Increasing averaging beats improves the test accuracy on Holter-based late potentials in patients with myocardial infarction

BACKGROUND

The prevalence of Holter-based late potentials (H-LPs) in cases of fatal cardiac events has increased. Although the noise level of H-LP is higher than that of conventional real-time late potential (LP) recording, a procedure to reduce the noise severity in H-LP by increasing the averaging beats has not been investigated.

METHODS

We enrolled 104 patients with post-myocardial infarction (MI) and 86 control participants. Among the patients, 30 reported sustained ventricular tachycardia (VT), and the remaining 74 had unrecorded VT. H-LPs were measured twice in all groups to evaluate the efficacy of increasing the averaging beats for H-LPs. Thereafter, the average of LP was calculated at 250 (default setting), 300, 400, 500, 600, 700, and 800 beats.

RESULTS

Across all three groups (MI-VT group, MI non-VT group, and control group), the noise levels significantly decreased in consonance with the increase in averaging beats. In the MI-VT group, the H-LP positive rate considerably increased with the increase in the averaging beats from 250 to 800 both at night and daytime. In the MI-VT group, the LP parameters significantly deteriorated, which led to a positive judgment corresponding to the increment of the averaged night and day beats. The H-LP positive rates were unchanged in the MI non-VT and control groups, while the LP parameters remained consistent, despite the increased averaging beats in the MI non-VT and control groups.

CONCLUSION

Increasing the calculated averaging beats in H-LPs can improve the sensitivity of predicting fatal cardiac events in patients with MI.

Diurnal Variation in and Optimal Time to Measure Holter-Based Late Potentials to Predict Lethal Arrhythmia after Myocardial Infarction

Background and Objectives: Holter-based late potentials (LPs) are useful for predicting lethal arrhythmias in organic cardiac diseases. Although Holter-based LPs exhibit diurnal variation, no studies have evaluated the optimal timing of LP measurement over 24 h for predicting lethal arrhythmia that leads to sudden cardiac death. Thus, this study aimed to validate the most effective timing for Holter-based LP testing and to explore factors influencing the diurnal variability in LP parameters. Materials and Methods: We retrospectively analyzed 126 patients with post-myocardial infarction (MI) status and 60 control participants who underwent high-resolution Holter electrocardiography. Among the 126 post-MI patients, 23 developed sustained ventricular tachycardia (VT) (the MI-VT group), while 103 did not (the MI-non-VT group) during the observation period. Holter-based LPs were measured at 0:00, 4:00, 8:00, 12:00, 16:00, and 20:00, and heart rate variability analysis was simultaneously performed to investigate factors influencing the diurnal variability in LP parameters. Results: Holter-based LP parameters showed diurnal variation with significant deterioration at night and improvement during the day. Assessment at the time with the longest duration of low-amplitude signals < 40 μV in the filtered QRS complex terminus (LAS40) gave the highest receiver operating characteristics curve (area under the curve, 0.659) and the highest odds ratio (3.75; 95% confidence interval, 1.45-9.71; p = 0.006) for predicting VT. In the multiple regression analysis, heart rate and noise were significant factors affecting the LP parameters in the MI-VT and control groups. In the non-VT group, the LP parameters were significantly influenced by noise and parasympathetic heart rate variability parameters, such as logpNN50. Conclusions: For Holter-based LP measurements, the test accuracy was higher when the LP was measured at the time of the highest or worst value of LAS40. Changes in autonomic nervous system activity, including heart rate, were factors influencing diurnal variability. Increased parasympathetic activity or bradycardia may exacerbate Holter-based LP parameters.

Comparison between Standard and High-Definition Multi-Electrode Mapping Catheter in Ventricular Tachycardia Ablation

