Prognostic significance of electrical alternans versus signal averaged electrocardiography in predicting the outcome of electrophysiological testing and arrhythmia-free survival

Human Cardiac Fibroblast Number and Activation State Modulate Electromechanical Function of hiPSC-Cardiomyocytes in Engineered Myocardium

Cardiac tissue engineering using hiPSC-derived cardiomyocytes is a promising avenue for cardiovascular regeneration, pharmaceutical drug development, cardiotoxicity evaluation, and disease modeling. Limitations to these applications still exist due in part to the need for more robust structural support, organization, and electromechanical function of engineered cardiac tissues. It is well accepted that heterotypic cellular interactions impact the phenotype of cardiomyocytes. The current study evaluates the functional effects of coculturing adult human cardiac fibroblasts (hCFs) in 3D engineered tissues on excitation and contraction with the goal of recapitulating healthy, nonarrhythmogenic myocardium in vitro. A small population (5% of total cell number) of hCFs in tissues improves tissue formation, material properties, and contractile function. However, two perturbations to the hCF population create disease-like phenotypes in engineered cardiac tissues. First, increasing the percentage of hCFs to 15% resulted in tissues with increased ectopic activity and spontaneous excitation rate. Second, hCFs undergo myofibroblast activation in traditional two-dimensional culture, and this altered phenotype ablated the functional benefits of hCFs when incorporated into engineered cardiac tissues. Taken together, the results of this study demonstrate that human cardiac fibroblast number and activation state modulate electromechanical function of hiPSC-cardiomyocytes and that a low percentage of quiescent hCFs are a valuable cell source to advance a healthy electromechanical response of engineered cardiac tissue for regenerative medicine applications.

Sudden Cardiac Death Risk Stratification - An Update

Sudden cardiac death (SCD) remains a major public health problem worldwide, yet current methods to identify those at greatest risk are inadequate. High-risk individuals may benefit from potentially life-saving treatment, such as insertion of an implantable-cardioverter defibrillator (ICD). However, such treatments are expensive and have their own associated risks. Furthermore, most cases of SCD occur in the general adult population who may be relatively asymptomatic but yet have an underlying predisposition to SCD. Hence, there is great interest and clinical need in improving methods for risk stratification of SCD to identify those at greatest risk and implement the most appropriate treatment. This review provides an update on current risk-stratification methods for SCD in high-risk groups, in particular patients with reduced left ventricular function following acute myocardial infarction and those with non-ischaemic dilated cardiomyopathy, and highlights some novel methods that may have a role to play in future risk-stratification schemes. Approaches and challenges for SCD risk stratification among the general public are also discussed.

Comparison of standard versus orthogonal ECG leads for T-wave alternans identification

T-wave alternans (TWA), an electrophysiologic phenomenon associated with ventricular arrhythmias, is usually detected from selected ECG leads. TWA amplitude measured in the 12-standard and the 3-orthogonal (vectorcardiographic) leads were compared here to identify which lead system yields a more adequate detection of TWA as a noninvasive marker for cardiac vulnerability to ventricular arrhythmias. Our adaptive match filter (AMF) was applied to exercise ECG tracings from 58 patients with an implanted cardiac defibrillator, 29 of which had ventricular tachycardia or fibrillation during follow-up (cases), while the remaining 29 were used as controls. Two kinds of TWA indexes were considered, the single-lead indexes, defined as the mean TWA amplitude over each lead (MTWAA), and lead-system indexes, defined as the mean and the maximum MTWAA values over the standard leads and over the orthogonal leads. Significantly (P < 0.05) higher TWA in the cases versus controls was identified only occasionally by the single-lead indexes (odds ratio: 1.0-9.9, sensitivity: 24-76%, specificity: 76-86%), and consistently by the lead-system indexes (odds ratio: 4.5-8.3, sensitivity: 57-72%, specificity: 76%). The latter indexes also showed a significant correlation (0.65-0.83) between standard and orthogonal leads. Hence, when using the AMF, TWA should be detected in all leads of a system to compute the lead-system indexes, which provide a more reliable TWA identification than single-lead indexes, and a better discrimination of patients at increased risk of cardiac instability. The standard and the orthogonal leads can be considered equivalent for TWA identification, so that TWA analysis can be limited to one-lead system.

A novel lead configuration for optimal spatio-temporal detection of intracardiac repolarization alternans

BACKGROUND

Electric alternans is a pattern of variation in the shape of ECG waveform that occurs every other beat. In humans, alternation in ventricular repolarization, known as repolarization alternans (RA), has been associated with increased vulnerability to ventricular tachycardia/fibrillation and sudden cardiac death.

METHODS AND RESULTS

This study investigates the spatio-temporal variability of intracardiac RA and its relationship to body surface RA in an acute myocardial ischemia model in swine. We developed a real-time multichannel repolarization signal acquisition, display, and analysis system to record ECG signals from catheters in the right ventricle, coronary sinus, left ventricle, and epicardial surface before and after circumflex coronary artery balloon occlusion. We found that RA is detectable within 4 minutes after the onset ischemia and is most prominently seen during the first half of the repolarization interval. Ischemia-induced RA was detectable on unipolar and bipolar leads (both in near- and far-field configurations) and on body surface leads. Far-field bipolar intracardiac leads were more sensitive for RA detection than body surface leads, with the probability of body surface RA detection increasing as the number of intracardiac leads detecting RA increased, approaching 100% when at least three intracardiac leads detected RA. We developed a novel, clinically applicable intracardiac lead system based on a triangular arrangement of leads spanning the right ventricular and coronary sinus catheters, which provided the highest sensitivity for intracardiac RA detection when compared with any other far-field bipolar sensing configurations.

