Changes in ventricular activation time on the signal-averaged electrocardiogram in the first year after acute myocardial infarction

Effects of early captopril therapy after myocardial infarction on the incidence of late potentials

BACKGROUND

Late potentials (LP) on signal-averaged electrocardiography (SAECG), recorded 6 to 30 days after an acute myocardial infarction (AMI), identify patients at risk for late arrhythmic events. Angiotensin-converting enzyme (ACE) inhibitors have been shown to reduce ventricular remodeling and cardiovascular mortality after AMI.

HYPOTHESIS

The aim of this study was to investigate the effect of early (< 24 h) administration of captopril on the presence of LP on Days 6-30 after AMI.

METHODS

The study included 117 patients with a first AMI; 63 patients (53 men and 10 women, aged 59 +/- 12 years), 35 with an anterior and 28 with an inferior AMI (44 thrombolyzed), received early captopril therapy. The control group consisted of 54 age-matched patients (39 men and 15 women, aged 60 +/- 12 years), 19 with an anterior and 35 with an inferior AMI (31 thrombolyzed, p = NS), who did not receive early therapy with an ACE inhibitor. The mean left ventricular ejection fraction was similar in both groups (48 vs. 46%). Time domain analysis of SAECG was performed using a band-pass filter of 40-250 Hz. Late potentials were considered present if any two of three criteria were met: (1) Filtered QRS duration (QRSD) > 114 ms, (2) root-mean-square voltage of the last 40 ms of the QRS complex (RMS) < 20 microV, and (3) duration of low amplitude (< 40 microV) signal of the terminal portion of the QRS (LAS) > 38 ms.

RESULTS

In the two groups of patients there were no differences in mean values of SAECG parameters. No patient was receiving any antiarrhythmic drugs. In the captopril group LPs were present in 9 of 63 patients (14%) and in the control group in 17 of 54 patients (31%) (p = 0.046). There was no difference in the number of patients with a patent infarct-related artery in the two groups (76 vs. 59%).

CONCLUSION

Captopril treatment early after an AMI reduces the incidence of LPs recorded on Days 6-30 and may thus favorably affect the arrhythmogenic substrate.

Mechanisms, prediction and treatment of ventricular tachyarrhythmias occurring late after myocardial infarction

Studies from the 1980s, refined in the intervening years, have examined the milieu for ventricular tachycardia (VT) and ventricular fibrillation (VF) occurring late after acute myocardial infarction (AMI). The arrhythmogenic substrate appears to be patchy areas of fibrous tissue interdigitating with viable bundles of myocardium which have distorted orientation and tortuous interconnections. These promote conduction delay in sinus rhythm. Factors found to promote induction of VT rather than VF are longer conduction delay in sinus rhythm, larger infarct size, a more ragged infarct edge and longer ventricular extrastimulus coupling intervals. Predictors of spontaneous VT and VF late after AMI include inducible VT at electrophysiological studies (EPS), delayed conduction in sinus rhythm detected as late potentials on signal-averaged surface electrocardiogram (ECG), and low left ventricular ejection fraction (LVEF). Treatments of propensity for VT or VF after AMI include insertion of a defibrillator (ICD), which has the best track record, antiarrhythmic medication (less reliable), and ablation or excision of arrhythmogenic substrate (for refractory VT and VF).

Evolution of QRS duration after myocardial infarction: clinical consequences

The natural history of late potentials after acute myocardial infarction (AMI) has been studied in the first 2 years following myocardial infarction (MI). The purpose of the study was to assess the influence of some time delays since MI, including a time delay longer than 2 years on signal-averaged ECG (SAECG). SAECG was recorded at 40-Hz high pass filtering in 40 patients 10 days after acute MI (SAECG 1), then repeated 6-12 months later (mean 9 +/- 3 months) (SAECG 2), and then, 2-4 years later (mean 3 +/- 2 years) (SAECG 3). QRS duration, root mean square voltage of the last 40 ms of QRS (RMS 40), and low amplitude signal duration (LAS) were measured at the first (1), second (2), and third recording (3).

