Prediction of sudden death by electrophysiologic studies in high risk patients surviving acute myocardial infarction

[Development and clinical value of programmed ventricular stimulation in coronary artery disease and dilated cardiomyopathy]

Programmed ventricular stimulation (PVS), a clinical tool introduced in the early 1980s, aims to prove the electrical vulnerability of the heart and, independent of spontaneous arrhythmia variability, to trigger arrhythmias under controlled conditions. A specific response is the inducibility of monomorphic sustained ventricular tachycardia. This depends on the underlying heart disease, e.g., only for coronary artery disease but not for nonischemic diseases. The value of pharmacologic arrhythmia control as serial electrical testing is uncertain. Up to now there seems to be no prognostic value of PVS concerning sudden cardiac death. PVS is used as a tool to monitor the results of ventricular tachycardia (VT)-catheter ablation in patients who were primarily inducible.

Long-term prognosis of inducible ventricular flutter: not an innocent finding

BACKGROUND

The prognostic significance of ventricular flutter (VFL) induced during programmed electrical stimulation (PES) is currently unknown.

METHODS

This study examined patients who had PES-induced VFL and assessed their long-term prognosis compared with patients who had inducible sustained monomorphic ventricular tachycardia (SMVT).

RESULTS

Of 3414 patients undergoing PES, 74 (2%) had sustained VFL. They were compared with a group of 71 patients undergoing PES in the same time frame who had inducible SMVT. Patients with inducible VFL had a higher ejection fraction than patients with SMVT (0.39 vs 0.33; P =.05). More aggressive pacing was required for arrhythmia induction in patients with VFL, with more stimuli (2.7 +/- 0.5 vs 2.2 +/- 0.6; P <.01) and tighter S(2), S(3), and S(4) intervals. After a mean follow-up of 30 +/- 31 months, the mortality rate was 34% in patients with VFL and 30% in patients with SMVT (P =.41). No difference in the 2 groups in overall survival or a combined end point of sudden death or appropriate implantable cardioverter defibrillator shock was revealed with Kaplan-Meier analysis.

CONCLUSION

The long-term prognosis of patients with inducible VFL is similar to that of patients with inducible SMVT, even when VFL is induced with a relatively aggressive protocol.

Trends in hospital treatment of ventricular arrhythmias among Medicare beneficiaries, 1985 to 1995

BACKGROUND

Treatment options for patients with ventricular arrhythmias have undergone major changes in the last 2 decades. Trends in use of invasive procedures, clinical outcomes, and expenditures have not been well documented.

METHODS

We used administrative databases of Medicare beneficiaries from 1985 to 1995 to identify patients hospitalized with ventricular arrhythmias. We created a longitudinal patient profile by linking the index admission with all earlier and subsequent admissions and with death records.

RESULTS

Approximately 85,000 patients aged > or =65 years went to hospitals in the United States with ventricular arrhythmias each year, and about 20,000 lived to admission. From 1987 to 1995, the use of electrophysiology studies and implantable cardioverter defibrillators in patients who were hospitalized grew substantially, from 3% to 22% and from 1% to 13%, respectively. Hospital expenditures rose 8% per year, primarily because of the increased use of invasive procedures. Survival improved, particularly in the medium term, with 1-year survival rates increasing between 1987 and 1994 from 52.9% to 58.3%, or half a percentage point each year.

CONCLUSION

Survival of patients who sustain a ventricular arrhythmia is poor, but improving. For patients who are admitted, more intensive treatment has been accompanied by increased hospital expenditures.

Value of programmed ventricular stimulation for prophylactic internal cardioverter-defibrillator implantation in postinfarction patients preselected by noninvasive risk stratifiers

OBJECTIVES

The aim of this prospective study was to evaluate the role of programmed ventricular stimulation (PVS) after noninvasive risk stratification to identify a subgroup of acute myocardial infarction (AMI) survivors considered at risk for ventricular arrhythmias and whether these patients could benefit from internal cardioverter-defibrillators (ICDs).

BACKGROUND

The predictive value of noninvasive and invasive risk stratifiers after AMI has been questioned. The question of whether the group of patients with inducible monomorphic ventricular tachycardia (VT) after AMI could profit from ICD implantation is unanswered.

METHODS

A consecutive series of 1,436 AMI survivors was screened noninvasively by Holter monitoring, heart rate variability, ventricular late potentials, and ejection fraction. A subgroup of 248 patients (17.3%) were identified as high-risk patients and scheduled for PVS. Due to the study design, 54 patients >75 years were excluded; thus, 194 patients were eligible for PVS. Triple extrastimuli at two paced cycle lengths (600 ms and 400 ms) were applied.

RESULTS

In a subgroup of 98 (51%) high-risk patients, PVS was performed; 21 patients had an abnormal response, and in 20 patients an ICD was implanted. During a mean follow-up of 607 days the arrhythmic event rate (sudden cardiac death, symptomatic VT, cardiac arrest) was 33% with a positive electrophysiological test versus 2.6% (p < 0.0001) with a negative electrophysiological test. A subgroup of 96 high-risk patients declined electrophysiological study. In this nonconsent group, cardiac mortality (combined sudden and nonsudden) was significantly higher (log-rank chi-square 9.38, p = 0.0022, relative risk 4.7, 1.6 to 13.9) compared to the group guided by electrophysiological testing and consecutive ICD implantation.

CONCLUSIONS

After a two-step risk stratification, PVS is helpful in selecting a subgroup of AMI survivors without spontaneous ventricular arrhythmias who benefit from prophylactic ICD implantation.

