R Peak Detection Method Using Wavelet Transform and Modified Shannon Energy Envelope

Abstract

Rapid automatic detection of the fiducial points-namely, the P wave, QRS complex, and T wave-is necessary for early detection of cardiovascular diseases (CVDs). In this paper, we present an R peak detection method using the wavelet transform (WT) and a modified Shannon energy envelope (SEE) for rapid ECG analysis. The proposed WTSEE algorithm performs a wavelet transform to reduce the size and noise of ECG signals and creates SEE after first-order differentiation and amplitude normalization. Subsequently, the peak energy envelope (PEE) is extracted from the SEE. Then, R peaks are estimated from the PEE, and the estimated peaks are adjusted from the input ECG. Finally, the algorithm generates the final R features by validating R-R intervals and updating the extracted R peaks. The proposed R peak detection method was validated using 48 first-channel ECG records of the MIT-BIH arrhythmia database with a sensitivity of 99.93%, positive predictability of 99.91%, detection error rate of 0.16%, and accuracy of 99.84%. Considering the high detection accuracy and fast processing speed due to the wavelet transform applied before calculating SEE, the proposed method is highly effective for real-time applications in early detection of CVDs.

Figure 1

Fiducial points of an ECG signal: P wave, QRS complex, T wave, and time intervals.

Figure 2

Data flow in the proposed R peak detection method using WT and modified SEE.

Figure 3

Procedure of wavelet transform comprising filtering, down-sampling, thresholding, up-sampling, and reconstruction.

Figure 4

Comparison of scaling function and wavelet function with symlets 5 [28].

Figure 5

Example flow of the proposed R peak detection methods using WT and modified SEE. (a) Input ECG signal of record 121, (b) resized ECG after wavelet transform, (c) output of 1st-order differential, (d) squared differential, (e) normalized differential, (f) calculated Shannon energy (SE), (g) extracted Shannon energy envelope (SEE) after moving average, (h) normalized difference of SEE, (i) calculated peak energy (PE) after square operation, (j) extracted peak energy envelope (PEE) after moving average, (k) estimated peaks in PEE (red circles), and (l) true detected R peaks in ECG signal (red circles).

Figure 6

Examples of the detected R peaks from various normal records: (a) 101, (b) 108, (c) 111, (d) 112, (e) 202, (f) 221, (g) 222, and (h) 232. In the figure, black asterisks (^∗) denote the annotated beats in MIT DB and red circles (O) denote the extracted R peaks.

Figure 7

Examples of the annotated beats and detected real peaks from various records: (a) 106, (b) 111, (c) 117, (d) 119, (e) 207, and (f) 233. In the figure, the numbers such as 1, 2, 3, 5, 14, and 18 indicate the annotation types of each beat.

Figure 8

Detection failure of the proposed WTSEE method.

Figure 9

HRV measurements of the MIT-BIH DB. MRR: mean R-R intervals (ms), SDNN: standard deviation of normal to normal R-R intervals, RMSSD: root mean square of normal to normal R-R intervals.