Predictive value of microvolt T-wave alternans for sudden cardiac death in patients with preserved cardiac function after acute myocardial infarction: results of a collaborative cohort study

Risk Stratification for Ventricular Tachyarrhythmias by Ambulatory Electrocardiogram-Based Frequency Domain T-Wave Alternans

BACKGROUND

Ambulatory electrocardiogram (ECG)-based T-wave alternans (TWA) quantified by the modified moving average method (MMA) can be used to identify patients at risk for sudden cardiac death. However, there is no information available on ambulatory ECG-based TWA as quantified by the frequency domain (FD) method to identify patients with an implantable cardioverter defibrillator (ICD) who are at high risk for ventricular tachyarrhythmias. Further, there are few data regarding the comparison of clinical utility of FD-TWA with MMA-TWA, heart rate variability (HRV), and heart rate turbulence (HRT).

METHODS AND RESULTS

In 41 patients with ICD, of whom 14 patients had a past history of at least one appropriate ICD discharge, FD-TWA, MMA-TWA, HRV, and HRT were analyzed from 24-hour Holter ECG monitoring recordings. Only positive results of FD-TWA and abnormal HRV (standard deviation of all normal-to-normal intervals ≤111 ms) were significantly more frequently observed in patients with than without appropriate ICD discharge. Patients with FD-TWA positive had a significantly higher risk of appropriate ICD discharge than those with FD-TWA negative (50% vs 16%; odds ratio, 5.3 [95% confidence interval, 1.2-23.7], P = 0.02). When FD-TWA and HRV were combined, the specificity (93% vs 59%, P = 0.003) and predictive accuracy (83% vs 66%, P = 0.07) for the identification of patients with appropriate ICD discharge were greater than those for FD-TWA only.

CONCLUSION

The ambulatory ECG-based FD-TWA might be useful to detect patients with ICD who are at high risk for ventricular tachyarrhythmias, and the combination of FD-TWA and HRV might improve the ability to detect such high-risk patients.

T-Wave Alternans Is Linked to Microvascular Obstruction and to Recurrent Coronary Ischemia After Myocardial Infarction

The purpose of this study is to investigate the relationship between T-wave alternans (TWA), infarct size and microvascular obstruction (MVO) and recurrent cardiac morbidity after ST elevation myocardial infarction (STEMI). One hundred six patients underwent TWA testing 1-12 months and 57 patients underwent cardiac magnetic resonance imaging (MRI) in the first 2-4 days after STEMI. During follow-up (3.5 ± 0.5 years), death (n = 2), ventricular tachycardia (n = 3), supraventricular tachycardia (n = 4), heart failure (n = 3) and recurrent coronary ischemia (n = 25) were observed. After multivariate analysis, positive TWA (HR2.59, CI1.10-6.11, p0.024) and larger MVO (HR1.08, CI1.01-1.16, p0.034) were associated with recurrent angina or ACS. Presence of MVO was correlated with TWA (Spearman rho 0.404, p0.002) and the impairment of LVEF (-0.524, p < 0.001). Patients after STEMI remain at a high risk of symptoms of coronary ischemia. The presence of MVO and TWA 1-12 months after STEMI is related to each other and to recurrent angina or ACS.

Cardiac innervation and sudden cardiac death

Afferent and efferent cardiac neurotransmission via the cardiac nerves intricately modulates nearly all physiological functions of the heart (chronotropy, dromotropy, lusitropy, and inotropy). Afferent information from the heart is transmitted to higher levels of the nervous system for processing (intrinsic cardiac nervous system, extracardiac-intrathoracic ganglia, spinal cord, brain stem, and higher centers), which ultimately results in efferent cardiomotor neural impulses (via the sympathetic and parasympathetic nerves). This system forms interacting feedback loops that provide physiological stability for maintaining normal rhythm and life-sustaining circulation. This system also ensures that there is fine-tuned regulation of sympathetic-parasympathetic balance in the heart under normal and stressed states in the short (beat to beat), intermediate (minutes to hours), and long term (days to years). This important neurovisceral/autonomic nervous system also plays a major role in the pathophysiology and progression of heart disease, including heart failure and arrhythmias leading to sudden cardiac death. Transdifferentiation of neurons in heart failure, functional denervation, cardiac and extracardiac neural remodeling has also been identified and characterized during the progression of disease. Recent advances in understanding the cellular and molecular processes governing innervation and the functional control of the myocardium in health and disease provide a rational mechanistic basis for the development of neuraxial therapies for preventing sudden cardiac death and other arrhythmias. Advances in cellular, molecular, and bioengineering realms have underscored the emergence of this area as an important avenue of scientific inquiry and therapeutic intervention.

[Microvolt T-wave alternans. Ischemic vs. nonischemic dilated cardiomyopathy]

The use of implantable cardioverter defibrillators (ICD) for primary preventive therapy of sudden arrhythmogenic death has become a mainstay in selected patients with systolic congestive heart failure, particularly in the setting of ischemic and nonischemic cardiomyopathy (Moss et al., N Engl J Med 346:877–883, 2002; Bardy et al., N Engl J Med 352:225–237, 2005). However, more accurate identification of high-risk patients is desirable in order to avoid unnecessary ICD implants. Since currently available risk stratification methods have limited predictive accuracy, development of new techniques is important in order to noninvasively assess arrhythmogenic risk in patients prone to sudden death.Microvolt level T-wave alternans (mTWA) has recently been proposed to assess abnormalities in ventricular repolarization favoring the occurrence of reentrant arrhythmias (Adam et al., J Electrocardiol 17:209–218, 1984; Pastore et al., Circulation 99:1385–1394, 1999). In 1994, a preliminary clinical study by Rosenbaum et al. convincingly demonstrated that mTWA is closely related to arrhythmia induction in the electrophysiology laboratory as well as to the occurrence of spontaneous ventricular tachyarrhythmias during follow-up (Rosenbaum et al., N Engl J Med 330:235–241,1994). More recently, a number of clinical studies have examined its clinical applicability in ischemic and nonischemic cardiomyopathy.

Tensor-based detection of T wave alternans using ECG

T wave alternans is defined as changes in the T wave amplitude in an ABABAB-pattern. It can be found in ECG signals of patients with heart diseases and is a possible indicator to predict the risk on sudden cardiac death. Due to its low amplitude, robust automatic T wave alternans detection is a difficult task. We present a new method to detect T wave alternans in multichannel ECG signals. The use of tensors (multidimensional matrices) permits the combination of the information present in different channels, making detection more reliable. The possibility of decomposition of incomplete tensors is exploited to deal with noisy ECG segments. Using a sliding window of 128 heartbeats, a tensor is constructed of the T waves of all channels. Canonical Polyadic Decomposition is applied to this tensor and the resulting loading vectors are examined for information about the T wave behavior in three dimensions. T wave alternans is detected using a sign change counting method that is able to extract both the T wave alternans length and magnitude. When applying this novel method to a database of patients with multiple positive T wave alternans tests using the clinically available spectral method tests, both the length and the magnitude of the detected T wave alternans is larger for these subjects than for subjects in a control group.

