undergoing surgical division (n = 12) or transcatheter electrical ablation (n = 8) of accessory pathways. Patients with spontaneous atrial fibrillation were characterized by the trend (not significant) of a shorter antegrade accessory pathway effective refractory period (256 +/- 26 vs 303 +/- 109 msec). However, patients with and without spontaneous atrial fibrillation did not differ with respect to prevalence of structural heart disease (3 of 11 vs 2 of 9), intra-atrial conduction time (34 +/- 10 vs 32 +/- 10 msec), or interatrial conduction time (86 +/- 21 vs 88 +/- 17 msec). Thus, atrial and accessory pathway electrophysiologic properties (per se) were not clear determinants of susceptibility to atrial fibrillation. Among the 20 patients, 10 to 35 beats of nonsustained ventricular tachycardia (seven patients) or ventricular fibrillation (three patients) were induced at electrophysiologic study with one to three programmed extrastimuli. Clinically, a ventricular arrhythmia (ventricular fibrillation during atrial fibrillation) had occurred in only one of these patients. The discordance of these observations was significant (p less than 0.01). Patients with and without inducible ventricular arrhythmias were not distinguished by clinical factors or by electrophysiologic properties of the accessory pathway or ventricles. Accessory pathway conduction was completely or partially eliminated by ablation procedures in 14 of 20 patients. During a mean follow-up of 27 months, atrial fibrillation recurred in two patients with failed ablation procedures and in one patient with left atrial enlargement (despite accessory pathway division) (p = 0.019 vs pre-ablation). Ventricular arrhythmias remained inducible in two patients in whom accessory pathway ablation failed (p = 0.01 vs initial study). However, spontaneous ventricular tachyarrhythmias did not occur during follow-up. We conclude that susceptibility to spontaneous or inducible atrial fibrillation and ventricular tachyarrhythmia in patients with WPW syndrome and no organic heart disease depends primarily on the existence of a functional accessory pathway. These susceptibilities are eliminated by interruption of accessory pathway conduction. Ventricular tachyarrhythmias remain infrequent spontaneous events in the WPW syndrome. Their more frequent induction at electrophysiologic study is not predictive of clinical occurrence.

Programmed electrical stimulation studies for ventricular tachycardia induction in humans. II. Comparison of indwelling electrode catheter and daily catheter replacement

Suppression of the ability to induce ventricular tachycardia by programmed electrical stimulation during serial drug testing has been used as a therapeutic end point to identify long-term prophylactic antiarrhythmic therapy. However, ventricular tachycardia induction, particularly with an indwelling electrode catheter, has not been systematically assessed over the time period required for serial drug testing. In this study, the results of programmed electrical stimulation were evaluated daily during serial drug-free conditions before testing various antiarrhythmic drugs. Twenty-four patients were randomly allocated to be studied with the electrode catheter left in place or replaced daily. All patients had inducible sustained ventricular tachycardia during the first study. Loss of the ability to induce ventricular tachycardia occurred in 8 of 13 patients whose catheter was left in place whereas this did not occur in patients whose catheter was replaced daily (p less than 0.01). In addition, use of an in situ catheter was accompanied by significant (p less than 0.05) changes in other electrophysiologic measurements, including number of extrastimuli required to induce ventricular tachycardia and length of ventricular functional and effective refractory periods. The serial changes seen with indwelling catheters in the drug-free state may mimic effective antiarrhythmic drug action.

Value of physical and pharmacological tests in predicting intrinsic and extrinsic sick sinus syndrome

We studied 13 patients with sick sinus syndrome using various physical (postural reflex testing. Valsalva manoeuvre, carotid sinus massage), pharmacological (intravenous isoprenaline, atropine, neostigmine and total autonomic blockade) and electrophysiological tests in order to identify simple non-invasive markers of intrinsic sick sinus syndrome. Following autonomic blockade, 6 patients had normal and the remaining 7 had an abnormal intrinsic heart rate. Electrophysiological testing revealed abnormal sinus node parameters in 8 (62%) subjects in the basal state and 11 (85%) after autonomic blockade. Carotid sinus massage was abnormal in all patients (100%) with an abnormal intrinsic heart rate, and in only 2 of the 6 (33%) with normal intrinsic heart rate (P less than 0.05). The heart rate response to isoprenaline was abnormal in 5 of the 6 (83%) patients with normal as compared to only 1 of the 7 with abnormal intrinsic heart rate. With isoprenaline there was a significantly (P less than 0.05) higher increase in heart rate in patients with abnormal as compared to those with normal intrinsic heart rate. The other physical and drug tests were not helpful to differentiate between intrinsic and extrinsic mechanisms. Thus, carotid sinus massage and, to some extent, isoprenaline administration appear simple bedside tests which may be helpful in identifying the underlying mechanism of sick sinus syndrome.