Risk stratification after acute myocardial infarction in the reperfusion era

Historically, risk stratification for survivors of acute myocardial infarction (AMI) has centered on 3 principles: assessment of left ventricular function, detection of residual myocardial ischemia, and estimation of the risk for sudden cardiac death. Although these factors still have important prognostic implications for these patients, our ability to predict adverse cardiac events has significantly improved over the last several years. Recent studies have identified powerful predictors of adverse cardiac events available from the patient history, physical examination, initial electrocardiogram, and blood testing early in the evaluation of patients with AMI. Numerous studies performed in patients receiving early reperfusion therapy with either thrombolysis or primary angioplasty have emphasized the importance of a patent infarct related artery for long-term survival. The predictive value of a variety of noninvasive and invasive tests to predict myocardial electrical instability have been under active investigation in patients receiving early reperfusion therapy. The current understanding of the clinically important predictors of clinical outcomes in survivors of AMI is reviewed in this article.

Effects of procainamide and dl-sotalol on the changes of atrial electrophysiology induced by high current stimulation

The relation between high current atrial stimulation and antiarrhythmic drugs was not clear. We evaluated the effects of procainamide and dl-sotalol on the electrophysiological changes induced by high current stimulation. Effects of high current atrial stimulation on effective refractory period, dispersion of refractoriness, conduction velocity, and wavelength of the earliest atrial premature beat were evaluated at baseline and after infusion of procainamide (10 patients) and dl-sotalol (10 patients). High current atrial stimulation shortened effective refractory period locally (-12% +/- 4.0%, -7.0% +/- 3.0%, -5.1 +/- 3.3%, and -3.0 +/- 2.0%, at 0, 7, 14, and 21 mm from the S1 stimulation site, respectively; P < 0.001); increased the dispersion of refractoriness (from 17.8 +/- 8.5 to 27.4 +/- 12.5 ms, P < 0.001); decreased conduction velocity of the earliest premature beat (from 0.58 +/- 0.10 to 0.52 +/- 0.09 ms, P = 0.01); and decreased wavelength of the earliest atrial premature beat (from 10.9 +/- 2.4 to 8.8 +/- 2.1 cm, P < 0.001). These effects of high current stimulation persisted after procainamide infusion. However, after dl-sotalol infusion, high current atrial stimuli did not change the dispersion of refractoriness (23.1 +/- 10 ms vs 26.4 +/- 10.4 ms; P > 0.05, twice diastolic threshold vs 10 mA); conduction velocity of the earliest premature beat (0.54 +/- 0.06 ms vs 0.50 +/- 0.06 ms, P > 0.05); or wavelength of the earliest premature atrial beat (11.5 +/- 1.6 m/s vs 10.1 +/- 1.7 cm; P > 0.05). Although high current atrial stimulation shortened effective refractory period locally, increased dispersion of refractoriness, and decreased the wavelength of the earliest premature atrial impulse, these effects were abolished by dl-sotalol but not procainamide.

[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.

Arrhythmias in hypertrophic cardiomyopathy

Supraventricular and ventricular arrhythmias, particularly nonsustained ventricular tachycardia, and ventricular premature beats are a common finding in patients with hypertrophic cardiomyopathy. Several investigations have demonstrated that nonsustained ventricular tachycardia on Holter monitoring is associated with an increased risk of sudden cardiac death. It has been a long lasting controversial discussion whether suppression of these arrhythmias with drugs, such as amiodarone is capable to reduce the incidence of sudden cardiac death. While recent studies have indicated that nonsustained ventricular tachycardia in asymptomatic patients without additional risk factors, such as a positive family history of sudden cardiac death or syncope should not be treated prophylactically with amiodarone. Symptomatic patients with sustained ventricular tachycardias and/or syncope related to ventricular arrhythmias should undergo ICD implantation. The implantation of an ICD in asymptomatic patients should be limited to those who have several risk factors for sudden cardiac death. It is questionable whether other risk stratifiers, such as programmed electrical stimulation may be helpful to identify asymptomatic patients who are at risk to die suddenly. Moreover, whether the demonstration of electrocardiogram fractionation during electrophysiological study is superior to the induction of sustained ventricular arrhythmias for risk stratification, needs further investigation.

Time- versus frequency-domain analysis in predicting cycle length of inducible ventricular tachycardia after myocardial infarction

To determine whether time- and frequency-domain analyses differ in their ability to predict sustained ventricular tachycardia (VT) induced by programmed ventricular stimulation, 60 consecutive patients with myocardial infarction and 30 healthy control subjects were evaluated. Programmed ventricular stimulation using three extrastimuli and signal-averaged ECG recordings were performed in patients with myocardial infarction. Of the 60 patients, sustained monomorphic VT (SMVT) with cycle length (CL) > or = 250 ms (slow SMVT) was inducible in 9, and SMVT with CL < 250 ms (fast SMVT) was inducible in 9. The durations of the filtered QRS (f-QRS) at each high-pass filter (25, 40, and 80 Hz) and the low amplitude signal (LAS) at 25-Hz high-pass filtering were significantly longer in the slow SMVT group than in the fast SMVT, no VT, or normal control group. The root-mean-square voltages at 25-Hz and 80-Hz high-pass filters in the slow SMVT group were significantly lower than in the fast SMVT, no VT, or normal control group. There was no significant difference in time-domain variables among fast SMVT, no VT, and normal control groups. The CL of the induced sustained VT was significantly correlated with the durations of f-QRS and LAS. Concerning frequency-domain variables (area ratio and factor of normality), there was no significant difference between slow and fast SMVT groups. Both the slow and fast SMVT groups had a significantly higher area ratio and a significantly lower factor of normality than the group with no VT or the normal control subjects. In conclusion, there were significant correlations between time-domain variables and CL of SMVT, while there was no correlation when using frequency-domain parameters.

