Automated ST-segment analysis during cesarean delivery: effects of ECG filtering modality.

STUDY OBJECTIVES

To determine the effect of different electrocardiographic (ECG) filtering modalities on ST-segment changes during cesarean delivery. We compared the use of narrow and standard bandwidth ECG filtering modes in assessing ECG-detected ischemic changes in healthy patients undergoing routine, elective cesarean delivery.

DESIGN

Prospective, nonrandomized clinical trial.

SETTING

Academic medical center.

PATIENTS

20 healthy parturients undergoing elective cesarean delivery with regional anesthesia.

INTERVENTION

Continuous 5-lead ECG monitoring was performed in all 20 study parturients. The same incoming ECG signal was divided by a special cable and displayed on two Marquette 7010 monitors. Leads I, II, and V5 were analyzed. One of the monitors filtered the signal with a 0.07 to 100 Hz filter (DIAG), the other with a 0.3 to 40 Hz filter (MON). The ST segment was analyzed continuously by electronic comparison with a template established as a baseline at the beginning of the case. This continuous output was led in digital form every 15 seconds to an IBM PC computer for data analysis.

MEASUREMENTS AND MAIN RESULTS

In each of the leads analyzed, the mean MON versus DIAG different showed a bias, with MON showing consistently lower (ie, more negative) readings than DIAG. Using different criteria for ST depression (> 0.25, > 0.5, or > 1.0mm), we categorized patients as showing more ST depression on either MON or DIAG. With the 0.25 mm criterion, ST depression was identified significantly more often in MON then DIAG in leads H and V5 (p < 0.05). Using the other criteria, the differences were similar, but were not statistically significant. In general, very few instances of ST depression were identified in lead I. No patient had sequelae indicative of intraoperative myocardial ischemia, such as chest pain, dyspnea, persistent ectopy, or hemodynamic instability.

CONCLUSIONS

In patients at low risk for myocardial ischemia, narrow bandwidth (monitor mode) ECG filtering reveals greater degrees of ST-segment depression than does standard (diagnostic mode) ECG filtering. Studies examining ST-segment phenomena would be facilitated by including a description of the ECG filtering-technique.