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.

Combination of procainamide and quinidine for better tolerance and additive effects for ventricular arrhythmias

The efficacy and tolerance of quinidine and procainamide used individually and in combination were studied in 19 patients with frequent ventricular premature complexes (VPCs). During single-drug treatment, the maximum tolerated dose of quinidine without extracardiac dose-related side effects was 1.6 +/- 0.21 g/day and that of procainamide was 4.1 +/- 1.05 g/day. During combination therapy with smaller doses (p less than 0.05) of quinidine (1.16 +/- 0.26 g/day) and procainamide (2.80 +/- 0.98 g/day), no patient had side effects. Before treatment, all patients had frequent (more than 60 per hour) VPCs and 17 had ventricular tachycardia on Holter monitoring. The frequency of VPCs was reduced to 22 +/- 19% with quinidine, 47 +/- 40% with procainamide and 9 +/- 11% with combination therapy (p less than 0.05, combination vs procainamide or quinidine alone). Individually, an effective regimen (more than 83% reduction of VPCs and abolition of ventricular tachycardia) was found in 5 patients (26%) receiving quinidine alone at maximal tolerated dose, in 4 (21%) receiving procainamide alone at maximal tolerated dose, and in 14 (74%) receiving combination therapy (p less than 0.01 vs quinidine or procainamide). Thus, the antiarrhythmic effects of quinidine and procainamide are additive. When quinidine or procainamide are additive. When quinidine or procainamide is ineffective because dose-related extracardiac side effects limit the maximal tolerated dose, combination therapy in smaller and tolerable doses avoids side effects and is more effective than either drug alone at the maximal tolerated dose.

Prediction of sudden death and spontaneous ventricular tachycardia in survivors of complicated myocardial infarction: value of the response to programmed stimulation using a maximum of three ventricular extrastimuli

The prognostic significance of ventricular arrhythmias induced by programmed electrical stimulation was evaluated in 50 survivors of acute myocardial infarction complicated by a major new conduction disturbance (38 patients), congestive heart failure (33 patients) or sustained ventricular tachyarrhythmias (22 patients), alone or in combination. Programmed stimulation was performed in patients in stable condition 7 to 36 days (mean 16) after infarction using one to three extrastimuli at four times diastolic threshold at a maximum of two right ventricular sites. Two groups were identified by the response to programmed stimulation: 17 patients with sustained (greater than 15 seconds) or nonsustained (greater than 7 beats but less than or equal to 15 seconds) ventricular tachycardia (group I), and 33 patients with 0 to 7 intraventricular reentrant complexes in response to maximal stimulation efforts (group II). Group I patients had a higher incidence of anterior infarction than that of patients in group II (71 versus 42%), had lower left ventricular ejection fraction (mean 0.35 versus 0.48) and were more often treated with antiarrhythmic drugs (47 versus 18%, p less than 0.05). There were no significant differences between groups in the occurrence of congestive failure, new conduction disorders or sustained ventricular arrhythmias with infarction, or in the proportions treated with a beta-receptor blocking agent, coronary bypass grafting or a permanent pacemaker. Total cardiac mortality was 24% during a mean follow-up period of 23 months and did not differ between groups; however, the response to programmed stimulation identified a group at high risk of late sudden death or spontaneous ventricular tachycardia: 7 (41%) of 17 group I patients compared with 0 of 33 group II patients (p less than 0.001). The induction of sustained or nonsustained ventricular tachycardia identified all patients who died suddenly or had spontaneous tachycardia (sensitivity 100%), but triple extrastimuli were required to induce prognostically significant arrhythmias in five of these seven patients; the specificity of this protocol was only 57%. When the clinical variables of the group were evaluated individually, the response to programmed stimulation had a stronger association with occurrence of late sudden death than did any other factor (Fisher's exact test, p less than 0.001); however, a type II error could not be excluded.(ABSTRACT TRUNCATED AT 400 WORDS)

Activation mapping in patients with coronary artery disease with multiple ventricular tachycardia configurations: occurrence and therapeutic implications of widely separate apparent sites of origin

