Influence of thrombolysis on signal-averaged electrocardiogram and late arrhythmic events after acute myocardial infarction

Reduced ejection fraction after myocardial infarction: is it sufficient to justify implantation of a defibrillator?

BACKGROUND

Improved survival after prophylactic implantation of a defibrillator in patients with reduced left ventricular ejection fraction (EF) after myocardial infarction (MI) has been demonstrated in patients who experienced remote MIs in the 1990s. The absolute survival benefit conferred by this recommended strategy must be related to the current risk of arrhythmic death, which is evolving. This study evaluates the mortality rate in survivors of MI with impaired left ventricular function and its relation to pre-hospital discharge baseline characteristics.

METHODS

The clinical records of patients who had sustained an acute MI between 1999 and 2000 and had been discharged from the hospital with an EF of < or = 40% were included. Baseline characteristics, drug prescriptions, and invasive procedures were recorded. Bivariate and multivariate analyses were performed using a primary end point of total mortality.

RESULTS

One hundred sixty-five patients were included. During a median follow-up period of 30 months (interquartile range, 22 to 36 months) 18 patients died. The 1-year and 2-year mortality rates were 6.7% and 8.6%, respectively. Variables reflecting coronary artery disease and its management (ie, prior MI, acute reperfusion, and complete revascularization) had a greater impact on mortality than variables reflecting mechanical dysfunction (ie, EF and Killip class).

CONCLUSIONS

The mortality rate among survivors of MIs with reduced EF was substantially lower than that reported in the 1990s. The strong decrease in the arrhythmic risk implies a proportional increase in the number of patients needed to treat with a prophylactic defibrillator to prevent one adverse event. The risk of an event may even be sufficiently low to limit the detectable benefit of defibrillators in patients with the prognostic features identified in our study. This argues for additional risk stratification prior to the prophylactic implantation of a defibrillator.

Role of noninvasive studies in risk stratification for sudden cardiac death

Sudden cardiac death (SCD) is one of the leading causes of mortality in developing countries. To prevent SCD, it is crucial to have effective tools for identifying patients at risk, given that there are now effective devices and medications that can prevent SCD. Two noninvasive electrocardiographic tools have been approved by the Food and Drug Administration and are being used clinically for identifying patients at risk for SCD: the signal-averaged electrocardiogram (SAECG) and T-wave alternans (TWA). This article reviews each of these approaches and includes a discussion of the mechanisms and a summary of the clinical studies published to date.

The relationship of late potentials to assessment of heart rate variability in post-infarction patients

In order to investigate the relationship of late potential (LP) to assessment of heart rate variability (HRV) after acute myocardial infarction (AMI), we studied 101 Chinese patients with AMI (10+/-2.4 days) in Taiwan by collecting 24-h ECG from a Holter tape recorder and signal-averaged ECG from a high-resolution ECG cart. Of the 101 patients, 36 patients had LP (LP group) and 65 patients did not (NLP group). The mean heart rate was significantly lower in the LP group than in the NLP group (P<0.05). The LP group had a significantly increased high-frequency (HF) spectral component of HRV compared with the NLP group (P<0.005), but their low-frequency (LF) to HF ratio (LF/HF) was lower (P<0.05). Analysis of the circadian variation of HRV revealed significant difference of morning SDRR (standard deviation of normal RR intervals) compared with noon SDRR (P<0.05 in the LP group, P<0.005 in the NLP group) and evening SDRR (P<0.05 in the LP group, P<0.005 in the NLP group). In the NLP group, morning HF (normalized unit, nu) was 0.258+/-0.098 compared with noon HF (nu) of 0.219+/-0.83 (P<0.05) and evening HF (nu) of 0. 225+/-0.085 (P<0.05). Nine patients died during follow-up from cardiac causes, three (8.3%) in the LP group and six (9.2%) in the NLP group. In post-MI patients, there was higher vagal tone in patients with late potentials compared to those without late potentials. NLP patients had more circadian change in vagal tone compared with LP patients.