Dependency of exercise-induced T-wave alternans predictive power for the occurrence of ventricular arrhythmias from heart rate

BACKGROUND

T-wave alternans (TWA) is a noninvasive index of risk for the occurrence of ventricular arrhythmias. It is known that TWA amplitude (TWAA) increases with heart rate (HR) but how the TWA predictive power varies with HR remains unknown. Thus, the aim of this study was to evaluate the dependency of exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias from HR.

METHODS

TWA was identified using our HR adaptive match filter in exercise ECGs from 248 patients with implanted cardiac defibrillator (ICD), of which 72 developed ventricular tachycardia and/or fibrillation during the 4 year follow-up (ICD_Cases) and 176 did not (ICD_Controls). TWA predictive power was evaluated at HRs from 80 to 120 bpm by computing the area under the receiver operating characteristic curve (AUC) obtained using the maximum TWAA (maxTWAA) and the TWAA ratio (TWAAratio; i.e., the ratio between TWAA at a specific HR and at 80 bpm).

RESULTS

TWAA increased with HR. At 80 bpm maxTWAA was lower than at 120 bpm in both ICD_Cases (22 μV vs 41 μV; P < 10(-2) ) and ICD_ Controls (16 μV vs 36 μV; P < 10(-4) ). However, only at 80 bpm ICD_Cases showed significantly higher maxTWAA than ICD_Controls (AUC = 0.6486; P = 0.0080). TWAAratio was higher in ICD_Controls than ICD_Cases for all HR but 120 bpm, and its predictive power was maximum at 115 bpm (AUC = 0.6914; P < 0.05).

CONCLUSIONS

Exercise-induced TWA predictive power for the occurrence of ventricular arrhythmias, quantified using both maxTWAA and TWAAratio, was higher at low rather than at high HR.

Infarct tissue heterogeneity by contrast-enhanced magnetic resonance imaging is a novel predictor of mortality in patients with chronic coronary artery disease and left ventricular dysfunction

BACKGROUND

Strategies for prevention of sudden cardiac death focus on severe left ventricular (LV) dysfunction, although most sudden cardiac death postmyocardial infarction occurs in patients with mild/moderate LV dysfunction. We tested the hypothesis that infarct heterogeneity by cardiac magnetic resonance is associated with mortality beyond LV ejection fraction (LVEF) in patients with coronary artery disease and LV dysfunction. In addition, we examined the association between infarct heterogeneity and mortality in those with LVEF >35%.

METHODS AND RESULTS

We studied 301 patients with coronary artery disease and LV dysfunction referred for cardiac magnetic resonance. We quantified total infarct mass, infarct core mass, and peri-infarct zone (PIZ) normalized for total infarct mass (%PIZ) using signal-intensity criteria of >2 SDs, >3 SDs, and 2- to -3 SDs above remote myocardium, respectively. Mean LVEF was 41 ± 14%. After 3.9 years median follow-up, 66 (22%) patients died (13 sudden cardiac death; 33 with LVEF >35%). In patients with LVEF >35%, below-median %PIZ carried an annual death rate of 2.8% versus 12% in patients with above-median %PIZ (P<0.001). In a multivariable model, %PIZ maintained strong association with mortality adjusted to patient age, LVEF, right ventricular ejection fraction, prolonged QT interval, and total infarct size and resulted in improve risk reclassification 0.492 (95% confidence interval, 0.183-0.817).

CONCLUSIONS

Cardiac magnetic resonance infarct heterogeneity has a strong association with mortality independent of LVEF in patients with coronary artery disease and LV dysfunction, particularly in patients with mild or moderate LV dysfunction. Further studies incorporating cardiac magnetic resonance in clinical decision making for defibrillator therapy are warranted.

Risk stratification for sudden cardiac death: current status and challenges for the future

Sudden cardiac death (SCD) remains a daunting problem. It is a major public health issue for several reasons: from its prevalence (20% of total mortality in the industrialized world) to the devastating psycho-social impact on society and on the families of victims often still in their prime, and it represents a challenge for medicine, and especially for cardiology. This text summarizes the discussions and opinions of a group of investigators with a long-standing interest in this field. We addressed the occurrence of SCD in individuals apparently healthy, in patients with heart disease and mild or severe cardiac dysfunction, and in those with genetically based arrhythmic diseases. Recognizing the need for more accurate registries of the global and regional distribution of SCD in these different categories, we focused on the assessment of risk for SCD in these four groups, looking at the significance of alterations in cardiac function, of signs of electrical instability identified by ECG abnormalities or by autonomic tests, and of the progressive impact of genetic screening. Special attention was given to the identification of areas of research more or less likely to provide useful information, and thereby more or less suitable for the investment of time and of research funds.

Time-domain T-wave alternans is strongly associated with a history of ventricular fibrillation in patients with Brugada syndrome

AIMS

T-wave alternans (TWA) is an indicator of vulnerability to ventricular arrhythmias and is useful for predicting sudden cardiac death (SCD) in patients with various structural heart diseases. We evaluated whether high levels of time-domain TWA on ambulatory ECG (AECG) are associated with a history of ventricular fibrillation (VF) in Brugada syndrome (BrS) patients.

METHODS AND RESULTS

We examined the associations among VF history, family history of SCD, spontaneous type 1 electrocardiogram (ECG), late potentials, VF induction by programmed electrical stimulation, and TWA in 45 BrS patients (44 males; mean age, 45 ± 15 years). TWA analyzed from 24-h AECG recordings using the modified moving average method was positive in 13 of 43 patients (30%). Patients with a history of VF had a significantly higher incidence of a positive TWA test (82% vs. 13%; P < 0.001) and spontaneous type 1 ECG (92% vs. 38%; P = 0.007) than those without VF history. Multivariate analysis indicated that positive TWA (OR 7.217; 95% CI 2.503-35.504; P = 0.002) and spontaneous type 1 ECG (OR 5.530; 95% CI 1.651-34.337; P = 0.020) were closely associated with VF history. Spontaneous type 1 ECG had high sensitivity (92%) but low specificity (63%). Positive TWA was a reliable marker with high sensitivity and specificity (82% and 88%, respectively).

CONCLUSION

Elevated time-domain TWA on AECG confirms arrhythmia risk in symptomatic BrS patients without the need for provocative stimuli.

