Programmed electrical stimulation of the heart in coronary artery disease

Programmed Ventricular Stimulation: Risk Stratification and Guiding Antiarrhythmic Therapies

Electrophysiologic testing with programmed ventricular stimulation (PVS) has been utilized to induce ventricular tachycardia (VT), thereby improving risk stratification for patients with ischemic and nonischemic cardiomyopathies and determining the effectiveness of antiarrhythmic therapies, especially catheter ablation. A variety of procedural aspects can be modified during PVS in order to alter the sensitivity and specificity of the test including the addition of multiple baseline pacing cycle lengths, extrastimuli, and pacing locations. The definition of a positive result is also critically important, which has varied from exclusively sustained monomorphic VT (>30 seconds) to any ventricular arrhythmia regardless of morphology. In this review, we discuss the history of PVS and evaluate its role in sudden cardiac death risk stratification in a variety of patient populations. We propose an approach to future investigations that will capitalize on the unique ability to vary the sensitivity and specificity of this test. We then discuss the application of PVS during and following catheter ablation. The strategies that have been utilized to improve the efficacy of intraprocedural PVS are highlighted during a discussion of the limitations of this probabilistic strategy. The role of noninvasive programmed stimulation is also reviewed in predicting recurrent VT and informing management decisions including repeat ablations, modifications in antiarrhythmic drugs, and implantable cardioverter-defibrillator programming. Based on the available evidence and guidelines, we propose an approach to future investigations that will allow clinicians to optimize the use of PVS for risk stratification and assessment of therapeutic efficacy.

[Holter monitoring and programmed ventricular stimulation]

Long-term ECG recordings are the method of choice to evaluate quantity and quality of spontaneous rhythm disturbances. However, this method is limited by the variability of the arrhythmias. Invasive procedures such as programmed stimulation allow the provocation of tachyarrhythmias. Indications for both methods are diagnostic clarification of clinical symptoms, risk stratification with respect to arrhythmogenic sudden cardiac death as well as the control of antiarrhythmic therapy.Due to the high variability of spontaneous complex ventricular arrhythmias, Holter monitoring often fails to document the cause of severe symptoms such as syncope or sudden cardiac death. In these patients, invasive electrophysiological testing is required to provoke the arrhythmia.The prognostic significance of spontaneous ventricular arrhythmias recorded during ambulatory monitoring depends on the underlying cardiac disease. In patients with coronary artery disease and a history of myocardial infarction there is evidence that frequent single and/or complex ventricular extrasystoles indicate an increased risk of sudden cardiac death, especially in the presence of a reduced left ventricular function. In these patients, programmed ventricular stimulation can further characterize a highrisk group.For the management of antiarrhythmic therapy in symptomatic patients, under certain conditions both methods appear to be helpful. For the majority of these patients, however, the invasive electrophysiologic study should be preferred.Thus, long-term ECG recordings and programmed electrical stimulation are no competing, but complementary methods in clinical cardiology.

Effect of the intertrain pause on the ventricular effective refractory period measured by the extrastimulus technique

This study determined the effect of the duration of the intertrain pause on the ventricular effective refractory period (VERP) measured by the extrastimulus technique using conventional eight-beat basic drive trains. In 50 subjects, the VERP was measured using a basic drive train cycle length of 500 msec, 2-msec steps in the extrastimulus coupling interval, and intertrain pauses of 0, 1, 4, 8, 20, 40, 60, or 180 seconds. The VERP increased significantly with each stepwise increment in the intertrain pause up to 20 seconds, then reached a plateau. The VERP measured with an intertrain pause of 20 seconds was a mean of 13 msec longer than when measured with a conventional 4-second pause. The results of this study demonstrate a direct relationship between the VERP and the duration of the pause separating the eight-beat basic drive trains used to measure the VERP. When the cycle length of the basic drive train is 500 msec, the VERP lengthens as the duration of the intertrain pause increases from 1 to 20 seconds, demonstrating that the basic drive trains exert a cumulative effect on the VERP when the intertrain pause is shorter than 20 seconds. A cumulative effect of the basic drive trains on the VERP is lost when the intertrain pause is 20 seconds or more.