Predictive value of hemostatic factors for sudden death in patients with stable angina pectoris

To assess hemostatic risk factors for sudden death in patients with stable angina, 323 consecutive patients were recruited prospectively. Patients with clinical heart failure or recent myocardial infarction were excluded. The following clinical variables were recorded: age, gender, smoking habits, hypertension, previous myocardial infarction, left ventricular hypertrophy, and severe ventricular arrhythmia. Angiographic variables included coronary extent, assessed from Jenkins' and mean atherosclerotic scores, and left ventricular ejection fraction. Lipid variables included total cholesterol, triglycerides, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, and apolipoproteins A-I and B. Hemostatic factors included fibrinogen, fibrinopeptide A, antithrombin III, factor VIII antigen, factor VIII coagulant, protein C, plasminogen, alpha 2 antiplasmin, euglobulin clot lysis time, tissue plasminogen activator before and after venous occlusion, and plasminogen activator inhibitor. There were 34 deaths, 19 of which were sudden during the follow-up period (60 +/- 17 months). The association between each variable and the risk of sudden death was assessed by calculating the relative risk with the Cox univariate model. All significant predictors from the univariate analysis were then incorporated in a Cox multivariate model to select the independent predictors of sudden death. The independent predictors of sudden death were left ventricular hypertrophy (p < 0.04), lower left ventricular ejection fraction (p < 0.04), and shorter euglobulin clot lysis time after venous occlusion (p < 0.02), whereas fibrinogen (p < 0.07) and Jenkins' score (p < 0.08) were borderline. Determination of hemostatic variables, especially those pertaining to dynamic fibrinolysis, may thus be of value in assessing risk of sudden death.

Programmed ventricular stimulation in survivors of acute myocardial infarction: long-term follow-up

The prognostic significance of ventricular tachyarrhythmias induced by programmed ventricular stimulation was evaluated in 492 consecutive survivors of acute myocardial infarction (AMI). Holter monitoring, signal-averaged electrocardiogram (ECG) and measurement of left ventricular ejection fraction (EF) were also performed. The protocol used up to 3 extrastimuli. Sustained monomorphic ventricular tachycardia (VT) < 270 beats/min, > 270 beats/min (ventricular flutter) (VFI), and ventricular fibrillation (VF) were induced in 99, 66 and 52 patients, respectively. Long term follow-up (mean 3.7 +/- 2.2 years) showed that most episodes of VT occurred during the first months following AMI (n = 14), but some patients (n = 6) could develop VT as late as 4 years after AMI. Sudden death (SD) (n = 22) always occurred during the first year following AMI. Multivariate analysis demonstrated that EF < 30% and induction of a VT < 270 beats/min were the only predictors for total cardiac death (P < 0.001). EF < 30%, induction of a VT < 270 beats/min and also of VFI (P < 0.05) were predictors for VT and SD: the risk was 4% in patients without inducible VT, 12% in those with inducible VF1, and 21% in those with inducible VT < 270 beats/min. In conclusion, induction of a sustained monomorphic VT < 270 beats/min or > 270 beats/min is a predictor of arrhythmic events during the first year as well as 4 years after myocardial infarction. However the risk of arrhythmic sudden death decreases after the first year, while the risk of VT persists. Because of the low positive predictive value of programmed stimulation (respectively 21% and 12% for the induction of a sustained VT and VFI), we recommended the indication of programmed stimulation in only the patients with one abnormal non-invasive investigation.

Are there gender differences in patients with coronary artery disease presenting with spontaneous sustained ventricular tachycardia and ventricular fibrillation?

The incidence of coronary artery disease (CAD) is greater in men than in women. The aim of the study was to analyze whether any gender-related differences in patients with CAD and documented spontaneous sustained ventricular tachyarrhythmias exist, and which parameters influence the induction of sustained ventricular tachyarrhythmias. The data of 250 patients [43 women (17.2%) and 207 men (82.8%)] with spontaneous sustained ventricular tachycardia [n = 190 (76%)] and fibrillation [n = 60 (24%)] who underwent coronary and left ventricular angiography, electrophysiological study, and signal-averaging electrocardiogram (ECG) form the basis of this analysis. No gender-related differences could be observed in age, number of diseased coronary arteries, history, location and number of myocardial infarctions, presence of left ventricular aneurysm, ejection fraction, type of spontaneous or induced arrhythmias, right ventricular effective refractory period, and signal-averaged ECG parameters. Age, presence of previous myocardial infarction, and ejection fraction were significant predictors (p < 0.001) of inducibility of sustained ventricular tachyarrhythmias. Once CAD has begun, female and male patients present similar clinical and electrophysiologic characteristics. Thus, both genders should benefit similarly from diagnostic and therapeutic approaches if they are referred to the hospital or to invasive interventions at similar intervals in the course of their illness.

Prediction of electrophysiologic study results in patients treated with amiodarone

To identify whether electrophysiologic study results during early-phase amiodarone therapy can be predicted by previous electrophysiologic study, we reviewed the electrophysiologic data of 50 patients with inducible sustained ventricular arrhythmias who underwent 4.3 +/- 1.3 drug trials before being given amiodarone. Study results during testing with agents of the modified Vaughan Williams Ia classification were compared with data obtained after 2 weeks of amiodarone therapy. Partial response by electrophysiologic study was defined as well-tolerated ventricular tachycardia < 150 beats/min associated with a blood pressure > or = 90 mm Hg. Significant slowing in the rate of induced ventricular tachycardia was seen during therapy with both Ia agents and amiodarone, although there was a trend toward greater slowing during amiodarone treatment (180 +/- 45 beats/min vs 164 +/- 65 beats/min; p = 0.09). Two of three patients with noninducible ventricular tachycardia during amiodarone showed profound ventricular tachycardia slowing during Ia therapy. Thirty-eight of 50 patients demonstrated concordance of electrophysiologic study results with regard to achieving partial response criteria. Twenty patients died during a mean follow-up period of 37 +/- 29 months; 7 of the 10 sudden deaths occurred in patients who did not meet partial response criteria. We conclude that patients with inducible sustained ventricular arrhythmias failing serial drug testing with Ia agents only rarely have their ventricular tachycardia suppressed during amiodarone therapy. Partial response criteria are often concordant between testing on agents of the Ia classification and amiodarone, and there was no significant difference in survival in patients based on their partial response status.

