Programmed electrical stimulation: its role in the management of ventricular arrhythmias in coronary heart disease

[Risk stratification for sudden cardiac death in ischemic heart disease. Programmed ventricular stimulation]

Programmed ventricular stimulation was used extensively in the 1970s and has markedly improved our knowledge about the electrophysiological mechanisms of reentrant ventricular arrhythmias. In numerous observational but also randomized studies, it was shown that the induction of a monomorphic ventricular tachycardia by programmed ventricular stimulation was associated with an increased risk of spontaneous ventricular tachycardia or even sudden cardiac death in the future. Despite these results and the guidelines of ACC and ESC recommending the use of programmed ventricular stimulation in patients with recent and remote myocardial infarction, reduced ejection fraction, and complex ventricular arrhythmias or syncope, programmed ventricular stimulation is only seldom used and does not play a relevant role in clinical practice today. The purpose of this overview is to reevaluate the importance of programmed ventricular stimulation for the risk evaluation of patients with ischemic heart disease in consideration of the current literature.

Suppression of inducible ventricular arrhythmias by intravenous azimilide in dogs with previous myocardial infarction

The class III antiarrhythmics azimilide dihydrochloride and dl-sotalol were evaluated for ability to suppress induction of ventricular tachyarrhythmias (VT) in anesthetized, male mongrel dogs 4-6 days after surgical infarction of the left ventricle (LV) produced by ligation/reperfusion of the left anterior descending coronary artery. Postmortem infarcts averaged 28.2 +/- 3.3% and 27.5 +/- 3.9% of the LV for azimilide- and sotalol-treated dogs, respectively. Both agents (0.3-30 mg/kg i.v.) increased ventricular effective refractory period as a function of dose in LV normal and infarcted zones without increasing conduction time. Azimilide was well tolerated hemodynamically up to 30 mg/kg i.v., whereas sotalol produced a significant and dose-related decrease in both blood pressure and heart rate. Azimilide was effective in five (56%) of nine dogs in preventing induction of ventricular arrhythmias by programmed electrical stimulation (PES) at doses from 1 to 30 mg/kg. Efficacy was seen for nonsustained and sustained VT and for ventricular fibrillation. Although sotalol (0.3-10 mg/kg) was effective in all five VT dogs tested, one of two nonsustained ventricular tachyarrhythmia (NSVT) dogs and two of three sustained ventricular tachyarrhythmia (SVT) dogs were reinducible with the baseline arrhythmia at doses higher than the effective dose, and one dog died after 30 mg/kg of sotalol. Both agents increased the cycle length of VT. Thus azimilide simultaneously increased refractoriness and provided antiarrhythmic efficacy as suppression of PES-induced ventricular arrhythmias in infarcted dogs without the hemodynamic depression seen with sotalol.

Use of 24 h ambulatory ECG recordings in the assessment of new chemical entities in healthy volunteers

1. Ambulatory (24 h) cardiac monitoring (ACM) is frequently used to screen healthy volunteers before inclusion in trials of new chemical entities in man. We analysed 156 consecutive ACM recordings in 'healthy' volunteers (on no medication). 2. Only 20 (13%) of the recordings showed normal sinus rhythm throughout. 3. Supraventricular ectopics were the commonest abnormality (83%). Ventricular ectopics occurred in 11%; ventricular tachycardia (unsustained) in 2% and sinus pauses in 6.5%. One volunteer was found to be in atrial fibrillation throughout. 4. The data indicate that when ACM recordings are performed in the assessment of the effects of experimental drugs, guidelines are needed to assess 'normality' to suggest when cardiological investigation is needed and to assign causality of the arrhythmia to the new chemical entity. 5. Proposed guidelines are presented.

Triggered activity as arrhythmogenic mechanism after myocardial infarction: clinical and electrophysiologic study of one case

In a woman with an old infarction and sustained ventricular tachycardia, tachycardias were only inducible after short-long RR sequences. After isoprenaline, tachycardias became incessant and all were preceded by short-long RR sequences. This strongly suggests that triggered activity plays a role in initiation of ventricular tachycardias in postinfarction patients.

