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Interact CardioVasc Thorac Surg 2009;9:255-259. doi:10.1510/icvts.2009.202309 © 2009 European Association of Cardio-Thoracic Surgery
Left ventricular performance in aortic valve replacementDepartment of Cardiovascular Surgery, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan Received 8 January 2009; received in revised form 21 April 2009; accepted 22 April 2009
*Corresponding author. Tel.: +81-92-642-5557; fax: +81-92-642-5566.
We analyzed the mid-term left ventricular (LV) performance after aortic valve replacement (AVR). We measured LV contractility (end-systolic elastance: Ees), afterload (effective arterial elastance: Ea) and efficiency (ventriculoarterial coupling: Ea/Ees; ratio of stroke work and pressure-volume area: SW/PVA) based on transthoracic echocardiography data obtained before, after and approximately 1 year after isolated AVR in 263 patients with aortic stenosis (AS group; n=116), aortic regurgitation (AR group; n=93) or aortic stenosis and regurgitation (ASR group; n=54). The LV volume was calculated by the Teichholz M-mode method. Ees and Ea were approximated as follows: Ees=mean blood pressure/minimal LV volume; Ea=systolic blood pressure/(maximal LV volume–minimal LV volume). Thereafter, Ea/Ees and SW/PVA were calculated. Arterial blood pressure was measured using manchette methods. Ees and Ea decreased after AVR in the AS group, but increased in the AR group. Ea/Ees and SW/PVA worsened after AVR in the AR group, but improved during a 1-year period after AVR in all groups. Contrasting effects of AVR on LV contractility and afterload between AS and AR were clearly demonstrated. The mid-term LV contractility and efficiency after AVR were excellent and satisfactory. However, LV efficiency worsened early after AVR in AR patients.
Key Words: Aortic valve replacement; Cardiac function
Aortic valve replacement (AVR) is one of the standard operations for aortic valve disease patients. The operative methods of AVR are almost established and recent postoperative mortality and morbidity have been significantly decreased owing to evolving modifications in surgical techniques and improvement in the materials used for prosthetic valves, as well as development of the cardiopulmonary bypass method and the myocardial preservation technique during cardiac arrest. Many studies and reports have evaluated the clinical results of AVR [1, 2]. However, few reports have referred to left ventricular (LV) performance after AVR due to the difficulty and complexity of the analyses involved. The concept of end-systolic elastance (Ees), representing the load-independent index of contractility, effective arterial elastance (Ea), representing the index of afterload, and ventriculoarterial coupling (Ea/Ees), representing the index of energy efficiency, provides a useful framework for analyzing ventricular performance [3, 4]. We previously reported an approximation of Ees and Ea using a canine right heart bypass preparation with a conductance catheter system, and then analyzed the cardiac performance of Fontan candidates [5–8], patients with postinfarction dyskinetic anterior LV aneurysms who underwent the Dor procedure [9] and patients who underwent aortic root replacement for annuloaortic ectasia with aortic regurgitation (AR) [10]. Using this approximation of Ees and Ea, we analyzed LV performance before and after AVR based on transthoracic cardiac echocardiography data in the present study. The purpose of this study was to quantify the effects of isolated AVR on ventricular performance based on the concept of Ees and Ea.
2.1. Patient information From 1990 to 2005, 316 consecutive patients underwent elective isolated AVR at Kyushu University Hospital. Re-do cases and cases complicated with other diseases (ischemic heart disease, aortic disease, malignancy, etc.) were excluded from this study. As a result, a total of 263 patients were retrospectively selected for this study. The selected patients were divided into the following three groups for subgroup analyses: aortic stenosis (AS) patients whose peak transvalvular pressure gradient was >50 mmHg and AR grades were less than mild (AS group; n=116); pure AR patients whose peak transvalvular pressure gradient was <50 mmHg and AR grades were more than moderate (AR group; n=93); and aortic stenosis and regurgitation (ASR) patients whose peak transvalvular pressure gradient was >50 mmHg and AR grades were more than moderate (ASR group; n=54). The preoperative characteristics of the patients are shown in Table 1. Informed consent for the operation was obtained from all patients. All data used in this study were obtained retrospectively by means of chart and electronic database reviews, and the individual patients are not identified.
2.2. Operative techniques AVR was performed using the routine methods of Kyushu University Hospital. Myocardial preservation was achieved with cold crystalloid cardioplegic solution and ice slush. The cardiopulmonary bypass times were 154±49 min in all patients, 170±55 min in the AS group, 135±40 min in the AR group and 153±38 min in the ASR group. The aortic cross-clamp times were 96±37 min in all patients, 109±39 min in the AS group, 78±27 min in the AR group and 100±34 min in the ASR group. All values are presented as the mean±S.D. The types of the prosthetic valves used for AVR are shown in Table 2. Overall, nine patients in the AS group and four patients in the ASR group underwent aortic root enlargement due to small aortic annulus sizes [11].