Thrombolytic therapy can reduce the arrhythmogenic substrate after acute myocardial infarction: a study using the signal-averaged electrocardiogram, endocardial catheter mapping and programmed ventricular stimulation

Thrombolytic therapy improves survival after acute myocardial infarction (AMI) primarily by preserving left ventricular function. Its influence on the arrhythmogenic substrate remains uncertain. To investigate the electrophysiologic effects of thrombolytic therapy, signal-averaged electrocardiography, endocardial catheter mapping and programmed stimulation were performed in 93 consecutive patients with their first AMI who underwent thrombolytic therapy. Early reperfusion was achieved in 75 patients (group 1), but not in 18 patients (group 2). The incidence of the signal-averaged electrocardiogram abnormality was 11% in group 1 (8 of 75 patients) and 33% in group 2 (6 of 18 patients) (p<0.02). Catheter mapping detected delayed endocardial electrograms in 30 group 1 patients and 10 group 2 patients (p=NS). The spatial distribution of these electrograms was smaller, and the longest duration of endocardial electrograms was shorter in group 1 than in group 2 (p<0.01). Sustained monomorphic ventricular tachycardia was induced less commonly in group 1 (20%) than in group 2 (44%) (p<0.05). In conclusion, thrombolytic therapy can reduce the arrhythmogenic substrate and improve electrical stability after AMI. This antiarrhythmic effect may contribute, in part, to the improved survival of patients treated with thrombolytic drugs.

Prognosis in myocardial infarction survivors with left ventricular dysfunction is predicted by electrocardiographic RR interval but not QT dispersion

OBJECTIVES

The aim of the study was to assess if QT dispersion and RR interval on the standard 12-lead electrocardiogram (ECG) predict cardiac death and late arrhythmic events in postinfarction patients with low left ventricular ejection fraction (LVEF). QT dispersion on a standard electrocardiogram (ECG) is a measure of repolarization inhomogeneity, but its prognostic meaning in myocardial infarction (MI) survivors is unclear, especially in patients with left ventricular dysfunction. RR interval has been shown to predict mortality in post-MI patients, but its prognostic power has not been compared with other noninvasive risk factors.

METHODS

Retrospective cohort study. Ninety patients were identified, from a series of 547 consecutive postinfarction patients admitted to our institution for phase II cardiac rehabilitation, as having a LVEF of <0.40 at two-dimensional echocardiography (mean LVEF 0.35+/-0.04; range 0.20-0.39). QT dispersion and RR interval were analyzed on the admission 12-lead electrocardiogram, 20+/-10 (range 8-45) days after MI, using specially designed software. Additional risk markers were collected from clinical variables, signal-averaged ECG and Holter recording.

RESULTS

During 24+/-18 (range 1-63) months of follow-up, 10 of 90 patients (11%) died, all from cardiac causes, and there were 18 late arrhythmic events, defined as sudden death or the occurrence of a sustained ventricular arrhythmia > or =5 days after the index MI. QT interval and dispersion were not significantly prolonged in patients who died compared to survivors and not significantly different between patients with and without arrhythmic events. Mean RR interval from standard ECG was significantly shorter in patients with both cardiac death (682+/-99 vs. 811+/-134 ms; P=0.004) and arrhythmic events (720+/-100 vs. 818+/-139 ms; P=0.006). A Cox proportional hazards model identified RR interval from standard ECG (P<0.001) and a history of more than one MI (P=0.002) as significant predictors of cardiac death independent of thrombolytic therapy, LVEF, filtered QRS complex duration at signal-averaged ECG, mean RR and its standard deviation at 24-h Holter monitoring.

CONCLUSIONS

Measurement of QT interval and dispersion 3 weeks after MI has no prognostic power in patients with LV dysfunction after a recent MI. RR interval on standard 12-lead ECG is as good a prognostic indicator as other, more expensive, noninvasive markers. These findings may be relevant in this era of limited health care resources.

Late coronary angioplasty and ventricular late potentials

To assess the effect of successful late coronary angioplasty of an occluded infarct-related artery on the prevalence of ventricular late potentials, signal-averaged electrocardiograms were recorded in 123 consecutive patients surviving a first acute myocardial infarction (58 with and 65 without mechanical reperfusion of the occluded coronary artery). Multivariate analysis showed that successful reperfusion by late angioplasty of the infarct artery contributes to a decrease in the prevalence of late potentials.