Pacing-induced angina pectoris and induction of ventricular arrhythmias in coronary artery disease

Ischemia caused by rapid pacing during electrophysiologic study could facilitate induction of ventricular arrhythmias. The results of extrastimulation were retrospectively analyzed in 32 patients with coronary artery disease (CAD) without a history of symptomatic arrhythmia. These patients were studied at cardiac catheterization for angina pectoris refractory to medical therapy. Eleven patients (group I) had typical angina during trains of rapid right ventricular pacing (repeated trains of 8 stimuli [mean cycle length (CL) 473 +/- 47 ms]) but were asymptomatic during slower trains (CL 800 +/- 100 ms). Twenty-one patients (group II) had no symptoms with either rapid (CL 448 +/- 51 ms) or slow (CL 688 +/- 105 ms) trains, despite comparable left ventricular function, CAD severity and medication. Effective refractory periods (S1S2) after rapid drive were shorter in group I than in group II patients (225 +/- 9 vs 240 +/- 14 ms, p less than 0.002), but refractory periods during slow pacing were similar (251 +/- 12 vs 253 +/- 17 ms, difference not significant). No patient in either group had sustained arrhythmia (more than 15 beats) induced by single and double ventricular extrastimuli, decrementally applied at the right ventricular apex. The number of extra beats provoked in group I when rapid trains caused angina (4.3 +/- 3.6) was similar to that induced by extra-stimulation after slower pacing without angina (4.4 +/- 3.5) and to that obtained with rapid or slow pacing in group II (3.1 +/- 3.3 and 2.8 +/- 2.2).(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic value of programmed electrical stimulation in patients with a recent episode of unstable angina

Patients with a recent episode of unstable angina have a 10% 1-year risk of sudden cardiac death. To determine prospectively whether electrophysiologic testing might be useful in predicting sudden death, 20 patients admitted to our hospital underwent programmed electrical stimulation as part of their evaluation. None had persistent angina, severe congestive heart failure, or sustained arrhythmias at the time of testing. Because of their long-term benefits, beta-blocking agents were continued whenever possible (18 of 20 patients). Ten of 20 patients (50%) had inducible ventricular tachycardia. In 19.5 months' mean follow-up, three patients (15%) either died suddenly or survived an episode of ventricular fibrillation. Programmed electrical stimulation was an insensitive (33%) and nonspecific (47%) predictor of sudden death in these patients. Programmed ventricular stimulation soon after admission for unstable angina is not a useful prognostic indicator for sudden death. Such patients do have a frequent induction of ventricular arrhythmias which appears to be a nonspecific marker of underlying coronary disease.

Effects of early reperfusion in acute myocardial infarction on arrhythmias induced by programmed stimulation: a prospective, randomized study

This study compares inducibility of ventricular tachyarrhythmias by programmed electrical stimulation of the heart in patients with myocardial infarction with and without reperfusion after streptokinase therapy. Sixty-two consecutive patients admitted with an acute myocardial infarction were randomized to either combined intravenous and intracoronary streptokinase (streptokinase group) or to standard coronary care unit treatment (control group). Thirty-six of the 62 patients (21 patients from the streptokinase and 15 from the control group) with a first myocardial infarction were studied by programmed ventricular stimulation after a mean of 26 +/- 14 days. No patient had a history of antiarrhythmic drug use or documentation of a ventricular arrhythmia before the initial admission. A sustained ventricular arrhythmia was induced in 10 (48%) of the 21 patients randomized to streptokinase therapy and in all 15 (100%) control patients (p less than 0.001). Sustained monomorphic ventricular tachycardia was induced in 6 (29%) and 10 (67%) patients, respectively (p less than 0.05). To terminate an induced arrhythmia, direct current countershock was required in 33% of patients in the streptokinase group and 73% of patients in the control group (p less than 0.02). Seventeen of the 21 patients treated with streptokinase and no control patient had evidence of early reperfusion 200 +/- 70 minutes after the onset of pain. In comparison with patients without early reperfusion, patients in the reperfused group had a lower maximal serum creatine kinase value (p less than 0.01), a shorter time to peak creatine kinase value (p less than 0.001) and a higher angiographic left ventricular ejection fraction (62 versus 45%, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Ambulatory electrocardiographic correlates of ventricular inducibility during programmed electrical stimulation