Prevention of sudden death in survivors of myocardial infarction: a decision analysis approach

During the first year after myocardial infarction, 5% to 15% of patients die, and the majority of deaths occur suddenly. Highly efficacious therapy, such as the implantable cardioverter-defibrillator, may reduce the chance of sudden death, but broad application is limited by associated risks. Hence, attempts to identify patients at high risk so they can receive therapy are desirable. Subgroups with high or low sudden death risks can be identified based on left ventricular function. Further risk stratification using programmed electrical stimulation and the signal-averaged ECG has been advocated, but the best strategy is unknown. Using a decision analysis model, we compared the 1-year survival rates in survivors of myocardial infarction treated with the implantable cardioverter-defibrillator either empirically or based on screening with the signal-averaged ECG and programmed electrical stimulation. The best strategy for selecting patients for therapy depended on the pre-therapy sudden death risk. For patients at low risk, such as those with well-preserved ventricular function, antiarrhythmic therapy selected with screening tests or given empirically increased both the mortality rate resulting from the adverse effects of therapy and the excellent survival rate without therapy. In the moderate-risk population, both empiric and stratified approaches reduced mortality, but stratification substantially limited the number of patients receiving unnecessary therapy. In the high-risk population, empiric treatment achieved the best survival rate, and screening resulted in only a small reduction in the number of patients treated unnecessarily.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced induction of ventricular arrhythmias during sympathetic stimulation before and during coronary artery occlusion

We used programmed electrical stimulation to examine the arrhythmogenic influence of the sympathetic nervous system before and during coronary artery occlusion. In 29 anesthetized dogs the left and/or right stellate ganglia were stimulated at 2-8 hertz. Program-induced ventricular arrhythmias included single premature ventricular depolarizations, doublets, triplets, ventricular tachycardia and ventricular fibrillation. Both the number of extrastimuli and the duration of coronary occlusion significantly influenced ventricular arrhythmia induction. After pooling the number of extrastimuli, type of artery occluded, and the duration of occlusion, the influences of unilateral and bilateral stellate stimulations were evaluated. The incidence of induced ventricular arrhythmias was 54% during control conditions (prior to sympathetic stimulation). Right stellate stimulation had no influence on arrhythmogenesis, causing ventricular arrhythmia induction in 52% (NS) of the trials. Left stellate stimulation resulted in increased ventricular arrhythmias (68%; P less than 0.05) in response to programmed electrical stimulation. Bilateral stellate stimulation elevated program-induced ventricular arrhythmias (63%; P less than 0.05). The effects of the stellate stimulations on arrhythmia induction were similar during and up to 180 minutes of coronary occlusion. Thus, the arrhythmogenic influence of sympathetic stimulation was present before and during coronary artery occlusion.

Electrophysiologic profile of ibopamine in patients with congestive heart failure and ventricular tachycardia and relation to its effects on hemodynamics and plasma catecholamines

Programmed electrical stimulation was performed in 12 patients with moderate to severe congestive heart failure and ventricular tachycardia (VT) to study possible arrhythmogenic properties of ibopamine, a new orally active dopamine agonist. Ibopamine induced no significant changes in spontaneous cycle length, PR, QRS, QTc, AH or HV intervals, and also right ventricular effective refractory periods were unaffected (for paced cycle lengths of 600 and 430 ms, respectively, using 1 extrastimulus: 287 +/- 16 ms at baseline vs 283 +/- 27 ms after ibopamine and 270 +/- 23 ms during the control study vs 262 +/- 19 ms after ibopamine). In 6 of the 8 patients with coronary artery disease but in none of the 4 patients with dilated cardiomyopathy, sustained VT was induced before and after ibopamine. Proarrhythmia was present in 1 patient, who became inducible after ibopamine. However, 1 patient had sustained VT only at baseline but not after ibopamine. The number of extrastimuli required for VT induction was equal (2.7 +/- 0.2 vs 2.7 +/- 0.2). Holter monitoring showed no changes in ventricular premature complexes, ventricular couplets and runs of VT after 1 week of ibopamine therapy. The signal-averaged electrocardiogram was abnormal in 11 and showed late potentials in 5 patients, but no changes occurred after ibopamine. During hemodynamic evaluation, increases in cardiac (32%) and stroke volume (34%) indexes were seen after administration of 100 mg of ibopamine, accompanied by a decrease in vascular resistance and filling pressures. Plasma norepinephrine decreased significantly after ibopamine (p = 0.02) but plasma epinephrine was unaffected.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophysiologic mechanisms for ventricular arrhythmias in left ventricular dysfunction: electrolytes, catecholamines and drugs