[Prognostic evaluation of post-infarction patients using two-dimensional echocardiography, late ventricular potentials and baroreflex sensitivity]

BACKGROUND

Although many variables are useful predictors of post-infarction mortality, their predictive positive values are weak when applied individually. The aim of this study was to determine the prognostic value of the combination of left ventricular ejection fraction, ventricular late potentials and baroreflex sensitivity.

PATIENTS AND METHODS

We studied 69 consecutive post-infarction patients. On the day of their discharge from the coronary unit, all patients underwent a two-dimensional echocardiography, to determine the ejection fraction as well as a high resolution electrocardiogram to detect late potentials. To a subset of 49 patients was carried out to learn their baroreflex sensitivity. The patients were followed for 14 +/- 7 months and the following cardiac end points were considered: sudden cardiac death, non sudden cardiac death and non-fatal episodes of sustained ventricular tachycardia or ventricular fibrillation.

RESULTS

There were 8 end points: 3 sudden cardiac deaths, 3 non sudden cardiac deaths and 2 successfully resuscitated sustained ventricular tachycardia episodes. The rate of fibrinolysis was 55%. An ejection fraction < 45%, the presence of late potentials and a baroreflex sensitivity < 3.0 msec/mmHg were univariate predictors with predictive positive values of 33%, 24% and 16%, respectively. When ejection fraction < 45%, late potentials and baroreflex sensitivity < 3.0 were combined, we found a significant increase in the positive predictive value (50%).

CONCLUSION

The combined determination of ejection fraction, ventricular late potentials and baroreflex sensitivity allows us to identify subset postinfarction patients with a high rate of cardiac complications.

Prognostic value of thrombolysis, coronary artery patency, signal-averaged electrocardiography, left ventricular ejection fraction, and Holter electrocardiographic monitoring for life-threatening ventricular arrhythmias after a first acute myocardial infarction

Prognostic studies after acute myocardial infarction (AMI) have mainly been performed in the prethrombolytic era. Despite the fact that modern management of AMI has reduced mortality rates, the occurrence of malignant ventricular arrhythmias in the late phase of AMI remains an important issue. We prospectively studied 244 consecutive patients (97 treated with thrombolytics) who survived a first AMI. All patients underwent time domain signal-averaged electrocardiography (vector magnitude: measurements of total QRS duration, terminal low [<40 microV] amplitude signal duration, and root-mean-square voltage of the last 40 ms of the QRS complex), Holter electrocardiographic monitoring, and cardiac catheterization. Late life-threatening ventricular arrhythmias were recorded. Eighteen arrhythmic events occurred during a mean follow-up period of 57 +/- 18 months. Three independent factors were associated with a higher risk of arrhythmic events: (1) left ventricular ejection fraction (odds ratio 1.9/0.10 decrease), (2) terminal low-amplitude signal duration (odds ratio 1.5/5 ms increase), and (3) absence of thrombolytic therapy (odds ratio 3.9). Low-amplitude signal duration sensitivity for sudden cardiac death was low (30%). Left ventricular ejection fraction had the highest positive predictive value for sudden cardiac death (10%). Thus, thrombolysis decreases both the incidence of ventricular tachycardia and sudden cardiac death with a higher reopening rate of the infarct-related vessel. Signal averaging predicts the occurrence of ventricular tachycardia and an impaired left ventricular ejection fraction predicts the occurrence of sudden cardiac death.

