Vital sign parameters are not associated with electrical capture during transcutaneous pacing

Failure to achieve electrical capture during transcutaneous pacing (TCP) is common and underrecognized. We aimed to identify whether pulse oximetry plethysmograph waveform synchrony, end-tidal capnometry increases, and systolic blood pressure increases were associated with sustained electrical capture during prehospital TCP.

This secondary analysis of a multi-center retrospective observational study enrolled patients from four emergency medical service agencies. Sustained electrical capture was defined as a wide QRS and T wave for ≥90% of ongoing TCP time. Pulse oximetry plethysmograph wave synchronization with the TCP rate and vital sign values were obtained from cardiac monitor/defibrillator files. A diagnostic framework was used to evaluate plethysmograph synchronization. We used linear regression modeling to detect whether increases in end-tidal carbon dioxide (ETCO₂) and blood pressure measurements were associated with sustained electrical capture.

Of 253 patients, 29 (11.5%) had sustained electrical capture. An increase in SBP had a sensitivity of 75.0% (42.8, 94.5) and a specificity of 40.0% (29.8, 50.9) for the outcome of sustained electrical capture. An increase in ETCO₂ had a sensitivity of 41.7% (15.2, 72.3) and a specificity of 64.4% (53.7, 74.3). Linear regression modeling did not suggest that sustained electrical capture was associated with post-TCP SBP (-2.5 mmHg (-27.3, +22.4)) or post-TCP ETCO₂ (2.6 mmHg (-2.9, +8.1)). Plethysmograph synchronization had a sensitivity of 58.8% (32.9, 81.6) and a specificity of 81.1% (73.2, 87.5).

These findings suggest that plethysmograph waveforms, capnometry, and blood pressure monitoring alone are not reliable indicators of electrical capture during TCP performed by paramedics.