title: Transthoracic defibrillation: effect of sternotomy on chest impedance.
abstract: The purpose of this study was to determine the effect of sternotomy on transthoracic impedance, a major determinant of current flow and defibrillation success. Transthoracic impedance was determined by using a validated test-pulse technique that does not require actual shocks. Seventeen patients undergoing median sternotomy were studied prospectively. Transthoracic impedance was determined before operation, 3 to 5 days after operation and (in eight patients) greater than or equal to 1 month after operation. When measured using paddle electrodes placed in the standard apex-right parasternal defibrillating position, transthoracic impedance declined after sternotomy in all patients, from 77 +/- 18 to 59 +/- 17 omega (p less than 0.01); smaller declines were demonstrated by using other electrode positions. Transthoracic impedance remained below the preoperative level in the eight patients who underwent a second set of measurements at least 1 month after operation. Six normal subjects not undergoing sternotomy underwent serial transthoracic impedance measurements at least 5 days apart; mean transthoracic impedance did not change. It is concluded that transthoracic impedance declines after sternotomy. At any operator-selected energy level a higher current flow will result after sternotomy; this may facilitate postoperative defibrillation.
authors.affiliation: Cardiovascular Division, University of Iowa Hospital, Iowa City 52242.
authors.forename: R E
authors.initials: RE
authors.lastname: Kerber
authors.forename: S
authors.initials: S
authors.lastname: Vance
authors.forename: S J
authors.initials: SJ
authors.lastname: Schomer
authors.forename: D J
authors.initials: DJ
authors.lastname: Mariano
authors.forename: F
authors.initials: F
authors.lastname: Charbonnier
mesh_terms: D002307:Cardiography, Impedance; D004554:Electric Countershock; D006801:Humans; D011184:Postoperative Period; D013249:Sternum / Q000502:physiology* / Q000601:surgery*