Catheter or intraoperative activation mapping studies, or both, were performed in 17 patients with coronary artery disease with two to four distinct configurations of ventricular tachycardia, resistant to a mean of 12.1 +/- 6.0 antiarrhythmic drug trials per patient. Mapping studies were performed to guide anticipated surgical ablation of arrhythmias. Activation map data were adequate to determine sites of origin of 30 (64%) of 47 observed tachycardia configurations. These 30 ventricular tachycardias (26 observed clinically) were mapped to 22 separate endocardial sites of origin. Sites of origin of distinct tachycardias were identical or closely adjacent (within 3 cm) in six patients and widely separate (greater than or equal to 4 cm) in eight patients (47% of the group). Activation maps were not adequate to determine sites of origin of 17 (36%) of the 47 tachycardias, including all configurations in three patients. Fifteen patients underwent surgery for control of ventricular tachycardia: aggressive, map-guided endocardial resection (mean 26.5 +/- 14.2 cm2) in 12 patients with identified sites of tachycardia origin and extensive resection of visible endocardial scar (2 patients) or encircling endocardial ventriculotomy (1 patient) in those in whom the sites of origin of all clinical tachycardias remained undetermined. Two inoperable patients were treated with amiodarone. During postoperative electrophysiologic tests (11 of 13 surgical survivors), ventricular tachyarrhythmias were initially uninducible in only 4 of 11 patients. However, in two patients only nonclinical arrhythmias (ventricular flutter) were induced. Six (21%) of 29 clinical tachycardias whose sites of origin were either not determined or not resected (right septum or papillary muscle) remained inducible in five patients. Using previously ineffective antiarrhythmic drugs, initially inducible arrhythmias became uninducible (two patients), or harder to induce than preoperatively (five patients). As a result of surgical resections alone or in combination with previously ineffective drugs (and amiodarone in two inoperable patients), there were no recurrences of ventricular tachycardia in 14 (93%) of 15 patients discharged during 19.0 +/- 14.3 months of follow-up study. Thus, activation mapping may commonly reveal separate apparent sites of origin for clinically observed, morphologically distinct, highly drug-refractory ventricular tachycardias in patients with coronary artery disease with multiple tachycardia configurations. Extensive surgical resection of identified sites of origin may be required to ablate arrhythmias in these patients.(ABSTRACT TRUNCATED AT 400 WORDS)

Disopyramide-pyridostigmine: report of a beneficial drug interaction

A previously unrecognized beneficial drug interaction is described. Without affecting the antiarrhythmic properties of disopyramide, a sustained-release form of pyridostigmine (a cholinesterase inhibitor) was shown to prevent completely anticholinergic side effects in a study population (17 patients), whereas side effects occurred in 26 of 89 patients (29%) in a control group (p less than 0.025). Pyridostigmine also diminished or abolished disopyramide-induced anticholinergic side effects in each of 10 patients in whom they were already present. Pyridostigmine allowed an increase in tolerated disopyramide blood levels (4.53 +/- 1.59 micrograms/ml versus 3.85 +/- 1.78 micrograms/ml) and a significant increase in disopyramide dosages (224 +/- 68 mg versus 188 +/- 68 mg every 6 h) (p less than 0.02). No patients suffered side effects from pyridostigmine. These data suggest that pyridostigmine can be used to prevent as well as to treat the anticholinergic side effects of disopyramide. The usefulness of disopyramide has previously been limited by these anticholinergic side effects. Further investigation is in progress to determine what role pyridostigmine can play in making disopyramide therapy available to patients who otherwise could not benefit from its use.

Pacing for ventricular tachycardia

Many problems remain to be solved before implanted pacers can assume a major role in the treatment of ventricular tachycardia. Case histories are cited to illustrate some of the difficulties to be overcome. Possible mechanisms for the success and failure of antitachycardia pacing are reviewed. Prospects for antitachycardia pacing will increase with the advent of cardioverter/defibrillator back-up.

Implantation of automatic cardioverter-defibrillators via median sternotomy

15 AICD (automatic implantable cardioverter-defibrillator) Model B units were implanted in 10 patients. The median sternotomy is our preferred surgical approach using a right atrial patch electrode, a left ventricular apex patch electrode, and two closely placed epicardial sensing electrodes. Follow-up is 109 patient months and all patients are alive. AICD units discharged for ventricular tachycardia, ventricular flutter, and ventricular fibrillation. Discharges also occurred for sinus tachycardia and atrial fibrillation above the rate limit in three units. Premature pulse generator depletion has occurred in four AICD-B units 3 to 18 months postimplant and appears due to a defect in original battery design. Discharge of the AICD for supraventricular tachycardia is a problem that will remain until a better means of differentiating supraventricular tachycardia from ventricular tachyarrhythmias is found. The AICD appears to prevent sudden death from ventricular tachyarrhythmias.