RESULTS

(***P < 0.001) [table: see text] The analysis of individual results showed a lengthening QRS duration at the third recording only in patients who had a decreased left ventricular ejection fraction (LVEF) at the third recording. In 12 patients with LVEF > 40%, QRS duration did not change at the first and third recording (104 +/- 15 vs 101 +/- 12 ms). In all 28 patients, but one with LVEF < 40%, QRS duration increased from 107 +/- 12 to 128 +/- 18 ms***. There was no correlation between QRS duration and LVEF at the second recording and no correlation between QRS duration increase at the third recording and the presence or not of late potentials at the first recording. QRS duration lengthening at the third recording was significantly correlated with a left ventricular (LV) dilatation occurrence at the two-dimensional echocardiogram. All arrhythmic events, but two, occurred in patients who developed a QRS duration prolongation and were significantly correlated (P < 0.01) to a mean longer QRS duration (132 +/- 20 ms) than in patients without arrhythmic events (113 +/- 17 ms). In conclusion, the patients with a LV impairment, and who developed a LV dilatation several months after AMI, presented a delayed lengthening of QRS duration noted only at least 2 years after infarction. These patients are at risk of arrhythmic events.

Determinants of the natural course of ventricular late potentials after thrombolytic therapy for acute myocardial infarction

The intraindividual changes of ventricular late potentials and their possible determinants were examined prospectively in 88 consecutive patients (male: 75; mean age: 58 +/- 9 years) after thrombolytic therapy for acute myocardial infarction. Late potential analysis was performed 4 weeks and 12 months after acute myocardial infarction. At the same time, a left heart catheterization was performed to assess the extent of coronary heart disease and left ventricular ejection fraction. The incidence of late potential 4 weeks after acute myocardial infarction was 15% (13/88 patients). Eighteen percent (16/88) of the patients revealed changing results of late potential analysis: 9 patients lost late potential (late potential pos./neg.) 1 year after acute myocardial infarction and 7 patients presented new formation of late potential (late potential neg./pos.). Preserved late potentials were found in four patients (late potential pos./pos.). Late potential analysis remained negative in 68 patients (late potential neg./neg.). There was no influence of age, gender, site of infarction, clinical course, and medical treatment on the natural course of late potential. Changing results of late potential analysis seemed to be correlated with the evolution of left ventricular ejection fraction and the dynamics of coronary heart disease. In the group late potential pos./pos., comparable values for left ventricular ejection fraction were measured at both examinations, whereas late potential neg./neg. had a significant increase in ejection fraction. In the group late potential pos./neg., a significant improvement in left ventricular function was also measured. In contrast, the late potential neg./pos. group tended to have lower left ventricular ejection fractions 1 year after infarction. In the late potential neg./pos. and late potential pos./pos. groups, the extent of coronary artery disease returned to conditions comparable to baseline despite an initial reduction after coronary revascularization performed 4 weeks after infarction. Late potential neg./neg. and late potential pos./neg. revealed a stable benefit gained from coronary revascularization with a persistent reduction in the number of diseased vessels. Dynamic changes in the results of the signal-averaged ECG 1 year after thrombolytic therapy for acute myocardial infarction were observed in 18% of the patients. These changes seem to be correlated with the evolution of left ventricular function and the dynamics of coronary artery disease.

Voltage sum of filtered ECG signal--a sensitive parameter of ventricular activation

On the basis of the signal averaged ECG (SA ECG) principle the authors analyse the gradually filtered ECG signal (in ranges of 0-120 Hz with increments of 10 Hz). The voltage sums are determined in eight segments of the QRS complex. The described VSF-ECG method (Voltage Sum of Filtered ECG) was applied in a group of healthy probands and in groups of selected patients. The measurements in healthy probands were used to determine the value of standard in healthy subjects. Repeated measurements confirmed a good reproducibility of the VSF-ECG method. The method enables a precise quantification of heart activation progression. VSF-ECG is a method revealing the changes of heart activation progression being not reflected as late potentials. Parameters of the method are indicators of activation splitting upon the infarction area and also an indicator of the electric milieu of the entire heart.

High resolution ECG and left ventricular volume after acute myocardial infarction

The presence of ventricular late potentials (LPs) early after acute myocardial infarction (AMI) was recently reported to correlate with left ventricular dilatation subsequent to AMI. We assessed prospectively the relationship between LP (time domain) in the late phase of AMI and left ventricular end-diastolic volume (EDV) measured by equilibrium radionuclide angiocardiography 4 weeks and 12 months after AMI. In 80 consecutive patients 4 weeks and 12 months after thrombolytic therapy for AMI, LP and EDV were determined (EDV1, EDV2). There was no significant correlation between QRS duration (r = 0.18), RMS40 (r = 0.08), or LAS40 (r = 0.1) and EDV1 or EDV2 in patients with or without LP at baseline. In both groups (patients with [n = 15] and without LP [n = 65]), EDV1 and EDV2 were comparable (128 +/- 32 mL vs 126 +/- 35 mL; 114 +/- 40 mL vs 117 +/- 36 mL; P = NS). In addition, there was no significant difference between EDV1 and EDV2 in patients who developed new LP (n = 6) or lost LP (n = 9) 12 months after AMI. In contrast to LP in the very early phase after AMI, there seems to be no significant correlation between the high resolution ECG in the late phase after thrombolytic therapy for AMI and left ventricular EDV.

