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

The role of beat-by-beat cardiac features in machine learning classification of ischemic heart disease (IHD) in magnetocardiogram (MCG)

Cardiac electrical changes associated with ischemic heart disease (IHD) are subtle and could be detected even in rest condition in magnetocardiography (MCG) which measures weak cardiac magnetic fields. Cardiac features that are derived from MCG recorded from multiple locations on the chest of subjects and some conventional time domain indices are widely used in Machine learning (ML) classifiers to objectively distinguish IHD and control subjects. Most of the earlier studies have employed features that are derived from signal-averaged cardiac beats and have ignored inter-beat information. The present study demonstrates the utility of beat-by-beat features to be useful in classifying IHD subjects (n = 23) and healthy controls (n = 75) in 37-channel MCG data taken under rest condition of subjects. The study reveals the importance of three features (out of eight measured features) namely, the field map angle (FMA) computed from magnetic field map, beat-by-beat variations of alpha angle in the ST-T region and T wave magnitude variations in yielding a better classification accuracy (92.7 %) against that achieved by conventional features (81 %). Further, beat-by-beat features are also found to augment the accuracy in classifying myocardial infarction (MI) Versus control subjects in two public ECG databases (92 % from 88 % and 94 % from 77 %). These demonstrations summarily suggest the importance of beat-by-beat features in clinical diagnosis of ischemia.

QT variability unrelated to RR variability during stress testing for identification of coronary artery disease

Stress test electrocardiogram (ECG) analysis is widely used for coronary artery disease (CAD) diagnosis despite its limited accuracy. Alterations in autonomic modulation of cardiac electrical activity have been reported in CAD patients during acute ischemia. We hypothesized that those alterations could be reflected in changes in ventricular repolarization dynamics during stress testing that could be measured through QT interval variability (QTV). However, QTV is largely dependent on RR interval variability (RRV), which might hinder intrinsic ventricular repolarization dynamics. In this study, we investigated whether different markers accounting for low-frequency (LF) oscillations of QTV unrelated to RRV during stress testing could be used to separate patients with and without CAD. Power spectral density of QTV unrelated to RRV was obtained based on time-frequency coherence estimation. Instantaneous LF power of QTV and QTV unrelated to RRV were obtained. LF power of QTV unrelated to RRV normalized by LF power of QTV was also studied. Stress test ECG of 100 patients were analysed. Patients referred to coronary angiography were classified into non-CAD or CAD group. LF oscillations in QTV did not show significant differences between CAD and non-CAD groups. However, LF oscillations in QTV unrelated to RRV were significantly higher in the CAD group as compared with the non-CAD group when measured during the first phases of exercise and last phases of recovery. ROC analysis of these indices revealed area under the curve values ranging from 61 to 73%. Binomial logistic regression analysis revealed LF power of QTV unrelated to RRV, both during the first phase of exercise and last phase of recovery, as independent predictors of CAD. In conclusion, this study highlights the importance of removing the influence of RRV when measuring QTV during stress testing for CAD identification and supports the added value of LF oscillations of QTV unrelated to RRV to diagnose CAD from the first minutes of exercise. This article is part of the theme issue 'Advanced computation in cardiovascular physiology: new challenges and opportunities'.

Reference values for a novel ambulatory-based frequency domain T-wave alternans in subjects without structural heart disease

BACKGROUND

Conventional frequency domain T wave alternans (FD-TWA) is a noninvasive risk stratification marker for identifying arrhythmic sudden cardiac death, but the conventional FD-TWA device that was considered the gold standard device has been discontinued commercially. Recently, a newly developed ambulatory electrocardiogram (AECG) device that can detect FD-TWA continuously for 24 hours is available in clinical settings. However, information on the normal values using the novel AECG-based frequency domain TWA (FD-TWA) is lacking.

METHODS

FD-TWA for AECG was examined in 312 subjects without heart disease (Sb-wHD) (range 20-89 years, 146 men) and 30 heart disease patients (HD-P) (mean age 57±17 years, 24 men). The maximum FD-TWA amplitude over 24 hours was measured with manual editing. The upper limit of local noise levels for measurement of FD-TWA was set to both <10 μV and <20 μV (acceptable noise level <10 μV and <20 μV).

RESULTS

The reference values (95th percentiles) of FD-TWA in Sb-wHD were 19.9 μV for the acceptable noise level <10 μV and 23.6 μV for the acceptable noise level <20 μV. The 75th percentile of FD-TWA amplitude in HD-P was 19.5 µV at an acceptable noise level <10 µV and 21.5 µV at an acceptable noise level <20 µV. FD-TWA amplitude without heart disease was significantly affected by heart rate when the maximum FD-TWA was measured (β = 0.274 p < 0.001 for the acceptable noise level <10 μV; β = 0.263, p < 0.001 for the acceptable noise level <20 μV) and age (β = 0.204, p = 0.004 for the acceptable noise level <10 μV; β = 0.149, p = 0.034 for the acceptable noise level <20 μV).

CONCLUSIONS

In the present study, the reference values for a novel FD-TWA in Sb-wHD and the distribution of TWA values in HD-P were established. In future research, the cut-off values of FD-TWA in HD-P will need to be examined.

Microvolt T-wave alternans in young myocardial infarction patients with preserved cardiac function treated with single-vessel primary percutaneous coronary intervention

Introduction

Myocardial infarction continues to be the most important cause of morbidity and mortality, and recently this disease has begun to be seen commonly at young ages. In our study we aimed to assess microvolt T-wave alternans in young patients who had ST segment elevation myocardial infarction with preserved left ventricular function and who underwent single-vessel revascularization.

Material and methods

We enrolled 108 consecutive patients (age: 39.5 ±4.1) with ST segment elevation myocardial infarction (STEMI) undergoing percutaneous coronary intervention and 43 patients (age: 38.5 ±3.7) with normal coronary angiograms as a control group. The myocardial infarction patients were younger than 45 and had a preserved left ventricular ejection fraction. They were divided into three groups according to the culprit artery. The microvolt T-wave alternans (MTWA) values were calculated an average of 12 months after the primary percutaneous coronary intervention using the modified moving average method.

Results

The MTWA positivity was significantly higher in the STEMI group compared to the controls (p < 0.001). It was also significantly higher in STEMI patients with left anterior descending artery lesions compared to patients with circumflex artery and right coronary artery lesions (p = 0.013). Moreover, the culprit artery was independent predictor of MTWA positivity (p = 0.043).

Conclusions

In STEMI patients of a young age, MTWA positivity was higher than in healthy individuals, especially when the responsible vessel fed a wider region.