Predicting and preventing sudden death from cardiac causes

Sudden cardiac death usually occurs secondary to a ventricular tachyarrhythmia. Even under ideal circumstances only 20% of patients who have an out-of-hospital cardiac arrest survive to hospital discharge. Therefore, aggressive treatment and screening of high-risk patients are mandatory to improve survival rates. Risk stratification of high-risk patients, such as the post-myocardial infarction (MI) population, has been of limited value. Between 70% and 85% of "high-risk" post-MI patients, as defined by these screening tests, will not have a sustained ventricular tachyarrhythmia over several years of follow-up. The use of beta-blockers and possibly amiodarone may have some benefit in reducing mortality in high-risk patients after an MI. Several ongoing trials are studying the use of serial drug testing, amiodarone, and implantable cardioverter-defibrillators in reducing the incidence of sudden cardiac death in patients with potentially lethal ventricular arrhythmias. Although implantable cardioverter-defibrillators appear to be superior to antiarrhythmic drugs in reducing sudden cardiac death, total mortality may not be altered. In sustained ventricular tachyarrhythmias, sotalol and amiodarone appear to be superior to other drugs in preventing arrhythmia recurrence. Ongoing trials, such as the Antiarrhythmic Drug versus Implantable Device (AVID) trial may define the best strategy in these high-risk patients.

Should electrophysiological studies be performed in asymptomatic patients following myocardial infarction? A pragmatic approach

We analyze the arguments commonly afforded by advocates of electrophysiological evaluation for patients with recent myocardial infarction. These arguments are: (1) electrophysiological evaluation is useful for risk stratification of infarct survivors; and (2) it may be used for guiding drug therapy or to identify a group of asymptomatic patients who will benefit from implantation of an automatic cardioverter defibrillator. A positive electrophysiological study is apparently the single best predictor of future arrhythmic events in infarct survivors. However, several noninvasive tests combined may provide just as valuable information. Therefore, electrophysiological evaluation should not be advised, to the majority of infarct survivors, for the mere purpose of risk stratification. Nevertheless, electrophysiological evaluation may be proposed to patients with impaired left ventricular function or high grade ventricular arrhythmias. Patients without inducible arrhythmias have a good prognosis and may be spared the risk of long-term treatment with antiarrhythmic drugs. However, before proceeding with invasive electrophysiological evaluation, both physician and patient should ask themselves if they are willing to go ahead with defibrillator implantation in case sustained monomorphic ventricular tachycardia is induced.

Signal averaging in patients with coronary artery disease: how helpful is it?

In patients who have survived acute myocardial infarction, the presence of ventricular late potentials using the high resolution signal-averaged ECG indicates areas of slow conduction and delayed activation that may potentially serve as a substrate for malignant ventricular arrhythmias. Although detection of late potentials is technique specific, signal-averaged analysis in the time or frequency domain may be a useful index for risk stratification with regard to ventricular tachycardia or sudden cardiac death. The sensitivity and specificity of late potentials for this purpose may be enhanced by combination with other variables, such as left ventricular ejection fraction and presence of complex ventricular ectopy. Therefore, the presence of ventricular late potentials in postmyocardial infarction patients, particularly in those patients with impaired left ventricular function, identifies those patients who are at high risk of malignant ventricular tachyarrhythmias. However, the strategies for prevention of serious arrhythmia complications during follow-up need to be established. The negative predictive value of late potentials is very high. Thus, the absence of late potentials indicates a low propensity to sustained ventricular tachycardia or sudden death, even in the presence of complex ventricular ectopy. Interventions may therefore not be necessary or should even be avoided. The incidence of late potentials in patients with spontaneous or induced ventricular fibrillation is lower and, if present, less pronounced than in those with sustained monomorphic ventricular tachycardia. This presumably is due to a lower degree of conduction delay, which serves as a substrate for reentry. Therefore, the ability of the signal-averaged ECG to predict a propensity to ventricular fibrillation is limited. Despite these limitations, the signal-averaged ECG may be used as a risk predictor in evaluation of patients after myocardial infarction. Unfortunately, at least as far as time domain analysis is concerned, it cannot be used as an efficacy predictor for response to pharmacologic interventions. Further studies will determine whether other modes of signal-averaged analysis can predict the response to drugs.

Contraindications to vasoconstrictors in dentistry: Part I. Cardiovascular diseases

This article reviews the main contraindications of vasoconstrictors in cardiac patients, notably unstable angina, recent myocardial infarction, recent coronary artery bypass surgery, refractory arrhythmias, untreated or uncontrolled hypertension, and untreated or uncontrolled congestive heart failure. Extensive survey of the literature has been completed, giving specific guidelines for a rational use of vasoconstrictors in this category of medically compromised patients.

Combined use of time and frequency domain variables in signal-averaged ECG as a predictor of inducible sustained monomorphic ventricular tachycardia in myocardial infarction

BACKGROUND

Time and frequency domain analyses of signal-averaged ECG (SAECG) have several individual limitations, and the results of the two methods sometimes vary considerably. The purpose of this study was to determine whether the combined use of time and frequency domain variables facilitates identification of patients who will have ventricular tachycardia (VT) induced during programmed ventricular stimulation (PVS).