Factors influencing changes in the signal-averaged electrocardiogram within the first year after a first myocardial infarction

One hundred twenty-nine patients were prospectively studied after a first myocardial infarction. A first signal-averaged electrocardiogram (SAECG-1) was performed in the acute phase (within 48 hours after onset of symptoms) and a second one (SAECG-2) in the late phase (6 to 18 months after hospital discharge). We studied the influence of nine parameters on the evolution of the signal-averaged electrocardiogram: age, gender, myocardial infarction location, number of diseased coronary vessels, infarct-related coronary artery patency, use of thrombolytic therapy or percutaneous transluminal coronary angioplasty in the acute phase, left ventricular ejection fraction, and recurrence of ischemic events. No follow-up data were available in 15 patients. Of the remaining 114 patients, an ischemic event occurred in 25 (22%). The signal-averaged electrocardiogram remained unchanged in 97 (85%) (remaining normal in 78 and abnormal in 19). It became abnormal in 13 (11.5%) and became normal in 4 (3.5%). In patients with a normal SAECG-1, two factors were associated with the change to an abnormal SAECG-2: (1) an ischemic event occurred in 11 (85%) of 13 patients whose SAECG-2 was abnormal compared with only 13 (17%) of 78 patients whose SAECG-2 remained normal (p < 0.0001), and (2) 100% of patients with an abnormal SAECG-2 had an inferior myocardial infarction compared with 54% of patients with a normal SAECG-2 (p = 0.004).(ABSTRACT TRUNCATED AT 250 WORDS)

Prognostic implications of loss of late potentials following acute myocardial infarction

The prognosis of patients following myocardial infarction is adversely affected by the finding of late potentials at the time of hospital discharge. Loss of late potentials has been previously reported during serial testing during the first year after infarction, but it is not known whether such patients remain at risk of arrhythmic events. This study prospectively followed 243 patients after myocardial infarction. Late potentials were observed in 92 patients (group I) at the time of hospital discharge. Of these patients, 23 no longer had late potentials at 6-week follow-up and 8 had had an arrhythmic event (sudden death or ventricular tachycardia). In patients with loss of late potentials, overall QRS duration had decreased from 109 +/- 11 msec at discharge to 104 +/- 11 msec (P < 0.01), terminal QRS voltage rose from 15 +/- 4 microV to 31 +/- 9 microV (P = 0.001), and late potential duration fell from 42 +/- 6 msec to 28 +/- 6 msec (P = 0.001) at the 6-week study. Predictors of loss of late potentials were: initial duration of the QRS duration (P < 0.001) and terminal voltage (P < 0.005); non-Q wave infarction (P < 0.001); and being a male (P < 0.05). After the 6-week assessment, 11 additional arrhythmic events occurred during median follow-up of 31 months. The risk of arrhythmic events was similar in patients with loss of late potentials and those who retained late potentials in group I (9% vs 11%, P = NS) but significantly greater than patients with no late potentials at discharge (group II, 2%).(ABSTRACT TRUNCATED AT 250 WORDS)

Current usefulness of the signal-averaged electrocardiogram

Signal-averaged electrocardiography is a relatively simple, noninvasive technique by which valuable information can be gained to help in the management of patients with cardiovascular disease. The presence of late potentials on the SAECG is a good marker for the presence of an arrhythmogenic substrate that is believed to be the source of ventricular tachycardia in patients with coronary artery disease. The value of the detection of late potentials has been studied best after myocardial infarction, when the absence of late potentials makes the occurrence of an arrhythmic event very unlikely. The positive predictive value for an arrhythmic event to occur in the presence of late potentials is low, however, comparable to the predictive value of decreased left ventricular function, complex ventricular ectopy, or abnormal autonomic tone. This appears to have its explanation in the complex pathophysiology behind the occurrence of arrhythmic events. Improved accuracy for the SAECG is achieved when the result of the test is interpreted with consideration of the presence or absence of other predictive markers. A thorough understanding of the signal-averaged electrocardiogram makes optimal clinical use of the information gained from this easily acquired test possible.

