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.

A Systematic Review of the Transthoracic Impedance during Cardiac Defibrillation

“…In summary, TTI was lower in the AP position than in the AA and AL electrode positions, although in some studies this was not sufficient to be significant. Most authors agree that despite slight differences, pad positioning is not a critical determinant of TTI [ 21 , 42 , 44 , 45 , 46 , 47 , 48 ].…”

“…Kerber et al reported that this surgical procedure greatly reduces TTI ( ), with changes persisting after wound healing. The changes were most prominent in the apex-right parasternal and left parasternal-right infrascapular position and less pronounced in the lateral-lateral position, where the current path does not cross the incision path [ 46 ].…”

“…The increase in blood and extracellular fluids results in improved current conduction and thus decreased resistance. Long-term decreased TTI is thought to be due to scarring and adhesions that alter the properties of tissue [ 46 ].…”

Cardioversion and defibrillation

“…Ekokardiyografi jellerinin iletken jel olarak kullanılması doğru değildir [13]. Sternotomi empedansı düşürür ve bu etki en az 1 ay devam eder [14]. Son olarak, verilen her uyarı empedansı bir miktar düşürür.…”

Optimal technique for electrical cardioversion of atrial fibrillation.

“…19 Finally, for at least 1 month after the procedure, a sternotomy lowers transchest impedance. 20 Optimal electrode position is also important since a critical mass of the atrium must be defibrillated for cardioversion to occur. Lown and colleagues'-3reported that the anteroposterior electrode position was more effective for cardioversion of atrial fibrillation than the anterior-anterior electrode position.…”