Evolution of late potential parameters in thrombolyzed acute myocardial infarction might predict patency of the infarct-related artery

The objective was to predict the patency grade of an infarct-related artery by identifying the time course of the changes of the late potential parameters before, during, and shortly after thrombolysis. The study population consisted of 51 patients with acute myocardial infarction (AMI) who received thrombolytic therapy within 3.2 +/- 1.3 hours from the onset of symptoms. Multiple signal-averaged electrocardiograms (SAECGs) were recorded before, during, and shortly after thrombolysis. A total of 489 single-averaged electrocardiographic tracings were evaluated. Late potentials were defined as: QRS duration > 114 ms, low amplitude signals (LASs) > 38 ms, and root mean square (RMS) < 20 microV. Late potentials were found in 37% of patients (21 before and 16 during the first 2 hours of thrombolysis), disappeared in all of patients within 89 +/- 75 minutes (range 25 to 350) but reappeared and persisted in 12% of patients, all with an occluded artery (grade 0). The late potential parameters (QRS, LAS, RMS) showed a gradual improvement which occurred earlier (2 vs 4 hours) and was more marked (0.01 vs 0.05) in cases with a patent artery. This improvement expressed by the late potential parameter index (LnQRS + LnLAS - LnRMS) predicts the patent artery with a sensitivity of 0.94 and specificity of 0.79. The improvement of late potential parameters jointly with close to normal initial values or the late potential parameter index and its changes constituted a satisfactory prediction of the patency grade. Thus, the signal-averaged electrocardiographic technique is capable of predicting the early success or failure of thrombolytic therapy.

The signal-averaged electrocardiogram: update on clinical applications

The signal-averaged electrocardiogram (SAECG) facilitates noninvasive recording of low-amplitude cardiac signals such as ventricular late potentials. The SAECG has been used to accurately predict life-threatening ventricular tachyarrhythmias in patients after acute myocardial infarction and with nonischemic dilated cardiomyopathy, and to screen for inducible ventricular tachycardia in patients with unexplained syncope and with nonsustained ventricular tachycardia. This review focuses on currently accepted methodology and clinical and research applications of the SAECG.

A prophylactic implantable cardioverter-defibrillator?

Antiarrhythmic drugs have systematically failed to improve--or have even worsened prognosis--when given prophylactically to "high-risk" patients without previous spontaneous sustained ventricular arrhythmias. In patients who have had > or = 1 episode(s) of near sudden cardiac death or sustained ventricular arrhythmias, randomized studies against placebo have been considered unethical. Therefore, no information exists on the value of treatment with antiarrhythmic drugs in the prevention of sudden death in these patients. Sudden death is quite predictable and almost expected in some situations. The number of "very high risk" patients is small, but the incidence of sudden death among them is very high. A prophylactic implantable cardioverter-defibrillator (ICD) can be easily justified in them. Unfortunately, the greatest absolute number of sudden deaths occurs in patients from a very large population with a rather low risk for sudden death. Truly unexpected cardiac death is most frequently caused by the first acute ischemic event in a previously asymptomatic individual. While the causes of sudden cardiac death are multiple, the final link is frequently the same: ventricular fibrillation. This arrhythmia can be effectively recognized and treated by an ICD, irrespective of its initiating cause. The time when an ICD will be given prophylactically to a truly asymptomatic individual may never come, but there is an urgent need to implant this device prophylactically in patients who are clearly at risk for sudden death. There are medical, ethical, statistical, technical, practical, financial, and even philosophical obstacles involved in the concept of a prophylactic ICD, but they can be solved, because this therapy is effective. Deciding on the benefits of a prophylactic ICD is a probabilistic issue analogous to deciding on mass vaccination against a preventable infection. To the political community, the decision to accept a prophylactic ICD is too much a matter of expenses, because the benefits may not seem that obvious to them. To the device industry, the cleaves between doctors and politicians have to be the best stimuli to come along with cost-effective technology acceptable to both sides.

The time course and relation of positive signal-averaged electrocardiograms by time-domain and spectral temporal mapping analyses after infarction

We evaluated the time course of development of positive signal-averaged electrocardiograms (SA-ECGs) by time-domain and Spectral Temporal Mapping (STM) analyses after myocardial infarction in 88 patients without bundle branch block. The incidence of positive SA-ECGs by time-domain analysis peaked at 4 to 8 weeks postinfarction whereas the peak incidence by STM analysis varied from 4 days to 4 to 10 months postinfarction. Positive time-domain SA-ECGs demonstrated a significantly reduced factor of normality (NF) compared with negative time-domain SA-ECGs by X, Z, or vector STM analyses, but marked overlap was present for the standard deviations of positive and negative SA-ECGs in all STM leads. Chi square analysis demonstrated a significant correlation only between X-lead STM analysis and time-domain analysis; however, the two methods were markedly discordant. Although there is a statistically significant relation between time-domain and STM analyses of SA-ECGs, the two analyses are not clinically interchangeable.