[Ventricular tachycardia in postinfarction patients and coronary heart disease. Treatment and prognostic significance]

Patients with coronary heart disease are subject to an increased risk for sudden cardiac death (SCD). Within the first 30-90 days after the myocardial infarct the risk is particularly high. In times of implantable cardioverter-defibrillator (ICD) on the one hand and the ability to bridge high-risk periods with e. g. wearable defibrillator vests on the other, adequate risk stratification is essential. Currently, the main parameter for this is the left ventricular ejection fraction (LVEF). However, risk stratification by measurement of the LVEF has severe limitations, especially since the majority of patients suffering from SCD have a normal LVEF. Various other methods like ventricular ectopy, signal-averaged ECG, QRS width, microvolt T-wave alternans and programmed ventricular stimulation have been previously evaluated. None of these methods alone or in combination with a left ventricular function assessment was capable of improving the predictability of arrhythmic events significantly. Considering the multiple mechanisms that can lead to SCD, a single risk stratifier seems unrealistic. However, patients with chronic total occlusion of a coronary artery and residual or provocable ischemia have an increased risk for SCD. Therefore a combination of clinical and angiographic parameters seems reasonable. Advanced echocardiographic parameters e.g. mechanical dispersion could be used on a complementary role.

A translational approach to probe the proarrhythmic potential of cardiac alternans: a reversible overture to arrhythmogenesis?

Electrocardiographic alternans, a phenomenon of beat-to-beat alternation in cardiac electrical waveforms, has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death (SCD). In the clinical setting, a positive microvolt T-wave alternans test has been associated with a heightened risk of arrhythmic mortality and SCD during medium- and long-term follow-up. However, rather than merely being associated with an increased risk for SCD, several lines of preclinical and clinical evidence suggest that cardiac alternans may play a causative role in generating the acute electrophysiological substrate necessary for the onset of ventricular arrhythmias. Deficiencies in Ca(2+) transport processes have been implicated in the genesis of alternans at the subcellular and cellular level and are hypothesized to contribute to the conditions necessary for dispersion of refractoriness, wave break, reentry, and onset of arrhythmia. As such, detecting acute surges in alternans may provide a mechanism for predicting the impending onset of arrhythmia and opens the door to delivering upstream antiarrhythmic therapies. In this review, we discuss the preclinical and clinical evidence to support a causative association between alternans and acute arrhythmogenesis and outline the potential clinical implications of such an association.

The detection of T-wave variation linked to arrhythmic risk: an industry perspective

Although the scientific literature contains ample descriptions of peculiar patterns of repolarization linked to arrhythmic risk, the objective quantification and classification of these patterns continues to be a challenge that impacts their widespread adoption in clinical practice. To advance the science, computerized algorithms spawned in the academic environment have been essential in order to find, extract and measure these patterns. However, outside the strict control of a core lab, these algorithms are exposed to poor quality signals and need to be effective in the presence of different forms of noise that can either obscure or mimic the T-wave variation (TWV) of interest. To provide a practical solution that can be verified and validated for the market, important tradeoffs need to be made that are based on an intimate understanding of the end-user as well as the key characteristics of either the signal or the noise that can be used by the signal processing engineer to best differentiate them. To illustrate this, two contemporary medical devices used for quantifying T-wave variation are presented, including the modified moving average (MMA) for the detection of T-wave Alternans (TWA) and the quantification of T-wave shape as inputs to the Morphology Combination Score (MCS) for the trending of drug-induced repolarization abnormalities.

In-hospital heart rate turbulence and microvolt T-wave alternans abnormalities for prediction of early life-threatening ventricular arrhythmia after acute myocardial infarction

BACKGROUND

In the setting of primary prevention, most implantable cardiac defibrillators (ICD) are implanted more than 6 months after acute myocardial infarction (AMI). Abnormal heart rate turbulence (HRT) and T-wave alternans (TWA) are predictors of long-term sudden cardiac death (SCD). We intended to assess the predictive value of HRT and TWA for early post-AMI SCD and life-threatening ventricular arrhythmias (VA).

METHODS

One hundred ninety-nine consecutive patients with AMI were prospectively included (age 61.7 years, LV ejection fraction 45%). One hundred eighty-three patients (92%) underwent percutaneous coronary intervention. We assessed HRT using turbulence slope (TS), turbulence onset (TO), and TWA on channels 1 and 2 (TWA1 and TWA2) using the modified moving average method. Predictive performance for SCD/VA was assessed by area under the receiver operating curve characteristic (ROC-AUC).

RESULTS

Within 6 months after AMI, 2 patients (1%) developed life-threatening VA and 3 (1.5%) experienced SCD. TO and TWA1 had poor ROC-AUC (both 0.64) whereas TS and TWA2 failed to show any predictive performance (ROC-AUC 0.48 and 0.57, respectively). When combining TO and TWA1, ROC-AUC increased to 0.80. Importantly, when considering the subset of patients with a LV ejection fraction ≤40%, the combined variable of TO and TWA1 remained strongly predictive of a short-term event (ROC-AUC 0.86).

CONCLUSIONS

Combined assessment of HRT and TWA showed a high predictive performance for SCD or life-threatening VA within 6 months after AMI. This combined Holter ECG index could be useful to identify high-risk patients who might benefit from early ICD implantation.

A combined anatomic and electrophysiologic substrate based approach for sudden cardiac death risk stratification

BACKGROUND

Although left ventricular ejection fraction (LVEF) is the primary determinant for sudden cardiac death (SCD) risk stratification, in isolation, LVEF is a sub-optimal risk stratifier. We assessed whether a multi-marker strategy would provide more robust SCD risk stratification than LVEF alone.

METHODS

We collected patient-level data (n = 3355) from 6 studies assessing the prognostic utility of microvolt T-wave alternans (MTWA) testing. Two thirds of the group was used for derivation (n = 2242) and one-third for validation (n = 1113). The discriminative capacity of the multivariable model was assessed using the area under the receiver-operating characteristic curve (c-index). The primary endpoint was SCD at 24 months.

RESULTS

In the derivation cohort, 59 patients experienced SCD by 24 months. Stepwise selection suggested that a model based on 3 parameters (LVEF, coronary artery disease and MTWA status) provided optimal SCD risk prediction. In the derivation cohort, the c-index of the model was 0.817, which was significantly better than LVEF used as a single variable (0.637, P < .001). In the validation cohort, 36 patients experienced SCD by 24 months. The c-index of the model for predicting the primary endpoint was again significantly better than LVEF alone (0.774 vs 0.671, P = .020).

CONCLUSIONS

A multivariable model based on presence of coronary artery disease, LVEF and MTWA status provides significantly more robust SCD risk prediction than LVEF as a single risk marker. These findings suggest that multi-marker strategies based on different aspects of the electro-anatomic substrate may be capable of improving primary prevention implantable cardioverter-defibrillator treatment algorithms.