CONCLUSIONS

In conclusion, intracardiac alternans, a complex spatio-temporal phenomenon associated with arrhythmia susceptibility and sudden cardiac death, can be reliably detected through a novel triangular right ventricular-coronary sinus lead configuration.

Risk Stratification for Sudden Cardiac Death after Acute Myocardial Infarction

Many patients who survive an acute myocardial infarction (AMI) remain at risk of recurrent cardiac events and sudden cardiac death after discharge, despite optimal medical treatment. Assessment of the degree of left ventricular dysfunction and residual myocardial ischaemia is useful to identify the patients at greatest risk. In addition, there is increasing evidence that a number of other cardiovascular tests can be used to detect autonomic dysfunction and myocardial substrate abnormalities postAMI that increase the risk of life-threatening ventricular arrhythmias. These investigations include ECG-based tests (signal averaged ECG and T-wave alternans), Holter-based recordings (heart rate variability and heart rate turbulence) and imaging techniques echocardiography and cardiac magnetic resonance), as well as invasive electrophysiological testing. This article reviews the current evidence for the use of these additional cardiac investigations among survivors of AMI to aid in their risk stratification for malignant ventricular arrhythmias and sudden cardiac death. Key words: Electrophysiological study, Holter recording, Non-invasive tests, Ventricular tachycardia

T-wave alternans found in preventricular tachyarrhythmias in CCU patients using a wavelet transform-based methodology

Ventricular tachyarrhythmias are potentially lethal cardiac pathologies and the commonest cause of sudden cardiac death. Efforts to predict the onset of such events are based on feature extraction from the surface ECG. T-wave alternans (TWAs) are considered a marker of abnormal ventricular function that may be associated with ventricular tachycardia (VT) and ventricular fibrillation. A novel TWA detection algorithm utilizing the continuous wavelet transform is described in this paper. Simulated ECGs containing artificial TWA were used to test the algorithm that achieved a sensitivity of 91.40% and a specificity of 94.00%. The algorithm was subsequently used to analyze the ECGs of eight patients prior to the onset of VT. Of these, the algorithm indicated that five patients exhibited TWA prior to the onset of the tachyarrhythmic events, while the remaining three patients did not exhibit identifiable TWA. Healthy individuals were also studied in which one short TWA episode was detected by the algorithm. However, closer visual inspection of the data revealed this to be a likely false positive result.

Electrocardiographic abnormalities and ventricular tachyarrhythmias after myocardial infarction

AIMS

To assess the association of electrocardiographic repolarization and depolarization patterns to vulnerability to ventricular tachyarrhythmias.

METHODS

In the present case-control study, a 12-lead ECG, signal-averaged ECG (SAECG), T-wave and QRS morphology, and T-wave alternans (TWA) were analyzed in post-MI patients with and without documented sustained ventricular tachycardia (VT) or fibrillation (VF) (VT/VF group, n=40, Non-VT/VF group, n=37, respectively) and healthy subjects (n=41).

RESULTS

The QRS complex duration, measured from standard ECG (128 +/- 32 ms vs. 102 +/- 21 ms, p<0.001) or SAECG (125 +/- 25 ms vs. 99 +/- 20 ms, p<0.001), was significantly longer in the VT/VF than Non-VT/VF group. Several T-wave morphology variables, e.g., the total cosine of the angle between the main vectors of T-wave and QRS loops (TCRT), were different in the VT/VF (-0.13 +/- 0.58) and Non-VT/VF group (-0.11 +/- 0.48) compared to the healthy controls (0.47 +/- 0.50, p<0.001). However, there were no significant differences in any of the T-wave morphology variables including TWA between the two post-MI groups.

CONCLUSION

Abnormalities in ventricular depolarization are more common among post-MI patients with prior VT/VF than in those without documented ventricular tachyarrhythmias. Abnormal T-wave morphology and TWA seem to reflect the heart disease rather than specifically vulnerability to VT/VF.

Microvolt T-wave alternans for risk stratification in athletes with ventricular arrhythmias: correlation with programmed ventricular stimulation

BACKGROUND

Aim of our study is to evaluate the role of T-wave alternans (TWA) to stratify the risk of sudden cardiac death in athletes (Ath) with complex ventricular arrhythmias (VA), and to document a possible correlation between TWA and electrophysiological testing (EPS) results.

METHODS

We studied 85 Ath with VA (61 M, mean age 32 +/- 11 years). In all cases a cardiological evaluation was performed, including TWA and EPS. The patients were evaluated during a follow-up of 30 +/- 21 months. The end point was the occurrence of sudden death (SD) or malignant ventricular tachyarrhythmias (VT).