METHODS AND RESULTS

Nine myocardial infarction (MI) patients with clinically documented sustained monomorphic VT (SMVT), 40 MI patients without clinical VT, and 30 normal healthy control subjects were evaluated. PVS using three extrastimuli and SAECG recording were performed in the MI patients on day 36 +/- 4 after infarction. Of 40 MI patients, SMVT was inducible in 14, sustained polymorphic VT in three, nonsustained monomorphic VT in three, nonsustained polymorphic VT in two, and no inducible arrhythmia was obtained in 18. There were significant differences between MI patients with inducible SMVT and without inducible SMVT in the following SAECG variables: filtered QRS durations (high-pass filter setting, 25, 40, and 80 Hz); low-amplitude signal durations (LAS) under 10, 20, 30, and 40 microV (high-pass filter setting, 40 and 80 Hz); root-mean-square voltages (RMS) of the terminal 20, 30, 40, 50, and 60 msec (high-pass filter setting, 40 and 80 Hz); area ratio (area 20-50 Hz/area 0-20 Hz x 10(5)) of a 120-msec sampling interval starting 20 msec before QRS offset; factor of normality on lead X; and minimum value of the variables on lead X, Y, or Z. Stepwise logistic regression analysis selected only LAS under 30 microV (high-pass filter setting, 80 Hz) and area ratio as independent predictors of inducible SMVT. With these two variables, the predicted probability of inducible SMVT [p(VT)] was expressed as p(VT) = 1/[1+exp (6.2-0.11 LAS-0.01 area ratio)]. This function had 93% sensitivity, 81% specificity, 72% positive predictive value, 95% negative predictive value, and 85% predictive accuracy with greater than or equal to 0.3 as the criterion of a positive test.

CONCLUSIONS

The combined use of time and frequency domain analysis of SAECG can enhance the accuracy of this technique as a screening test for results of PVS in MI patients without clinical VT.

Selection of patients for programmed ventricular stimulation: a clinical decision-making model based on multivariate analysis of clinical variables

OBJECTIVE

This study was conducted to assess the utility of clinical variables in predicting the inducibility of sustained ventricular arrhythmias in a heterogeneous group of patients undergoing programmed ventricular stimulation.

METHODS

Variables were considered in a simulated chronologic order to determine the incremental information added by the signal-averaged electrocardiogram (ECG) and left ventricular ejection fraction. All patients undergoing baseline programmed ventricular stimulation for induction of ventricular tachyarrhythmia during a 30-month period were included in the study. Fourteen historical, ECG, signal-averaged ECG and left ventricular wall motion variables were evaluated for their ability in predicting inducibility of a sustained ventricular arrhythmia, a "positive" event, at programmed ventricular stimulation.

RESULTS

On univariate analysis of the clinical variables, comparison between patients with positive or negative results showed significant differences in 10 of the 14 clinical variables: major cardiac diagnosis, history of ventricular tachycardia, myocardial infarction by history or ECG, all five signal-averaged ECG variables, left ventricular ejection fraction and presence of left ventricular aneurysm. On multivariate analysis, five independent variables were determined to be important: history of ventricular tachycardia, historical or ECG evidence of myocardial infarction, history of loss of consciousness, filtered QRS duration on the signal-averaged ECG and left ventricular ejection fraction. However, with sequential multivariate analysis, a model based only on historical and conventional ECG data was found to do as well as a model that included signal-averaged ECG and left ventricular ejection fraction data.

CONCLUSIONS

Routinely available noninvasive historical, ECG, signal-averaged ECG and left ventricular wall motion variables can be used to accurately predict the outcome of programmed ventricular stimulation. The majority of the predictive power was obtained with the routine model, using only historical and ECG data. The signal-averaged ECG and left ventricular wall motion analysis added no significant incremental information.

Ventricular arrhythmias induced by programmed ventricular stimulation after uncomplicated myocardial infarction

The aim of this study was to correlate the occurrence of ventricular dysrhythmias induced by programmed ventricular stimulation and sudden cardiac death (SCD) after a first episode of acute myocardial infarction (AMI). Twenty-seven consecutive male patients aged fifty-four +/- six (forty-seven to seventy) years were studied prospectively. Thirty days after AMI, patients were submitted to coronary arteriography and programmed ventricular stimulation with the S2-S3-S4 protocol. Noninvasive assessments, including Holter monitoring, ECG stress test, and radionuclide ejection fraction, were also repeated six and twelve months after AMI. Ventricular dysrhythmias were induced in all patients. According to such response, patients were divided into three groups: (1) repetitive ventricular response (n = 9); (2) nonsustained ventricular tachycardia (n = 8); and (3) sustained ventricular tachycardia (n = 10). All patients consistently developed complex ventricular dysrhythmias at Holter monitoring and ECG stress test. One patient from group 2 suffered SCD and another presented a syncope. Similarly, in group 3, 2 patients suffered SCD, 1 during a documented episode of recurrent AMI. Except for 1 patient, radionuclide ejection fraction remained unchanged throughout the study in all cases. SCD was also unrelated to the presence and type of dysrhythmias at noninvasive evaluation. Therefore, the type of ventricular dysrhythmia induced by the S2-S3-S4 protocol has no correlation with late SCD in patients with a first AMI and preserved ejection fraction.

Prognostic significance of programmed ventricular stimulation in patients surviving complicated acute myocardial infarction: a prospective study

In survivors of complicated myocardial infarction, the inducibility of sustained ventricular tachycardia may help identify a subset that is at increased risk for subsequent sudden cardiac death or spontaneous sustained ventricular tachycardia. We performed prehospital discharge programmed ventricular stimulation in 86 survivors of acute myocardial infarction complicated by heart failure, angina pectoris, or nonsustained ventricular tachycardia. These patients also underwent cardiac catheterization with coronary angiography and 24-hour ambulatory ECG recording. Programmed ventricular stimulation induced sustained ventricular tachycardia in 19 patients (22%) and ventricular fibrillation in six (7%) and did not induce these arrhythmias in 61 patients (71%). During an average follow-up of 18 +/- 13 months, 11 patients had arrhythmic events (seven sudden death and four nonfatal spontaneous sustained ventricular tachycardia) and 10 patients had nonsudden cardiac death. The total cardiac mortality rate was 20%. Arrhythmic events occurred in 32% of the 19 patients with inducible sustained ventricular tachycardia compared with 7% of the remaining 67 patients (p less than 0.003). By multivariate analysis the occurrence of arrhythmic events was independently predicted by both inducible sustained ventricular tachycardia and Killip class III or IV heart failure. The risk of arrhythmic events was 4.4% in the absence of both variables versus 38.4% (p less than 0.001) when both variables were present. The total cardiac mortality rate was best predicted by low left ventricular ejection fraction (less than 30%). Thus programmed ventricular stimulation is useful in risk stratification of survivors of complicated acute myocardial infarction. The prognostic utility appears to be particularly high in patients with infarction complicated by Killip class III or IV heart failure.