Attempted nonsurgical electrical ablation of accessory pathways via the coronary sinus in the Wolff-Parkinson-White syndrome

Previous canine experiments suggested that transvenous catheters placed in the coronary sinus could be used to deliver limited energy shocks, resulting in fibrosis in the atrial wall and coronary sulcus with sparing of the coronary artery. From the distribution of the fibrosis, it appeared that this approach could be used for attempted ablation of accessory pathways in patients with the Wolff-Parkinson-White syndrome. Eight patients with symptomatic Wolff-Parkinson-White syndrome underwent electrophysiologic testing with attempted ablation of 10 accessory pathways. Shocks were limited to 40 to 80 J, except in one patient who received shocks of 100 and 150 J. From 2 to 26 shocks were given to each accessory pathway. All the accessory pathways were blocked completely immediately after the shocks. Subsequently, evidence of accessory pathway conduction recurred in each patient. Three had early promise of long-term improvement after the procedure, with prolongation of the refractory periods of the accessory pathways during the remainder of the initial hospitalization. Several weeks later, however, there was evidence of return toward original values in two of these. Another patient who appeared not to benefit during her initial hospitalization returned 7 weeks later with very depressed accessory pathway conduction, possibly due to developing fibrosis. The only significant complication occurred in the patient receiving shocks of 100 and 150 J; he had apparent rupture of the coronary sinus requiring pericardial drainage. In two patients in whom nonsurgical ablation was not successful, intraoperative mapping showed that the accessory pathway was located in an area of fibrosis at the site of the attempted ablation. In summary, nonsurgical electrical ablation of accessory pathways via the coronary sinus may be successful using limited energy levels in a few patients. The procedure remains experimental, and widespread application must await more effective means of delivering the shocks.

DDD/DDT pacemakers in the treatment of ventricular tachycardia

The possibility of adapting multimode dual-chamber pacemakers for programmed and burst stimulation was explored in a group of patients with ventricular tachycardia. The potential usefulness and pitfalls of these pacemakers were exemplified in one patient, presented in detail. The implanted DDD pacemaker was programmed to an all-synchronous mode (DDT), permitting programmed ventricular stimulation through synchronization with chest wall stimulation provided by a standard external programmable stimulator. With the ventricular sensing refractory period shortened to 200 ms, both programmed electrical stimulation and burst pacing for termination of induced tachycardias were possible. When medications failed to offer protection against the patient's tachycardias, the ventricular sensing refractory period (and minimum stimulation interval) was increased to 300 ms, thereby permitting burst pacing at up to 200 beats/minute for termination of spontaneous episodes. After many trials to confirm the efficacy of such stimulation, and the lack of muscle potential triggering, the patient was discharged home with the pacemaker in the DDT mode. He was instructed to go to his local emergency room, and was equipped with a portable device to trigger his implanted unit. Subsequently, the patient had successful termination of several spontaneous episodes of ventricular tachycardia in an emergency room. Later, he began to experience palpitations during certain exercises, and it was found that the implanted unit was being triggered by pectoral myopotentials. The unit was therefore reprogrammed to decrease the sensitivity, and the patient was again discharged. The need for careful evaluation and close follow-up is emphasized to maximize the benefits and to minimize the very serious potential risks of this pacing mode.

Results of electrophysiologically guided operations for drug-resistant recurrent ventricular tachycardia and ventricular fibrillation due to coronary artery disease

Over a 39 month period, 143 patients with coronary artery disease had programmed stimulation (PES) for recurrent ventricular tachycardia (VT) or ventricular fibrillation (VF). Twenty-two patients underwent operations. Ages ranged from 40 to 71 years; 20 of the 22 were men. All patients had coronary artery disease and 11 had left ventricular aneurysms. The mean ejection fraction was 31% (16% to 50%). Eighteen of the 22 patients underwent operations for drug-resistant ventricular arrhythmias (more than six different drugs plus drug combinations tested per patient). Nineteen patients had intraoperative mapping, endocardial resection, and/or an encircling endocardial ventriculotomy. Three patients with ischemia-related VT had coronary artery bypass (CABG) alone. The 30 day operative mortality was 14%. Thirteen of 19 (68%) operative survivors were effectively controlled with operation alone or a combination of operation and previously ineffective drug therapy. Of the six patients whose VT was inducible postoperatively, three have experienced episodes of sustained VT and one patient died suddenly. Three of these patients have the automatic implantable defibrillator. Operation guided by endocardial mapping is effective alone or in combination with drugs in this select group of patients. If the patients' VT was uninducible postoperatively with or without the addition of antiarrhythmic therapy, late deaths (3/19) were due to poor myocardial reserve and coronary artery disease, not the reemergence of sustained ventricular arrhythmias during a mean follow-up of 15 months.