RESULTS

TWA was negative in 57 Ath (68%), positive in 15 (18%) and indeterminate in 13 (14%). All subjects with negative TWA did not show induction of VT at EPS, with significant correlation between negative TWA and negative EPS (P < 0.001). All Ath with positive TWA also had VT induced by a EPS, with significant correlation (P < 0.001). By contrast, our data did not show significant correlation between indeterminate TWA and positive or negative EPS. However, there was significant correlation between abnormal TWA test (positive + indeterminate) and inducibility of VT at EPS (P < 0.001). During follow-up we observed a significant difference in end point occurrence (VT or SD) between Ath with negative or abnormal TWA and between Ath with negative or positive EPS.

CONCLUSION

TWA confirm its role as a simple and noninvasive test, and it seems useful for prognostic stratification of Ath with VA.

Comparison of microvolt T-wave alternans measurements using atrial pacing compared to atropine administration

BACKGROUND

Microvolt T-wave alternans (MTWA) has been associated with malignant ventricular arrhythmias in patients (pts) with structural heart disease. MTWA has been shown to be a strong heart rate-dependent arrhythmia marker. However, in clinical practice some pts in which MTWA should be assessed are unable to perform physical exercise to increase heart rate due to various reasons.

METHODS

In this study, we investigated the feasibility of noninvasive MTWA measurement by using intravenous atropine to increase heart rate and compared the results to MTWA measurement by right atrial (RA) pacing during electrophysiologic (EP) study in 27 consecutive pts (53 +/- 14 years; nine women). Determining the arrhythmia event-rate, a follow-up of 18 months was performed in all pts.

RESULTS

Using atropine, five pts (18%) did not reach the target heart rate (105 bpm). In the remaining group of pts, concordant results for MTWA assessment could be found in 21 pts (96%). Comparing MTWA positive tests there were slightly higher amplitudes using right atrial (RA) pacing than atropine (7.0 +/- 2.3 microV vs 6.3 +/- 2.2 microV, P = 0.03; r = 0.97). During follow-up all pts with a positive MTWA test had documented ventricular arrhythmias. There were no arrhythmic events in the MTWA negative group.

CONCLUSION

Whenever target heart rate for MTWA evaluation is obtained by intravenous atropine, the results are comparable to RA pacing. In using atropine there has been observed no pharmacologically influenced increase of MTWA voltage leading to false positive MTWA results. Therefore the use of atropine can be recommended as a safe, non-invasive, and reliable method for MTWA assessment.

Temporal variations in microvolt T-wave alternans testing after acute myocardial infarction

BACKGROUND

Microvolt T-wave alternans (TWA) have been accepted as a tool for assessing vulnerability to ventricular tachyarrhythmias. There is lack of data concerning prospective temporal variations in TWA measurements after acute myocardial infarction (AMI). We analysed the temporal patterns of TWA in post-AMI patients.

METHODS AND RESULTS

TWA tests were performed <1 month (TWA_early) and 6 months (TWA_late) after AMI in 51 consecutive patients treated with successful percutaneous coronary intervention (PCI). Twenty seven patients (53%) had anterior wall infarctions and 24 (47%) had inferior/lateral wall infarctions. TWA was measured during a treadmill manual exercise protocol and defined as positive, negative and indeterminate. Group A included patients with TWA negative in both tests and Group B included those with TWA abnormal (positive or indeterminate) at first or second determinations. TWA_early was negative, positive and indeterminate in 38 (74.6%), 8 (15.6%) and 5 (9.8%) patients, respectively, whereas TWA_late was negative, positive and indeterminate in 30 (58.9%), 14 (27.4%) and 7 (13.7%) patients, respectively. TWA_early was classified as normal in 74.6% and abnormal in 25.4% of the cases, and TWA_late was normal in 58.9% and abnormal in 41.1%. TWA tests were concordant in 36 patients (70.6%) and discordant 15 patients (29.4%). At TWA_late, 10 patients (19.6%) changed from TWA negative to TWA abnormal and 4 patients (7.8%) from TWA abnormal to TWA negative. After TWA_early+TWA_late, 45% of the patients had 1 test classified as abnormal. Left ventricular ejection fraction was <50% in 22% of Group A and 52% of Group B (P = 0.037).

CONCLUSIONS

In the era of primary PCI, temporal changes in TWA measurements may occur frequently during the first 6 months post-AMI. These findings should be considered in risk stratification strategies following AMI.

Ventricular arrhythmias in competitive athletes: risk stratification with T-wave alternans

Introduction:

Aim of our study is to evaluate the role of TWA to stratify the risk of sudden cardiac death in athletes (Ath) with complex ventricular arrhythmias (VA), and to document a possible correlation between TWA and electrophysiological testing (EES) results.

Methods:

We studied 43 Ath with VA (31 M, mean age 34 ± 12 years). In all cases a cardiological evaluation was performed, including TWA and EES. The patients were evaluated during a follow-up of 25 ± 22 months. The end-point was the occurrence of sudden death or malignant ventricular tachyarrhythmias (VT).