Jatene correction of the ventricular geometry in postinfarction left ventricular aneurysm. Results of 62 operations

Jatene correction of left ventricular aneurysm was performed on 62 patients (including 11 emergency operations) with mean age 60 years, 80% of them in NYHA class 3-4, with mean left ventricular ejection fraction c. 30%and mean left ventricular end-diastolic pressure c. 24 mm. Concomitant bypass grafting was performed in 58 cases (mean grafts per patient 3.7). Perioperative mortality was 12.9%. One patient had peroperative myocardial infarction. Postoperatively 13 patients had low cardiac output, requiring intra-aortic balloon pump in seven cases. There were no bleeding problems and 28 patients (45%) had no postoperative complications. The average hospital stay was 10.2 days. Left ventricular cavity size (echocardiography) showed significant reduction 1 week postoperatively, which was unchanged after 1 month. The left ventricular ejection fraction was significantly increased 1 month postoperatively. After follow-up averaging 15 months there was significant improvement in mean NYHA class. One patient underwent heart transplantation and died, but there were no other late deaths or cardiac-related complications. Jatene correction of left ventricular aneurysm is simple, carries acceptable mortality and low morbidity and significantly improves left ventricular function.

Open infarct artery, late potentials, and other prognostic factors in patients after acute myocardial infarction in the thrombolytic era. A prospective trial

BACKGROUND

Successful reperfusion of the infarct-related artery in patients with acute myocardial infarction has been shown to reduce in-hospital as well as 1-year mortality. Besides the thrombolysis-induced myocardial salvage, there is increasing evidence that an open infarct-related artery results in increased electrical stability of the heart and that this effect is at least in part responsible for the favorable long-term outcome of these patients. The exact incidence of arrhythmic events during the first year after myocardial infarction and the predictive value of different risk factors for these complications, however, have not been determined in patients in the thrombolytic era.

METHODS AND RESULTS

A total of 173 patients with acute myocardial infarction, 51% treated with thrombolysis, were prospectively entered into the study. At the time of hospital discharge, signal-averaged ECG, Holter monitoring, radionuclide angiography, coronary angiography, and levocardiography were performed in all patients. An open infarct-related artery was documented in 136 patients. The overall incidence of late potentials was 24% (41 patients). By multivariate analysis, an occluded infarct-related artery (P = .04) and the presence of regional wall motion abnormalities (P = .02) were the strongest independent predictors for the development of a late potential. Residual ischemia was treated by either percutaneous transluminal coronary angioplasty or surgery in 86 of 173 patients (50%). Seventy percent of the patients received beta-blocker therapy. During a mean follow-up of 12 +/- 5 months, 7 patients died suddenly or had ventricular fibrillation documented, while only 2 developed sustained monomorphic ventricular tachycardia. Overall 1-year mortality was 4.1%. Multivariate analysis revealed only an occluded infarct-related artery as an independent predictor of arrhythmic complications (P = .017).

CONCLUSIONS

In patients with acute myocardial infarction treated according to contemporary therapeutic guidelines, with a large proportion of individuals undergoing coronary artery revascularization, a low incidence of arrhythmic events, particularly of ventricular tachycardia, was observed in the first year after the index infarction. The presence or absence of an open infarct-related artery was the strongest independent predictor of these events, whereas other traditional risk factors, such as late potentials, were less helpful in identifying patients prone to sudden death. These findings emphasize the importance of the open artery hypothesis in patients recovering from acute myocardial infarction.

