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Effects of preload alterations on peak early diastolic mitral annulus velocities evaluated by tissue Doppler echocardiography

Jonassen, A. A.*; Bjørnerheim, R.; Edvardsen, T.; Veel, T.*‡; Kirkebøen, K. A.

European Journal of Anaesthesiology: February 2007 - Volume 24 - Issue 2 - p 159–165
doi: 10.1017/S026502150600127X
Original Article
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Background and objective: Tissue Doppler echocardiography is proposed to be a relatively preload independent tool for assessment of diastolic function. No data exist on anaesthetized patients in whom myocardial contractility, vascular tone and baroreceptor reflexes are depressed. The aim of this study was to evaluate the effects of preload alterations on tissue velocities in patients during general anaesthesia for coronary arterial bypass surgery.

Methods: Fifteen patients referred for elective aorto-coronary bypass surgery were examined by tissue Doppler echocardiography. Early diastolic velocities in the septal and lateral portion of the mitral annulus were measured during preload interventions induced by tilting of the operating table in patients during general anaesthesia both before surgery and after chest closure. To verify changes in preload we used right atrial pressure and pulmonary artery occlusion pressure.

Results: Tissue velocities in both the septal and lateral portion of the mitral annulus were significantly higher when preload was increased, compared to when it was decreased. Alterations in diastolic velocities in the septal portion of the mitral annulus prior to surgery: 0.8 ± 0.2 cm s−1, P < 0.001, after surgery: 1.1 ± 0.2 cm s−1, P < 0.001. Alterations in diastolic velocities in the lateral portion of the mitral annulus prior to surgery: 1.4 ± 0.2 cm s−1, P < 0.001, after surgery: 1.1 ± 0.3 cm s−1, P < 0.01. Concomitant changes in right atrial pressure and pulmonary artery occlusion pressure were 11 ± 1 and 12 ± 1 mmHg before surgery and 13 ± 1 and 12 ± 1 mmHg after surgery (P < 0.001 for all), respectively.

Conclusion: These results show that tissue velocities of the mitral annulus are preload dependent in patients during general anaesthesia both before and after coronary surgery.

*Ullevål University Hospital, Department of Anaesthesiology, Oslo, Norway

Ullevål University Hospital, Department of Cardiology, Oslo, Norway

Rikshospitalet University Hospital, Department of Cardiology, Oslo, Norway

Feiring Heart Clinic, Feiring, Norway

§Ullevål University Hospital, Institute for Experimental Medical Research, Oslo, Norway

Correspondence to: Alf A. Jonassen, Department of Anaesthesiology, Ullevål, University Hospital, Kirkeveien 166, 0407 Oslo, Norway. E-mail: alf.arne.jonassen@uus.no; Tel: +47 22 119 690; Fax: +47 22 119 857

Accepted for publication 25 June 2006

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Introduction

Diastolic dysfunction is important in development of heart failure and in the pathophysiology of ischaemic, hypertensive and valvular diseases. The condition is more prevalent among elderly people, and morbidity is high [1]. Indices of diastolic function can be derived invasively and non-invasively. Measurements of these indices is complicated because diastolic function depends on several determinants: active, energy dependent forces (isovolumetric relaxation); passive and dynamic filling characteristics (myocardial stiffness) and extrinsic factors such as atrial function, ventricular interaction, valvular integrity, pericardial restraint and myocardial blood flow. Diastolic function is also affected by factors like preload, afterload, heart rate (HR) and inotropic state.

Echocardiography is the principal clinical tool to assess left ventricular (LV) diastolic function. Antegrade mitral flow signal indices, such as peak early filling velocity (E′max), peak velocity during atrial contraction (A′max), duration of atrial contraction, isovolumetric relaxation time (IVRT), E/A ratio and pulmonary venous Doppler indices, such as peak velocity of the systolic and diastolic component and the duration of the atrial reversal signal give important information on diastolic function [2]. However, blood flow signals are affected by several physiologic variables, as mentioned above.

In the last decade, tissue Doppler echocardiography (TDE), which selectively detects myocardial wall velocities [2], has gained interest in assessment of LV function. Attempts to characterize diastolic properties by this method have been promising and TDE has been proposed as a tool for assessment of LV diastolic function. The most commonly used TDE indices on diastolic function are peak velocity during early diastolic filling (E′max), peak velocity during atrial contraction (A′max) with the sample volume placed in the septal and lateral portion of the mitral annulus using an apical 4-chamber view. Shortening of the LV in the long-axis view is found to indicate global LV function [2]. Initial studies suggested TDE, in contrast to conventional Doppler indices of LV filling, to be preload independent [3–5]. However, recent studies on anaesthetized dogs [6,7] and conscious human beings [8–10] indicate that TDE measurements are more influenced by preload changes than previously believed.

