Temporal Variations in Microvolt T‐Wave Alternans Testing after Acute Myocardial Infarction

Man

Noninvasive Electrocardiol

et al. 2012

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.

Section: Discussionmentioning

confidence: 99%

Comparison of Standard versus Orthogonal ECG Leads for T‐Wave Alternans Identification

Man

Noninvasive Electrocardiol

et al. 2012

Journal of the American College of Cardiology

“…Data on long-term stability of TWA results with the Spectral Method are sparse (86). Repeatability has not been reported with the MMA method.…”

Section: Methodology For Twa Assessmentmentioning

confidence: 99%

Microvolt T-Wave Alternans

Verrier

Klingenheben

Malík

et al. 2011

369

139

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.

“…Obavou při použití MTWA je fakt, že výsledek se může měnit v čase s tím, jak dochází k remodelaci substrátu po revaskularizaci. Oliveira a spol., 87 kteří provedli u pacientů po úspěšné PCI vyšetření pomocí MTWA jeden měsíc před a dalších šest měsíců po IM zjistili, že u 29 % pacientů se výsledky MTWA lišily. I když může parametr MTWA sloužit jako užitečný marker úmrtí z kardiálních pří-čin a snad i NSS v subakutním a pozdějším období po IM, nejsou k dispozici žádné důkazy podporující použití tohoto parametru při rozhodování o časné implantaci ICD.…”

Section: Variabilita Srdeční Frekvence a Zvýšení Klidové Srdeční Frekunclassified

“…A concern with MTWA is that results can change with time as the myocardial substrate remodels after revascularization. Oliveira et al 87 performed MTWA before 1 month and repeated it at 6 months after MI in patients treated with successful PCI and found that MTWA results were discordant in 29% of patients. Although MTWA may be a useful marker for cardiac death and possibly SCD in the subacute or remote post-MI stage, there is no evidence to support its use to guide early ICD implantation.…”

Section: Microvolt T-wave Alternansmentioning

confidence: 99%

Sudden Cardiac Death Early After Myocardial Infarction

Zaman

Kovoor

2014

Circulation

The issue of SCD primary prevention early after MI remains unresolved. The focus is now firmly centered on the elucidation of risk stratification tests that effectively select patients at high risk of SCD who benefit from early ICD implantation. Zaman and Kovoor Primary Prevention of SCD Early After MI 2429A summary of major risk stratification tests currently used to identify patients at high risk of SCD is given in Table 2. LV DysfunctionImpaired LVEF, one of the most powerful predictors of survival, 64 has been shown to identify patients who derive a mortality benefit from an ICD when implanted predominantly in the remote period after MI. 16,65 However, there are major concerns with the use of LVEF alone as a risk stratifier to guide ICD implantation. One such concern is the low specificity of LVEF for selecting patients who experience arrhythmic versus nonarrhythmic death. In the MADIT II trial, the use of LVEF ≤30% alone to stratify patients for an ICD resulted in relatively small absolute improvement in mortality with low therapeutic efficiency (15-17 defibrillators per life saved). 66 Another concern is the sensitivity of LVEF, given that a large proportion of SCDs still occur in patients with preserved LV function. VALIANT demonstrated that, although the risk of SCD is greatest in patients with severe dysfunction (LVEF ≤30%), almost half of all sudden deaths occur in patients with a higher ejection fraction (LVEF, 31%-40%). 5 The use of LVEF as a risk stratification tool has been tested in the early post-MI stage in the DINAMIT and IRIS trials, which selected patients with LVEF ≤35% and ≤40%, respectively, and failed to show a benefit of early ICD implantation. 12,17 The major limitation with the use of an early LVEF cutoff is the phenomenon of myocardial stunning with variable and unpredictable recovery of LV function after MI. This is especially relevant in the contemporary era of primary PCI for STEMI. Of STEMI patients with LVEF ≤40% at day 3, 24% will improve to have an LVEF >40% at 6 months with a mean 6% relative improvement. 67 Hence, although LV function will invariably be incorporated into risk stratification models for the prevention of SCD, it is clear that other tests are required to adequately select high-risk patients early after MI. RV DysfunctionAlthough impaired LV function has been studied extensively as a predictor of mortality and arrhythmic death, RV dysfunction has been largely overlooked. We know from the VALIANT study that almost 50% of arrhythmic deaths occur in patients with a preserved LVEF.5 RV involvement in inferior MI has been shown to be a predictor of morbidity and mortality, with a higher rate of serious arrhythmias in patients with inferior MI and RV dysfunction. 68,69 In addition, RV dysfunction has been correlated with increased inducibility of VT at EPS. 70 Although there is no current evidence to support the role of early RV assessment to guide ICD implantation, these findings highlight the inadequacy of LVEF alone as a risk stratification tool for the prevention...