The power of exercise-induced T-wave alternans to predict ventricular arrhythmias in patients with implanted cardiac defibrillator

The power of exercise-induced T-wave alternans (TWA) to predict the occurrence of ventricular arrhythmias was evaluated in 67 patients with an implanted cardiac defibrillator (ICD). During the 4-year follow-up, electrocardiographic (ECG) tracings were recorded in a bicycle ergometer test with increasing workload ranging from zero (NoWL) to the patient's maximal capacity (MaxWL). After the follow-up, patients were classified as either ICD_Cases (n = 29), if developed ventricular tachycardia/fibrillation, or ICD_Controls (n = 38). TWA was quantified using our heart-rate adaptive match filter. Compared to NoWL, MaxWL was characterized by faster heart rates and higher TWA in both ICD_Cases (12-18 μ V vs. 20-39 μ V; P < 0.05) and ICD_Controls (9-15 μ V vs. 20-32 μ V; P < 0.05). Still, TWA was able to discriminate the two ICD groups during NoWL (sensitivity = 59-83%, specificity = 53-84%) but not MaxWL (sensitivity = 55-69%, specificity = 39-74%). Thus, this retrospective observational case-control study suggests that TWA's predictive power for the occurrence of ventricular arrhythmias could increase at low heart rates.

Risk stratification after myocardial infarction: is left ventricular ejection fraction enough to prevent sudden cardiac death?

Patients who have experienced a myocardial infarction (MI) are at increased risk of sudden cardiac death (SCD). With the advent of implantable cardioverter-defibrillators (ICDs), accurate risk stratification has become very relevant. Numerous investigations have proven that a reduced left ventricular ejection fraction (LVEF) significantly increases the SCD risk. Furthermore, ICD implantation in patients with reduced LVEF confers significant survival benefit. As a result, LVEF is the cornerstone of current decision making for prophylactic ICD implantation after MI. However, LVEF as standalone risk stratifier has major limitations: (i) the majority of SCD cases occur in patients with preserved or moderately reduced LVEF, (ii) only relatively few patients with reduced LVEF will benefit from an ICD (most will never experience a threatening arrhythmic event, others have a high risk for non-sudden death), (iii) a reduced LVEF is a risk factor for both sudden and non-sudden death. Several other non-invasive and invasive risk stratifiers, such as ventricular ectopy, QRS duration, signal-averaged electrocardiogram, microvolt T-wave alternans, markers of autonomic tone as well as programmed ventricular stimulation, have been evaluated. However, none of these techniques has unequivocally demonstrated the efficacy when applied alone or in combination with LVEF. Apart from their limited sensitivity, most of them are risk factors for both sudden and non-sudden death. Considering the multiple mechanisms involved in SCD, it seems unlikely that a single test will prove adequate for all patients. A combination of clinical characteristics with selected stratification tools may significantly improve risk stratification in the future.

Microvolt T-wave alternans predicts cardiac events after acute myocardial infarction in patients treated with primary percutaneous coronary intervention

BACKGROUND

Current risk stratification after acute myocardial infarction (MI) depends on left ventricular ejection fraction. Microvolt T-wave alternans (MTWA) is one of promising markers to predict cardiac events in patients after acute MI treated according to current guidelines.

METHODS

In this single center study, 112 consecutive patients with the first anterior ST-elevation MI undergoing PCI <12 hours from symptom onset, were enrolled prospectively. Demographics, established risk factors, myocardial contrast echocardiography (MCE) perfusion, index event data and MTWA were assessed. Composite cardiac events (CCE) defined as: death, recurrent MI, sustained ventricular tachycardia (sVT) or readmission for acute heart failure (HF) were recorded during follow-up.

RESULTS

MTWA test was negative in 76, positive in 18 and undetermined in 7 patients. MTWA negative patients had significantly higher LVEF at 30 days. At 4 years, 26 patients experienced CCE (10 died, 2 reinfarcted and 14 HF events). In multivariate Cox proportional hazard model maximum CKMB, non-negative MTWA and reduced LVEF made the best model to predict CCE. Four year CCE free survival was 77% and was significantly lower for non-negative MTWA (94% vs 50%, p<0.003).

CONCLUSIONS

Non-negative MTWA with infarct size index and reduced LVEF could predict cardiac events in patients with anterior STEMI treated with primary PCI. MTWA non-negative patients have significantly worse outcome.

Ambulatory ECG-based T-wave alternans and heart rate turbulence can predict cardiac mortality in patients with myocardial infarction with or without diabetes mellitus

Background

Many patients who survive a myocardial infarction (MI) remain at risk of sudden cardiac death despite revascularization and optimal medical treatment. We used the modified moving average (MMA) method to assess the utility of T-wave alternans (TWA) and heart rate turbulence (HRT) as risk markers in MI patients with or without diabetes mellitus (DM).

Methods

We prospectively enrolled 248 consecutive patients: 96 with MI (post-MI patients); 77 MI with DM (post-MI + DM patients); 75 controls without cardiovascular disease (group control). Both TWA and HRT were measured on ambulatory electrocardiograms (AECGs). HRT was assessed by two parameters ─ turbulence onset (TO) and turbulence slope (TS). HRT was considered positive when both TO ≥0% and TS ≤2.5 ms/R-R interval were met. The endpoint was cardiac mortality.

Results

TWA values differed significantly between MI and controls. Post-MI + DM patients had higher TWA values than post-MI patients (58 ± 21 μV VS 52 ± 18 μV, P = 0.029). Impaired HRT--increased TO and decreased TS were observed in MI patients with or without DM. During follow-up of 578 ± 146 days, cardiac death occurred in ten patients and three of them suffered sudden cardiac death (SCD). Multivariate analysis determined that a HRT-positive outcome [HR (95% CI): 5.01, 1.33–18.85; P = 0.017], as well as the combination of abnormal TWA (≥47 μV) and positive HRT had significant association with the endpoint [HR (95% CI): 9.08, 2.21–37.2; P = 0.002)].

Conclusion

This study indicates that AECGs-based TWA and HRT can predict cardiac mortality in MI patients with or without DM. Combined analysis TWA and HRT may be a convenient and useful method of identifying patients at high risk for cardiovascular death.

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.

Predictive value of beat-to-beat QT variability index across the continuum of left ventricular dysfunction: competing risks of noncardiac or cardiovascular death and sudden or nonsudden cardiac death

BACKGROUND

The goal of the present study was to determine the predictive value of beat-to-beat QT variability in heart failure patients across the continuum of left ventricular dysfunction.

METHODS AND RESULTS

Beat-to-beat QT variability index (QTVI), log-transformed heart rate variance, normalized QT variance, and coherence between heart rate variability and QT variability have been measured at rest during sinus rhythm in 533 participants of the Muerte Subita en Insuficiencia Cardiaca heart failure study (mean age, 63.1±11.7; men, 70.6%; left ventricular ejection fraction >35% in 254 [48%]) and in 181 healthy participants from the Intercity Digital Electrocardiogram Alliance database. During a median of 3.7 years of follow-up, 116 patients died, 52 from sudden cardiac death (SCD). In multivariate competing risk analyses, the highest QTVI quartile was associated with cardiovascular death (subhazard ratio, 1.67 [95% CI, 1.14-2.47]; P=0.009) and, in particular, with non-SCD (subhazard ratio, 2.91 [1.69-5.01]; P<0.001). Elevated QTVI separated 97.5% of healthy individuals from subjects at risk for cardiovascular (subhazard ratio, 1.57 [1.04-2.35]; P=0.031) and non-SCD in multivariate competing risk model (subhazard ratio, 2.58 [1.13-3.78]; P=0.001). No interaction between QTVI and left ventricular ejection fraction was found. QTVI predicted neither noncardiac death (P=0.546) nor SCD (P=0.945). Decreased heart rate variability rather than increased QT variability was the reason for increased QTVI in the present study.

