Summers R L, Kolb J C, Woodward L H, Galli R L
Department of Emergency Medicine, University of Mississippi Medical Center, Jackson 39216, USA.
Acad Emerg Med. 1999 Jul;6(7):693-9. doi: 10.1111/j.1553-2712.1999.tb00437.x.
Differentiating systolic from diastolic congestive heart failure (CHF) is often difficult in the ED. Impedance cardiography (IC) allows for the noninvasive evaluation of systolic function and measurement of diastolic time intervals. This study was designed to assess the ability of IC to accurately measure isovolumic relaxation time (IVRT) and determine relative cardiac contractility, thereby differentiating systolic from diastolic mechanisms in acute CHF.
In an evaluation of the technique, the average differences in the diastolic time intervals measured in normal subjects by both IC tracings and phonocardiography were compared. Likewise, the average Heather index (HI) of patients with known systolic dysfunction (ejection fraction < 30% by echo-cardiography) was compared with the mean HI measured in the normal subjects. In a retrospective analysis, the clinical performance of the method was examined by extracting the values of IVRT and HI from IC tracings of patients presenting with CHF. The determined IVRT and HI values were then correlated to clinical markers for diastolic and systolic dysfunction.
Analysis of 280 IC tracings in eight healthy volunteers revealed an average difference of 0.0075 seconds (95% CI = -0.0067 to 0.0217) when IVRT intervals measured by phonocardiography and IC are compared. The HI in this normal group averaged 14.2 (95% CI = 9.4 to 19.0), contrasting to the much lower value of 2.8 (95% CI = 1.98 to 3.62) seen in eight subjects with documented systolic dysfunction. In 26 patients with decompensated CHF, there was a close correlation (r = 0.81) of the measured IVRT to left ventricular hypertrophy by voltage criteria and while a fall in the HI was correlated with intravascular volume expansion. Though there was considerable overlap (46%) in mechanisms of CHF, 35% of the patients were found to have only systolic dysfunction (HI < 5 and IVRT < 0.125), while 19% had a predominantly diastolic etiology (IVRT > 0.125 and HI > 5) for their failure.
IC measures of contractility and diastolic time intervals are a potentially effective method for differentiating the dominant mechanisms of CHF in the emergent setting and categorizing CHF patients into different subsets.
在急诊科，区分收缩性与舒张性充血性心力衰竭（CHF）往往很困难。阻抗心动图（IC）可用于对收缩功能进行无创评估并测量舒张时间间期。本研究旨在评估IC准确测量等容舒张时间（IVRT）以及确定相对心脏收缩力的能力，从而区分急性CHF中的收缩机制与舒张机制。
在对该技术的评估中，比较了通过IC描记法和心音图在正常受试者中测量的舒张时间间期的平均差异。同样，将已知收缩功能障碍（经超声心动图测定射血分数<30%）患者的平均希瑟指数（HI）与正常受试者中测得的平均HI进行比较。在一项回顾性分析中，通过从CHF患者的IC描记图中提取IVRT和HI值来检查该方法的临床性能。然后将确定的IVRT和HI值与舒张和收缩功能障碍的临床指标相关联。
对8名健康志愿者的280份IC描记图进行分析发现，当比较通过心音图和IC测量的IVRT间期时，平均差异为0.0075秒（95%可信区间=-0.0067至0.0217）。该正常组的HI平均为14.2（95%可信区间=9.4至19.0），与之形成对比的是，在8名有记录的收缩功能障碍受试者中，HI值低得多，为2.8（95%可信区间=1.98至3.62）。在26例失代偿性CHF患者中，测量的IVRT与根据电压标准判定的左心室肥厚密切相关（r=0.81），而HI下降与血管内容量扩张相关。尽管CHF机制存在相当大的重叠（46%），但发现35%的患者仅存在收缩功能障碍（HI<5且IVRT<0.125），而19%的患者其心力衰竭主要由舒张病因引起（IVRT>0.125且HI>5）。
IC对收缩力和舒张时间间期的测量是在紧急情况下区分CHF主要机制并将CHF患者分类为不同亚组的一种潜在有效方法。