Effects on the signal-averaged electrocardiogram of opening the coronary artery by thrombolytic therapy or percutaneous transluminal coronary angioplasty during acute myocardial infarction

One hundred twenty-nine patients were retrospectively analyzed and divided into 3 groups according to (1) the presence of a patent artery obtained either spontaneously or after thrombolytic therapy but without percutaneous transluminal coronary angioplasty (PTCA) (group I, n = 83), (2) the presence of a patent artery after opening by PTCA (group II, n = 29), or (3) absence of reperfusion despite thrombolytic therapy or PTCA (group III, n = 17). Thrombolytic therapy was given within 4 hours after onset of symptoms (mean 2.5 +/- 1.0 hours) and PTCA was performed within 24 hours after the onset of symptoms (mean 6 +/- 6 hours). Signal averaging was performed within 24 hours after cardiac catheterization. An abnormal signal-averaged electrocardiogram was present in 10 of 83 (12%) group I, 9 of 29 (31%) group II and 7 of 17 (41%) group III patients (p < 0.05 group I vs II, p < 0.01 group I vs III, no statistical difference group II vs III). Therefore, in contrast to reperfusion by thrombolytic therapy the incidence of abnormalities on the signal-averaged electrocardiogram early after myocardial infarction is not reduced by an early opening of the culprit vessel by PTCA.

Variation in late potentials and the reproducibility of their measurement

The usefulness of a test depends on its reproducibility. This determines how closely the test result indicates the actual pathophysiologic state, how well it will predict that state in the future, and if interventions or further pathologic changes are reflected by the test. There is a variation in the parameters of the signal-averaged ECG, more so with spectral than with time domain measurements. These must be accounted for when estimating risk. If one presumes that risk is proportional to the extent of abnormality, then the variation in measurements simply means that only borderline cases can potentially be miscategorized. More important, the lack of reproducibility of measurements made from the signal-averaged ECG indicates that changes noted in an individual after an intervention, such as a surgical intervention, must be viewed with a jaundiced eye. Group changes are perhaps meaningful, and indicate a physiologic effect, but clinical decisions cannot be made unless the changes observed in an individual patient exceed the confidence limits of expected variation. There has been debate as to the usefulness of measurements made from the signal-averaged ECG in predicting antiarrhythmic drug effects (the effect of drugs is discussed elsewhere in this symposium). Here an analogy must be made to the suppression of asymptomatic ventricular ectopy. First, we cannot make a statement that there has been a drug effect unless the parameter measured changes beyond the confidence limits of normal variation or reproducibility. Second, we cannot translate a change in a measurement into a change in risk for arrhythmic events without subjecting that hypothesized relationship to a long-term placebo-controlled clinical trial, albeit acute electrophysiologic trials correlating changes in the signal-averaged ECG to ventricular tachycardia induction provide some insight. And perhaps the relationship must be tested independently for each drug assessed. In the same regard, there is much excitement about the benefits of thrombolytic therapy, but when diagnosing benefit to the individual patient we have to remember the lack of reproducibility of the measurements and also keep in mind that an improved signal-averaged ECG cannot be translated into an improved prognosis without long-term controlled studies. In summarizing the variation and reproducibility of measurements made from the signal-averaged ECG we avoided providing more than a sense of the extent of variation expected because precise confidence intervals depend on the particular techniques used to make the measurements.(ABSTRACT TRUNCATED AT 400 WORDS)

Frequency versus time domain analysis of signal-averaged electrocardiograms. II. Identification of patients with ventricular tachycardia after myocardial infarction

Late potentials detected by the time domain signal-averaged electrocardiogram (ECG) are a well established marker for ventricular tachycardia in patients after a myocardial infarction, but the value of frequency domain analysis of the signal-averaged ECG in identifying these patients remains controversial. This study compared the results of time domain, frequency domain and spectral temporal mapping analyses of the signal-averaged ECG in 30 postinfarction patients with spontaneous sustained ventricular tachycardia and in 30 postinfarction patients without ventricular tachycardia matched for age, gender and infarct site. No patient with bundle branch block was included. Time domain signal-averaged ECG indexes were significantly different in patients with and without ventricular tachycardia (p less than 0.001). Frequency domain results were not consistently different between these groups. The values of the normality factor of spectral temporal mapping were significantly lower in patients with ventricular tachycardia (p less than 0.04). Results of the time domain signal-averaged ECG were abnormal in 22 patients with ventricular tachycardia (73%) but in only 3 control patients (10%) (p less than 0.001). Spectral temporal mapping results were abnormal in 21 patients with ventricular tachycardia (70%) compared with 12 control patients (40%) (p less than 0.04). When the optimal numeric values of dichotomy points were computed for patient stratification at different sensitivity levels, time domain analysis identified patients with ventricular tachycardia with significantly fewer false positive results than were obtained with either frequency analysis or spectral temporal mapping. It is concluded that frequency domain analysis and spectral temporal mapping of the signal-averaged ECG did not improve the identification of postinfarction patients with ventricular tachycardia and without bundle branch block.