Reproducibility of electrophysiologic testing during antiarrhythmic therapy for ventricular arrhythmias secondary to coronary artery disease

Although electrophysiologic studies are often used to assess antiarrhythmic drug efficacy in patients with ventricular tachycardia (VT), the reproducibility of these studies during therapy has not been definitively established. Confirmation studies were performed during drug therapy in 64 patients (51 men, mean age 63 years) with sustained ventricular arrhythmias induced during initial study to assess the reproducibility of drug effect. All patients had coronary artery disease. The stimulation protocol used included the serial introduction of up to 3 premature ventricular stimuli during sinus rhythm and with ventricular pacing at 2 pacing rates. Rapid ventricular pacing techniques were also used. Antiarrhythmic drug efficacy was confirmed in 77% of patients. Sustained VT was induced at repeat electrophysiologic study in 19% of patients during antiarrhythmic therapy that was previously thought to be effective. In summary, electrophysiologic study results during antiarrhythmic therapy exhibit significant day-to-day variability. Sustained VT can be induced during antiarrhythmic therapy that was previously defined as effective by programmed stimulation in a substantial number of patients.

Survivors of acute myocardial infarction: who is at risk for sudden cardiac death?

Coronary artery disease is the leading cause of death in the United States. Approximately half of the deaths attributable to coronary artery disease are sudden cardiac deaths. A logical approach to prevention of sudden death is to identify those who are at risk and then to initiate effective therapy. Left ventricular dysfunction, frequent ventricular ectopic activity, nonsustained ventricular tachycardia, and late potentials have been identified as markers for increased risk of sudden cardiac death. The sensitivity and specificity of these risk factors vary, and the positive predictive power is less than satisfactory. The value of invasive electrophysiologic testing for risk stratification in the general postinfarction patient population remains unclear. In addition to these diagnostic difficulties, prevention of sudden death also has been limited by imperfect efficacy and potential lethal effects of the currently available antiarrhythmic agents. Automatic implantable defibrillators are effective for aborting sudden death; however, the potential for more general use of automatic defibrillators in asymptomatic but high-risk postinfarction patients has not been evaluated.

Usefulness of early versus late programmed ventricular stimulation in acute myocardial infarction

To determine the influence of timing on the prognostic value of programmed ventricular stimulation after acute myocardial infarction (AMI), 32 patients were studied on day 19 (early study) and again on day 36 (late study) after AMI using up to 3 extrastimuli. At the early study, sustained monomorphic ventricular tachycardia (VT) was induced in 12 patients (38%), sustained polymorphic VT in 8 (25%), nonsustained monomorphic VT in 1 (3%), nonsustained polymorphic VT in 1 (3%) and no inducible arrhythmia in 10 (31%). At the late study, sustained monomorphic VT, nonsustained monomorphic VT and nonsustained polymorphic VT were induced in 8 patients (25%) each, and no inducible arrhythmia in 8 (25%). Of the 12 patients who had inducible sustained monomorphic VT at the early study, 7 had noninducibility of sustained monomorphic VT at the late study. Of the 20 patients who had noninducibility of sustained monomorphic VT at the early study, 3 had inducible sustained monomorphic VT at the late study. During the follow-up period (mean +/- standard deviation 21 +/- 8 months), there were 2 sudden cardiac deaths and 3 occurrences of sustained VT. Univariate analysis revealed both inducibilities of sustained monomorphic VT at the early study (p = 0.045) and at the late study (p less than 0.001) to be predictive of sudden cardiac death or clinical occurrence of sustained VT. However, inducibility of sustained monomorphic VT at the late study had a higher sensitivity (100%), specificity (89%), positive predictive value (63%) and negative predictive value (100%) than at the early study (80, 70, 33 and 95%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

What is the best predictor of spontaneous ventricular tachycardia and sudden death after myocardial infarction?

BACKGROUND

Death during the first year after myocardial infarction is most commonly due to spontaneous ventricular tachycardia (VT) or fibrillation (VF). The purpose of this study was to compare, in a single cohort of patients, the values of inducible VT, delayed ventricular activation, low left ventricular ejection fraction, high-grade ventricular ectopy, and ST segment displacement on exercise in predicting electrical events (witnessed instantaneous death and spontaneous VT or VF) during the first year after myocardial infarction.

METHODS AND RESULTS

Three hundred sixty one patients aged less than 71 years underwent electrophysiological study, signal-averaged electrocardiogram, gated blood-pool scan, 24 hour ambulatory electrocardiographic monitoring, and exercise testing 1-2 weeks after myocardial infarction and were then followed up for at least 1 year. There were 34 deaths (eight witnessed instantaneous, 26 other), and nine patients survived one or more episodes of spontaneous VF or VT. Patients with inducible VT were 15.2 times more likely to suffer electrical events than patients without inducible VT. No proportional-hazards model excluding inducible VT was as good a predictor of electrical events as was inducible VT alone.

CONCLUSIONS

Inducible VT at electrophysiological study was the single best predictor of spontaneous VT and sudden death after myocardial infarction.