Cardiac arrhythmias are generated as the result of disorders of automaticity or of impulse conduction. Regardless of the mechanism, calcium is likely to be involved, although calcium antagonists are rarely useful antiarrhythmics in ventricular arrhythmias. Myocardial cells that do not ordinarily initiate action potentials may do so when they are partially depolarized, giving rise to an ectopic focus. Early afterdepolarizations (EADs) are also induced in cardiac cells by partial depolarization, whereas delayed afterdepolarizations (DADs) are induced by Ca++ overloading. EADs may be the initiating mechanism of torsade de pointes, a complication of QT prolongation associated with quinidine therapy. Both in the animal model and in humans, treatment with magnesium, isoproterenol, or pacing, all of which suppress EADs, will also suppress torsade de pointes. Ventricular tachycardia is a manifestation of ordered re-entry, and may be exacerbated by antiarrhythmics, especially class 1c drugs. In the individual patient, prediction of proarrhythmia is not possible. The risk of proarrhythmia is increased in patients with episodes of sustained ventricular tachycardia or with significant left ventricular dysfunction.

Ventricular late potentials and induced ventricular arrhythmias after surgical repair of tetralogy of Fallot

Ventricular tachycardia (VT) and sudden death are rare but recognized complications after surgical repair of tetralogy of Fallot. We prospectively studied 31 patients (19 boys and 12 girls, mean age +/- standard deviation 7 +/- 4 years) with postoperative tetralogy of Fallot, by means of right-sided cardiac catheterization, 24-hour Holter monitoring, body-surface and intracavitary signal-averaging (gain 10(5) to 10(6), filters of 100 and 300 Hz) and programmed ventricular stimulation (1 and 2 extrastimuli, 3 basic cycle lengths, right ventricular apex and outflow tract). All patients were asymptomatic and none had documented or suspected ventricular arrhythmias. Ventricular late potentials were detected in 10 of 31 patients (32%) and spontaneous ventricular arrhythmias in 12 of 31 patients (39%). No sustained VT was induced by programmed ventricular stimulation but nonsustained VT was induced in 3 patients (10%). Patients with inducible VT more often had late potentials (3 of 3 vs 7 of 28, p less than 0.01), and spontaneous ventricular premature complexes (VPCs) during Holter monitoring (3 of 3 vs 9 of 28, p less than 0.05). To predict VT inducibility, late potentials had a sensitivity of 100%, a specificity of 75%, a positive predictive value of 30% and a negative predictive value of 100%. For spontaneous VPCs, the figures were 100, 68, 25 and 100%, respectively. It is concluded that shortly after repair of tetralogy of Fallot, the presence of both spontaneous VPCs and ventricular late potentials are associated with an increased incidence of inducible VT. Conversely, the absence of VPCs and ventricular late potentials may identify patients at low risk of subsequent ventricular arrhythmias.

Feasibility and cost savings of outpatient electrophysiologic testing

The feasibility of outpatient electrophysiologic testing was examined by reviewing 100 consecutive outpatient tests performed in 95 patients. Seventy-one of the patients (75%) had no underlying heart disease. The electrophysiologic tests were performed to evaluate supraventricular tachycardias (n = 47), nonsustained ventricular tachycardia (n = 20), unexplained syncope (n = 21), palpitation (n = 9) or intermittent heart block (n = 2). A mean of 2.8 +/- 0.5 6F electrode catheters were inserted through a femoral vein. An electrode catheter was inserted into a subclavian or internal jugular vein in 28 tests and a 5F cannula was inserted into a femoral artery to monitor the blood pressure in 20 tests. The results of 61 tests (61%) were abnormal. Patients were monitored for a mean of 3.8 +/- 1.2 h after the procedure and then discharged. No complications occurred. For cost analysis a subgroup of 60 of these patients was matched for age, gender, heart disease and indication for electrophysiologic testing with a group of 60 patients who underwent electrophysiologic testing as inpatients. Physicians' fees for the two groups were similar; however, the mean hospital charge was $5,845 +/- 3,763 for the inpatient group compared with only $2,120 +/- 1,244 for the outpatient group (p less than 0.001). Thus, outpatient electrophysiologic testing is feasible and safe and results in substantial cost savings in patients without life-threatening arrhythmias.