2.3. Data analysis All patients underwent transthoracic cardiac echocardiography before and approximately 2–3 weeks after the operation in-hospital, and approximately 1 year after leaving the hospital. LV volume was calculated by the Teichholz M-mode method based on the cardiac echocardiography data, LV end-diastolic dimension (EDD) and end-systolic dimension (ESD) [12]. Arterial blood pressure was measured by the Korotkoff technique using manchette methods. The LV end-diastolic volume index (EDVI), end-systolic volume index (ESVI) and ejection fraction (EF) were calculated. The EF was calculated as follows: EF (%)=(1–LV end-systolic volume/end-diastolic volume)x100. The calculations of Ees (contractility) and Ea (afterload) were performed by an approximation method as previously described [5, 10]. Ees and Ea were approximated as follows: Ees=mean blood pressure/minimal LV volume; Ea=maximal LV pressure/(maximal LV volume–minimal LV volume). In this study, mean blood pressure was calculated as follows: mean blood pressure=(systolic blood pressure+ diastolic blood pressurex2)/3. Maximal LV pressure was defined as being the same as the systolic blood pressure and maximal blood pressure was corrected by the peak transvalvular pressure gradient in the AS and ASR groups before AVR. The maximal LV volume was defined as being the same as the LV end-diastolic volume and the minimal LV volume was defined as being the same as the LV end-systolic volume. The LV volume was normalized by the body surface area (BSA). The ratio of Ea to Ees (Ea/Ees) and the ratio of stroke work and pressure-volume area (SW/PVA) were calculated as indices of ventricular efficiency. Ea/Ees represents the ventriculoarterial coupling between the LV and the arterial system [4]. SW/PVA was calculated using the theoretical formula: SW/PVA=1/(1+0.5Ea/Ees) [13]. Preoperative values of EDD, ESD, EDVI, ESVI, EF, Ees, Ea, Ea/Ees, and SW/PVA of 96 (73 males and 23 females) normal-cardiac-function patients who electively underwent coronary artery bypass graft surgery due to stable effort angina from 2001 to 2005 at Kyushu University Hospital were shown as normal values. All patients have no symptom of congestive heart failure. The age of these patients was 66.3±9.6 years old; weight, 61.6±11.3 kg and BSA, 1.65±0.18 m2. The results are presented as the mean±S.D. Analysis of variance with repeated measures on one factor was used for the variables measured at the three points (before and after the operation, and approximately 1 year after the operation) in all patients (Total) and each subgroup (AS, AR and ASR groups). The Student–Newman–Keuls test was used as a post hoc test.
EDD of 96 normal-cardiac-function patients were 47.3±5.0 mm, ESD were 28.7±4.7 mm, EDVI were 64.0±14.3 ml/m2, ESVI were 19.8±8.1 ml/m2, EF were 69.6±7.5%, Ees were 5.07±2.03 mmHg/ml/m2, Ea were 3.01±0.76 mmHg/ml/m2, Ea/Ees were 0.66±0.26, and SW/PVA were 75.8±6.7%. The analyzed data are shown in Table 3. EDD, ESD, EDVI and ESVI decreased in a stepwise manner after AVR and at one year after the operation in all patients and all subgroups. EF decreased after AVR, but increased at one year after the operation in all patients and all subgroups. Ees decreased after AVR in the AS group, but increased in the AR group. Ea also decreased after AVR in the AS group, but increased in the AR group. Ees increased at one year after AVR in all patients and all subgroups. Ea increased at one year after AVR in all patients. Ea/Ees and SW/PVA significantly worsened after AVR in the AR group, but remained unchanged in the AS and ASR groups. Ea/Ees and SW/PVA improved during a 1-year period after AVR in all patients and all subgroups. Ea/Ees and SW/PVA one year after AVR was superior to before AVR in AS and ASR groups, but Ea/Ees and SW/PVA one year after AVR was almost the same as before AVR in AR group.