CONCLUSIONS

Increased QTVI because of depressed heart rate variability predicts cardiovascular mortality and non-SCD but neither SCD nor extracardiac mortality in heart failure across the continuum of left ventricular dysfunction. Abnormally augmented QTVI separates 97.5% of healthy individuals from heart failure patients at risk.

Implantable cardioverter defibrillator therapy activation for high risk patients with relatively well preserved left ventricular ejection fraction. Does it really work?

BACKGROUND

Current guidelines for the primary prevention of sudden cardiac death have used a left ventricular ejection fraction (LVEF) ≤ 35% as a critical point to justify implantable cardioverter defibrillator (ICD) implantation in post myocardial infarction patients and in those with nonischemic dilated cardiomyopathy. We compared mortality and ICD activation rates among different ICD group recipients using a cut-off value for LVEF ≤ 35%.

METHODS

We followed up for a mean period of 41.1 months 495 ICD recipients (442 males, 65.6 years old, 68.9% post myocardial infarction patients, 422 with LVEF ≤ 35%). Prevention was considered primary in patients who fulfilled guidelines criteria or had inducible ventricular arrhythmia during programmed ventricular stimulation for patients with LVEF >35%.

RESULTS

Over the course of the trial, 84 of 495 patients died; 69 experienced cardiac death (6 sudden) and 15 non cardiac death. ICD recipients with LVEF ≤ 35% compared to those with preserved LVEF (mean LVEF=43%) had a greater incidence of total mortality (18% vs. 11%, log rank p=0.028) and cardiac death (15.4% vs. 5.5%, log rank p=0.005). There was no difference in the incidence for appropriate device therapy between patients with LVEF ≤ 35% and those with LVEF >35% (56.9% vs. 65.8%, log rank p=0.93). In the multivariate analysis the presence of advanced New York Heart Association stage predicted both total mortality (HR=2.69, 95% CI 1.771-4.086) and cardiac death (HR=3.437, 95% CI 2.163-5.463).

CONCLUSIONS

ICD therapy may protect heart failure patients at early stages from arrhythmic morbidity and mortality, based on an electrophysiology-guided risk stratification approach.

Clinical utility of microvolt T-wave alternans testing in identifying patients at high or low risk of sudden cardiac death

BACKGROUND

Previous studies have demonstrated that microvolt T-wave alternans (MTWA) testing is a robust predictor of ventricular tachyarrhythmias and sudden cardiac death (SCD) in at-risk patients. However, recent studies have suggested that MTWA testing is not as good a predictor of "appropriate" implantable cardioverter-defibrillator (ICD) therapy as it is a predictor of SCD in patients without ICDs.

OBJECTIVE

To evaluate the utility of MTWA testing for SCD risk stratification in patients without ICDs.

METHODS

Patient-level data were obtained from 5 prospective studies of MTWA testing in patients with no history of ventricular arrhythmia or SCD. In these studies, ICDs were implanted in only a minority of patients and patients with ICDs were excluded from the analysis. We conducted a pooled analysis and examined the 2-year risk for SCD based on the MTWA test result.

RESULTS

The pooled cohort included 2883 patients. MTWA testing was positive in 856 (30%), negative in 1627 (56%), and indeterminate in 400 (14%) patients. Among patients with a left ventricular ejection fraction (LVEF) of ≤35%, annual SCD event rates were 4.0%, 0.9%, and 4.6% among groups with MTWA positive, negative, and indeterminate test results. The SCD rate was significantly lower among patients with a negative MTWA test result than in patients with either positive or indeterminate MTWA test results (P <.001 for both comparisons). In patients with an LVEF of >35%, annual SCD event rates were 3.0%, 0.3%, and 0.3% among the groups with MTWA positive, negative, and indeterminate test results. The SCD rate associated with a positive MTWA test result was significantly higher than that associated with either negative (P <.001) or indeterminate MTWA test results (P = .003).

CONCLUSIONS

In patients without ICDs, MTWA testing is a powerful predictor of SCD. Among patients with an LVEF of ≤35%, a negative MTWA test result is associated with a low risk for SCD. Conversely, among patients with an LVEF of >35%, a positive MTWA test result identifies patients at significantly heightened SCD risk. These findings may have important implications for refining primary prevention ICD treatment algorithms.

Ability of microvolt T-wave alternans to modify risk assessment of ventricular tachyarrhythmic events: a meta-analysis

BACKGROUND

Prior studies have indicated that the magnitude of risk association of microvolt T-wave alternans (MTWA) testing appears to vary with the population studied. We performed a meta-analysis to determine the ability of MTWA to modify risk assessment of ventricular tachyarrhythmic events (VTEs) and sudden cardiac death (SCD) across a series of patient risk profiles using likelihood ratio (LR) testing, a measure of test performance independent of disease prevalence.

METHODS

We identified original research articles published from January 1990 to January 2011 that investigate spectrally derived MTWA. Ventricular tachyarrhythmic event was defined as the total and arrhythmic mortality and nonfatal sustained or implantable cardioverter-defibrillator-treated ventricular tachyarrhythmias. Summary estimates were created for positive and nonnegative MTWA results using a random-effects model and were expressed as positive (LR+) and negative (LR-) LRs.

RESULTS

Of 1,534 articles, 20 prospective cohort studies met our inclusion criteria, consisting of 5,945 subjects predominantly with prior myocardial infarction or left ventricular dysfunction. Although there was a modest association between positive MTWA and VTE (relative risk 2.45, 1.58-3.79) and nonnegative MTWA and VTE (3.68, 2.23-6.07), test performance was poor (positive MTWA: LR+ 1.78, LR- 0.43; nonnegative MTWA: LR+ 1.38, LR- 0.56). Subgroup analyses of subjects classified as prior VTE, post-myocardial infarction, SCD-HeFT type, and MADIT-II type had a similar poor test performance. A negative MTWA result would decrease the annualized risk of VTE from 8.85% to 6.37% in MADIT-II-type patients and from 5.91% to 2.60% in SCD-HeFT-type patients.

CONCLUSIONS

Despite a modest association, results of spectrally derived MTWA testing do not sufficiently modify the risk of VTE to change clinical decisions.

Predictive value of microvolt T-wave alternans for cardiac death or ventricular tachyarrhythmic events in ischemic and nonischemic cardiomyopathy patients: a meta-analysis

BACKGROUND

Microvolt T-wave alternans (MTWA) has been proposed as a predictor of the risk of ventricular tachyarrhythmias (VT) and sudden cardiac death (SCD). Aim of this study was to perform a systematic review of the literature and a meta-analysis of MTWA in primary prevention patients with ischemic and nonischemic cardiomyopathy.