Antiarrhythmic efficacy of labetalol as assessed by programmed electrical stimulation

1. The purpose of the present study was to investigate the haemodynamic, electrophysiological and antiarrhythmic effects of labetalol in the late reperfusion phase after myocardial infarction in conscious dogs. 2. Labetalol was administered in cumulative doses (0.5, 1 and 3 mg kg-1 90 min-1, i.v.). Compared to control the systolic blood pressure was significantly decreased 20 min after 0.5, 1 and 3 mg kg-1 and up to 30 min after 3 mg kg-1 labetalol. The diastolic blood pressure was significantly decreased 20 and 30 min after 0.5 and 3 mg kg-1 but was not significantly altered after 1 mg kg-1 labetalol. 3. Labetalol significantly increased the PQ, QRS, QT and QTc intervals, the 2:1 AV-conduction point, the ventricular effective refractory periods and the intraventricular conduction time from the apex of the right ventricle to the infarcted LAD-area. With the exception of the alterations in the PQ interval and 2:1 AV-conduction point the effects described above were dose-dependent. 4. Labetalol was active against arrhythmias induced by programmed electrical stimulation. This effect was already present after the lowest dose (0.5 mg kg-1). 5. The good antiarrhythmic activity of labetalol in this study can be explained by the adrenoceptor blocking properties and both the class I and III activity of this drug. Labetalol may be of potential benefit in controlling arrhythmias arising following myocardial infarction.

Usefulness of right ventricular pulse pressure as a potential sensor for hemodynamically unstable ventricular tachycardia

The automatic implantable cardioverter defibrillator has had a major impact on the management of patients with ventricular tachyarrhythmias. Future devices will offer tiered therapy for ventricular arrhythmias, based on a sensor capable of discriminating hemodynamically stable from unstable ventricular tachycardia (VT). We studied 27 patients with sustained VT/ventricular fibrillation during 70 episodes of sustained ventricular arrhythmias (greater than 30 seconds or requiring cardioversion). In this study, phasic arterial pressure (mm Hg), VT cycle length (ms) and right ventricular (RV) pulse pressure (mm Hg) were measured before, during the first 30 beats and after each episode of VT. During the first 10 beats of 23 episodes of unstable VT, the mean (+/- standard error of the mean) decrease in RV pulse pressure from baseline was 22 +/- 1.8 mm Hg; it was 13.8 +/- 2.4 mm Hg during the first 10 beats of 47 episodes of stable VT, (p = 0.01, stable vs unstable). For the next 20 beats of VT, RV pulse pressure decreased from baseline by 22 +/- 2.5 mm Hg during unstable and by 12.0 +/- 2.5 mm Hg during stable VT (p = 0.0001, stable vs unstable). The percent decrease of RV pulse pressure correlated well with the percent decrease in mean arterial pressure and percent decrease in systolic arterial pressure (r = 0.70; r = 0.69, respectively; p less than 0.001) during VT, but poorly with the VT cycle length (r = 0.27, p less than 0.05). The percent decrease in RV pulse pressure is a useful hemodynamic sensor for discriminating between stable and unstable VT.

Selecting therapy for sustained ventricular tachycardias: importance of the sensitivity and specificity of programmed electrical stimulation for predicting arrhythmia recurrences