Syncope in the elderly

This report describes the evaluation of syncope in 210 elderly patients as compared with 190 younger patients. The elderly group had a mean age of 71 years (range 60 to 90) and the younger group had a mean age of 39 years (range 15 to 59). A cardiovascular cause was found in 33.8 percent of the elderly and in 16.8 percent of the young (p = 0.0001), a noncardiovascular cause in 26.7 percent of the elderly and 37.9 percent of the young (p = 0.02), and unknown cause in 38.5 percent of the elderly and 45.3 percent of the young (NS). Prolonged electrocardiographic monitoring established the diagnosis in 17 percent of the elderly but in only 8 percent of the young (p = 0.008). Syncope resulted in trauma in 39 percent of the elderly and in 32 percent of the young, but the elderly more often had major trauma. The two-year overall mortality was 26.9 +/- 3.4 percent in the elderly and 8.3 +/- 2.1 percent in the young (p less than 0.0001). The overall mortality and incidence of sudden death in the elderly with a cardiovascular diagnosis were similar to those in the young; however, in the elderly with a noncardiovascular diagnosis and syncope of unknown cause, the mortality and incidence of sudden death were higher. Multivariate analyses using mortality and sudden death as endpoints revealed that a cardiovascular cause of syncope was a very strong risk factor. In patients with a noncardiovascular cause or unknown cause of syncope, a history of congestive heart failure, older age, and male sex are important prognostic factors.

Syncope as a symptom. A practical approach to etiologic diagnosis

Etiologic diagnosis of syncope is best approached within the framework of three categories: cardiovascular, noncardiovascular, and unexplained. A meticulous history and physical examination plus screening laboratory studies will pinpoint a cause in nearly half of cases. In patients who have recurrent syncope, a history suggestive of dysrhythmia, or structural heart disease, further testing may include a variety of procedures such as 24-hour electrocardiographic monitoring, two-dimensional echocardiography, exercise stress testing, and electrophysiologic testing.

Comparison of ramp and stepwise incremental pacing in assessment of antegrade and retrograde conduction

Conventional assessment of antegrade (AV) and retrograde (VA) conduction involves stepwise increments in pacing rates until block in conduction is observed. This study was designed to establish the comparative characteristics of ramp pacing, in which the rate is continuously and smoothly incremented until block occurs. Two hundred and ten patients participated in portions of this study. Stepwise pacing was performed in 10 beat/minute steps, with the rate held for at least 15 seconds at each step; if marked prolongation or variability in conduction was observed, the rate was held constant for up to 60 seconds to allow for accommodation. With ramp pacing, the rate was gradually increased at a steady 2-4 beats/minute/second. Whenever possible, both stepwise and ramp pacing were performed for assessment of both antegrade and retrograde conduction. All patients had conducted sinus rhythm as their baseline mechanism. Antegrade conduction was similar using incremental stepwise and ramp pacing. The AH interval at a cycle length (CL) of 500 ms, the maximum AH increment, the cycle length at AV block were all remarkably similar (p = NS). Assessment of retrograde conduction produced similar results, with insignificant differences between maximum conducted VA intervals, and cycle length at VA block using the two pacing techniques. Ramp pacing provides a useful and rapid alternative to conventional stepwise incremental pacing in the assessment of antegrade and retrograde conduction in patients using both normal and accessory pathways. Ramp pacing was better tolerated, and some correlations between antegrade and retrograde conduction were stronger with the ramp pacing technique.

The anticholinergic side effects of disopyramide and controlled-release disopyramide

Until now, the potential antiarrhythmic benefits of disopyramide have been restricted by anticholinergic side effects. These side effects have included xerostomia (dry mouth, nose or eyes), abdominal discomfort, nausea, constipation and, most importantly, urinary hesitancy and retention. A sustained-release form of pyridostigmine, an acetyl-cholinesterase inhibitor, has been shown to a) prevent the anticholinergic side effects of disopyramide when used prophylactically and b) to eliminate or attenuate these symptoms if they are already present. Pyridostigmine has no measurable effect on disopyramide's antiarrhythmic properties. This represents a beneficial new drug interaction which will improve tolerance of disopyramide and increase patient compliance with disopyramide-containing regimens.