Results:

TWA was negative in 28 Ath (65%), positive in 8 (19%) and indeterminate in 7 (16%). All subjects with negative TWA did not show induction of VT at EES, with significant correlation between negative TWA and negative EES (p<0.001). All Ath with positive TWA also had VT induced by a EES, but without significant correlation between positive TWA and positive EES. In 2 Ath with undetermined TWA (29%) VT were induced at EES. Our data did not show significant correlation between indeterminate TWA and positive or negative EES. However, logistic regression analysis showed significant correlation between abnormal TWA test (positive or indeterminate) and inducibility of VT at EES (p<0.001). During follow-up we observed a significant difference in end-point occurrence between Ath with negative or positive TWA and between Ath with negative or positive EES.

Conclusion:

TWA confirm its role as a simple and non-invasive test, and it seems useful for prognostic stratification of Ath with VA.

Action potential duration dispersion and alternans in simulated heterogeneous cardiac tissue with a structural barrier

Structural barriers to wave propagation in cardiac tissue are associated with a decreased threshold for repolarization alternans both experimentally and clinically. Using computer simulations, we investigated the effects of a structural barrier on the onset of spatially concordant and discordant alternans. We used two-dimensional tissue geometry with heterogeneity in selected potassium conductances to mimic known apex-base gradients. Although we found that the actual onset of alternans was similar with and without the structural barrier, the increase in alternans magnitude with faster pacing was steeper with the barrier--giving the appearance of an earlier alternans onset in its presence. This is consistent with both experimental structural barrier findings and the clinical observation of T-wave alternans occurring at slower pacing rates in patients with structural heart disease. In ionically homogeneous tissue, discordant alternans induced by the presence of the structural barrier arose at intermediate pacing rates due to a source-sink mismatch behind the barrier. In heterogeneous tissue, discordant alternans occurred during fast pacing due to a barrier-induced decoupling of tissue with different restitution properties. Our results demonstrate a causal relationship between the presence of a structural barrier and increased alternans magnitude and action potential duration dispersion, which may contribute to why patients with structural heart disease are at higher risk for ventricular tachyarrhythmias.

Assessing the proarrhythmic potential of drugs: current status of models and surrogate parameters of torsades de pointes arrhythmias

Torsades de pointes (TdP) is a potentially lethal cardiac arrhythmia that can occur as an unwanted adverse effect of various pharmacological therapies. Before a drug is approved for marketing, its effects on cardiac repolarisation are examined clinically and experimentally. This paper expresses the opinion that effects on repolarisation duration cannot directly be translated to risk of proarrhythmia. Current safety assessments of drugs only involve repolarisation assays, however the proarrhythmic profile can only be determined in the predisposed model. The availability of these proarrhythmic animal models is emphasised in the present paper. It is feasible for the pharmaceutical industry to establish one or more of these proarrhythmic animal models and large benefits are potentially available if pharmaceutical industries and patient-care authorities embraced these models. Furthermore, suggested surrogate parameters possessing predictive power of TdP arrhythmia are reviewed. As these parameters are not developed to finalisation, any meaningful study of the proarrhythmic potential of a new drug will include evaluation in an integrated model of TdP arrhythmia.

T-wave alternans and the susceptibility to ventricular arrhythmias

T-wave alternans (TWA) reflects beat-to-beat fluctuations in the electrocardiographic T-wave, and is associated with dispersion of repolarization and the mechanisms for sudden cardiac arrest (SCA). This review examines the bench-to-bedside literature that, over decades, has linked alternans of repolarization in cellular, whole-heart, and human studies with spatial dispersion of repolarization, alternans of cellular action potential, and fluctuations in ionic currents that may lead to ventricular arrhythmias. Collectively, these studies provide a foundation for the clinical use of TWA to reflect susceptibility to ventricular arrhythmias in several disease states. This review then provides a contemporary evidence-based framework for the use of TWA to enhance risk stratification for SCA, identifying populations for whom TWA is best established, those for whom further studies are required, and areas for additional investigation.

Can microvolt T-wave alternans testing reduce unnecessary defibrillator implantation?

The Multicenter Automatic Defibrillator Implantation Trial II (MADIT II) and the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT) have established that patients with a reduced ejection fraction gain an overall mortality benefit from prophylactic implantable cardioverter-defibrillator therapy. Only a small proportion of the patients in these studies, however, have received life-saving therapy from the defibrillator. Because defibrillator therapy is invasive and expensive, patients with a low ejection fraction would benefit from effective risk stratification so that defibrillator therapy was used only in those at significant risk. In this review, we analyze prospective clinical trials that have evaluated microvolt T-wave alternans (MTWA) testing as a predictor of ventricular tachyarrhythmic events in populations of patients similar to those studied in MADIT II or SCD-HeFT; that is, patients with a reduced ejection fraction who were not selected on the basis of a history of ventricular tachyarrhythmias. In these studies, the average annual rate of fatal and nonfatal ventricular tachyarrhythmic events among the patients who tested negative for MTWA was around 1%. This rate is so low that it is unlikely that such patients would benefit from implantable cardioverter-defibrillator therapy. The mortality, moreover, was lower among MTWA-negative patients who did not receive implantable defibrillators than that observed in the MADIT II and SCD-HeFT patients who received implantable cardioverter-defibrillators. In response, patients with a low ejection fraction who are being considered for implantable cardioverter-defibrillator therapy should undergo MTWA testing as part of their evaluation.