Antiarrhythmic therapy for prevention of sustained ventricular tachycardia is commonly guided by programmed electrical stimulation, and the persistent ability to initiate ventricular tachycardia during drug therapy often leads to the use of nonpharmacologic therapies such as surgery. Prior studies suggest that programmed stimulation has a high sensitivity but a lower specificity for predicting recurrences of ventricular tachycardia during drug therapy. We constructed a model to evaluate the impact of various programmed stimulation specificities and sensitivities on total mortality when patients with inducible ventricular tachycardia during drug therapy proceed to arrhythmia surgery. Assumptions for this model included an 11.5% surgical mortality, a 13% risk of arrhythmia recurrence for surgery survivors, and that 33% of ventricular tachycardia recurrences are fatal. In this model the relative impact of test sensitivity and specificity on total population mortality depended on the pretest probability that drug therapy would be effective. When this probability was high, variations in test sensitivity had relatively little impact on mortality, but a low specificity increased mortality by increasing the number of false positive patients treated surgically who then suffered the surgical mortality. When the probability of effective drug therapy was low, varying test specificity had relatively little impact on mortality, but a low sensitivity increased mortality by increasing the number of patients with a false negative test who suffered fatal arrhythmia recurrences. If the specificity of programmed stimulation is low and the probability that drug therapy will be effective is high, the total population mortality can exceed the mortality expected from drug therapy alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Programmed electrical stimulation after myocardial infarction and reperfusion in conscious dogs

The hemodynamic and electrophysiologic variables and the inducibility of arrhythmias were studied before coronary artery occlusion (CAO, 4h) and on days 4, 14, and 28 of the late reperfusion phase in conscious, chronically instrumented dogs. Despite a lack of significant changes in the hemodynamic and the electrophysiologic variables, the response to programmed electrical stimulation (PES) before and after CAO with subsequent reperfusion varied substantially. Before intervention arrhythmias such as sustained ventricular tachycardia (SVT) or ventricular fibrillation (VFib) could not be induced by PES via ultrasonic crystals located subendocardially (LAD and LCX region) or via common stimulation electrodes (right ventricle) in any of six instrumented animals. All six animals were inducible after CAO and reperfusion. Five animals showed SVT and one animal showed VFib in response to stimulation on days 4 and 14 of the late reperfusion phase after CAO. On day 28 four animals showed SVT, and two showed VFib. Antiarrhythmic drug testing carried out in the late reperfusion phase with lidocaine (1 mg/kg bolus followed by continuous infusion) revealed 50% efficacy at a dosage of 40 micrograms/kg/min, 100% at 80 micrograms/kg/min, and 67% at 120 mu/kg/min. The persistent inducibility of arrhythmias for the entire experimental period of 24 days may be attributable to the following features of our model: 1. Electrical stimulation carried out from three different locations. 2. The use of up to three extrastimuli in the PES studies. 3. The use of conscious dogs during CAO, reperfusion, and PES. This novel experimental approach thus promises to be of clinical relevance for the investigation of new antiarrhythmic drugs.

The diagnostic sensitivity of electrophysiologic testing in patients with syncope caused by transient bradycardia

Although electrophysiologic testing accurately delineates abnormalities in patients with fixed cardiac-conduction defects, its sensitivity in identifying transient rhythm disturbances is unknown. We prospectively studied 21 patients who had electrocardiographically documented intermittent atrioventricular block (n = 13) or sinus pauses (n = 8) causing syncope, but whose cardiac rhythm had reverted to normal by the time of referral. There were 14 men and 7 women, with a mean age (+/- SD) of 63 +/- 13 years. Fourteen patients had organic heart disease, and 8 were taking cardioactive medications. Electrophysiologic testing was performed before the implantation of a permanent pacemaker. Only three of the eight patients with documented sinus pauses had abnormalities during their tests that suggested the correct diagnosis (sensitivity, 37.5 percent), including a prolonged sinus-node recovery time in one and carotid-sinus hypersensitivity in two. Three of the eight patients had abnormalities detected that were unrelated to syncope, including atrial flutter, dual atrioventricular nodal pathways, and sustained monomorphic ventricular tachycardia. Of the 13 patients with documented atrioventricular block, only 2 had abnormalities suggesting the correct diagnosis (sensitivity, 15.4 percent). Additional observations unrelated to syncope among these 13 patients included abnormal sinus-node function, atrial flutter, and atrial fibrillation causing hypotension. These preliminary observations suggest that a negative electrophysiologic test in a patient with a normal cardiac rhythm who has experienced syncope does not exclude a transient bradyarrhythmia as a cause of the syncope. Furthermore, electrophysiologic testing may sometimes reveal unrelated rhythm disturbances that may mistakenly be designated as the cause of the syncope.