METHODS

The positive predictive value (PPV), negative predictive value (NPV), and relative risk (RR) of MTWA in predicting death, cardiac death, and SCD during follow-up were reported.

RESULTS

Fifteen studies involving 5681 patients (mean age 62 years, mean ejection fraction 32%) were included. The summary PPV during the average 26-month follow-up was 14% (95% CI: 13-15); NPV was 95% (95% CI: 94-96), and the univariate RR was 2.35 (95% CI: 1.68-3.28). The predictive value of MTWA was similar in patients with ischemic and nonischemic cardiomyopathy. The average RR for SCD or VT events of an abnormal MTWA was 2.40, similar to that for cardiac death. When we grouped the studies together depending upon whether beta-blockers were withheld prior to MTWA screening, the beta-blockers group showed an RR of 5.88. By contrast, the group in which beta-blocker therapy was withheld had an RR of 1.63.

CONCLUSION

A positive MTWA determined an approximately 2.5-fold higher risk of cardiac death and life-threatening arrhythmia and showed a very high NPV both in ischemic and nonischemic patients. An abnormal MTWA test was associated with a 5-fold increased risk for cardiac mortality in the low-indeterminate group and about a 6-fold increased risk in beta-blockers group.

T-wave alternans and heart rate variability: a comparison in patients with myocardial infarction with or without diabetes mellitus

BACKGROUND

The aim of this study was to investigate the differences in T-wave alternans (TWA) and heart rate variability (HRV) among patients with myocardial infarction with or without diabetes mellitus and the relationship between TWA and HRV.

METHODS

The study population included 133 patients: 59 patients with myocardial infarction (MI) (group post-MI without diabetes); 40 myocardial infarction with diabetes (group post-MI with diabetes); and 34 controls (group control). Cardiac autonomic neuropathy assessment was made using frequency domain (low-frequency [LF] power, high-frequency [HF] power, LF/HF) and time domain (SDNN, standard deviation of the averaged normal sinus RR intervals for all 5-minute segments [SDANN]) of HRV indexes. Both TWA and HRV were measured on the Holter monitor, and TWA was calculated automatically using the time-domain modified moving average method.

RESULTS

TWA values differed significantly between controls (40 ± 16 μV) and group post-MI with (62 ± 17 μV, P < 0.05) or without (60 ± 15 μV, P < 0.05) diabetes. In addition, group post-MI with diabetes had lower standard deviation of all normal sinus RR intervals (SDNN), standard deviation of the averaged normal sinus RR intervals for all 5-minute segments (SDANN), and HF, indicating depressed vagus nerve activity, and higher LF/HF ratio, indicating elevated sympathetic nerve activity, than controls and group post-MI without diabetes (P < 0.05). TWA correlated with SDNN and SDANN (r = 0.29, 0.31; P < 0.001).

CONCLUSIONS

TWA was elevated in patients following myocardial infarction, both in those with or without diabetes. Myocardial infarction patients had a lower time domain, HF, and a higher LF/HF ratio HRV, especially in those with diabetes. The analysis of modified moving agerage (MMA)-based TWA and HRV can be a useful tool for identifying post-myocardial infarction patients at high risk of arrhythmic events.

Microvolt T-wave alternans physiological basis, methods of measurement, and clinical utility--consensus guideline by International Society for Holter and Noninvasive Electrocardiology

This consensus guideline was prepared on behalf of the International Society for Holter and Noninvasive Electrocardiology and is cosponsored by the Japanese Circulation Society, the Computers in Cardiology Working Group on e-Cardiology of the European Society of Cardiology, and the European Cardiac Arrhythmia Society. It discusses the electrocardiographic phenomenon of T-wave alternans (TWA) (i.e., a beat-to-beat alternation in the morphology and amplitude of the ST-segment or T-wave). This statement focuses on its physiological basis and measurement technologies and its clinical utility in stratifying risk for life-threatening ventricular arrhythmias. Signal processing techniques including the frequency-domain Spectral Method and the time-domain Modified Moving Average method have demonstrated the utility of TWA in arrhythmia risk stratification in prospective studies in >12,000 patients. The majority of exercise-based studies using both methods have reported high relative risks for cardiovascular mortality and for sudden cardiac death in patients with preserved as well as depressed left ventricular ejection fraction. Studies with ambulatory electrocardiogram-based TWA analysis with Modified Moving Average method have yielded significant predictive capacity. However, negative studies with the Spectral Method have also appeared, including 2 interventional studies in patients with implantable defibrillators. Meta-analyses have been performed to gain insights into this issue. Frontiers of TWA research include use in arrhythmia risk stratification of individuals with preserved ejection fraction, improvements in predictivity with quantitative analysis, and utility in guiding medical as well as device-based therapy. Overall, although TWA appears to be a useful marker of risk for arrhythmic and cardiovascular death, there is as yet no definitive evidence that it can guide therapy.

Prediction of sudden cardiac death in patients after acute myocardial infarction using T-wave alternans: a prospective study

BACKGROUND AND PURPOSE

We assessed the value of T-wave alternans (TWA) in prediction of sudden cardiac death (SCD) in patients with acute myocardial infarction (AMI).

METHODS

Consecutive patients (N = 227) were enrolled and were monitored with 24-hour ambulatory electrocardiogram within 1 to 15 days after AMI. T-wave alternans was identified by a modified moving average (MMA) algorithm computer software. The primary end point was SCD or lethal ventricular arrhythmia. We analyzed the hazard ratios (HRs) using the previously determined 47 μV TWA cutpoint.

RESULTS

During the 16 ± 7-month follow-up, 10 (4.4%) patients died suddenly. T-wave alternans (≥47 μV) predicted SCD (HR, 17.78 [95% confidence interval, 3.75-84.31]; P < .0001). Moreover, patients with 5 or more TWA episodes (≥47 μV) were at higher risk for SCD (HR, 20.75 [95% confidence interval, 5.77-74.57]; P < .0001).

CONCLUSIONS

T-wave alternans (≥47 μV) monitored at 1 to 15 days after AMI-predicted heightened risk of SCD. Prediction is improved when the frequency of TWA episodes (≥47 μV) is analyzed.

T-wave alternans in apparently healthy subjects and in different subsets of patients with ischaemic heart disease

AIMS

Microvolt T-wave alternans (TWA) predicts arrhythmic risk in patients with ischaemic heart disease (IHD). While TWA has widely been assessed by the spectral method, it has been poorly characterized in healthy people as well as in IHD patients by the modified moving average (MMA) method.