Importance of ST-segment depression as a determinant of ventricular premature complex frequency after thrombolysis for acute myocardial infarction. Tissue Plasminogen Activator: Toronto (TPAT) Study Group

Ventricular premature complexes (VPCs) after acute myocardial infarction (AMI) remain important determinants of survival in the post-thrombolytic era. The role of thrombolysis, left ventricular function, and Holter ST-segment depression in modulating VPC frequency is unclear. In a placebo-controlled, randomized study of tissue-type plasminogen activator (t-PA) in 103 patients with AMI (Tissue Plasminogen Activator: Toronto study), VPC frequency and ST depression on Holter monitoring (day 7), ejection fraction by radionuclide scan (day 9), and infarct artery patency and cross-sectional area on day 1 (n = 42) were assessed. After administering t-PA, VPC frequency was 10 +/- 58/hour (mean +/- SD), similar to that after placebo (23.5 +/- 91.7, p = NS). However, patients with ST depression had greater VPC frequency (56 +/- 140/hour) than those without it (1.3 +/- 2.6/hour, p = 0.05). Ejection fraction was negatively correlated with VPC frequency (r = -0.33, p < 0.001). By multivariate analysis, ejection fraction (F = 7.0, p < 0.01) and ST depression (F = 5.8, p < 0.02) were the only independent predictors of VPC frequency. In this placebo-controlled study, VPC frequency after AMI was not related to thrombolytic administration but was associated with ST depression and ejection fraction. This suggests that the underlying extent of both infarcted and ischemic myocardium is important in modulating ventricular arrhythmias after AMI.

The effect of successful angioplasty on variables of signal-averaged electrocardiogram and ventricular wall motion in patients with a first myocardial infarction

The correlation among three variables of late potentials (LPs) obtained by signal-averaged electrocardiography (SAECG) and improvement of ventricular wall motion estimated by echocardiography were studied in 66 patients with a first acute myocardial infarction (MI). Patients with bundle-branch block, intraventricular conduction delay, multi-vessel disease, previous MI, repeat percutaneous transluminal coronary angioplasty (PTCA), or evidence of reinfarction during a 6-month follow-up were excluded. A total of 66 patients was divided into two groups, with (Group 1: n = 27, age 56 +/- 11) or without (Group 2: n = 39, age 61 +/- 10) improvement of ventricular wall motion. Three variables of LPs and ventricular wall motion index (WMI) estimated and scored by echocardiography at admission (WMI 1) and at 6 months after MI (WMI 2) were compared in each group. In Group 1 (WMI 1 vs. WMI 2, p < 0.002), 20 of 27 patients underwent successful angioplasty; in Group 2 (WMI 1 vs. WMI 2, p = NS), 7 of 39 patients had successful emergency angioplasty. There were significant differences in three variables of LPs between the time of admission and at 6 months after MI in Group 1 but not in Group 2. Higher incidence of LPs and greater frequency of successful emergency PTCA were found in Group 1 compared with Group 2. These results suggest that because myocardial ischemia is reversed by successful angioplasty, ventricular wall motion is improved and the arrhythmogenic substrate that generates LPs is stabilized electrically. Stunned or hibernating myocardium may be the arrhythmogenic substrate that generates LPs.

Effects of thrombolytic therapy administered 6 to 24 hours after myocardial infarction on the signal-averaged ECG. Results of a multicenter randomized trial. LATE Ancillary Study Investigators. Late Assessment of Thrombolytic Efficacy

BACKGROUND

Thrombolytic therapy reduces mortality after acute myocardial infarction, even when treatment is initiated relatively late after onset of symptoms. The mechanism underlying this survival benefit is incompletely understood.

METHODS AND RESULTS

In a prospectively designed ancillary study of a randomized, placebo-controlled trial of late thrombolytic therapy (LATE), the signal-averaged (SA) ECG was recorded before hospital discharge in an effort to assess the effect of thrombolytic therapy on arrhythmia substrate. Three hundred ten patients were enrolled at 23 participating sites; 160 patients received placebo, and 150 patients received recombinant tissue-type plasminogen activator (rTPA) therapy 6 to 24 hours after onset of symptoms. Compared with placebo, rTPA tended to reduce the frequency of SAECG abnormality (filtered QRS duration > 120 milliseconds) by 37% (95% CI, -64%, +6%; P = .087) and the filtered QRS duration (105.7 +/- 13.8 versus 108.8 +/- 14.6 milliseconds, P = .05). In the prespecified subgroup of 185 patients with ST elevation on the qualifying ECG, rTPA resulted in a 52% reduction (95% CI, 4% to 77%, P = .011) of SAECG abnormality and a shorter filtered QRS duration (105.7 +/- 10.9 versus 110.7 +/- 15.9 milliseconds, P = .01). No benefit was seen in patients without ST elevation on ECG.