A high-definition mapping catheter has been introduced, allowing for bipolar recording along and across the spline with a rapid assessment of voltage, activation, and directionality of conduction. We aimed to evaluate differences in mapping density, accuracy, time, and consequently RF time between different mapping catheters used for ventricular tachycardia (VT) ablation. We enrolled consecutive patients undergoing VT ablation at our center. Patients were divided into the LiveWire 2-2-2 mm catheter (group A) and the HD Grid SE (group B). Primary endpoints were total RF delivery time, the number of points acquired in sinus rhythm and VT, and the scar area. Fifty-one patients were enrolled, 22 in group A and 29 in group B. More points were acquired in the Grid group in sinus rhythm (SR) and during VT (2060.78 ± 1600.38 vs. 3278.63 ± 3214.45, p = 0.05; 4201.13 ± 5141.61 vs. 10,569.43 ± 13,644.94, p = 0.02, respectively). The scar area was smaller in group B (Bipolar area, cm2 4.52 ± 2.72 vs. 2.89 ± 2.81, p = 0.05. Unipolar area, cm2 7.47 ± 4.55 vs. 5.56 ± 2.79, p = 0.03). Radiofrequency (RF) time was shorter in the Grid group (30.52 ± 13.94 vs. 22.16 ± 11.03, p = 0.014). LPs and LAVAs were eliminated in overall >93% of patients. No differences were found in terms of arrhythmia-free survival at follow-up. In conclusion, the use of a high-definition mapping catheter was associated with significantly shorter mapping time during VT and RF time. Significantly more points were acquired in SR and during VT. During remap, we also observed more LAVAs and LPs requiring further ablation.

Association of non-invasive electrocardiographic risk factors with left ventricular systolic function in post-myocardial infarction patients with mildly reduced or preserved ejection fraction: Insights from the PRESERVE-EF study

Background

Electrocardiographic non‐invasive risk factors (NIRFs) have an important role in the arrhythmic risk stratification of post‐myocardial infarction (post‐MI) patients with preserved or mildly reduced left ventricular ejection fraction (LVEF). However, their specific relation to left ventricular systolic function remains unclear. We aimed to evaluate the association between NIRFs and LVEF in the patients included in the PRESERVE‐EF trial.

Methods

We studied 575 post‐MI ischemia‐free patients with LVEF≥40% (mean age: 57.0 ± 10.4 years, 86.2% men). The following NIRFs were evaluated: premature ventricular complexes, non‐sustained ventricular tachycardia (NSVT), late potentials (LPs), prolonged QTc, increased T‐wave alternans, reduced heart rate variability, and abnormal deceleration capacity with abnormal turbulence.

Results

There was a statistically significant relationship between LPs (Chi‐squared = 4.975; p < .05), nsVT (Chi‐squared = 5.749, p < .05), PVCs (r= −.136; p < .01), and the LVEF. The multivariate linear regression analysis showed that LPs (p = .001) and NSVT (p < .001) were significant predictors of the LVEF. The results of the multivariate logistic regression analysis indicated that LPs (OR: 1.76; 95% CI: 1.02–3.05; p = .004) and NSVT (OR: 2.44; 95% CI: 1.18–5.04; p = .001) were independent predictors of the mildly reduced LVEF: 40%–49% versus the preserved LVEF: ≥50%.

Conclusion

Late potentials and NSVT are independently related to reduced LVEF while they are independent predictors of mildly reduced LVEF versus the preserved LVEF. These findings may have important implications for the arrhythmic risk stratification of post‐MI patients with mildly reduced or preserved LVEF.

Ambulatory electrocardiographic markers predict serious cardiac events in patients with chronic kidney disease: The Japanese Noninvasive Electrocardiographic Risk Stratification of Sudden Cardiac Death in Chronic Kidney Disease (JANIES-CKD) study

Background

Noninvasive electrocardiographic markers (NIEMs) are promising arrhythmic risk stratification tools for assessing the risk of sudden cardiac death. However, little is known about their utility in patients with chronic kidney disease (CKD) and organic heart disease. This study aimed to determine whether NIEMs can predict cardiac events in patients with CKD and structural heart disease (CKD‐SHD).

Methods

We prospectively analyzed 183 CKD‐SHD patients (median age, 69 years [interquartile range, 61−77 years]) who underwent 24‐h ambulatory electrocardiographic monitoring and assessed the worst values for ambulatory‐based late potentials (w‐LPs), heart rate turbulence, and nonsustained ventricular tachycardia (NSVT). The primary endpoint was the occurrence of documented lethal ventricular tachyarrhythmias (ventricular fibrillation or sustained ventricular tachycardia) or cardiac death. The secondary endpoint was admission for cardiovascular causes.

