Euler DE, Whitman TA, Kallok MJ. Inspiration induced by phrenic nerve stimulation increases internal defibrillation energy requirements.
J Cardiovasc Electrophysiol 1999;
10:1402-8. [PMID:
10515565 DOI:
10.1111/j.1540-8167.1999.tb00196.x]
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Abstract
INTRODUCTION
The purpose of this study was to systematically evaluate the effects of active inspiration induced by phrenic nerve stimulation on the energy required for 50% successful defibrillation (E50).
METHODS AND RESULTS
Shocks (95-microF biphasic waveform) were delivered after 10 seconds of ventricular fibrillation between a right ventricular coil and left pectoral test can in ten anesthetized pigs (25 to 37 kg). Using a 1-J step size, the E50 was determined with an up/down, three-reversal method. Positive-pressure ventilation was halted just before fibrillation, and shocks were delivered during expiration or at the end of 2 seconds of bilateral phrenic stimulation (50 Hz, 0.3 msec, 5 to 6 V). Phrenic stimulation produced inspiratory volumes that were 15.3 +/- 1.7 mL/kg (mean +/- SD). The E50 was 9.8 +/- 1.9 J during expiration and increased to 13.0 +/- 1.7 during inspiration (P = 0.001). The leading-edge voltage at the E50 was 451 +/- 46 V during expiration and 519 +/- 33 V during inspiration (P = 0.001). The leading-edge current at the E50 was 9.7 +/- 1.0 A during expiration and increased to 11.3 +/- 1.4 A during inspiration (P = 0.002). The average impedance was 47.8 +/- 2.7 omega during expiration and 47.3 +/- 3.3 omega during inspiration (P = 0.12).
CONCLUSION
Inspiration induced by phrenic stimulation results in a 31% increase in the E50 compared with expiration. The decrease in shock efficacy occurs in the absence of a change in impedance. Active inspiration may alter the distribution of the electrical field leading to a decrease in shock efficacy.
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