Microvolt T-wave alternans: a review of techniques, interpretation, utility, clinical studies, and future perspectives

Microvolt T-wave alternans (TWA) testing involves measuring variation in the morphology of the T-wave on an every other beat basis. The magnitude of the variation observed is typically on the order of a few microvolts. Thus in order to detect microvolt TWA, specialized recording and signal processing methods must be employed for reliable measurement. Additionally, microvolt TWA is not generally present at rest even in patients at risk of ventricular tachyarrhythmias and therefore exercise stress, pharmacologic stress, or atrial pacing must be utilized in order to elevate the heart rate. A positive MTWA test is one in which sustained TWA is present with an onset heart rate < or = 110 bpm. With current instrumentation, microvolt TWA represents an inexpensive, convenient non-invasive testing modality. Microvolt TWA has been evaluated prospectively in a variety of patient populations as a means of predicting occurrence of ventricular tachyarrhythmic events and its association with the genesis of ventricular arrhythmias has been demonstrated. Future role of microvolt TWA testing in noninvasive risk stratification is awaiting results of ongoing clinical trials. In this article, we tried to review the techniques, interpretation, indications, clinical studies, and future perspectives of microvolt TWA.

Detection of Repolarization Alternans With an Implantable Cardioverter Defibrillator Lead in a Porcine Model

Mechanistic links have been suggested between repolarization alternans (RPA) and the onset of ventricular tachycardia (VT) and/or fibrillation. Endocardial detection of RPA may, therefore, be an important step in future device-based treatments of arrhythmias. Here, we investigate if RPA could be detected during acute ischemia using an implantable cardioverter defibrillator (ICD) lead (tip to distal coil) located in the right ventricular apex. In 18 pigs, the right coronary (n = 10) or left anterior descending coronary (n = 8) artery was occluded for 10 min using a balloon catheter, followed by reperfusion for 30 min, and re-occlusion for 30 min. RPA magnitude, computed using the modified moving average (MMA) method, showed a sharp increase in all 18 animals, from a mean baseline level of 1.9 +/- 1.3 mV to 3.0 +/- 1.3 mV during first occlusion (p < 0.001). RPA magnitude showed a prominent increase in 10 animals during re-occlusion, from a mean baseline level of 1.7 +/- 1.0 mV to 3.3 +/- 1.5 mV (p < 0.001). The protocol was terminated during the first two stages of occlusion and reperfusion for the remaining 8 animals due to the occurrence of ventricular fibrillation (VF). These results confirm that RPA increases under ischemic conditions and that it is possible to detect and track RPA dynamics with an ICD lead that is positioned in a clinically realistic location. Such an approach may be useful in formulating improved arrhythmia detection and control algorithms.

Microvolt T-Wave Alternans for the Risk Stratification of Ventricular Tachyarrhythmic Events

OBJECTIVES

The objective of this study was to perform a meta-analysis of the predictive value of microvolt T-wave alternans (MTWA) testing for arrhythmic events in a wide variety of populations.

BACKGROUND

Previous studies describing the use of MTWA as a predictor of ventricular tachyarrhythmic events have been limited by small sample sizes and disparate populations.

METHODS

Prospective studies of the predictive value of exercise-induced MTWA published between January 1990 and December 2004 were retrieved. Data from each article were abstracted independently by two authors using a standardized protocol. Summary estimates of the predictive value of MTWA were made using a random-effects model.

RESULTS

Data were accumulated from 19 studies (2,608 subjects) across a wide range of populations. Overall, the positive predictive value of MTWA for arrhythmic events was 19.3% at an average of 21 months' follow-up (95% confidence interval [CI] 17.7% to 21.0%), the negative predictive value was 97.2% (95% CI 96.5% to 97.9%), and the univariate relative risk of an arrhythmic event was 3.77 (95% CI 2.39 to 5.95). There was no difference in predictive value between ischemic and nonischemic heart failure subgroups. The positive predictive value varied depending on the population of patients studied (p < 0.0001).

CONCLUSIONS

Microvolt T-wave alternans testing has significant value for the prediction of ventricular tachyarrhythmic events; however, there are significant limitations to its use. The predictive value of MTWA varies significantly depending on the population studied. Careful standardization is needed for what constitutes abnormal MTWA. The incremental prognostic value of MTWA when used with other methods of risk stratification is unclear.

T-wave alternans phase following ventricular extrasystoles predicts arrhythmia-free survival

OBJECTIVE

The purpose of this study was to assess the value of T-wave alternans (TWA) following ventricular extrasystoles in predicting arrhythmia-free survival.

BACKGROUND

Stratifying risk for sudden death in patients with coronary disease and moderate left ventricular (LV) dysfunction remains a challenge. We hypothesized that, in such patients, a discontinuity in beat-to-beat T-wave alternation (TWA phase reversal) following single ventricular extrasystoles reflects transiently exaggerated repolarization dispersion, and predicts spontaneous ventricular arrhythmias.

METHODS

We studied 59 patients with ischemic LV dysfunction (mean LV ejection fraction 38.7 +/- 5.3%) and nonsustained ventricular tachycardia undergoing programmed stimulation. TWA was computed spectrally from the ECG during ventricular pacing, and TWA phase reversal was reflected by a discontinuity in T-wave oscillation after single ventricular extrasystoles.