Mechanisms and risk factors for proarrhythmia with type Ia compared with Ic antiarrhythmic drug therapy

Proarrhythmia defined as the exacerbation of existing arrhythmias or the genesis of new arrhythmias de novo may result from any antiarrhythmic agent. The two general clinical syndromes of sustained arrhythmias that result appear to have distinct clinical properties that are consistent with the proposed basic mechanisms of arrhythmogenesis. Torsades de points occurs most commonly in association with administration of type Ia antiarrhythmic agents and has characteristics most consistent with triggered activity mediated by early after depolarization. Conversely, incessant, sustained, monomorphic, wide complex ventricular tachycardia occurs most commonly in association with type Ic antiarrhythmic agents and has characteristics most consistent with incessant reentry. These general subdivisions are probably oversimplified, and in fact, much overlap likely exists. In addition, these proposed mechanisms may not apply to other forms of proarrhythmia such as an increased frequency of isolated ventricular premature couplets or repetitive forms. Furthermore, proarrhythmia may also occur during treatment of supraventricular arrhythmias; although some of these described syndromes are consistent with incessant reentry, the clinical syndromes are not sufficiently defined to better characterize potential mechanisms. Further investigation, therefore, is needed to better define the mechanisms in question, but the mechanisms proposed in this article help to provide a rational approach toward understanding and dealing with clinical proarrhythmia.

Effect of changes in the definition of ventricular tachycardia on the prevalence of complex ventricular ectopy

The presence of ventricular tachycardia (VT) is commonly considered to represent a risk factor for sudden cardiac death as well as an indication for antiarrhythmic drug therapy. Although spontaneous VT is generally diagnosed by the presence of three or more consecutive ectopic beats, proposed criteria for induced VT require six or more complexes at rates exceeding 90 or 100 beats/min. To determine the clinical implications of a similar change in the diagnostic criteria for spontaneous VT, the authors examined 324 consecutive 24-hour ambulatory electrocardiograms. Of these, 111 (34.3%) had episodes of three or more ventricular premature beats. If six or more beats were required, only 34 (30.6%) would have been diagnosed as having VT. Requiring a minimum rate of 90 or 100 beats/min had less consequence, eliminating only 10 (9.0%) and 12 (10.8%) patients, respectively. Patients with only three to five beat runs had significantly fewer isolated premature beats (4,462.8 +/- 588.4 vs 7,158.1 +/- 1,688.1) and ventricular couplets (186.2 +/- 39.2 vs 294.3 +/- 74.4) per day, and slower average rates (142.1 +/- 4.6 vs 171.8 +/- 6.7 beats/min) during ventricular tachycardia than did those with runs of six or more beats. Thus, altering the definition of spontaneous VT has marked effects on the prevalence of this arrhythmia. Those patients excluded did, however, have a lower prevalence of associated electrocardiographic risk factors.

Prognosis of patients with ventricular tachycardia and ventricular fibrillation: role of the underlying etiology

The prognosis of 149 patients with ventricular tachycardia (n = 108) or ventricular fibrillation (n = 41) was analyzed to assess the importance of the underlying etiology of the arrhythmia. Seventy-three patients (Group I) had a previous myocardial infarction and documented late sustained monomorphic ventricular tachycardia. Thirty-five (Group II) also had a previous myocardial infarction but had late ventricular fibrillation. There were 41 patients (Group III) without coronary artery disease: 9 patients with right ventricular dysplasia, 26 with idiopathic sustained ventricular tachycardia and 6 with idiopathic ventricular fibrillation. The mean follow-up period for all patients was 22 to 57 months. The total mortality rate in Group I (16%) and Group II (34%) and the arrhythmic mortality rate in Group I (5%) and Group II (11%) were significantly higher than the rates in Group III. In the latter group the total mortality rate was 4% for those with idiopathic ventricular tachycardia and 11% for those with right ventricular dysplasia, and there were no deaths due to arrhythmia (p less than 0.05). Left ventricular ejection fraction was significantly lower and left ventricular end-diastolic pressure was significantly higher in Group I and Group II than in Group III. There were nonfatal recurrences of ventricular tachycardia in 33 to 56% of patients, and the number of these episodes did not differ significantly in those with and without coronary artery disease.(ABSTRACT TRUNCATED AT 250 WORDS)