To determine the relation between spontaneous and induced ventricular arrhythmias, ambulatory electrocardiographic (Holter) monitoring and programmed electrical stimulation were performed in 48 adult patients with suspected life-threatening ventricular arrhythmias. Nine had no inducible arrhythmia, 11 demonstrated 1 to 2 beats of intraventricular reentry, 19 exhibited non-sustained ventricular tachycardia and 9 exhibited sustained ventricular tachycardia during electrophysiologic studies. Patients without arrhythmia inducibility had a high incidence of multiformity (56%) and bigeminy (44%), but a low incidence of either couplets (11%) or spontaneous ventricular tachycardia (11%) on Holter monitoring. An increasing incidence of all "complex" ectopic features was found with increasing degrees of ventricular inducibility. In patients with inducible sustained ventricular tachycardia, multiformity was present in 100%, bigeminy and couplets in 89% and spontaneous ventricular tachycardia in 78%. Premature ventricular complex frequency, couplet frequency and the repetition index (the ratio of couplets to premature ventricular complexes) were also found to be directly correlated with the degree of ventricular inducibility. Three quantitative arrhythmia variables were identified which predicted ventricular tachycardia inducibility. Seven (78%) of 9 patients with a mean premature ventricular complex frequency of 100 or more/1,000 normal beats, 11 (85%) of 13 with a mean couplet frequency of 1 or more/1,000 normal beats and 19 (83%) of 23 with a mean repetition index value of 15 or more/1,000 premature ventricular complexes proved to have inducible ventricular tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)

Utility of electrophysiologic studies in the management of tachycardia, sudden death, and syncope

The demonstrable value of EP studies for any given diagnostic or therapeutic category, in the last analysis, is largely a function of the subjects studied. Extrapolations from published data (that generally reflect a highly select patient population) to an individual patient can be fraught with error. Considerations of sensitivity and specificity must be balanced against the important need for information in patients at risk from life-threatening arrhythmias. We must never forget, however, that the EP substrate for any arrhythmia is not, as one might wish, a "black box" that should be expected to respond in a reproducible fashion to stimulation. The substrate is dynamic and subject to modification by change in autonomic tone, stretch, blood flow, basal rate, pH, electrolytes, oxygenation, and exposure to perhaps as yet undiscovered humoral mediators. The challenge to the clinical electrophysiologist is therefore not to exaggerate his efforts in one direction (i.e. programmed stimulation) while disregarding the other variables mentioned. Nor should we be disappointed and discard this approach because our expectations of an oversimplified model of arrhythmia testing are not fulfilled. Thus, in addition to careful stratification of patients, baseline studies should perhaps be carried out with more deliberate consideration of autonomic tone (exercise, isoproterenol), stretch (volume, handgrip, afterload), stress (physical and psychological), local anesthetic used, and body position. Only in this way will the scientific basis for acute and chronic EP testing be firmly established.

Vulnerability to ventricular fibrillation in patients with clinically manifest ventricular tachycardia

Ventricular vulnerability may be assessed by measuring the threshold current for the induction of ventricular fibrillation (VF). This technique has been widely utilized in animal experimentation and has been safely applied in a small number of clinical studies. We measured the VF threshold (VFT), using the single stimulus technique in 10 patients with coronary artery disease just prior to the institution of cardiopulmonary bypass. There were no adverse effects of VFT measurement. Three patients had nonsustained ventricular tachycardia (VT) on 24-hour ambulatory monitoring and had VFTs of 10, 14, and 16 mA. In this group VF was induced without any preceding repetitive ventricular responses. Seven patients had no repetitive forms on ambulatory monitoring. Their VFTs ranged from 30 to greater than 40 mA (mean greater than 37). Repetitive extrasystoles were regularly observed in this group at current intensities which ranged from 53% to 80% of the VFT. Thus patients with manifest VT appear to have an enhanced vulnerability to VF. Single or multiple responses were not observed in these patients but appeared to be present in patients with coronary disease and no demonstrable rhythm disorder.

