Evaluation of the T-wave alternans detection methods: a simulation study.

OBJECTIVE: The aim of this study was to evaluate influence of noise, T-wave jitter and electrocardiographic (ECG) signal parameters on sensitivity of T-wave alternans (TWA) detection methods. METHODS: Methods of the TWA detection were tested: correlation (CM), spectral (FFTM), spectral with coherent averaging (CFFTM), complex demodulation (CDM), Karhunen-Loeve transform (KLT) and KLT realized by adaptive filtering. The TWA amplitude and duration time were estimated on simulated ECG signals. Gaussian and physiological noises at different level were added. Influence of sampling frequency and amplitude resolution of the ECG signal was tested. Detection sensitivity was calculated. RESULTS: The TWA episodes in presence of white noise with signal to noise ratio (SNR) greater then 15 dB were reliably detected. For signals with high noise level better sensitivity was received with the CM. For the spectral methods, the best parameters were obtained with the CFFTM but for physiological noises all the methods were unable to detect the TWA episodes when SNR was lower then 10 dB. Analysis done using the CM and the CDM strongly depended on sampling frequency if the TWA episodes were short and had low amplitude. CONCLUSIONS: All spectral methods are sensitive to physiological interference. Changes of the sampling frequency should be very carefully applied.

Relationship between duration of repolarisation and T wave amplitude in patients with positive or negative T wave alternans.

BACKGROUND: Experimental studies documented the relationship between T wave alternans (TWA) and duration of refractoriness. To date, association between TWA and QT interval on standard ECG has not been examined. Aim. To assess the relationship between TWA and QT interval. METHODS: The study group consisted of 70 patients (57 males, mean age 56+/-16 years) with implantable cardioverterdefibrillator (ICD). TWA was measured using a high-resolution ECG obtained from surface orthogonal bipolar XYZ leads and analysed using a Fast Fourier transform. All recordings were performed during ventricular pacing at 100 betas/min. Correlation between T wave amplitude (T max) and QT interval (measured from R wave to T max) was calculated. RESULTS: TWA was found in 18 patients. In this group of patients, there was a significant positive correlation between Tmax and QT (r = 0.766), whereas in patients with negative TWA no such correlation was detected. CONCLUSIONS: (1) Positive correlation between QT and T max probably depicts the relationship between T wave amplitude and duration of repolarisation, which is associated with TWA; (2) methods used for T wave localisation, based on the identification of Q wave (with possible QT-RR correction) overestimate TWA due to periodic changes (with TWA frequency) in location of T wave in the analysed window; and (3) these results provide new insights in the genesis of TWA.