A Low-Pass Filter of 300 Hz Improved the Detection of Pacemaker Spike on Remote and Bedside Electrocardiogram
Electrocardiogram (ECG) has been a cornerstone in clinical cardiology since its invention by Willem Einthoven in 1902. It is widely used to diagnose and monitor various cardiovascular conditions, including those in patients with pacemakers. One critical feature of pacemaker ECGs is the pacemaker spike, a small signal that precedes the P wave or QRS complex. Accurate detection of this spike is essential for diagnosing pacemaker function and ensuring proper patient management. However, with the widespread use of bipolar pacemakers, the detection of pacemaker spikes has become increasingly challenging. The current standard upper-frequency cutoff of 150 Hz, recommended by the American Heart Association (AHA) and the American College of Cardiology (ACC), often results in the loss of pacemaker spikes, leading to misdiagnosis. This study aimed to investigate the impact of different low-pass filter (LPF) settings on the detection of pacemaker spikes in both remote and bedside ECGs, with the hypothesis that a higher upper-frequency cutoff could improve spike detection.
The study was conducted at the Department of Cardiology, Xinhua Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China. A total of 109 consecutive patients with permanent pacemaker implantation were initially considered for the study during routine follow-up from January 1, 2015, to June 30, 2015. After excluding 21 patients due to technical issues and other factors, 88 patients were included in the final analysis. The mean age of the participants was 73.8 ± 10.2 years, with 43 (48.9%) being female. Among the 88 patients, 39 (44.3%) had sick sinus syndrome, 35 (39.8%) had atrioventricular block, 11 (12.5%) had tachycardia-bradycardia syndrome, and 3 (3.4%) had other conditions. All pacemakers used in the study were bipolar leads, with 85 (96.6%) being dual-chamber pacemakers.
Standard 12-lead ECGs were recorded for each patient at six different upper-frequency cutoffs: 40 Hz, 100 Hz, 150 Hz, 200 Hz, 300 Hz, and 400 Hz. These ECGs were collected at the bedside and then transmitted to a remote clinical center for analysis. The ECGs were recorded and stored at a sampling rate of 500 Hz and printed at a paper speed of 25 mm/s. The lower-frequency cutoff was set at 0.5 Hz. The ECG device used in the study was the MCA-22-12UP, designed by MedEx Beijing Company. This device is equipped with a sensitivity of 10 mm/mV, an input impedance of more than 5 MΩ, and a common-mode rejection ratio of more than 100 dB. The noise level during ECG acquisition was kept below 15 mV, ensuring high-quality recordings.
Two independent medical practitioners, trained in pacemaker ECG interpretation, analyzed the ECGs. They were blinded to the patients’ treatment allocation and pacemaker programming outcomes. A ventricular-paced ECG was defined as one in which a ventricular pacemaker spike could be identified in more than five leads by both readers. Similarly, an atrial-paced ECG was defined as one in which an atrial spike was visible in lead II and aVR. Baseline interference was defined as an absolute value of baseline clutter exceeding 0.01 mV in at least six leads. In cases of disagreement between the two readers, a third cardiologist adjudicated the results.
The results of the study revealed significant differences in the detection of pacemaker spikes across the different upper-frequency cutoffs. For atrial-paced spikes, the 300 Hz LPF performed the best on bedside ECGs, with an area under the curve (AUC) of 0.73 (95% confidence interval [CI]: 0.61–0.84), compared to the standard 150 Hz LPF, which had an AUC of 0.56 (95% CI: 0.43–0.70). The sensitivity of the 300 Hz LPF for detecting atrial-paced spikes was 59.4%, with a specificity of 85.7%. The positive predictive value (PPV) was 92.7%, and the negative predictive value (NPV) was 40.9%. The results were similar for remote ECGs, indicating that remote ECG systems can perform as well as bedside ECGs when using a 300 Hz LPF.
For ventricular-paced spikes, the 300 Hz LPF also demonstrated superior performance compared to the 150 Hz LPF. On bedside ECGs, the AUC for the 300 Hz LPF was 0.93 (95% CI: 0.84–1.00), compared to 0.86 (95% CI: 0.77–0.94) for the 150 Hz LPF. The sensitivity of the 300 Hz LPF for detecting ventricular-paced spikes was 95.5%, with a specificity of 90.9%. The PPV was 96.9%, and the NPV was 87.0%. Again, the results for remote ECGs were comparable to those for bedside ECGs.
The study also highlighted the impact of the upper-frequency cutoff on baseline interference. As the upper-frequency cutoff increased, the baseline interference rate also increased. For bedside ECGs, the interference rate ranged from 4.5% at 40 Hz to 65.9% at 400 Hz. For remote ECGs, the interference rate ranged from 8.0% at 40 Hz to 75.0% at 400 Hz. Despite the increased interference, the 300 Hz LPF provided the best balance between spike detection and interference, making it the recommended setting for pacemaker ECG analysis.
The findings of this study have important implications for clinical practice. The current standard of using a 150 Hz LPF for ECG analysis is insufficient for reliable pacemaker spike detection, particularly for atrial-paced spikes. The use of a 300 Hz LPF significantly improves the detection of both atrial and ventricular-paced spikes, reducing the risk of misdiagnosis. This is especially critical in remote ECG systems, where the transmission of ECG data can sometimes weaken or distort the pacemaker spike signal. The study demonstrated that remote ECGs can perform as well as bedside ECGs when using a 300 Hz LPF, making it a viable option for remote patient monitoring.
The study also addressed the challenges associated with bipolar pacemakers, which have become increasingly common in clinical practice. Bipolar leads produce smaller pacemaker spikes compared to unipolar leads, making them more difficult to detect. The use of a higher upper-frequency cutoff, such as 300 Hz, helps to mitigate this issue by allowing the ECG device to capture the higher-frequency components of the pacemaker spike signal. This is particularly important for atrial-paced spikes, which are often more challenging to detect than ventricular-paced spikes.
In conclusion, this study provides compelling evidence that a low-pass filter with an upper-frequency cutoff of 300 Hz significantly improves the detection of pacemaker spikes in both remote and bedside ECGs. The findings suggest that the current standard of 150 Hz is inadequate for reliable pacemaker spike detection, particularly in the era of bipolar pacemakers and remote ECG monitoring. The use of a 300 Hz LPF offers a better balance between spike detection and baseline interference, making it the recommended setting for pacemaker ECG analysis. Future studies should explore the impact of other ECG parameters on pacemaker spike detection and continue to refine the standards for ECG analysis in pacemaker patients.
doi.org/10.1097/CM9.0000000000000110
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