The value of electrophysiologic studies in syncope of undetermined origin: report of 150 cases

A prospective study examined the diagnostic yield and therapeutic efficacy of electrophysiologic studies in patients with SUO. We defined SUO as those syncopal or near-syncopal events remaining unexplained after a standardized, noninvasive evaluation that included a history, physical examination, routine laboratory screening, EEG, nuclear brain scan or CAT scan, 12-lead ECG, chest x-ray, orthostatic vital signs, bedside carotid sinus massage, and at least 24 hours of continuous ECG monitoring. The 150 SUO patients included 95 men and 55 women (mean age 62.0 years); 35 had recurrent SUO, 75 (50%) had organic heart disease, and 129 (86%) had abnormal ECGs. There were 162 abnormal electrophysiologic findings that could explain the SUO uncovered in 112 patients, a diagnostic yield of 75%: one finding in 71 patients, two findings in 32, and three findings in nine. These findings were: His-Purkinje disease in 49 patients (30%), inducible ventricular arrhythmias in 36 (22%), AV nodal disease in 20 (12%), sinus node disease in 19 (12%), inducible supraventricular arrhythmias in 18 (11%), carotid sinus hypersensitivity (not elicited by carotid sinus massage prior to electrophysiologic studies) in 15 (9%), and hypervagotonia in five (3%). When electrophysiologic study findings were classified as clearly abnormal or borderline, 54 patients had at least one clearly abnormal finding, a diagnostic yield of 36%. Subgroups of patients presenting with only a single SUO event, no evidence of organic heart disease, or normal baseline ECGs all had substantial diagnostic yields during electrophysiologic studies. Follow-up data in 137 patients (91%) (mean 31 months) showed recurrences in 16 of 34 patients (47%) without and 15 of 103 patients (15%) with electrophysiologic findings despite therapy directed by electrophysiologic testing (p less than 0.0005). This study and a review of the literature indicate that electrophysiologic testing is useful in elucidating the causes of SUO and directing therapy. A significant number of patients benefit from electrophysiologic studies, even when only clearly abnormal findings are considered diagnostic, when only a single syncopal event has occurred, or whether or not organic heart disease or an abnormal ECG is present.

Nonsustained ventricular tachycardia during programmed ventricular stimulation: criteria for a positive test

Controversy persists among groups carrying out programmed ventricular stimulation (PVS) as to which criteria should be used to define a positive test. To examine this question, the results of PVS carried out in 50 patients with documented sustained ventricular tachycardia (VT) or ventricular fibrillation were retrospectively analyzed. All patients underwent serial PVS using single and double extrastimuli and ventricular burst pacing in the right ventricle and, when necessary, the left ventricle, with sustained VT elicited during the control study in each patient. Antiarrhythmic drugs were then administered, with therapy tailored to both PVS result and ambulatory Holter monitoring, when possible. All patients were maintained and followed on the same drugs and dosages as at the time of predischarge PVS. After mean 20 months follow-up, 28 patients either died suddenly (8 patients) or had documented sustained VT (20 patients). The ability to induce nonsustained or sustained VT on predischarge PVS was associated with a significantly higher likelihood of subsequent sudden death or VT recurrence than if VT could not be induced (p less than 0.001). In addition, using the criterion of 5 or more beats of induced VT to define a positive study maximized the predictive value of PVS and provided a significantly higher predictive accuracy than if only sustained VT were used to define a positive study.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid sinus massage. Its diagnostic and therapeutic value in arrhythmias

Carotid sinus massage is a simple bedside maneuver that helps to clarify the type and sometimes also the mechanism of different rhythm disturbances. The major indication for carotid sinus massage is the diagnosis of tachyarrhythmias in which the atrial activity is either absent or intermittently present. Carotid sinus massage is also useful in some patients with normal heart rates; increased vagal tone may normalize a bundle branch block or localize the site of type I second-degree atrioventricular block and can be used for evaluation of the sensing function of permanent pacemakers. Carotid sinus massage is also an important diagnostic procedure in patients with suspected hypersensitivity of the carotid sinus. Massage of the carotid sinus is contraindicated in patients with diseased carotid arteries because of the risk of cerebrovascular accident. In rare instances, carotid sinus massage may initiate ventricular tachycardia.

Cardiac electrophysiologic testing: its role in the selection of antiarrhythmic drug regimens for supraventricular and ventricular arrhythmias

Cardiac electrophysiology studies use intracardiac recording and programmed stimulation to define the mechanisms and most appropriate therapy for supraventricular and ventricular arrhythmias. Using these techniques, the majority of clinical tachycardias can be reproducibly initiated and terminated in the electrophysiology laboratory, thereby allowing the most appropriate therapy to be selected. With this approach, antiarrhythmic agents can be tested in a systematic, serialized fashion for efficacy, safety and patient tolerance. With both supraventricular and ventricular tachycardias, suppression of arrhythmia induction predicts freedom from recurrence, whereas inducibility carries a poor prognosis in clinical follow-up. Electrophysiology studies provide a safe and effective approach to the treatment of selected patients with cardiac arrhythmias.