LV filling characteristics can be a limiting factor during cardiac surgery, especially when LV hypertrophy is present. In the operating room we assessed information on diastolic function based on the effects of preload interventions, like fluid challenges and table tilting. Preload descriptors, like central venous pressure (CVP), right atrial pressure (RAP) and pulmonary artery occlusion pressure (PAOP), are used to evaluate these interventions.

General anaesthesia affects important aspects of the cardiovascular system, such as myocardial contractility, vascular tone and baroreceptor reflexes [11,12]. As far as the authors are aware of, there are no reports on the effects of preload alterations on diastolic tissue velocities in patients during general anaesthesia. The aim of this study was to evaluate the effects of preload interventions on E′max in the septal and lateral portion of the mitral annulus in patients during general anaesthesia. Fifteen patients undergoing elective coronary surgery were included and measurements by transoesophageal echocardiography (TOE) were obtained during general anaesthesia before start of surgery and after chest closure. Preload alterations were induced by tilting of the operating table and verified by RAP and PAOP measured by a pulmonary artery catheter (PAC).

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Methods

The regional Ethical Committee approved the study. All subjects gave their informed consent and the study was in accordance with the Helsinki Declaration. Echocardiography was performed in 15 patients referred for elective aorto-coronary bypass. All patients were in New York Heart Association (NYHA) class III and had three vessels disease. Characteristics of the study population are given in Table 1.

Table 1

Table 1

Echocardiography was performed using GE Vingmed System V ultrasound scanner with a 5 MHz transoesophageal probe. In the mid-oesophageal 4-chamber view the tissue velocities were examined with the sample volume in the septal and lateral portion of the mitral annulus, respectively. The frame rate was held >96 s−1 and the Nyquist limit was set to 12 cm s−1. Cine-loops recorded were saved on a magnetic optic disc for later analysis. The intraobserver variation was 10.0% and interobserver variation was 8.3%.

Data were obtained in steady state anaesthesia before start of surgery and after completion of surgery before leaving the operating room. Each examination followed the same three steps.

  1. In flat supine position we measured peak early diastolic velocity in the septal and lateral portion of the mitral annulus using TDE and RAP and PAOP were measured simultaneously.
  2. With the patient in anti-Trendelenburg position (15°) for 3 min, the same measurements as for step 1 were obtained.
  3. With the patient in Trendelenburg position (−15°) for 3 min the same measurements as for step 1 were obtained.

All patients had a central venous catheter (CVC) and a PAC inserted in the right internal jugular vein after induction of anaesthesia. The pressure transducer was kept in level with the left atrium during the whole procedure. The patients were operated in a standard manner using cardiopulmonary bypass (CPB) and moderate hypothermia. After weaning from CPB all patients had a positive end-expiratory pressure of 5 cmH2O.

For induction of anaesthesia we used diazepam, fentanyl and thiopental. Muscle relaxation was obtained by pancuronium. Isoflurane was used to maintain anaesthesia.

Statistics. Data are given as mean and standard error of the mean. Comparisons during different preload interventions were made by one-way analysis of variance (ANOVA) and regression analysis between tissue velocities and PAOP were performed. Comparisons before and after surgery were made by t-test. All statistics were made in Sigmastat 2.03. P < 0.05 was considered statistically significant.

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Results

Patient characteristics are given in Table 1. All patients were in NYHA class III, ejection fraction (EF) was 59 ± 9 and number of grafts received were 3.2 ± 0.5.

Alterations in RAP and PAOP at the time of measurements are given in Figure 1. Head tilting up produced a significant reduction in RAP and PAOP (P < 0.001 both before and after surgery). Head tilting down produced a significant increase in RAP and PAOP (P < 0.001 both before and after surgery). There were no significant changes in HR or mean arterial pressure (MAP) during the procedure either before or after surgery (Table 2). Head tilting up produced a significant reduction in mean pulmonary arterial pressure (MPAP) before (P < 0.01) and after surgery (P < 0.001). Head tilting down produced a significant increase in MPAP before (P < 0.01) and after surgery (P < 0.001).

Figure 1.

Figure 1.

Table 2

Table 2

Tissue velocities are given in Figure 2. Before surgery, reduced preload caused no significant change in E′max septal (P = 0.39), while there was significant reduction in E′max lateral (0.7 ± 0.03 cm s−1, P < 0.01). Elevated preload produced a significant increase in both E′max septal (0.7 ± 0.04 cm s−1, P < 0.001) and E′max lateral (1.5 ± 0.4 cm s−1, P < 0.001). After surgery, reduced preload did not produce significant changes in either E′max septal (P = 0.15) or in E′max lateral (P = 0.10). Elevated preload produced a significant increase in E′max septal (1.2 ± 0.04 cm s−1, P < 0.01), and marginally significant in E′max lateral (P = 0.06). Tissue velocities in both the septal and lateral portion of the mitral annulus were significantly higher when preload was increased, compared to when it was decreased.