Reduction in incidence of inducible ventricular tachycardia after myocardial infarction by treatment with streptokinase during infarct evolution

The aim of this study was to determine whether intravenous streptokinase administered with or without oral aspirin to patients with evolving myocardial infarction reduces the inducibility of ventricular tachycardia at electrophysiologic study and thus the risk of sudden death in infarct survivors. Of 159 patients randomized at Westmead Hospital to the multicenter Second International Study of Infarct Survival (ISIS-2) after streptokinase and aspirin in acute myocardial infarction, 87 underwent electrophysiologic testing 6 to 28 days after infarction to determine their risk of subsequent ventricular arrhythmias (streptokinase 20 patients; aspirin 25 patients; streptokinase and aspirin 21 patients; both placebos 21 patients). Patients who underwent electrophysiologic testing had similar clinical characteristics to those of patients who did not. The stimulation protocol comprised up to and including four extrastimuli applied to the right ventricular apex at twice diastolic threshold. An abnormal result was defined as ventricular tachycardia with a cycle length greater than or equal to 230 ms lasting greater than or equal to 10 s. Ventricular tachycardia was inducible at electrophysiologic study in 8 patients who received placebo streptokinase, but in no patient who received active streptokinase (8 of 46 versus 0 of 41; p = 0.005, Fischer's exact test). Ventricular tachycardia was inducible in 4 patients who received aspirin therapy and 4 who did not (4 of 41 versus 4 of 46; p = NS). During a mean follow-up period of 39 +/- 9 months, there were no spontaneous episodes of ventricular tachycardia, ventricular fibrillation or witnessed sudden death in the streptokinase-treated group compared with three such events in the placebo-treated group (p = 0.13). When compared with placebo therapy, intravenous streptokinase substantially reduced the incidence of inducible ventricular tachycardia in infarct survivors. No similar benefit was attributable to aspirin therapy.

Management of the patient following coronary thrombolysis

Myocardial salvage can be maximized by the early institution of thrombolytic therapy and aspirin. Certain patients may benefit from the administration of intravenous heparin, beta blockers, or nitroglycerin. The routine use of percutaneous transluminal coronary angioplasty (PTCA) or calcium-channel blockers does not appear to be warranted. Recurrent myocardial ischemia should be vigorously treated with medical therapy and there may be value in cardiac catheterization, followed by PTCA or bypass surgery, depending upon the extent of myocardium at risk and the underlying coronary anatomy. Long-term morbidity and mortality may be reduced by instituting aspirin and beta blockers as well as by modifying risk factors. There is no evidence for the long-term benefit from any calcium-channel blocker. Oral anticoagulation may be warranted in those patients with a mural thrombus, congestive heart failure, or atrial fibrillation. ACE inhibitors may be of value in the presence of left ventricular dysfunction and certainly in the presence of symptomatic congestive heart failure. Antiarrhythmic therapy is generally indicated only for symptomatic or life-threatening arrhythmias. Residual myocardial ischemia should be sought by exercise testing, and those patients with poor exercise tolerance generally warrant cardiac catheterization in consideration for revascularization.

Prognostic significance of sustained monomorphic ventricular tachycardia induced by programmed ventricular stimulation using up to triple extrastimuli in survivors of acute myocardial infarction

The prognostic significance of sustained monomorphic ventricular tachycardia (VT) induced by programmed ventricular stimulation using up to 3 extrastimuli was evaluated in 133 consecutive survivors of acute myocardial infarction (AMI) at a mean interval of 1.8 +/- 1.1 months after onset. This was compared with hemodynamic and angiographic abnormalities shown by cardiac catheterization and ventricular ectopic activity detected by Holter monitoring. Sustained monomorphic VT was induced in 25 (19%) patients, sustained polymorphic VT in 11 (8%) patients, nonsustained monomorphic VT (greater than or equal to 10 beats) in 12 patients (9%) and nonsustained polymorphic VT in 9 patients (7%). Multivariate logistic regression analysis of clinical, angiographic, hemodynamic and electrocardiographic variables showed that the presence of a left ventricular aneurysm (p = 0.005) and Lown grade 4B ventricular ectopic activity (p less than 0.001) were independent predictors of inducibility of sustained monomorphic VT. During a mean follow-up of 21 +/- 13 months, there were 8 (6%) sudden cardiac deaths and 3 (2.3%) spontaneous occurrences of life-threatening sustained VT. The 2-year probability of freedom from sudden cardiac death or sustained ventricular tachyarrhythmias was 53 +/- 13% for patients with inducible sustained monomorphic VT, 70 +/- 10% for those with a left ventricular ejection fraction less than 40% and 58 +/- 13% for those with Lown grade 4B ventricular ectopic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Day to day reproducibility of electrically inducible ventricular arrhythmias in survivors of acute myocardial infarction

Day to day reproducibility of the response to programmed ventricular stimulation has not been evaluated in survivors of acute myocardial infarction. Programmed ventricular stimulation was performed prospectively on 2 consecutive days in 56 patients on an average of 12 +/- 5 days (range 7 to 29) after an acute myocardial infarction. No patient had a history of documented or suspected sustained ventricular tachycardia or fibrillation occurring greater than 48 h after infarction. During initial programmed ventricular stimulation, 21 patients had induction of sustained ventricular tachycardia or fibrillation (Group I), and 35 patients had induction of either nonsustained ventricular tachycardia or no ventricular tachycardia (Group II). Repeat programmed ventricular stimulation in Group I patients induced sustained ventricular tachycardia or fibrillation in 16 of 21 patients (reproducibility 76%); the maximal induced response in the other 5 patients was nonsustained ventricular tachycardia in 2 patients and fewer than six repetitive ventricular responses in 3 patients. The day to day reproducibility was significantly higher for inducible sustained ventricular tachycardia of cycle length greater than or equal to 240 ms compared with rapid sustained ventricular tachycardia of cycle length less than 240 ms (100% versus 44%, p less than 0.009) or ventricular fibrillation (100% versus 43%, p less than 0.009). Repeat programmed ventricular stimulation in Group II patients did not induce sustained ventricular arrhythmias in 31 of 35 patients (reproducibility 89%). Thus, in survivors of acute myocardial infarction, inducible slow sustained ventricular tachycardia was a highly reproducible finding, whereas inducibility of rapid sustained ventricular tachycardia and ventricular fibrillation showed a significant day to day variability.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of pacing current strength on indexes of myocardial activation in humans: influence of chronic infarction and polarity of pacing

