Pagan-Carlo L A, Spencer K T, Robertson C E, Dengler A, Birkett C, Kerber R E
Department of Internal Medicine, University of Iowa Hospital, Iowa City 52242, USA.
J Am Coll Cardiol. 1996 Feb;27(2):449-52. doi: 10.1016/0735-1097(95)00487-4.
This study sought to determine the effect on transthoracic impedance of placement of defibrillation electrodes on the female breast versus adjacent to or under the breast.
Transthoracic impedance is a major determinant of transthoracic current flow in defibrillation. For a given energy setting, a high transthoracic impedance reduces current flow and may adversely affect the ability of electric shocks to accomplish defibrillation. We hypothesized that the increased interelectrode tissue associated with placement of the apex defibrillation electrode on the female breast would result in increased transthoracic impedance compared with electrode placement lateral to or under the breast.
Transthoracic impedance was measured noninvasively by passing a 5-V, 31.25-kHz square wave current through the chest and comparing the low level current flow to known references. We measured transthoracic impedance associated with three different apex defibrillation electrode positions--on the breast, under the breast and lateral to the breast--in 25 women (brassiere size 34A to 48C, 25 to 75 years old, body weight 128 to 328 lb [58 to 148 kg] and 2 men. The measurements were taken with a modified defibrillator that accurately predicts transthoracic impedance without delivering an actual shock. The measurement sequence was random.
The average measured transthoracic impedance with placement of the apex defibrillation electrode on the breast was 95 +/- 25 ohms (mean +/- SD), under the breast 84 +/- 17* ohms and lateral to the breast 83 +/- 20* ohms (asterisk indicates p < 0.01 vs. on the breast by analysis of variance). The study cohort was also classified into two groups: large breasted (brassiere size > or = 40) and small breasted (brassiere size < or = 39). The measured transthoracic impedances for the large-breasted group were 112 +/- 20 ohms for on the breast, 94 +/- 13* ohms for under the breast and 98 +/- 19* ohms for lateral to the breast. For the small breasted group, the similar transthoracic impedance measurements were 81 +/- 21, 77 +/- 16 and 71 +/- 13* ohms, respectively.
In women, placement of the apex defibrillation electrode on the breast results in higher transthoracic impedance, which will reduce current flow. We recommend placing the apex electrode lateral to or underneath the breast.
本研究旨在确定除颤电极放置在女性乳房上、乳房旁或乳房下对经胸阻抗的影响。
经胸阻抗是除颤时经胸电流流动的主要决定因素。对于给定的能量设置，高经胸阻抗会减少电流流动，并可能对电击除颤的能力产生不利影响。我们假设，与将心尖除颤电极放置在乳房旁或乳房下相比，将其放置在女性乳房上会导致电极间组织增加，从而使经胸阻抗增加。
通过让5V、31.25kHz的方波电流通过胸部，并将低水平电流与已知参考值进行比较，以无创方式测量经胸阻抗。我们在25名女性（胸罩尺寸34A至48C，年龄25至75岁，体重128至328磅[58至148千克]）和2名男性中测量了与三种不同的心尖除颤电极位置相关的经胸阻抗，这三种位置分别是：在乳房上、在乳房下和在乳房旁。测量使用的是经过改良的除颤器，它可以准确预测经胸阻抗而不实际发放电击。测量顺序是随机的。
心尖除颤电极放置在乳房上时，平均经胸阻抗测量值为95±25欧姆（均值±标准差），在乳房下为84±17欧姆，在乳房旁为83±20欧姆（星号表示通过方差分析，与在乳房上相比，p<0.01）。研究队列还被分为两组：大乳房组（胸罩尺寸≥40）和小乳房组（胸罩尺寸≤39）。大乳房组在心尖除颤电极放置在乳房上、乳房下和乳房旁时的经胸阻抗测量值分别为112±20欧姆、94±13欧姆和98±19欧姆。对于小乳房组，类似的经胸阻抗测量值分别为81±21、77±16和71±13*欧姆。
在女性中，将心尖除颤电极放置在乳房上会导致较高的经胸阻抗，这将减少电流流动。我们建议将心尖电极放置在乳房旁或乳房下。