Nonsurgical electrical ablation of tachycardias: importance of prior in vitro testing of catheter leads

Nonsurgical electrical ablation of tachycardia pathways or foci has been attempted or carried out using a variety of temporary pacing catheter leads. To determine the ability of such leads to withstand the high energies used in such procedures, 34 leads were suspended in saline, and subjected to repeated electrical shocks. Small (4 French) temporary pacing leads made by a variety of manufacturers tolerated multiple shocks up to 100 joules; above this level, failures became increasingly common, although usually the failure mode was benign with respect to patient care implications. Testing of 6, 7, and 8 French leads revealed considerable inter-and intra-manufacturer differences in the ability to withstand higher energy shocks, reflecting differences in materials and fabrication techniques. It is concluded that careful in vitro lead testing is required prior to using identical models in humans for arrhythmia ablation procedures.

Comparative effectiveness of pacing techniques for termination of well-tolerated sustained ventricular tachycardia

Ventricular tachycardias can be terminated by a variety of pacemaker techniques, including rapid and slow stimulation. Fast tachycardias are typically poorly tolerated, and require prompt intervention, usually with rapid pacing. Termination of ventricular tachycardia by slow or single capture pacemaker stimulation techniques is attractive, because of its presumed safety and the possibility of using simple implantable pacers. To identify factors favoring termination, single capture stimulation was used in 390 episodes of ventricular tachycardia in 21 patients, 16 with coronary artery disease, able to tolerate ventricular tachycardia for several minutes. Single capture stimulation terminated 223 episodes (57%) in 18 patients, and two were accelerated. Of 157 episodes exposed to 2-3 programmed extrastimuli or rapid pacing 149 (94%) were terminated and 7 were accelerated. Direct current cardioversion was needed in 12 episodes. Without medications, only two patients tolerated VT. Only one patient had reliable termination with single capture stimulation over several days. Systolic blood pressure was similar in episodes terminated and not terminated by single capture stimulation, but the ventricular rate was significantly lower in episodes terminated, 116 +/- 19 vs. 1.33 +/- 24 (p less than 0.001). Termination of ventricular tachycardia was not affected by QRS morphology. Single capture termination of ventricular tachycardia is largely unpredictable, with limited reproducibility over a period of time. Although comparatively safe, single capture techniques are not likely to prove useful in the long-term treatment of many patients with recurrent ventricular tachycardia.

Mechanisms for the success and failure of pacing for termination of ventricular tachycardia: clinical and hypothetical considerations

The effectiveness of pacing techniques for termination of ventricular tachycardia is well established, and of great value in the electrophysiologic laboratory, and, to a more limited degree, for chronic therapy using implanted anti-tachycardia devices. Although it appears that most clinical ventricular tachycardias are due to reentrant mechanisms, responses to antitachycardia pacing have often been difficult to understand. In this paper, clinical observations are correlated with hypothetical constructs and considerations, in an attempt to derive some general principles related to the success and failure of pacing for ventricular tachycardia. In these analyses, it appears that properties of conductivity and refractoriness in the myocardium are as important as the properties of the tachycardia circuit. Programmed extrastimuli or rapid pacing result in shortening of the effective refractory period of the myocardium, together with depressed conduction velocity of the stimulated wavefront. However, the changes in wavefront conductivity do not occur in step with changes in the effective refractory period; as a result, the stimulated wavefront arrives at the tachycardia circuit in a pattern which differs from the stimulation pattern. In general, it appears that termination of the tachycardia is favored when the stimulated wavefront arrives at the tachycardia circuit at a point when it cannot enter the circuit in an antegrade direction. These conditions are favored by a refractory period in the circuit which is moderately long compared to that of the myocardium. Constructions explaining the observation of a tachycardia termination zone are presented, together with explanations for failure to achieve termination, and for various patterns of acceleration.

Ultrarapid single-capture train stimulation for termination of ventricular tachycardia

Termination of ventricular tachycardia (VT) with single programmed extrastimuli or slow underdrive competitive pacing is often possible. The usefulness of these techniques is limited because the zone in the cardiac cycle during which programmed stimuli are effective may be narrow, with significant time elapsing until termination of the VT, and the zone may vary markedly between episodes, rendering preset extrastimuli ineffective. Ultrarapid trains of stimuli beginning during the refractory period and of a duration sufficient to cause only a single capture should terminate all tachycardias whose termination zone begins just after the refractory period. To test this hypothesis, 21 patients with 371 well-tolerated episodes of VT had single programmed extrastimuli and trains of 10 bipolar stimuli at 25, 50, and 100 Hz. VT was terminated 1 or more times in 18 of the 21 patients with programmed extrastimuli or trains, or both. Forty-eight percent of 290 episodes were terminated with programmed stimulation, compared with 56% of 120 episodes with trains (difference not significant). In 98 episodes, the effects of trains and programmed stimulation could be matched (same patient, date, tachycardia morphology, rate, and drug therapy); the results were concordant (both techniques either terminated the VT or failed) in 92 and discordant in 6. With only 2 possible exceptions, the termination zone always began just after the refractory period; thus, for tachycardias terminating with single captures, the first train to achieve capture was effective, minimizing the duration of the VT.