Results

Thirteen patients reached the primary endpoint during a follow‐up period of 24 ± 11 months. Cox univariate regression analysis showed that existence of w‐LPs (hazard ratio [HR] = 6.04, 95% confidence interval [CI]: 1.4−22.3, p = .007) and NSVT [HR = 8.72, 95% CI: 2.8−26.5: p < .001] was significantly associated with the primary endpoint. Kaplan–Meier analysis demonstrated that the combination of w‐LPs and NSVT resulted in a lower event‐free survival rate than did other NIEMs (p < .0001). No NIEM was useful in predicting the secondary endpoint, although the left ventricular mass index was correlated with the secondary endpoint.

Conclusion

The combination of w‐LPs and NSVT was a significant risk factor for lethal ventricular tachyarrhythmias and cardiac death in CKD‐SHD patients.

The clinical utility of procainamide-induced late potentials on the signal averaged ECG

BACKGROUND

Late potentials (LPs) identified on the signal averaged electrocardiogram (SAECG) are a marker for an increased risk of arrhythmias in Brugada syndrome (BrS). Procainamide is a sodium channel blocker used to diagnose BrS. The effects of Procainamide on the SAECG in those with BrS and the significance of Procainamide-induced LPs are unknown.

METHODS

Procainamide provocation was performed for suspected BrS with 12-lead and SAECG pre- and post-infusion. Filtered QRS duration (fQRSd), duration of low amplitude signals <40 μV (LAS40) and root-mean-square voltage in the terminal 40 ms (RMS40) were determined.

RESULTS

Data from 150 patients were included in the analysis (mean age 44.5 years, 109 males). Procainamide increased fQRSd (Pre 118.8 ± 10.5 ms, post 121.2 ± 10.2 ms, p < 0.001) and LAS40 (Pre 38.7 ± 9.8 ms, post 40.2 ± 10.5 ms, p = 0.005) and decreased RMS40 (Pre 24.6 ± 12 ms, post 22.8 ± 12 ms, p = 0.002). LPs were present in 68/150 (45%) at baseline. Fifteen patients with negative baseline SAECGs had LPs unmasked by Procainamide, but six patients had LPs at baseline that were no longer present following Procainamide. Comparing those with normal hearts (n = 48) to those with a final diagnosis of BrS (n = 38), Procainamide prolonged fQRSd to a greater extent in those with BrS. Comparing those with Procainamide-induced LPs to those with no LPs at any time did not highlight any aspect of phenotype and did not correlate with a history of ventricular arrhythmias.

CONCLUSIONS

Procainamide influences the SAECG, provoking LPs in a small proportion of patients. However, there is no evidence that Procainamide-induced LPs provide additional diagnostic information or aid risk stratification.

Twelve-lead and signal-averaged electrocardiographic parameters among beta-thalassemia major patients

BACKGROUND

The majority of beta thalassemia major (β-TM) patients suffer from cardiac disease, while a significant proportion of them die suddenly. Twelve-lead and signal-averaged electrocardiography (SAECG) are simple, inexpensive, readily available tools for identifying an unfavorable arrhythmiological substrate by detecting the presence of arrhythmias, conduction abnormalities, and late potentials (LPs) in these patients.

METHODS

A total of 47 β-TM patients and 30 healthy controls were submitted to 12-lead and signal-averaged electrocardiography. Basic electrocardiographic parameters and prevalence of LPs were recorded. Basic echocardiographic parameters were estimated by transthoracic echocardiography. T2* was calculated by cardiac magnetic resonance imaging wherever available.

RESULTS

β-TM patients demonstrated a more prolonged PR interval (167.74 msec vs 147.07 msec) (P = .043), a higher prevalence of PR prolongation (21.05% vs 0%) (P = .013), and a higher prevalence of LPs (18/47, 38.3% vs 2/30, 6.7%) (P = .002) compared with controls. The prevalence of atrial fibrillation among b-TM patients was estimated at 10.64%. Patients had also greater E/e' ratio (8.35, SD = 2.2 vs 7, SD = 2.07) (P = .012) and LAVI (30.7 mL/m2, SD = 8.76 vs 24.6 mL/m2, SD = 6.57) (P = .002) than controls. Regression analysis showed that QTc and LAVI could correctly predict the presence of LPs in the 80.9% of the patients.

