Introduction: The use of transcutaneous pacing (TCP) for unstable bradycardia has a class 2B recommendation from the American Heart Association. Prior studies have not adequately described the frequency or possible causes of treatment failure. EMS clinicians and leaders have reported false electrical capture as a potential cause. In this study, we aimed to describe the frequency of true electrical capture, documented verification of mechanical capture, and its association with systolic blood pressure (SBP) and survival.
Methods: This was a retrospective study of patients treated by an urban, hospital-based EMS network comprising two EMS agencies between March 2021 and March 2023. Inclusion criteria were adults with a heart rate of <60 bpm and attempted TCP. Variables included: initial electrocardiogram rhythm, SBP, current applied, neurological status at discharge, and diagnosis. The primary outcome was true electrical capture, defined as the presence of a visible wide QRS and T wave. This enabled calculation of false electrical capture. Additional outcomes included change in SBP and neurological status at discharge.
Results: 19 of the 23 (82.6%) patients who underwent TCP had false electrical capture despite all 23 having documented mechanical capture by palpated pulse. For patients with true electrical capture, the median change in SBP was +40 mmHg (IQR = 24.25, range= -12 to +49 mmHg). For patients with false electrical capture, the median change in SBP was -1 mmHg (IQR = 58.50, range= -90 to +23 mmHg). Median current for patients with true electrical capture was 95 mA (IQR = 13.75, range = 85-110) versus 70 mA (IQR = 30, range = 55-160) in those with false electrical capture. 16 (69.6%) had outcome data available. Patients with true electrical capture and outcome data (n = 2) survived to admission but only one survived to discharge with good functional capacity. Of 14 with false electrical capture and outcome data, 10 (71.4%) survived to admission; none survived to discharge with functional capacity.
Conclusions: These findings suggest a high proportion of patients undergoing TCP are at risk of false electrical capture despite a recorded palpable pulse. While our analysis is limited to a single EMS network, these data raise concerns regarding the incidence of prehospital false electrical capture. Further research is warranted to calculate the incidence of false electrical capture and evaluate mitigation strategies.