Maximal rate of tachycardia development: sinus tachycardia with sudden exercise vs. spontaneous ventricular tachycardia

In addition to providing basic physiologic information, knowledge of the maximal rate of sinus tachycardia development may be helpful in developing algorithms permitting new generations of antitachycardia pacemakers to distinguish accurately between sinus and ventricular tachycardia. To determine the maximal rate of sinus tachycardia development, 50 normal subjects rushed up 100 stairs as rapidly as possible, with continuous electrocardiographic monitoring. During the first second of exercise, the mean cardiac cycle length shortened from 709 to 570 ms, equivalent to an increase in heart rate from 85 to 105 beats per minute, or 20 beats per minute per second. Thereafter, a more gradual decrease in cycle length occurred. Differences between men and women, smokers and non-smokers, and sedentary compared to active subjects were all insignificant. Analysis of 50 spontaneous episodes of ventricular tachycardia also revealed a sequential but more abrupt decrease in the cycle length during the first second from 757 to 360 ms, equivalent to a rate increase from 79 to 167 beats per minute, or 88 beats per minute per second. After approximately 1 1/4 seconds, the ventricular tachycardia cycle length remained virtually constant. Baseline cycle lengths were similar in the sinus and ventricular tachycardia groups, but differed in all subsequent beats, although overlap for individual subjects did occur.

Surgical treatment of Wolff-Parkinson-White syndrome: division of an anomalous pathway using the superior approach

The superior approach to the mitral valve through the dome of the left atrium was used for division of a left free wall anomalous pathway. It has been the approach of choice for mitral valve operations at our institution for the past 15 years, facilitating operations particularly when the left atrium is normal in size. Other approaches to the mitral valve are discussed.

Role of implantable pacemakers in control of recurrent ventricular tachycardia

Implanted pacemakers can provide a viable alternative to pharmacologic therapy or surgical management of patients with recurrent ventricular tachycardia. An increasing variety of pacemaker techniques are proving useful for preventing, controlling the effective rate of or terminating ventricular tachycardia. To assess the role of permanent pacing in the treatment of ventricular tachycardia, a consecutive series of 160 patients undergoing electrophysiologic testing for recurrent ventricular tachycardia were analyzed. Thirty-nine patients received implantable pacemakers, of which 13 were intended for bursts of rapid ventricular pacing. No adverse responses were attributed to these burst pacemakers, but concern for possible acceleration of tachycardia and appropriate identification of the arrhythmia were among factors limiting more widespread use of antitachycardia pacing. Some of these limitations may be resolved with further advances in electrophysiologic understanding of arrhythmias combined with strides in medical electronics, which will permit the development of new generations of highly sophisticated antitachycardia pacemakers.

Effect of potassium infusion on the human conduction system

His bundle electrograms were recorded in 12 patients before and after the intravenous administration of 5 mEq of potassium. Antegrade and retrograde refractory periods were determined with the extrastimulus technique. The AH interval was 84 +/- 7 msec before and 89 +/- 7 msec after potassium (P < 0.05). The AH interval at an atrial pacing rate of 140/minute was 129 +/- 13 msec before and 143 +/- 16 msec after potassium (P < 0.02). The effective refractory period of the atrium was 264 +/- 9 msec before and 280 +/- 9 msec after potassium (P < 0.001). Thus small amounts of potassium delay conduction at the atrial and AV nodal level.

Electrophysiologic properties of nitroprusside in man

The effects of nitroprusside on His bundle electrograms, when given intravenously for 10 minutes, were studied in 14 patients with heart disease. Recordings were made at varied heart rates using atrial and ventricular pacing. Nitroprusside significantly reduced the AH interval, but it had no effect on the HV interval. Functional and effective refractory periods were measured by the extrastimulus technique. The functional refractory period of the AV node as well as the effective refractory period of the ventriculoatrial conduction system significantly decreased after nitroprusside infusion. This improvement in conduction can probably be explained by the systemic hypotension produced by nitroprusside, which reflexly will increase sympathetic drive to the heart and decrease vagal tone.