CONCLUSIONS

β-TM patients have a higher prevalence of a prolonged PR interval, atrial fibrillation, and LPs. Twelve-lead and SAECG performance was feasible in all subjects and constitutes a readily available tool for assessing myocardial electrophysiological alterations in this patient group.

Multicenter Study of Dynamic High-Density Functional Substrate Mapping Improves Identification of Substrate Targets for Ischemic Ventricular Tachycardia Ablation

OBJECTIVES

The goal of this study was to evaluate the role of dynamic substrate changes in facilitating conduction delay and re-entry in ventricular tachycardia (VT) circuits.

BACKGROUND

The presence of dynamic substrate changes facilitate functional block and re-entry in VT but are rarely studied as part of clinical VT mapping.

METHODS

Thirty patients (age 67 ± 9 years; 27 male subjects) underwent ablation. Mapping was performed with the Advisor HD Grid multipolar catheter. A bipolar voltage map was obtained during sinus rhythm (SR) and right ventricular sense protocol (SP) single extra pacing. SR and SP maps of late potentials (LP) and local abnormal ventricular activity (LAVA) were made and compared with critical sites for ablation, defined as sites of best entrainment or pace mapping. Ablation was then performed to critical sites, and LP/LAVA identified by the SP.

RESULTS

At a median follow-up of 12 months, 90% of patients were free from antitachycardia pacing (ATP) or implantable cardioverter-defibrillator shocks. SP pacing resulted in a larger area of LP identified for ablation (19.3 mm² vs. 6.4 mm²) during SR mapping (p = 0.001), with a sensitivity of 87% and a specificity of 96%, compared with 78% and 65%, respectively, in SR.

CONCLUSIONS

LP and LAVA observed during the SP were able to identify regions critical for ablation in VT with a greater accuracy than SR mapping. This may improve substrate characterization in VT ablation. The combination of ablation to critical sites and SP-derived LP/LAVA requires further assessment in a randomized comparator study.

Effects of Extracardiac Factors in Signal-Averaged Electrocardiography-measured Late Potentials from Early Anterior Myocardial Infarction in Intensive Cardiac Care Unit

BACKGROUND

one modality that can predict ventricular arrhythmias after myocardial infarction (MI), particularly anterior MI, is signal-averaged electrocardiogram (SA-ECG), through the detection of late potentials (LP) which is a substrate for ventricular arrhythmias. Extracardiac factors, which are also risk factors for MI, such as hypertension, diabetes, dyslipidemia, and obesity, are apparently associated with post-MI ventricular arrhythmias, which in turn may be correlated with LP. This study aims to determine the effect of extracardiac risk factors on LP incidence in anterior MI patients treated in the intensive cardiac care unit (ICCU).

METHODS

this was a cross-sectional study in which 80 subjects with anterior MI during the period of December 2018-2019 underwent SA-ECG examination. The medical history and extracardiac risk factors were recapitulated, and then the SA-ECG data was taken from either direct examination or ICCU patients' database in that period. This study used multivariate analysis with logistic regression test.

RESULTS

the most common factors found were hypertension (70.00%), followed by dyslipidemia (56.25%), diabetes (46.25%), and obesity (38.75%). Obesity and dyslipidemia are extracardiac factors with the two biggest roles in the prevalence of LP. However, from additional analysis, we found that diabetes with acute hyperglycemia also had immense influence on the occurrence of LP. The OR for diabetes with acute hyperglycemia, obesity, and dyslipidemia were 4.806 (IK95% 0.522-44.232), 4.291 (IK95% 0.469-39.299), and 3.237 (IK95% 0.560-18.707). However, the association is not statistically significant.

CONCLUSION

patients with anterior MI who suffer from diabetes with hyperglycemia in admission, obesity, and dyslipidemia have a potentially higher LP prevalence, despite statistical insignificance. To increase the prognostic value of SA-ECG, serial examinations are needed during hospitalization.

[The Impact of Effective Therapy With Atorvastatin on the Dynamics of Parameters of Electrical Instability in Patients with ST-Elevation Myocardial Infarction]

AIM

To assess the dynamics of parameters of myocardial electrical instability in patients with ST-elevation (STE) myocardial infarction (MI) treated with various doses of atorvastatin.