METHODS AND RESULTS

We enrolled 729 consecutive subjects, referred for exercise stress test (EST). T-wave alternans was assessed by the MMA method, considering all 12 electrocardiogram (ECG) leads (TWA_tot) or the 6 ECG pre-cordial leads only (TWA_prec). Patients were divided into five groups: (i) no history of IHD and normal EST (Group 1); (ii) no history of IHD but positive EST (Group 2); (iii) ischaemic heart disease without any acute myocardial infarction [AMI (Group 3)]; (iv) old AMI (Group 4); (v) recent AMI (Group 5). T-wave alternans values >95th percentile of those measured in Group 1 were considered 'abnormal'. The 95th percentile of TWA values in Group 1 was 75 µV for TWA_tot and 65 µV for TWA_prec. T-wave alternans values and prevalence of abnormal TWA increased from Groups 1-2 to Group 5 (P< 0.00001 for both). Group 4 and Group 5, compared with Group 1, showed a significant higher prevalence of abnormal values of TWA_tot [odds ratio (OR) 1.70 (P= 0.002), and 2.07 (P= 0.01), respectively] and TWA_prec [OR 1.51 (P= 0.02) and 2.37 (P= 0.003), respectively] at multivariable analysis. In IHD patients EST-induced ischaemia did not influence TWA; in AMI patients, impaired left ventricular function was associated with higher TWA values.

CONCLUSIONS

In healthy people, TWA_tot and TWA_prec were ≤75 and ≤65 µV, respectively, in 95% of subjects. In IHD patients TWA values were higher compared with healthy individuals; a history of AMI was independently associated with abnormal TWA values.

Repolarization alternans heterogeneity in healthy subjects and acute myocardial infarction patients

An association between heterogeneity of repolarization alternans (RA) and cardiac electrical instability has been reported. Characterization of RA in health and identification of physiological RA heterogeneity may help discrimination of abnormal RA cases more likely associated to arrhythmic events. Thus, aim of the present study was the identification of a physiological RA region in terms of mean temporal location (MRAD) with respect to the T apex, and mean amplitude (MRAA), by application of our heart-rate adaptive match filter method to clinical ECG recordings from 51 control healthy (CH) subjects and 43 acute myocardial infarction (AMI) patients. Results indicate that RA occurring within the first half of the T wave is dominant in both CH and AMI populations (74.5% and 53.5% of cases, respectively; P<0.05). Definition of physiological RA region in the MRAD vs. MRAA plane (-83 ms ≤ MRAD ≤ 23 ms, 0≤ MRAA ≤ 30 μV) provided 0% and 32.6% abnormal RA cases among the CH subjects and AMI patients, respectively. We conclude that myocardial infarction may associate with an RA occurring early (MRAD<-83 ms) or late (MRAD >23 ms) along the JT segment, in addition or in alternative to an abnormally high RA amplitude (MRAA >30 μV).

Sudden cardiac death risk stratification in patients with heart failure

The multiplicity of mechanisms contributing to arrhythmogenesis in patients with heart failure carries obvious implications for risk stratification. If patients having the propensity to develop arrhythmias by these different mechanisms are to be identified, tests must be devised that reveal the substrates or other factors that relate to each mechanism. In the absence of this, efforts to risk stratify patients are likely to be neither cost-effective nor accurate. This article reviews the current knowledge base of risk stratification for sudden death in patients with heart failure, while acknowledging several limitations in the studies examined.

Relationship Between Early Diastolic Dysfunction and Abnormal Microvolt T-Wave Alternans in Patients With Type 2 Diabetes

Background—

Abnormal microvolt T-wave alternans (MTWA), a marker of ventricular arrhythmic risk, is a highly prevalent condition in patients with type 2 diabetes mellitus (T2DM) and is correlated with glycemic control. However, there is uncertainty as to whether central or peripheral hemodynamic factors are associated with abnormal MTWA in T2DM individuals.

Methods and Results—

We studied 50 consecutive, well-controlled T2DM outpatients without a history of ischemic heart disease and with normal systolic function. All patients underwent a complete echocardiographic Doppler evaluation with spectral tissue Doppler analysis. MTWA analysis was performed noninvasively during submaximal exercise. Effective arterial elastance, arterial compliance, and heart rate variability were also measured. Compared with patients with MTWA negativity (n=38), those with MTWA abnormality (n=12, 24%) had significantly lower e′ (7.6±1.3 versus 9.1±1.7 cm/s; P <0.01), a′ (10.2±1.6 versus 12.7±1.9 cm/s; P <0.001) and s′ velocities (8.7±1.1 versus 10.2±1.5 cm/s; P =0.001) and higher indexed left ventricular mass (121.3±16.4 versus 107.5±16.5 g/m 2 ; P =0.016), indexed left atrial volume (33.5±11.9 versus 23.6±5.6 mL/m 2 ; P <0.001), and E/e′ ratio (8.8±1.4 versus 6.5±1.3; P <0.001). Multivariable logistic regression analysis revealed that higher E/e′ ratio was the only independent correlate of abnormal MTWA (adjusted odds ratio, 3.52; 95% confidence interval, 1.19 to 10.6; P =0.02) after controlling for glycemic control and other potential confounders.

Conclusions—

In this pilot study, we found that early diastolic dysfunction, as measured by tissue Doppler imaging, is independently associated with MTWA abnormality in T2DM individuals with normal systolic function. Further larger studies are needed to examine the reproducibility of these results.

Risk stratification for sudden cardiac death

Sudden cardiac death (SCD) is a leading cause of mortality in industrialized countries, and ventricular fibrillation and sustained ventricular tachycardia are the major causes of SCD. Although there are now effective devices and medications that can prevent such serious arrhythmias, it is crucial to have methods of identifying patients at risk. Numerous studies suggest that most patients dying of SCD have coronary artery disease or cardiomyopathy. Functional or electrophysiological measurements are effective in risk stratification. Left ventricular ejection fraction measured by echocardiography or cardiac imaging techniques is the gold standard to detect high-risk patients. Electrophysiological studies have also been used for risk stratification. Noninvasive techniques and measurements, such as T-wave alternans, signal-averaged electrocardiography, nonsustained ventricular tachycardia, heart rate variability, and heart rate turbulence, have been proposed as useful tools in identifying patients at risk for SCD. This article reviews the epidemiology, mechanisms, substrates, and current status of risk stratification of SCD.

Prediction values of T wave alternans for sudden cardiac death in patients with chronic heart failure: a brief review

More than 50% of patients with heart failure die from sudden cardiac death as a result of malignant arrhythmia. T wave alternans (TWA) is a convenient, noninvasive, and inexpensive testing modality, with a higher sensitivity and specificity for sudden cardiac death. Its prediction value for malignant arrhythmia may even exceed electrophysiologic study. Generally, the algorithms of TWA can be divided into frequency-domain and time-domain methods, and the latter has a stronger anti-interference ability. So far, a unified measuring formula and diagnostic criteria about TWA measurements have been created. Large clinical studies in recent years strongly suggest that TWA can predict sudden cardiac death, which can be used as a guide for the implanting of implantable cardioverter-defibrillator. This article reviews the current literature on recording techniques and clinical implications of TWA.

T-wave alternans testing in pacemaker patients: comparison of pacing modes and long-term prognostic relevance

BACKGROUND

T-wave alternans (TWA) is a useful method for identifying patients who are at risk for sudden cardiac death. We aimed to determine the effects of different pacing modes on test results and long-term prognostic relevance of TWA in patients following a dual-chamber (DDD) pacemaker implantation.