Figure 2.

Figure 2.

There were no statistical differences when comparing the alterations in tissue velocities associated with preload interventions before and after surgery (P = 0.11 for E′max septal and P = 0.37 for E′max lateral, when comparing Trendelenburg with anti-Trendelenburg position before and after surgery).

There were no significant correlation between diastolic tissue velocities and PAOP. For E′max septal before and after surgery P values were 0.08 and 0.95 and r-values were 0.28 and 0.01, respectively. For E′max lateral before and after surgery P values were 0.22 and 0.54 and r-values were 0.2 and 0.1, respectively.

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Discussion

In the present study tissue velocities were altered during preload alterations in patients in general anaesthesia undergoing coronary surgery. When tissue velocities were compared between the Trendelenburg position and the anti-Trendelenburg position we found significant differences in tissue velocities in the septal and the lateral portion of the mitral annulus, both before and after surgery.

Conventional Doppler echocardiography has become the principal tool in assessing diastolic function in daily practice. Doppler measurements of the mitral inflow signal together with flow patterns of the pulmonary vein and 2D echocardiography have reasonable accuracy in assessment of diastolic function, but in many cases the information from these Doppler indices will be inconclusive. This method is affected by most haemodynamic factors, included preload [2] and is therefore difficult to interpret in the perioperative period due to rapid changes in preload, afterload and contractility.

The search for preload independent means to quantify diastolic function has lead to increased interest in tissue velocities, which selectively detect myocardial wall velocities. Movement of the mitral annulus reflects changes in LV long-axis dimension because the cardiac apex is relatively fixed during the cardiac cycle. In absence of great distortion of the ventricular shape or severe regional wall motion abnormalities, changes in long-axis dimensions could reflect LV volume. This method is of value in differentiating between constrictive pericarditis and restrictive cardiomyopathy [2] and between hypertrophic cardiomyopathy and athlete's hearts and LV hypertrophy due to hypertension [13]. Additionally, the method can detect regional LV dysfunction during ischaemia [14] and has better accuracy than conventional echocardiography when global systolic function is not affected [15].

Several investigators have found TDE to be preload independent. Sohn and colleagues [3] studied the effects of preload alterations on E′ max in the medial portion of the mitral annulus in patients with normal and abnormal diastolic function. They found no significant changes in E′ max medial during volume infusion (500–700 mL saline) in awake patients with known relaxation abnormalities (defined by mitral inflow variables) or during nitroglycerin in awake patients with normal LV systolic and diastolic function. Accordingly, Nagueh and colleagues [4] found no relationship between E′ max and PAOP in patients with different types of heart diseases. In heart transplant recipients Aranda and colleagues [5] found TDE to be preload independent during interventions with nitroglycerin.

In recent years several studies in conscious human beings and animals indicate that TDE measurements are preload dependent. Dumesnil and colleagues [8] found a significant reduction of E′ max in the lateral portion of the mitral annulus during the Valsalva procedure in conscious human beings with and without impaired relaxation (defined by mitral inflow variables). By using the Valsalva procedure, Pei-Ying and colleagues [9] also concluded that TDE velocities are preload dependent in conscious healthy human beings. However, the effects of the Valsalva procedure were not verified by pressure measurements. Dincer and colleagues [10] evaluated the effects of haemodialysis on TDE measurements in the lateral, medial, posterior and anterior portion of the mitral annulus and found significant reductions in velocities in all measured sites after haemodialysis (500–4300 mL extracted).

All these studies are performed on conscious human beings. Different preload interventions are used and many are inaccurate regarding changes in end-diastolic volume. Firstenberg and colleagues [6] tested the hypothesis that tissue velocities are insensitive to acute alterations in preload in healthy dogs during anaesthesia and positive-pressure ventilation. Caval occlusion via balloon catheter was used for preload interventions. Volumetric calculation of end-diastolic and end-systolic volumes was obtained by electrical impedance calibrated by 2D echocardiography and TDE was measured in the medial portion of the mitral annulus. They found that E′ max is preload depended and that E′ max is modulated by the rate of LV relaxation. Preload dependency seems less strong when diastolic function is impaired. Accordingly, Nagueh and colleagues [4], in patients with heart diseases, and Jacques and colleagues [7], in anaesthetized dogs, also found that preload dependency for tissue velocities is reduced when LV relaxation is impaired.