MATERIALS AND METHODS

Patients with STEMI (n=70), who received atorvastatin 20 or 80 mg/day for 48 weeks, were divided into two groups: group "Е" - 38 patients (54.3 %) in whom by 48‑th week target values of low density lipoprotein cholesterol (LDLC) were achieved, and group "NE" - 32 patients (45.7 %) in whom these levels were not achieved. On days 7-9, at 24th and 48th weeks after onset of MI the patients underwent 24‑hour 12‑leads ECG monitoring with subsequent analysis of parameters of myocardial electrical inhomogeneity: late ventricular potentials (LVP), dispersion of QT-interval duration, heart rate variability (HRV) and turbulence.

RESULTS

After of treatment with atorvastatin target value of LDLC was achieved in 73.5 and 36.1 % of patients receiving 80 and 20 mg/day, respectively. In the group "E" we observed positive dynamics of LVP parameters (QRSf - p.

Signal-averaged electrocardiography: Past, present, and future

Signal-averaged electrocardiography records delayed depolarization of myocardial areas with slow conduction that can form the substrate for monomorphic ventricular tachycardia. This technique has been examined mostly in patients with coronary artery disease, but its use has been declined over the years. However, several lines of evidence, derived from hitherto clinical data in patients with healed myocardial infarction, indicate that signal-averaged electrocardiography remains a valuable tool in risk stratification, especially when incorporated into algorithms encompassing invasive and noninvasive indices. Such an approach can aid the more precise identification of candidates for device therapy, in the context of primary prevention of sudden cardiac death. This article reappraises the value of signal-averaged electrocardiography as a predictor of arrhythmic outcome in patients with ischemic heart disease and discusses potential future indications.

Genotype-phenotype relationship and risk stratification in loss-of-function SCN5A mutation carriers

INTRODUCTION

Loss-of-function (LoF) mutations in the SCN5A gene cause multiple phenotypes including Brugada Syndrome (BrS) and a diffuse cardiac conduction defect. Markers of increased risk for sudden cardiac death (SCD) in LoF SCN5A mutation carriers are ill defined. We hypothesized that late potentials and fragmented QRS would be more prevalent in SCN5A mutation carriers compared to SCN5A-negative BrS patients and evaluated risk markers for SCD in SCN5A mutation carriers.

METHODS

We included all SCN5A loss-of-function mutation carriers and SCN5A-negative BrS patients from our center. A combined arrhythmic endpoint was defined as appropriate ICD shock or SCD.

RESULTS

Late potentials were more prevalent in 79 SCN5A mutation carriers compared to 39 SCN5A-negative BrS patients (66% versus 44%, p = .021), while there was no difference in the prevalence of fragmented QRS. PR interval prolongation was the only parameter that predicted the presence of a SCN5A mutation in BrS (OR 1.08; p < .001). Four SCN5A mutation carriers, of whom three did not have a diagnostic type 1 ECG either spontaneously or after provocation with a sodium channel blocker, reached the combined arrhythmic endpoint during a follow-up of 44 ± 52 months resulting in an annual incidence rate of 1.37%.

CONCLUSION

LP were more frequently observed in SCN5A mutation carriers, while fQRS was not. In SCN5A mutation carriers, the annual incidence rate of SCD was non-negligible, even in the absence of a spontaneous or induced type 1 ECG. Therefore, proper follow-up of SCN5A mutation carriers without Brugada syndrome phenotype is warranted.

Signal-Averaged Electrocardiography as a Noninvasive Tool for Evaluating the Outcomes After Radiofrequency Catheter Ablation of Ventricular Tachycardia in Patients With Ischemic Heart Disease: Reassessment of an Old Tool

BACKGROUND

Inducibility of ventricular tachycardia (VT) has limited ability to predict recurrent VT after catheter ablation (CA). We sought to correlate the signal-averaged ECG (SAECG) with the endocardial scar characteristics in patients with ischemic VTs. We suggest that successful CA can result in normalization of the SAECG.