CONCLUSIONS

Late thrombolytic therapy produced a more stable electrical substrate, which probably represents an important mechanism of mortality benefit.

Effect of thrombolysis on heart rate variability and life-threatening ventricular arrhythmias in survivors of acute myocardial infarction

OBJECTIVES

The aim of the present study was to determine the influence of early thrombolysis on ventricular tachyarrhythmias (clinical and inducible) and heart rate variability in survivors of myocardial infarction at high risk for life-threatening ventricular arrhythmias.

BACKGROUND

A greater electrical heart stability may be important in improving survival in patients treated with thrombolysis. Few data are available about the influence of fibrinolysis on postinfarction arrhythmic events and other prognostic variables, such as inducible ventricular tachycardia and heart rate variability.

METHODS

The study group comprised 51 consecutive patients who underwent electrophysiologic study within 30 days of infarction, owing to the presence of two or more of the following criteria: left ventricular ejection fraction < 40%, late potentials and repetitive ventricular ectopic beats. Thirty patients underwent thrombolysis within 6 h of the onset of symptoms (Group A), and 21 received conventional treatment (Group B). Inducibility of sustained monomorphic ventricular tachycardia was tested in both groups, and the standard deviation of all normal RR intervals during 24-h Holter monitoring was calculated. All patients were prospectively evaluated for occurrence of arrhythmic events.

RESULTS

The two groups were similar with regard to left ventricular ejection fraction (mean +/- 1 SD 38 +/- 6% [Group A] vs. 36 +/- 8% [Group B]). Ventricular tachycardia was induced in 6 (20%) of 30 Group A patients versus 14 (67%) of 21 Group B patients (p = 0.002). The standard deviation of normal RR intervals was higher in Group A than in Group B (113 +/- 36 vs. 90 +/- 39 ms, p = 0.05). In patients with anterior infarction, the standard deviation of normal RR intervals was higher in 19 patients with thrombolysis than in 16 patients with conventional treatment (118 +/- 41 vs. 74 +/- 24 ms, p = 0.0002). During a mean follow-up period of 23 +/- 11 months, 4 (13%) of 30 Group A patients had an arrhythmic event versus 9 (43%) of 21 Group B patients (p = 0.04).

CONCLUSIONS

After myocardial infarction, in high risk patients, thrombolysis significantly reduced the occurrence of arrhythmic events independently of left ventricular function. This effect may be related to both an improvement in electrical heart stability, as elucidated by electrophysiologic study, and a favorable action on the cardiac sympathovagal balance.

Effects of streptokinase during acute myocardial infarction on the signal-averaged electrocardiogram and on the frequency of late arrhythmias

Although a number of studies have shown that the incidence of late potentials is lower after thrombolytic therapy, it is not known whether this is paralleled by fewer arrhythmic events during long-term follow-up. In patients with first acute myocardial infarction, filtered QRS duration was significantly shorter when treated with streptokinase (95 +/- 11 ms, n = 53) than when treated with conventional therapy (99 +/- 12 ms, n = 77, p < 0.05). The low-amplitude signal (D40) was shorter after thrombolysis (28 +/- 11 vs 33 +/- 12 ms, p < 0.02). Terminal root-mean-square voltage did not differ significantly (41 +/- 24 vs 35 +/- 23 microV). Irrespective of treatment, late potentials were predictive in the complete group (n = 171) for arrhythmic events during follow-up (13 +/- 6 months, range 6 to 24) (hazard ratio 7.7, p < 0.02, Cox proportional-hazards survival analysis), but treatment (streptokinase vs conventional) did not significantly affect outcome when added to the model. It is concluded that thrombolysis prevents the development of late potentials. However, this study does not confirm the hypothesis that prevention of late potentials leads to a decrease in arrhythmic events.