The effects of current strength (threshold to 20 mA) and pacing polarity (bipolar versus unipolar) on indexes of ventricular activation during endocardial pacing (cycle length 400 to 500 ms) from 10 normal and 17 abnormal left ventricular sites were assessed in 19 patients. Abnormal sites were infarcted and demonstrated an electrogram duration greater than 70 ms and amplitude less than 3 mV during sinus rhythm. Bipolar pacing was performed from poles 1 (cathode) and 3 (1 cm interelectrode distance) of a quadripolar catheter. Unipolar cathodal pacing was performed from the tip electrode (pole 1). Local activation was indexed by the interval from the pacing stimulus to 1) the onset of the QRS complex, 2) the largest rapid deflection of the local electrogram, and 3) the end (total duration) of the local electrogram recorded from poles 2 and 4 of the quadripolar catheter used for left ventricular pacing. Distant activation was indexed by the interval from pacing stimulus to electrograms recorded at the right ventricular apex and outflow tract. Bipolar and unipolar pacing of normal sites produced a modest homogeneous reduction of all activation times by 3 to 11 ms (median) with increments in current strength from threshold (0.8 mA) to 20 mA. Bipolar pacing of abnormal sites showed marked (up to 110 ms) and heterogeneous changes in local (median 22 to 30 ms) as well as distant (median 14 to 23 ms) activation times with increases in current strength from threshold (2.7 mA) to 20 mA.(ABSTRACT TRUNCATED AT 250 WORDS)

Prediction of arrhythmic events in patients following myocardial infarction

The value of techniques used to predict arrhythmic events (sudden cardiac death not preceded by reinfarction and spontaneous sustained ventricular tachycardia) after acute myocardial infarction is reviewed. A full clinical assessment allows the detection of patients with major infarction, present in the majority of those suffering arrhythmic events during follow-up. More sophisticated noninvasive tests, including Holter monitoring, and the high gain, signal averaged ECG, add prognostic accuracy to clinical assessment in patients with major infarction but are by themselves nonspecific. Noninvasive assessment of autonomic function from baroreceptor sensitivity analysis and heart rate variability measurement may also provide useful prognostic information. The results of programmed ventricular stimulation studies in patients with recent acute infarction have been contradictory, though many of the disagreements can be explained by methodological differences. At best this technique is highly invasive, and probably adds little to what can be discovered from a thorough noninvasive assessment. The treatment to be adopted in those judged to be at high risk remains to be established, and this may include nonpharmacological modalities such as the implantable defibrillator and surgical ablation as alternatives to drug therapy.

Electrophysiologic evaluation of patients with hypertrophic cardiomyopathy

Ten consecutive patients with hypertrophic obstructive cardiomyopathy proven by echocardiography were subjected to detailed electrophysiologic evaluation and 24-hour ambulatory monitoring to detect the spectrum of arrhythmias and to identify their clinical correlates, if any. Two patients presented with syncope and the others with varying grades of dyspnea and angina. Ambulatory monitoring revealed isolated ventricular ectopics in five patients including couplets in two cases and runs of atrioventricular dissociation in two patients. Four patients had a normal study. Electrophysiologic evaluation demonstrated inducible nonsustained ventricular tachycardia in two patients (one with syncope and the other without syncope), short runs of supraventricular tachycardia in one (with a history of syncope), an accessory atrioventricular connexion in one patient (without any inducible arrhythmia), short atrio-His interval with minimal prolongation on incremental atrial pacing in three patients and ventriculoatrial conduction in two patients. A variety of electrophysiologic abnormalities was demonstrated in patients with hypertrophic cardiomyopathy. In two patients with a history of syncope only a nonsustained tachycardia was inducible. Further studies are warranted to find out the significance of these arrhythmias.

Influence of infarct age on reproducibility of ventricular tachycardia induction in a canine model

The inducibility and reproducibility of ventricular tachycardia were evaluated in 97 dogs after myocardial infarction produced by single stage coronary artery ligation. Arrhythmia induction was performed with use of an endocardial electrode catheter positioned at the right ventricular apex before each study. An aggressive protocol of programmed stimulation was used, employing up to seven extrastimuli and three attempts at arrhythmia induction in each study. Electrophysiologic study was performed in individual dogs at the following times after infarction: 1) 7.7 +/- 0.3 and 15 +/- 0.2 days (34 consecutive dogs); 2) 14 +/- 0.6 and 26 +/- 1.7 days (24 selected dogs); 19 +/- 2 and 43 +/- 3 days (12 selected dogs); 4) 36 +/- 2 and 60 +/- 6 days (8 selected dogs); and 5) 59 +/- 12 and 130 +/- 10 days (3 selected dogs). Inducibility of ventricular tachycardia decreased significantly from 74% 1 week after infarction to 41% 2 weeks after infarction. Thus, early reproducibility was low (48%). Reproducibility increased thereafter, with 88% of the dogs having reproducible ventricular tachycardia between 2 and 4 weeks (p less than 0.025) and 100% having reproducibly inducible ventricular tachycardia between 4 weeks and 4 months after infarction. Dogs with no inducible arrhythmia early after infarction did not develop inducible ventricular tachycardia or fibrillation at later studies. Twelve dogs developed spontaneous ventricular tachycardia or sudden arrhythmic death late after infarction. Overall, 22% of dogs with inducible ventricular tachycardia with a cycle length greater than 140 ms developed spontaneous ventricular tachycardia or sudden death. Arrhythmia induction decreases significantly during the 1st 2 weeks after myocardial infarction, but long-term reproducibility of ventricular tachycardia induced greater than or equal to 2 weeks after infarction is very high. This canine model of long-term, reliably inducible ventricular tachycardia is suitable for investigation of antiarrhythmic drugs, surgery and other interventions.