METHODS AND RESULTS

Fifty patients (42 male; aged 67±10 years, ejection fraction 34±12%) with ischemic VTs were prospectively enrolled. SAECG was performed before and after CA. Patients with at least 2 abnormal criteria (filtered QRS ≥114 ms; root mean square 40 <20 μV, and low-amplitude potentials 40 >38 ms) were defined as having positive SAECG. There was a linear correlation between endocardial scar area (<1.5 mV) and filtered QRS (r=0.414; P=0.003). CA resulted in normalization of the SAECG in 6 patients. In patients with filtered QRS ≤120 ms, 13 (40.6%) patients had normal SAECG after CA compared with 7 (21.9%) before ablation (P=0.034). Patients with normal or normalized SAECG after CA had better VT-free survival compared with those whose SAECG remained abnormal. Abnormal SAECG after CA was a predictor for VT recurrence: hazard ratio=3.64; P=0.039 for the overall population, and hazard ratio=5.80; P=0.022 for patients having QRS ≤120 ms.

CONCLUSIONS

There is a significant correlation between the surface SAECG and endocardial scar size in patients with ischemic VTs. A successful CA can result in normalization of SAECG that is associated with more favorable long-term outcomes. SAECG can be useful to assess the procedural success of VT ablation.

Correlation of scar in cardiac MRI and high-resolution contact mapping of left ventricle in a chronic infarct model

Background

Endocardial mapping for scars and abnormal electrograms forms the most essential component of ventricular tachycardia ablation. The utility of ultra‐high resolution mapping of ventricular scar was assessed using a multielectrode contact mapping system in a chronic canine infarct model.

Methods

Chronic infarcts were created in five anesthetized dogs by ligating the left anterior descending coronary artery. Late gadolinium‐enhanced magnetic resonance imaging (LGE MRI) was obtained 4.9 ± 0.9 months after infarction, with three‐dimensional (3D) gadolinium enhancement signal intensity maps at 1‐mm and 5‐mm depths from the endocardium. Ultra‐high resolution electroanatomical maps were created using a novel mapping system (Rhythmia Mapping System, Rhythmia Medical/Boston Scientific, Marlborough, MA, USA) Rhythmia Medical, Boston Scientific, Marlborough, MA, USA with an 8.5F catheter with mini‐basket electrode array (64 tiny electrodes, 2.5‐mm spacing, center‐to‐center).

Results

The maps contained 7,754 ± 1,960 electrograms per animal with a mean resolution of 2.8 ± 0.6 mm. Low bipolar voltage (<2 mV) correlated closely with scar on the LGE MRI and the 3D signal intensity map (1‐mm depth). The scar areas between the MRI signal intensity map and electroanatomic map matched at 87.7% of sites. Bipolar and unipolar voltages, compared in 592 electrograms from four MRI‐defined scar types (endocardial scar, epicardial scar, mottled transmural scar, and dense transmural scar) as well as normal tissue, were significantly different. A unipolar voltage of <13 mV correlated with transmural extension of scar in MRI. Electrograms exhibiting isolated late potentials (ILPs) were manually annotated and ILP maps were created showing ILP location and timing. ILPs were identified in 203 ± 159 electrograms per dog (within low‐voltage areas) and ILP maps showed gradation in timing of ILPs at different locations in the scar.

Conclusions

Ultra‐high resolution contact electroanatomical mapping accurately localizes ventricular scar and abnormal myocardial tissue in this chronic canine infarct model. The high fidelity electrograms provided clear identification of the very low amplitude ILPs within the scar tissue and has the potential to quickly identify targets for ablation.

Resolution of late potentials with improvement in left ventricular systolic function in patients with first acute myocardial infarction

BACKGROUND

Ventricular late potentials predict subsequent arrhythmic events and sudden death in postinfarction patients. Late potentials are recorded in the infarcted area, but it should be pointed out that they probably represent micropotentials in the area of delayed conduction found among isolated areas of scar tissue and normal myocardium.

HYPOTHESIS

The study was undertaken to investigate the relationship between chronic reversible myocardial ischemia, such as stunned or hibernating myocardium, and late potentials in 38 patients with a first myocardial infarction.

METHODS

The patients were divided into two groups, one with (Group 1) and one without (Group 2) resolution of late potentials recorded by signal-averaged electrocardiogram at 6 months after onset of myocardial infarction. We investigated the clinical, echocardiographic, and signal-averaged electrocardiographic characteristics of Groups 1 and 2.

RESULTS

In the chronic phase of myocardial infarction, a higher incidence of patency of the infarct-related artery and an improvement of wall motion score were found in Group 1, and left ventricular ejection fraction was better preserved in Group 1 than in Group 2.