RESULTS

Patients induced into ventricular arrhythmias (n = 36) had greater TWA magnitude (V(alt): 6.60 +/- 6.46 microV vs 2.61 +/- 1.97 microV; P = .001) and more frequent TWA phase reversal (62.1% vs 44.4%; P = .02) than those who were not (n = 23). During a mean follow-up of 36 +/- 12 months, positive TWA (V(alt) > or =1.9 microV) and TWA phase reversal both (P < .05) predicted events (all-cause mortality, ventricular tachycardia, ventricular fibrillation). Univariate predictors of arrhythmia-free survival were TWA phase reversal (P < .005), positive TWA (P < .05), age (P = .008), and LV mass index (P = .043). On multivariate analysis, only TWA phase reversal and age predicted events; if TWA phase was excluded, only positive TWA and age predicted events.

CONCLUSION

Phase reversal in TWA following ventricular extrasystoles predicts spontaneous ventricular arrhythmias and all-cause mortality in patients with moderate ischemic LV dysfunction and was a better predictor than positive TWA or programmed ventricular stimulation.

Electrocardiographic arrhythmia risk testing

Among the most compelling challenges facing cardiologists today is identification of which patients are at highest risk for sudden death. Automatic implantable cardioverter-defibrillators are now indicated in many of these patients, yet the role of noninvasive risk stratification in classifying patients at high risk is not well defined. The purpose of this review is to evaluate the various electrocardiographic (ECG) techniques that appear to have potential in assessment of risk for arrhythmia. The resting ECG (premature ventricular contractions, QRS duration, damage scores, QT dispersion, and ST segment and T wave abnormalities), T wave alternans, late potentials identified on signal-averaged ECGs, and heart rate variability are explored. Unequivocal evidence to support the widespread use of any single noninvasive technique is lacking; further research in this area is needed. It is likely that a combination of risk evaluation techniques will have the greatest predictive power in enabling identification of patients most likely to benefit from device therapy.

Utility of Implantable Cardioverter Defibrillator Electrograms to Estimate Repolarization Alternans Preceding a Tachyarrhythmic Event

Electrical alternans is a pattern of variation in the shape of the ECG waveform that appears on an every-other-beat basis. In humans, alternation in ventricular repolarization, namely, repolarization alternans, has been associated with increased vulnerability to ventricular tachycardia/ventricular fibrillation and sudden cardiac death. This study investigates the utility of implantable cardioverter defibrillator electrograms to estimate repolarization alternans preceding a tachyarrhythmic event. It is demonstrated that microvolt-level repolarization alternans is present prior to an arrhythmic event, and one can record low-amplitude-noise signals that can be used to obtain reliable estimates of repolarization alternans. This study eventually may lead to new methods that would prevent the onset of malignant tachyarrhythmias.

T-wave alternans: marker, mechanism, and methodology for predicting sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of cardiovascular mortality. Therefore, identifying patients at highest risk for SCD is crucial. Conventional noninvasive markers of SCD are inadequate because of low positive predictive value. The presence of visible T-wave alternans (TWA) on electrocardiogram often predicts the occurrence of lethal ventricular arrhythmias. Signal processing methods have made it possible to detect microvolt-level and visually inapparent TWA on electrocardiogram. TWA is caused by underlying regional inhomogeneities of ventricular repolarization, which predispose patients to have ventricular arrhythmias. Microvolt TWA provoked either by atrial pacing, pharmacological stress, or exercise is a promising marker of arrhythmia vulnerability. Several large trials have shown TWA to be comparable or superior to other noninvasive markers and electrophysiologic study in the prediction of SCD. The patient populations in these trials include post myocardial infarction, both ischemic and nonischemic heart failure, and suspected arrhythmias. Prospective trials regarding benefits of implantation of cardioverter-defibrillator therapy based on TWA results are ongoing.

T wave alternans is a predictor of death in patients with congestive heart failure

Few data are available about the prognostic role of T wave alternans in patients with congestive heart failure. To assess the ability of T wave alternans, used alone or in combination with other risk markers, to predict cardiac death in decompensated patients, we enrolled 46 patients, mean age 59+/-9, males 89%, ischemic etiology 61%, NYHA class III 35%, left ventricular ejection fraction 29+/-7%. After 1.6 years follow-up, seven patients died from cardiac death (16%), non-sudden in six (86%) and sudden in one (14%). T wave alternans was positive in 24 (52%), negative in 13 (28%), indeterminate in nine patients (20%). T wave alternans was positive in all patients with events (100%) but only in 16 of 37 patients without (41%) (P=0.02). Other predictors of cardiac death were O(2) consumption at the peak of exercise (P=0.03), standard deviation of all NN intervals (P=0.05) and Wedge pressure (P=0.03). When receiver operator characteristics curves were calculated, the highest area (0.73) was found for O(2) consumption at the peak of exercise considering the single variables and for O(2) consumption at the peak of exercise plus T wave alternans (0.79) for combination of them; the comparison of the two receiver operator characteristics curves did not reach statistical difference (P=0.5). In conclusion, this is the first study reporting that T wave alternans can predict cardiac death, with a marginal additional prognostic power when used in combination with measurement of O(2) consumption at the peak of exercise.