To our knowledge the present study is the first to investigate preload dependency for tissue velocities in patients in general anaesthesia undergoing coronary surgery. It should be noted that two of the patients had aortic valve replacement in addition to coronary surgery. This may alter the characteristics of the ventricle. However, these two patients did not qualitatively affect the data. During general anaesthesia almost all aspects of the cardiovascular system are affected. The patients in the present study were given isoflurane, diazepam, fentanyl, thiopental and pancuronium. Isoflurane leads to decreased systemic vascular resistance [16], depressed baroreceptor reflexes [17] and reduced myocardial contractility [18]. Barbiturates predominant cardiovascular effect is venodilatation followed by pooling of blood in the periphery [19], while myocardial contractility is depressed to a lesser extent than after volatile agents [20]. Diazepam reduces systemic vascular resistance and slightly depresses the baroreceptor reflex [21]. Opioids blunt significant haemodynamic responses to noxious stimuli and produces minimal myocardial depression, with minimal decreases in preload and afterload, little depression of great vessels and atrial baroreceptors and no effect on coronary vasomotion [12]. Pancuronium usually produces a moderate increase in HR, and to a lesser extent cardiac output, with small or no changes in systemic vascular resistance [22,23].

Our data confirm and extend findings previously obtained in awake human beings [8–10] and anaesthetized animals [6,7], indicating that tissue velocities are not preload independent and that there are no relationship between filling pressure and tissue velocities [4]. E′ max shows preload dependency in both the septal and lateral mitral annulus in anaesthetized human beings undergoing cardiac surgery. We also found that tissue velocities are preload dependent in the early postsurgery period. Yalcin and colleagues [24] reported that TDE was not significantly altered during preload alterations (Trendelenburg, anti-Trendelenburg and inhalation of amyl nitrate) in awake patients with chronic ischaemic syndrome. General anaesthesia, as discussed above, and positive-pressure ventilation, which will affect venous return and cardiac function directly, are the two most apparent causes for this discrepancy.

In the present study the absolute changes in tissue velocities are relatively small (≈20%) seen in relation to the huge variations in RAP and PAOP (>10 mmHg). It should be noted that all our patients were on β-blockade. In anaesthetized dogs, Firstenberg and colleagues [6] has demonstrated that β-blockade blunts the preload dependency for tissue velocities. The fact that the effects of preload on tissue velocities are less pronounced in models of diastolic dysfunction [4,6,7] might also contribute to the small alterations in E′ max seen in our patients, as all of our patients either were on medication or had coexisting diseases that affect the diastole (Table 1).

We found that velocities in the septal portion of the mitral annulus are lower than in the lateral portion of the mitral annulus. This finding is consistent with findings in healthy conscious patients [25]. In our study population, all patients have stenosis in the left anterior descending artery (LAD). This fact may also contribute to the lower velocities in the septal compared to the lateral portion of the mitral annulus.

This study was performed in a clinical setting on patients scheduled for elective coronary surgery. All patients in the study were monitored with a PAC. We used tilting of the operation table as preload interventions and RAP and PAOP as indicators of the preload changes. The patients were first examined in flat supine position, then in a state of decreased preload and finely in a state of increased preload. RAP and PAOP do not reflect changes in fibre length or changes in end-diastolic volume in all situations [26]. One can alter end-diastolic volume without detecting it in the end-diastolic ‘pressure’ parameters used. This may partly explain why we found preload dependency in tissue velocities (compared within the individual patient), but detected no significant correlation between PAOP and tissue velocities (comparison at three PAOP levels for the 15 patients). All patients had a period of physiologic stabilization between the interventions. Examinations were obtained by TOE and measurements were made both in the septal and lateral portion of the mitral annulus. The most frequent alteration of preload in surgical patients is hypovolaemia. To ensure a normovolaemic state prior to the first part of the experiment, we gave a Ringer acetate infusion of 0.5 mL kg−1 h−1 of fasting.

We conclude that tissue velocities of the mitral annulus are preload dependent in patients in general anaesthesia both before coronary arterial bypass surgery and in the early postsurgery phase.

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Acknowledgements

The authors thank the staff at the surgical and anaesthesiological departments, Feiring Heart Clinic and especially R. Salamanka for valuable technical assistance during the study. During the practical part of the study A. A. Jonassen had a fellowship financed by Feiring Heart Clinic.

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Keywords:

ANAESTHESIA GENERAL, SURGERY CARDIAC; CORONARY ARTERY BYPASS; ECHOCARDIOGRAPHY DOPPLER; MYOCARDIAL CONTRACTION

© 2007 European Society of Anaesthesiology