Prediction of late arrhythmic events after acute myocardial infarction from combined use of noninvasive prognostic variables and inducibility of sustained monomorphic ventricular tachycardia

A combined use of noninvasive techniques and electrophysiologic study in the prediction of arrhythmic events was prospectively evaluated in 303 surviving patients of acute myocardial infarction (AMI). The most powerful combination of noninvasive prognostic variables in identifying patients suitable for invasive strategies was also assessed. Patients who had > or = 2 variables among left ventricular ejection fraction < 0.4, ventricular late potentials and repetitive ventricular premature complexes (VPCs) were considered eligible for programmed ventricular stimulation. After 15 +/- 7 months of follow-up, 19 patients (6%) had an arrhythmic event. Left ventricular dyskinesia (p < 0.00001) and ejection fraction < 0.4 (p < 0.000001), late potentials (p < 0.001), filtered QRS duration > or = 106 ms (p < 0.00001), VPCs/hour > 6 (p < 0.05), paired VPCs (p < 0.01), > or = 2 runs of unsustained ventricular tachycardia (VT) per monitoring (p < 0.001), heart rate variability index < or = 29 (p < 0.00001) and mean RR interval < or = 750 ms (p < 0.01) were found to be significant univariate predictors of events. At multivariate analysis, only low left ventricular ejection fraction, prolonged filtered QRS duration, reduced heart rate variability index and detection of > or = 2 runs of unsustained VT per monitoring had an independent relation to late arrhythmic events. Of 67 eligible patients, 47 (70%) consented to undergo programmed stimulation. A positive electrophysiologic study was found to be the strongest independent predictor of events among patients preselected by noninvasive techniques. With a good sensitivity (81%), a combined use of noninvasive tests and electrophysiologic study selected a group of post-AMI patients at sufficiently high risk (event rate 65%) to be considered candidates for interventional therapy. The combination of > or = 2 variables among left ventricular ejection fraction < 0.4, filtered QRS duration > or = 106 ms and > or = 2 runs of unsustained VT was superior to the other ones in identifying high-risk subjects (positive and negative predictive values for arrhythmic events of 44 and 99%, respectively). On the basis of the data, this scheme appears to be the most appropriate for selecting patients suitable for electrophysiologic testing and invasive strategies after AMI.

Effects of late (1 to 30 days) reperfusion after acute myocardial infarction on the signal-averaged electrocardiogram

Early reperfusion (4 to 6 hours) after acute myocardial infarction reduces mortality and reduces the incidence of late potentials on a signal-averaged electrocardiogram (SAECG). Recent reports suggest that reperfusion accomplished after > 6 hours also may reduce mortality. The effect of such later reperfusion on the SAECG is not known. We hypothesized that reperfusion by angioplasty accomplished > 24 hours after onset of infarction would reduce late potentials and improve the parameters on the SAECG. Forty-one patients with a totally occluded infarct-related artery 12 +/- 8 days after infarction underwent attempted angioplasty. SAECG, echocardiography and thallium-201 imaging were performed before and 1 month after attempted angioplasty. Angioplasty resulted in successful reperfusion in 32 patients and was unsuccessful in 9. No change in the incidence of late potentials occurred after successful reperfusion (13 of 32 patients before and 13 of 32 patients 1 month later) or after unsuccessful reperfusion (6 of 9 patients before and 5 of 9 patients 1 month later). Among patients with successful reperfusion, no significant change occurred in the QRS duration or the terminal signal duration < 40 microV. The terminal root-mean-square voltage in microvolts improved significantly at 1 month (31 +/- 25 before to 38 +/- 29 after, p = 0.004). Twenty-two of 32 patients with successful reperfusion had improved wall motion in the infarct zone at 1 month. Despite an improvement in function in these patients, no change in the incidence of late potentials occurred by 1 month.(ABSTRACT TRUNCATED AT 250 WORDS)