Catecholamine-provoked microvoltage T wave alternans in genotyped long QT syndrome

Macrovoltage T wave alternans (TWA) has been described in congenital long QT syndrome (LQTS). Microvoltage T wave alternans (microV-TWA) at low heart rate (HR) is a marker of arrhythmogenic risk in many conditions, but its significance in LQTS has not been established. Twenty-three genotypically heterogeneous patients with LQTS and 16 control subjects were studied at rest and during phenylephrine and dobutamine provocation. Genotyping was established by PCR amplification and DNA sequencing of the three most common LQTS genes; KCNQ1/KVLQT1 (LQT1), KCNH2/HERG (LQT2), and SCN5A (LQT3). microV-TWA was determined using Fast Fourier transform. Precluded by ectopy, microV-TWA could not be assessed in 8 of 23 patients with LQTS. In the remaining 15 patients with LQTS, microV-TWA occurred at lower HR in LQTS than in controls (117 +/- 49 vs 153 +/- 37 beats/min; P < 0.05). Patients with LQTS developed microV-TWA at HR < 150 beats/min more often than controls (10/15 vs 2/16; P = 0.003). However, microV-TWA was not detected in the 3 individuals with a history of out-of-hospital cardiac arrest including a 14-year-old male with an F339del-KVLQT1 mutation (LQT1) who had dobutamine-provoked polymorphic ventricular tachycardia requiring external defibrillation. Catecholamine-provoked microV-TWA occurs at lower HR in patients with LQTS than in healthy people but does not identify high risk subjects.

Endocardial detection of repolarization alternans

Repolarization alternans (RPA) is prognostic of sudden cardiac death and is thought to be mechanistically linked to the initiation of ventricular tachyarrhythmias. Thus, implantable cardiac device detection of RPA may be therapeutically valuable. Because alternans detection is currently limited to surface electrocardiograms, we investigated whether RPA could be measured using a single right-ventricular endocardial lead in humans. Such a location was chosen because it is consistent with the requirements for long-term implantable-device implementation. During diagnostic electrophysiological testing, 28 patients (23 male, 5 female; 61 +/- 15 years) were evaluated for surface T-wave alternans (TWA; the current "gold standard" for RPA detection) and endocardial RPA during 5 min of 550-ms right-atrial pacing. Power spectral analysis indicated that 11/28 patients had both surface TWA and endocardial RPA, 9/28 patients had neither, and 8/28 patients had discordant results (71% concordance; p = 0.02). Importantly, unlike surface TWA, endocardial RPA was detectable on a beat-to-beat basis. Given the putative mechanistic link between RPA and ventricular arrhythmias, beat-to-beat endocardial RPA detection might be of diagnostic or therapeutic utility.

Combination of QT variability and signal-averaged electrocardiography in association with ventricular tachycardia in postinfarction patients

The authors investigate incidence of ventricular tachycardia/ventricular fibrillation (VT/VF) in relationship with combination of noninvasive arrhythmia risk markers as left ventricular ejection fraction (LVEF), late potentials (LP), and QT variability index (QTVI) and compare the utility of their combination in association with sustained ventricular arrhythmias in patients after myocardial infarction (MI). Fifty-four patients with old MI, among them 27 with documented spontaneous sustained VT/VF entered the study. All of them underwent evaluation for arrhythmias and noninvasive risk stratification. Logistic regression analysis demonstrated that the highest association with ventricular tachyarrhythmia had combination of LP and increased QTVI (13.8, P<.0002), followed then by combination of LVEF and LP (12.2, P<.0005), LP alone (P<.001), QTVI (P<.002) and LVEF (P<.003) alone and age (P<.01). After stepwise regression analysis showed that the model including association of LP and QTVI, age and EF is the best one for delineating patients having the risk of ventricular tachyarrhythmia development. In conclusion, patients with combination of positive LP and increased QTVI after MI have high likelihood for development of serious sustained arrhythmia.

Pathophysiological basis and clinical application of T-wave alternans

We review the contemporary understanding of the pathophysiology of repolarization alternans and present a perspective on the use of T-wave alternans (TWA) as a risk stratification marker of malignant ventricular arrhythmias. Several studies have demonstrated a high correlation of susceptibility to ventricular arrhythmias and sudden cardiac death with the existence of TWA. We describe a number of cellular and molecular alterations in the diseased heart that may provide a link between electrical and mechanical alternans and arrhythmia susceptibility. Repolarization alternans is likely the result of distinct and diverse cellular and molecular alterations that are associated with exaggerated regional repolarization heterogeneity, which renders the heart susceptible to malignant arrhythmias.

T Wave Alternans in high arrhythmic risk patients: analysis in time and frequency domains: a pilot study

BACKGROUND

T wave alternans (TA) is a repolarisation phenomenon manifesting as a microvolt beat to beat change in the amplitude of the T wave and ST segment. TA has been shown to be a predictor of arrhythmic risk in unselected myocardial infarction populations. TA has not been used to differentiate risk within the ischaemic cardiomyopathy population.

