# A Novel Wavelet-Based Algorithm for Detection of QRS Complex
## 4 Results and Discussion
### Limitations of the Proposed Algorithm  
The limitations of the proposed QRS peak detection algorithm caused 271 detection failures of QRS peaks, which can be classified into several types. Figure 12 illustrates the detection failure caused by sudden high-frequency noise. The red circles indicate the QRS peaks that were correctly identified, and the red arrow followed with FP:18569 indicates a false positive beat at sample 18569. Because the sudden high-frequency noise cannot be detected by the proposed noise evaluation method, the QRS peak detection was still based on the higher-frequency d3', and, hence, this sudden large-amplitude noise peak in Figure 12 is misidentified as a QRS peak. A total of 41 detection failures were caused by the sudden high-frequency noise. Figure 13 demonstrates the detection failure caused by the greatly reduced amplitude of the QRS peak compared to the adjacent QRS peaks. The black arrow followed by V:295133 indicates the peak of a VPC beat at sample 295133, which is misidentified as a false negative beat. Because the amplitude of this VPC beat is greatly reduced in comparison with those of other QRS complexes, the peak of the VPC beat was misidentified as not being a QRS peak. Greatly decreased amplitudes of QRS peaks caused a total of 62 detection failures.  
Figure 12: Illustration of the detection failure caused by sudden high-frequency noises.  
Figure 13: Illustration of the detection failures caused by greatly reduced amplitudes of QRS peaks compared to the adjacent QRS peaks.  
Figure 14 shows the detection failures caused by large-amplitude artifacts. It is obvious that the four peaks of large-amplitude artifacts are very similar to QRS peaks and are misidentified as QRS peaks. A total of 26 detection failures were caused by large-amplitude artifacts. Figure 15 illustrates the detection failure caused by a distance of less than 100 samples between two successive QRS peaks, which caused a total of 15 detection failures. The VPC beat marked by V:267025 was misidentified as not being a QRS peak because the distance between it and the previous QRS peak was less than 100 samples. Figure 16 demonstrates the detection failures caused by a P-peak sharper than the QRS peak. The FP:141706 denotes a false positive beat at sample 141706, and the N:141768 represents a normal beat at sample 141768, which is misidentified as a false negative beat. When a P- or T-peak is sharper than a QRS peak, it causes two detection failures. One is the P- or T-peak misidentified as a QRS peak, and the other is the QRS peak misidentified as not being a QRS peak. A total of 36 detection failures were caused by the P- or T-peak being sharper than the QRS peak. Figures 17 and 18 illustrate the detection failures caused by the inconsistent annotation of the MIT-BIH arrhythmia database. Not QRS peaks that were annotated as QRS peaks caused a total of 57 detection failures. It is obvious that the peaks indicated as N in Figure 17 are not QRS peaks but are annotated as peaks of the normal QRS complexes. QRS peaks that were annotated as Not QRS peaks caused a total of 10 detection failures, as illustrated in Figure 18. The peak indicated as FP should be a QRS peak, but the corresponding annotation was lost. The remaining 24 detection failures were caused by other types. The  
Figure 16: Illustration of the detection failures caused by the P-peak being sharper than the QRS peak.  
Figure 17: Illustration of the detection failures caused by Not QRS peaks being annotated as QRS peaks by the MIT-BIH Arrhythmia Database.  
Figure 18: Illustration of the detection failures caused by QRS peaks but annotated as Not QRS peaks by the MIT-BIH Arrhythmia Database.