CONCLUSIONS

These results suggest that the resolution of late potentials was influenced by the improvement of left ventricular systolic function and patency of the infarct-related artery. We concluded that chronic reversible myocardial ischemia, such as stunned or hibernating myocardium, might be the substrate that generated late potentials.

Abnormal signal-averaged electrocardiograms in patients with incomplete right bundle-branch block

BACKGROUND AND HYPOTHESIS

A hypothesis was formulated that regional delayed activation of the right ventricle, as seen in incomplete right bundle-branch (IRBBB) aberrancy, may simulate late potential activity and may be responsible for abnormal signal-averaged electrocardiograms (SAECGs). No previous studies have specifically addressed this issue in this particular group of patients (with IRBBB). Therefore, the aim of the present study was to investigate the incidence of abnormal SAECGs in patients with IRBBB. If this were confirmed, our purpose would further be to investigate ways of reducing the false positive results.

METHODS

The study group included 53 patients (28 men and 25 women), aged 53 +/- 13 years, with no history of previous myocardial infarction or ventricular tachycardia and who had an electrocardiogram (ECG) showing IRBBB. An SAECG was also performed in a control group of 19 age-matched individuals with a normal ECG. Time domain analysis was performed using a band pass filter of 40-250 Hz. The following parameters were considered normal: filtered QRS duration (QRSD) < 114 ms, root mean square of the voltage of the last 40 ms of the QRS complex (RMS) > 20 microV, and the duration of the low amplitude signal (< 40 microV) at the terminal portion of the QRS (LAS) < 38 ms. An SAECG was considered abnormal if any two of these criteria were abnormal.

RESULTS

The mean values of the SAECG parameters were: QRSD 101 +/- 11 ms, RMS 32 +/- 20 microV, LAS 32 +/- 12 ms, and noise 0.29 +/- 0.13 microV. Abnormal SAECGs with at least two criteria satisfied were present in 16 of 53 (30%) patients compared with 0 (0%) of 19 individuals in the control group (p = 0.02). Abnormal values included the combination of RMS and LAS in 12 patients and all three parameters in 4 patients. However, if the definition of late potentials were limited to the combination of abnormal QRSD and either RMS or LAS values, the incidence of false positive results (4 patients) (7.5%) would be significantly decreased (p = 0.007). At 21 months of follow-up, no arrhythmic events occurred.

CONCLUSIONS

Delayed terminal conduction observed in IRBBB may cause a high incidence of false positive late potentials on SAECGs. Based on this study, we propose that this can be largely remedied if the optimal criteria for the presence of late potentials in patients with IRBBB always include the combination of QRSD and either RMS or LAS.

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.

The effect of myocardial surgical revascularization on left ventricular late potentials

BACKGROUND

The presence of ventricular late potentials (LP) is an important indicator for the development of ventricular tachyarrhythmias due to ischemic heart disease. The effect of myocardial revascularization on LP has remained controversial. The purpose of this study was to determine whether complete myocardial surgical revascularization (CABG) documented by myocardial perfusion scintigraphy might alter the substrate responsible for LP.

METHODS

Prospectively, enrolled patients undergoing elective CABG were evaluated with thallium-201 myocardial perfusion scintigraphy and signal- averaged ECG pre- and postoperatively. SAECG recordings were obtained serially: before, 48-72 hours and 3 months after CABG. LPS were defined as positive if SAECG met at least two of Gomes criteria. Scintigraphies were performed pre- and 3 months postoperatively for determination of the success of revascularization. Changes observed in SAECG recordings after CABG were compared between those with and without successful revascularization.

RESULTS

CABG resulted in successful revascularization in 23 patients and was unsuccessful in 17 (no change or deterioration of the perfusion defects). Preoperative SAECG values were not different between groups except for RMS values. The incidence of LP decreased significantly postoperatively in patients with improved myocardial perfusion, whereas there were no changes in patients who did not have postoperative perfusion improvement (McNemar test, P < 0.05).

CONCLUSIONS

LPs disappear following the elimination of myocardial ischemia by complete surgical revascularization. Persistence of ischemia following CABG usually results in the persistence of late potentials. The incidence of ventricular arrhythmias is expected to be unchanged in these patients and they should be reevaluated for reinterventions.