Validation of continuous QTc measurement in critically ill patients

Agreement of Computerized QT and QTc Interval Measurements Between Both Bedside and Expert Nurses Using Electronic Calipers

BACKGROUND

In hospitalized patients, QT/QTc (heart rate corrected) prolongation on the electrocardiogram (ECG) increases the risk of torsade de pointes. Manual measurements are time-consuming and often inaccurate. Some bedside monitors automatically and continuously measure QT/QTc; however, the agreement between computerized versus nurse-measured values has not been evaluated.

OBJECTIVE

The aim of this study was to examine the agreement between computerized QT/QTc and bedside and expert nurses who used electronic calipers.

METHODS

This was a prospective observational study in 3 intensive care units. Up to 2 QT/QTc measurements (milliseconds) per patient were collected. Bland-Altman test was used to analyze measurement agreement.

RESULTS

A total of 54 QT/QTc measurements from 34 patients admitted to the ICU were included. The mean difference (bias) for QT comparisons was as follows: computerized versus expert nurses, -11.04 ± 4.45 milliseconds (95% confidence interval [CI], -2.3 to -19.8; P = .016), and computerized versus bedside nurses, -13.72 ± 6.70 (95% CI, -0.70 to -26.8; P = .044). The mean bias for QTc comparisons was as follows: computerized versus expert nurses, -12.46 ± 5.80 (95% CI, -1.1 to -23.8; P = .035), and computerized versus bedside nurses, -18.49 ± 7.90 (95% CI, -3.0 to -33.9; P = .022).

CONCLUSION

Computerized QT/QTc measurements calculated by bedside monitor software and measurements performed by nurses were in close agreement; statistically significant differences were found, but differences were less than 20 milliseconds (on-half of a small box), indicating no clinical significance. Computerized measurements may be a suitable alternative to nurse-measured QT/QTc. This could reduce inaccuracies and nurse burden while increasing adherence to practice recommendations. Further research comparing computerized QT/QTc from bedside monitoring to standard 12-lead electrocardiogram in a larger sample, including non-ICU patients, is needed.

A Comparative Study of the Validity and Reliability of Two Wireless Telemetry Electrocardiogram Devices in the Emergency Medicine Department

Background

This study aimed to compare the clinical validity and reliability of two wireless telemetry electrocardiogram (ECG) devices in the Emergency Medicine Department.

Material/Methods

Patients who attended the Emergency Medicine Department underwent wireless telemetry ECG testing (N=245) using the Infron Micro Cor and the Nihon Kohden Cardiofax M 1350 K devices. ECG recordings included heart rate, P-wave amplitude, PR segment length, QRS duration, QT and QTc intervals, ST depression and elevation, the number of ECG artifacts, the ECG diagnosis, and duration. Statistical analysis of reliability included the use of Cohen’s kappa (κ) values.

Results

One hundred women (40.8%) and 145 men (59.2%) were included in the study. The duration for the Infron Micro Cor ECG readings (57.5±0.93 seconds) was significantly shorter compared with the Nihon Kohden Cardiofax M ECG readings (65.2±9.72 seconds) (p=0.0001). The Infron Micro Cor ECG readings contained significantly more lead artifacts (93 or 37.9%) compared with the Nihon Kohden ECG readings (71 or 28.9%) (p=0.01). There was no difference between the two devices in terms of the other ECG parameters. The compatibility of ST-segment elevation detection was found to be almost in complete agreement between the Infron Micro Cor and Nihon Kohden Cardiofax M ECG devices, as determined by the κ-values for ST elevation and ST depression.

Conclusions

Two wireless telemetry ECG devices were found to be reliable for use in the Emergency Medicine Department. The Infron Micro Cor wireless telemetry ECG device provided more rapid results.

QTc prolongation during erythromycin used as prokinetic agent in ICU patients

Background

High-dose erythromycin used as antibiotic prolongs QTc interval. Low-dose erythromycin is frequently used as a prokinetic agent, especially in patients in the intensive care unit (ICU). It is unknown whether low-dose erythromycin affects cardiac repolarisation and puts patients at risk for torsades de pointes.

Methods

In this prospective study, we included ICU patients treated with erythromycin as prokinetic in a dose of 200 mg twice a day. An ECG was performed before, 15 min and 24 hours after the start of erythromycin. Cardiac repolarisation was assessed by rate-corrected analysis of the QT interval (QTc) on the ECG by two independent investigators. Starting or stopping other possibly QTc prolonging drugs during the study period was an exclusion criterion. Wilcoxon signed-rank test and Friedman's test were used for statistical analysis to assess prolongation of QTc. Primary outcome was defined by the prolongation of QTc after 15 min and 24 hours.

Results

51 patients were eligible for this study. In these patients, QTc increased significantly from 430 ms at baseline to 439 ms (p=0.03) after 15 min and 444 ms (p=0.01) after 24 hours. After 15 min and 24 hours, the upper limit of 95% CI for prolongation of QTc was well above 10 ms. No QTc-related arrhythmias were seen.

Conclusions

During treatment with erythromycin in a dose of 200 mg twice a day. QTc prolonged mildly but significantly. Sequential ECG registration should be performed when low-dose erythromycin is prescribed, especially in the presence of other risk factor for QTc prolongation.