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.

High gain signal averaged electrocardiogram combined with 24 hour monitoring in patients early after myocardial infarction for bedside prediction of arrhythmic events

The value of the high gain, signal averaged electrocardiogram combined with 24 hour electrocardiographic monitoring in the prediction of arrhythmic events was assessed in 159 patients in the first week after myocardial infarction. Eleven patients (7%) suffered arrhythmic events during a mean (SD) of 12 (6) months of follow up (range 2-22, median 13 months). The combination of high gain, signal averaged electrocardiography and 24 hour electrocardiographic monitoring was more accurate than either technique alone or than clinical information collected during admission in predicting these events. The combination identified a high risk group of 13 (8%) patients, with an arrhythmic event rate of 62% and a low risk group with an event rate of 2%. The combination of high gain, signal averaged electrocardiography and 24 hour electrocardiographic monitoring in the first week after myocardial infarction provides a rapid, cheap, and non-invasive bedside method for the prediction of arrhythmias.

Short-term effect of coronary artery bypass grafting on the signal-averaged electrocardiogram

Ventricular late potentials at the end of the QRS can be detected on the body surface during sinus rhythm by recording a signal-averaged electrocardiogram (SAECG). In patients with coronary artery disease, these late potentials have been shown to be markers for spontaneous or inducible ventricular tachycardia, or both. The short-term (before and 10 +/- 4 days after coronary revascularization) influence of coronary artery bypass grafting (CABG) on the quantitative SAECG variables was studied in 40 patients with chronic coronary artery disease. Twenty-five of these patients had a previous myocardial infarction. In the 15 patients without previous myocardial infarction, no abnormal SAECG indexes were recorded before CABG and no change in the quantitative SAECG variables was observed after surgery. In the patients with a previous myocardial infarction, 7 (28%) had a late potential before CABG. After CABG, 5 (71%) patients remained late potential-positive, whereas the other 2 (29%) lost their late potential. The mean values of their SAECG variables improved after coronary revascularization. In the entire group of postmyocardial infarction patients, the high-frequency QRS duration had shortened (p less than 0.01) after CABG (the other SAECG indexes did not change). The postoperative arrhythmic complications (transient atrial fibrillation, new onset of ventricular couplets) tended to be more frequent in the postmyocardial infarction group and in patients with late potentials. Our findings suggest that the reported increase in ventricular arrhythmias after CABG is probably not related to a change in the arrhythmogenic substrate for ventricular reentry but is associated with changes in the arrhythmogenic milieu.

Correlation between the signal-averaged electrocardiogram and electrophysiologic study findings in patients with coronary artery disease and sustained ventricular tachycardia

Ventricular late potentials at the end of the surface QRS, detected on the signal-averaged electrocardiogram (SAECG) have been shown to be markers for spontaneous and/or inducible ventricular tachycardia (VT) in patients with coronary artery disease (CAD). We examined the correlations between electrophysiologic study (EPS) findings and SAECG indexes in 50 patients with chronic CAD with documented spontaneous VT/ventricular fibrillation (VF), who had either syncope (24 patients) or aborted sudden cardiac death (SCD). The prevalence of late potentials was significantly higher in the syncope patients (75%) compared with the SCD group (46%) (p less than 0.05). No correlation was found between the ventricular refractoriness and the SAECG indexes. There was a significant difference in quantitative SAECG indexes comparing the induction mode of the sustained VT/VF by single and double versus triple extrastimuli; the types of the induced VT (sustained monomorphic, sustained pleomorphic or VF, noninducible); and the cycle length of the induced sustained monomorphic VT with the high frequency QRS duration (QRSD). In conclusion, differences in prevalence and characteristics of ventricular late potentials were found between patients with syncope and with SCD. The degree of abnormality of SAECG indexes correlated with the type and the mode of induction of sustained VT. The magnitude of QRSD of the SAECG correlated with the cycle length of monomorphic VT. The above findings suggest that in patients with CAD and sustained VT/VF the SAECG variables are related to the area of reentry.