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

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