Sustained arrhythmias in hypertrophic obstructive cardiomyopathy

Patients with hypertrophic obstructive cardiomyopathy are subject to syncope and sudden death. Ambulatory monitoring discloses frequent and complex ventricular ectopy in many of these patients, and the occurrence of ventricular tachycardia suggests an increased risk of sudden death. We prospectively evaluated whether induced sustained arrhythmia could explain episodes of cerebral dysfunction in hypertrophic cardiomyopathy. Seven consecutive symptomatic patients (six of whom had an intraventricular gradient of 40 to 130 mm Hg) were subjected to atrial and ventricular stimulation. An electrophysiologic abnormality that would explain the symptoms was identified in every patient: supraventricular tachycardia was present in two, sustained ventricular tachycardia in three, ventricular fibrillation in one, and a prolonged QT interval and dispersion of ventricular refractoriness in one. Antiarrhythmic drugs were selected on the basis of the response to electrophysiologic testing. There has been no recurrence of symptoms in 120 patient-months of follow-up. This experience suggests that arrhythmias are the principal cause of syncope or sudden death in obstructive cardiomyopathy and that electrophysiologic study may be useful in selecting prophylactic therapy.

Late induction of tachycardia in patients with ventricular fibrillation associated with acute myocardial infarction

A prospective study was made of 57 asymptomatic patients, 1 to 24 months after acute myocardial infarction, 17 with (Group I) and 40 without (Group II) ventricular fibrillation during the acute event. None of the 57 patients had symptomatic arrhythmias, uncontrolled heart failure or unstable angina. There was no significant difference between the two patient groups in time from acute myocardial infarction, medication used or left ventricular ejection fraction. Repetitive forms of arrhythmia (Lown grade 4) were more prevalent (29 versus 16%, not significant) during 24 hour ambulatory monitoring in patients in Group I (ventricular fibrillation group). Programmed extrastimulation was performed using 1 to 3 twice-threshold, 2 ms decremental extrastimuli delivered during right ventricular drive. Of the 17 patients in Group I, 8 had no induced arrhythmia (less than or equal to 4 extra responses), 4 had nonsustained ventricular tachycardia and 5 had sustained ventricular tachycardia (degenerating into ventricular fibrillation requiring electrical reversion in 4). None of the 40 patients in Group II had induced sustained ventricular tachycardia (p less than 0.005), although 9 had nonsustained ventricular tachycardia. Patients with ventricular fibrillation during acute myocardial infarction may have an increased risk for ventricular tachycardia or ventricular fibrillation that may be exposed by programmed electrical stimulation even when not yet clinically manifest.

Significance of ventricular arrhythmias initiated by programmed ventricular stimulation: the importance of the type of ventricular arrhythmia induced and the number of premature stimuli required

An increasing number of premature ventricular stimuli are being used during programmed stimulation of the heart in the investigation of patients with documented or suspected ventricular arrhythmias. To analyze the significance of the different types of ventricular arrhythmias that are initiated, we evaluated in a prospective study the effect of from one to four ventricular premature stimuli in 52 patients without (non-VT group) and 50 patients with (prior-VT group) documented ventricular tachycardia or ventricular fibrillation. More than half of the patients in the prior-VT group had coronary heart disease. In the majority of patients of the non-VT group the heart was normal. In 44 of the 50 patients in the prior-VT group the clinically documented ventricular arrhythmia was initiated by programmed ventricular stimulation of the heart. In 88% of these 44 patients, one or two ventricular premature beats were required to initiate the clinical arrhythmia. A ventricular arrhythmia could be initiated in 31 of the 52 patients in the non-VT group. The ventricular arrhythmias included nonsustained monomorphic ventricular tachycardia (two patients), six to 25 complexes of sustained polymorphic ventricular tachycardia (24 patients), and ventricular fibrillation (five patients). In 70% of patients in the non-VT group three or four ventricular premature beats were required to initiate the ventricular arrhythmia. Our results indicate that not only the number of extrastimuli required to initiate ventricular arrhythmias but also the type of ventricular arrhythmia initiated differed between the two groups of patients. Nonsustained polymorphic ventricular tachycardia and ventricular fibrillation are nonspecific responses to aggressive stimulation protocols.