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

Comparison of clinical outcomes in STEMI patients treated with primary PCI according to day-time of medical attention and its relationship with circadian pattern

OBJECTIVE

Relationship between STEMI time of presentation, its circadian pattern and cardiovascular outcomes is unclear. Our objective is to analyze clinical outcomes of STEMI according to time of presentation and circadian pattern.

METHODS

We analyzed data from patients treated within the regional STEMI Network from January 2010 to December 2015. On-hour group included patients treated between 8:00 h and 19:59 h on weekdays, the rest were catalogued as off-hour group. The primary endpoint was 1-year all-cause mortality. Secondary endpoints were 30-day all-cause mortality and in-hospital complications.

RESULTS

A total of 8608 patients were included, 44.1% in the on-hour group and 55.9% in the off-hour group. We observed a shorter patient delay and longer system delay in the off-hour group compared to on-hour group with no difference in total ischemic time. At 30-day and 1-year follow-up there were no differences in adjusted all-cause mortality between groups [OR 0.91 (CI95%: 0.73-1.12; p = 0.35) and OR 0.99 (CI95%: 0.83-1.17; p = 0.87), respectively]. A circadian pattern was observed between 9:00 am and 12:30 pm, with no differences in 30-day and 1-year mortality between patients included in this time interval [OR 1.02 (IC95%: 0.81-1.30; p = 0.85) and OR 1.12 (IC95%: 0.92-1.36; p = 0.25) respectively].

CONCLUSIONS

Off-hour STEMI presentation was associated with a shorter patient delay and longer system delay without an increase in total ischemic time. The off-hour presentation was not related to an increase in 1-year all-cause mortality when compared to on-hour. A circadian pattern was found, without differences in 30-day and 1-year mortality.

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.

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.

Circadian rhythms in patients with ST-elevation myocardial infarction

BACKGROUND

Circadian rhythms with regard to time of symptom onset for patients with acute myocardial infarction have been observed, although their relationship to outcomes has been debated. We evaluated these rhythms in patients with ST-elevation myocardial infarction as a function of the 24-hour circadian cycle.

METHODS AND RESULTS

The relationship between onset of symptoms during the 24-hour circadian cycle and prehospital delays from symptom onset to hospital arrival, timeliness of reperfusion, and in-hospital death was assessed in 2143 patients with ST-elevation myocardial infarction presenting from 2004-2008 at 1 of 3 tertiary-care healthcare ST-elevation myocardial infarction systems. There was a significant association between time of onset and the circadian cycle, with the greatest percentage (39%) of patients experiencing onset between 8 AM and 3 PM (P<0.001). Time of onset was associated with prehospital delay and timeliness of reperfusion. Patients with onset from 12 AM to 5:59 AM had median prehospital delays of 121 minutes versus 70 minutes from 12 PM to 5:59 PM (P<0.001). Patients with onset time from 12 AM to 5:59 AM had median door-to-balloon times of 75 minutes versus 60 minutes from 6 AM to 11:59 AM (P<0.001). Using multivariable modeling to control for baseline patient characteristics, prehospital delay, and timeliness of reperfusion, there was no significant association between time of symptom onset with in-hospital death.

CONCLUSIONS

Patients with ST-elevation myocardial infarction exhibit significant circadian patterns in symptom onset, prehospital delay, and timeliness of reperfusion. Patients who develop symptoms from 12 AM to 5:59 AM present with longer prehospital delays and have longer door-to-balloon times. After multivariable adjustment, there was no significant association between circadian patterns of time of onset and in-hospital death.

T-wave alternans: reviewing the clinical performance, understanding limitations, characterizing methodologies

Accurate recognition of individuals at higher immediate risk of sudden cardiac death (SCD) is still an open question. The fortuitous nature of acute cardiovascular events just does not seem to fit the well-known model of ventricular tachycardia/fibrillation induction in a static arrhythmogenic substrate by a synchronous trigger. On the mechanism of SCD, a dynamical electrical instability would better explain the rarity of the simultaneous association of a correct trigger and an appropriate cardiac substrate. Several studies have been conducted trying to measure this cardiac electrical instability (or any valid surrogate) in an ECG beat stream. Among the current possible candidates we can number QT prolongation, QT dispersion, late potentials, T-wave alternans (TWA), and heart rate turbulence. This article reviews the particular role of TWA in the current cardiac risk stratification scenario. TWA findings are still heterogeneous, ranging from very good to nearly null prognostic performance depending on the clinical population observed and clinical protocol in use. To fill the current gaps in the TWA base of knowledge, practitioners, and researchers should better explore the technical features of the several technologies available for TWA evaluation and pay greater attention to the fact that TWA values are responsive to several factors other than medications. Information about the cellular and subcellular mechanisms of TWA is outside the scope of this article, but the reader is referred to some of the good papers available on this topic whenever this extra information could help the understanding of the concepts and facts covered herein.