METHODS

The subjects investigated comprised, Group 1: 7 stable patients with remote (>20 months) extensive myocardial scarring and no arrhythmic events (NYHA 3 and 4). Group2: 9 post infarction patients with malignant arrhythmia and implantable defibrillator. During breath holding, 20 continuous QRST complexes from each patients X, Y and Z leads were digitally recorded. Time domain, resultant absolute difference vectors (ATA), were calculated for alternate resultant T wave sequences. Group differences between the magnitude and temporal distribution of mean ATAs and their spectral and cross-spectral analysis were compared.

RESULTS

Group 1 v Group 2 mean ATAs were 10.7 (7.17) v 11.7 (8.48) respectively, not significant. Each group had a homogenous temporal distribution of ATAs. Both group's largest mean ATA frequency components were between 0 to 25 Hz, the largest ATA component being at the DC frequency. Cross spectral analysis showed no significant differences in group ATA frequency content.

CONCLUSION

The frequency content and microvolt magnitude of T wave alternans was not significantly different in these two groups. The specificity of T wave alternans for differentiating arrhythmic risk in post infarction scarring and heart failure needs investigation.

Onset heart rate of microvolt-level T-wave alternans provides clinical and prognostic value in nonischemic dilated cardiomyopathy

OBJECTIVES

This study was designed to determine the prognostic value of onset heart rate (OHR) in T-wave alternans (TWA) in patients with nonischemic dilated cardiomyopathy (DCM).

BACKGROUND

One of the current major issues in DCM is to prevent sudden cardiac death (SCD). However, the value of the OHR of TWA as a prognostic indicator in DCM remains to be elucidated.

METHODS

We prospectively investigated 104 patients with DCM undergoing TWA testing. The end point of this study was defined as SCD, documented sustained ventricular tachycardia/ventricular fibrillation. Relations between clinical parameters and subsequent outcome were evaluated.

RESULTS

Forty-six patients presenting with TWA were assigned to one of the following two subgroups according to OHR for TWA of < or = 100 beats/min: group A (n = 24) with OHR < or = 100 beats/min and group B (n = 22) with 100 < OHR < or = 110 beats/min. T-wave alternans was negative in 37 patients (group C) and indeterminate in 21 patients. The follow-up result comprised 83 patients with determined TWA. During a follow-up duration of 21 +/- 14 months, there was a total of 12 arrhythmic events, nine of which included three SCDs in group A, two in group B and one in group C. The forward stepwise multivariate Cox hazard analysis revealed that TWA with an OHR < or = 100 beats/min and left ventricular ejection fraction were independent predictors of these arrhythmic events (p = 0.0001 and p = 0.0152, respectively).

CONCLUSIONS

The OHR of TWA is of additional prognostic value in DCM.

Arrhythmic risk stratification of post-myocardial infarction patients

Post-myocardial infarction risk stratification, especially arrhythmic risk stratification, is an issue that has still not been wholly addressed in modern clinical cardiology. In the past 10 years, arrhythmic risk stratification has been approached mainly by evaluating frequency and complexity of premature ventricular contractions, detected on Holter monitoring, often in association with determination of percent ejection fraction. This methodology has been proven to be limited and fallacious according to the Cardiac Arrhythmia Suppression Trial I and II (CAST I,II) results, in which suppression of premature ventricular contractions or premature ventricular beats throughout by antiarrhythmic drugs resulted in an increase in both cardiac and arrhythmic mortality. Only amiodarone as an antiarrhythmic drug, as proven in the recent European Myocardial Infarct Amiodarone Trial (EMIAT) and Canadian Amiodarone Myocardial Infarction Trial (CAMIAT), was effective in reducing arrhythmic mortality without affecting cardiac mortality, in patients selected mainly because of a reduced ejection fraction, with and without premature ventricular contractions. Conversely, it is well known that beta-blockers are effective in preventing sudden death in post-acute myocardial infarction (AMI) patients, thus reducing cardiac and arrhythmic mortality. Conversely, in other institutions, risk stratification in post-AMI patients has been performed by electrophysiologic study obtained, without any previous noninvasive arrhythmic risk stratification, in all post-AMI patients. In recent years, many other noninvasive electrocardiology parameters, such as late potentials (signal-averaged electrocardiography), heart rate variability, baroreflex sensitivity, and, more recently, T-wave alternance, have been shown to be useful, but they are associated with a low specificity in the noninvasive identification of patients at high risk for arrhythmic mortality. Conversely, in the Multicenter Automatic Defibrillation Implantation Trial (MADIT), electrophysiology confirmed that inducibility of ventricular tachycardia shows high specificity and a high predictive value for arrhythmic events. Nevertheless, the MADIT study population is not comparable to a cohort of consecutive patients who have recently had a myocardial infarction. In this setting, the highest risk of arrhythmic events can be observed in patients with depressed percent ejection fraction (< 35%) and in the first 6 months after AMI. Today, the most convincing approach seems to be the one combining both noninvasive risk stratification parameters (e.g., premature ventricular beats > 10/h or reduced heart rate variability < 70 ms or a positive signal-averaged electrocardiogram) followed by a further arrhythmic risk stratification, obtained through electrophysiologic study. Several published and ongoing trials that utilize various arrhythmic risk stratification techniques as part of their protocol are reviewed.