METHODS

Sixty-three patients (mean age 68 ± 13 years) with structural heart disease and recently implanted DDD pacemakers were enrolled. Left ventricular (LV) function was normal or moderately impaired (mean LV ejection fraction 61 ± 13%). All patients underwent sequential TWA testing using atrial and ventricular pacing.

RESULTS

During atrial pacing requiring physiologic conduction to the ventricles, 21% of TWA tests were positive, 43% negative, and 36% indeterminate. When using right ventricular (RV) pacing in the same patients, 19% of tests were positive, 40% negative, and 41% indeterminate. When positive and indeterminate tests were grouped as nonnegative, the concordance between atrial and ventricular pacing was 62% (κ= 0.22). After a mean follow-up of 5.9 ± 1.9 years, 18 (29%) patients had died. Improved survival was predicted by a negative TWA test using atrial pacing (P = 0.028), but not with ventricular pacing (P = 0.722).

CONCLUSIONS

In patients with dual-chamber pacemakers, there is a low concordance of TWA test results between atrial pacing with intrinsic conduction to the ventricles and apical RV pacing via pacemaker electrode. However, TWA during atrial pacing clearly exerts long-term prognostic relevance in a patient group with preserved LV function and structural heart disease.

Automatic microvolt T-wave alternans identification in relation to ECG interferences surviving preprocessing

The aim was to investigate the effect of interferences surviving preprocessing (residual noise, baseline wanderings, respiration modulation, replaced beats, missed beats and T-waves misalignment) on automatic identification of T-wave alternans (TWA), an ECG index of risk for sudden cardiac death. The procedures denominated fast-Fourier-transform spectral method (FFTSM), complex-demodulation method (CDM), modified-moving-average method (MMAM), Laplacian-likelihood-ratio method (LLRM), and adaptive-match-filter method (AMFM) were applied to interferences-corrupted synthetic ECG tracings and Holter ECG recordings from control-healthy subjects (CH-group; n=25) and acute-myocardial-infarction patients (AMI group; n=25). The presence of interferences in simulated data caused detection of false-positive TWA by all techniques but the FFTSM and AMFM. Clinical applications evidenced a discrepancy in that the FFTSM and LLRM detected no more than one TWA case in each population, whereas the CDM, MMAM, and AMFM detected TWA in all CH-subjects and AMI-patients, with significantly lower TWA amplitude in the former group. Because the AMFM is not prone to false-positive TWA detections, the latter finding suggests TWA as a phenomenon having continuously changing amplitude from physiological to pathological conditions. Only occasional detection of TWA by the FFTSM and LLRM in clinics can be ascribed to their limited ability in identifying TWA in the presence of interferences surviving preprocessing.

Importance of regional specificity of T-wave alternans in assessing risk for cardiovascular mortality and sudden cardiac death during routine exercise testing

BACKGROUND

T-wave alternans (TWA) indicates increased risk for life-threatening arrhythmias. However, the regional distribution and predictivity of TWA among precordial leads remain unknown.

OBJECTIVE

We analyzed the magnitude and prognostic power of TWA in precordial leads separately and in combination during routine exercise stress testing in the largest TWA study conducted to date.

METHODS

The Finnish Cardiovascular Study (FINCAVAS) enrolled consecutive patients (n = 3,598, 56 ± 13 [mean ± standard deviation] years old, 2,164 men, 1,434 women) with a clinically indicated exercise test with bicycle ergometer. TWA was analyzed with the time-domain modified moving average method.

RESULTS

During a follow-up of 55 months (interquartile range of 35-78 months), 231 patients died; 97 deaths were cardiovascular, and 46 were classified as sudden cardiac deaths (SCDs). In Cox analysis after adjustment for common coronary risk factors, each 20-μV increase in TWA in leads V1-V6 multiplied the hazard ratio for cardiovascular mortality by 1.486-fold (95% confidence interval [CI] 1.127-1.952; P = .005). Each 20-μV increase in TWA in lead V5 amplified the hazard ratio for cardiovascular mortality by 1.545 (95% CI 1.150-2.108; P = .004) and for SCD by 1.576 (95% CI 1.041-2.412; P = .033).

CONCLUSIONS

Maximum TWA monitored from anterolateral precordial lead V5 is the strongest predictor of cardiovascular mortality and SCD during routine exercise testing in our analysis. Higher TWA values indicate greater cardiovascular mortality and SCD risk, supporting the concept that quantification of TWA should receive more attention.

Identification of gender-related normality regions for T-wave alternans

BACKGROUND

T-wave alternans (TWA), a harbinger of sudden cardiac death, associates to a broad variety of pathologies. In a previous study, we observed the presence of unstable and low-amplitude TWA also in healthy subjects, and considered it as "physiological TWA." The possible existence of different TWA characteristics between males and female is investigated in the present work.

METHODS

Resting ECG recordings from 142 control healthy subjects, 77 males and 65 females, were submitted to our adaptive match filter (AMF) based method for TWA detection and characterization in terms of duration, amplitude, and their product. The 99.5th percentile of these parameters distributions over the entire control population and over the male and female subgroups, were used to define thresholds which delimit a gender-independent and male- and female-related TWA normality regions, respectively, out of which abnormal TWA cases (TWA+) are expected to fall. Clinical usefulness of these regions was tested using a population of 151 coronary artery disease (CAD) patients, divided into 128 males and 23 females.

RESULTS

In our control-female population, TWA duration was significantly longer than in control-male population (65 ± 13 beat vs 52 ± 14 beat; P < 10(-6) ). Our gender-related normality regions allowed identification of 36 (23.8%) TWA+ cases among the CAD patients, 17 more than those obtained from a gender-independent region. All these 17 patients were CAD males with over-threshold TWA duration.

CONCLUSIONS

TWA is a gender-related phenomenon. Definition of gender-related TWA normality regions improves identification of patients at increased TWA stability (i.e., prolonged TWA duration) and, thus, at increased risk of arrhythmic events.

Correlation method versus enhanced modified moving average method for automatic detection of T-wave alternans

Enhanced modified moving average method (EMMAM) and correlation method (CM) for microvolt TWA identification are compared by aid of simulated ECG tracings (cases of absence of TWA and presence of stationary or time-varying TWA) and ECG recordings from healthy subjects (H-group) and patients who survived an acute myocardial infarction (AMI-group). The two competing methods were found to be equivalent when analyzing clean ECGs affected by stationary TWA. Non-stationary TWA is correctly tracked by the CM, whereas it is identified as stationary by the EMMAM. Moreover, the EMMAM suffers for its tendency to identify as TWA noise and other kinds of repolarization variability. Such limitation is most likely the cause of its false-positive TWA production. Finally, only the CM incorporates a local threshold criterion in the TWA detection algorithm which allows better discrimination between H and AMI groups, who are well known to be at increased risk to develop TWA.

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