The major findings of the present study in patients who underwent isolated AVR were as follows: (1) LV contractility (Ees) and afterload (Ea) decreased after AVR in the AS group, but increased in the AR group; (2) LV efficiency (Ea/Ees and SW/PVA) worsened after AVR in the AR group; (3) LV efficiency improved during a 1-year period after AVR in all patients and all subgroups; and (4) LV efficiency one year after AVR was superior to before AVR in AS and ASR groups, but LV efficiency one year after AVR was almost the same as before AVR in AR group. The significance of these results is the contrasting effects of AVR on LV contractility and afterload between the AS and AR groups before and after AVR, and the improvement in LV efficiency at the mid-term period after AVR. AVR is one of the established cardiac operations, and many clinical reports have shown excellent clinical results according to expectations [1, 2]. LV performance at the mid-term period after AVR was found to be excellent in the present study. However, the detailed analysis carried out in this study revealed an early problem after AVR in some cases, especially AR cases. Contractility (Ees) improved and afterload (Ea) increased in the early stage after AVR in the AR group, and the LV efficiency (Ea/Ees and SW/PVA) significantly worsened. We previously reported that Ees improved, Ea increased and SW/PVA worsened after AVR in patients with simple AR in an operating-room study [14]. In the AS group, Ees decreased (worsened) after AVR, but Ea also decreased (improved), and then SW/PVA did not change. EF, which is the most commonly used index of cardiac function, decreased significantly after AVR in all patients and all subgroups. LV efficiency decreased significantly after AVR only in the AR group. The clinical significance of the decreased EF after AVR in AR patients would be different from that in AS and ASR patients. The worsening of LV efficiency after AVR could be critical in some AR patients whose LV function is impaired. LV efficiency in the AR group was consistently inferior to those in the AS group, and LV efficiency in the AS group improved to normal one year after AVR, whereas that in the AR group remained impaired. The improvements in LV performance after AVR in the AR group were inferior to those in the AS group. The preoperative conditions of AR patients would be worse than those of AS patients from the standpoint of the long-term LV performance after AVR. The clinical indication for AVR in the AR group in this series would have some problem. The timing of operation would be too late. The average of EDD was 64.3 mm and that of ESD was 43.1 mm before AVR in the AR group. Both were smaller than the values which ACC/AHA practice guidelines indicate AVR for chronic AR patients (75 mm and 55 mm, respectively). The results in this study would suggest the problem in the current surgical indications for AR, but these explanations are only speculation at this time. The prospective studies introducing a stress echocardiogram for the evaluation of the LV contractile reserve, especially chronic AR, are thus called for. The reason for the decrease in afterload (Ea) after AVR in the AS group is obvious because stenosis is released after the operation. However, the abrupt decrease in LV pressure after AVR in the AS group would bring about a decrease in contractility (Ees) at the same time. Although the reduction in LV volume after AVR in the AR group leads to an improvement in contractility, the abrupt volume change also brings about an increase in afterload, and the LV efficiency (Ea/Ees and SW/PVA) worsens. The contrasting effects of AVR on LV contractility and afterload between AS and AR should be taken into consideration during the perioperative period. The approximation of Ees and Ea used in this study has inherent limitations and does not amount to measurements obtained by a conductance catheter system. This approximation was validated using a canine right-heart bypass model, which can draw the maximum capacity of the conductance catheter system [5]. Furthermore, the validation was only performed on normal canine hearts, which differ from diseased human hearts with AS and/or AR. The diseased settings, especially the existence of the outflow obstruction, are not examined. The validity of substituting the LV volume calculated with echocardiography data and Teichholz M-mode method for that measured with a conductance catheter system was also not fully examined. However, this approximation enables us to evaluate ventricular contractility, afterload and ventriculoarterial coupling from the conventional pressure data of arterial blood pressure using manchette methods and volume data using cardiac echocardiography, which are non-invasive routine examinations [5–10]. This promising approximation method is simple and reproducible, and considered to be applicable to other clinical cases. The cardiac echocardiography data used in this study were obtained retrospectively by means of chart and electronic database reviews, which have inherent limitations. First, Simpson's method is more suitable than the Teichholz M-mode method for calculation of LV volumes. However, only the LV diameter values were available in this retrospective study. The calculations of the LV volume especially in the AR group would be underestimated due to the spherical change of the left ventricle. Secondly, the influence of AVR in the parameters of LV performance is not fully discussed. The impact of AVR on the LV geometry and mass is dramatically big and would influence the value of Ees intrinsically [15]. Finally, the influences of medication on the parameters of ventricular performance were not examined in this study because the postoperative medical managements were performed by many different physicians and hospitals. In conclusion, contrasting effects of AVR on LV contractility and afterload between AS and AR were clearly demonstrated by the framework of Ees and Ea based on transthoracic echocardiography data. The mid-term LV contractility and efficiency after AVR were excellent and satisfactory. However, AVR in AR cases with impaired LV function was still problematic because LV efficiency worsened early after AVR in AR patients.
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Abstract
1. Introduction
