BJA Advance Access originally published online on July 17, 2008
British Journal of Anaesthesia 2008 101(4):479-485; doi:10.1093/bja/aen212
Tei index to assess perioperative left ventricular systolic function in patients undergoing mitral valve repair
1 Department of Anaesthesiology and Critical Care
2 Department of Thoracic and Cardiovascular Surgery
3 Department of Emergency Medicine, Centre Hospitalier Universitaire (CHU) Pitié-Salpêtrière, Assistance Publique–Hôpitaux de Paris (AP-HP), UMPC Univ Paris 06, F-75013 Paris, France
4 Department of Cardiology, King's College, London, UK
* Corresponding author: Département Anesthésie Réanimation, Hôpital Pitié-Salpêtrière, 47 boulevard de l'Hôpital, 75651 Paris, Cedex 13, France. E-mail: alexandre.ouattara{at}psl.aphp.fr
Accepted for publication June 16, 2008.
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Abstract |
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Background: Using echocardiography, perioperative assessment of systolic function by fractional area change (FAC) is questionable in patients suffering from mitral regurgitation (MR). Tei index, an index expressing global cardiac function, has been reported to be unchanged after mitral valve surgery. We tested the hypothesis where the Tei index could be useful in assessing the perioperative cardiac function in patients undergoing mitral valve repair (MVR).
Methods: Twenty-five patients were enrolled. Transoesophageal echocardiography was performed perioperatively before and after the correction of MR. We compared the impact of the MVR on the left ventricular FAC and the Tei index. FAC was calculated from the transgastric short-axis view and Tei index was determined from the four chambers and deep transgastric views.
Results: Two patients were excluded because of poor acoustic windows. FAC significantly decreased after MVR from 53 (9)% to 42 (10)% (P<0.001), while Tei index was unaffected [0.46 (0.16) vs 0.47 (0.17), NS]. A significant relationship was found between the preoperative Tei index and the postoperative FAC (R=–0.64, P<0.001). Moreover, a significant and clinically relevant relationship was determined between the predicted (using preoperative Tei index) and the measured postoperative FAC (R=0.64, P<0.001).
Conclusions: FAC but not the Tei index is influenced by MVR. The preoperative determination of the Tei index allows predicting postoperative FAC and offers the opportunity to identify patients in whom a severe unsuspected systolic dysfunction could render difficult the weaning from cardiopulmonary bypass.
Keywords: heart, cardiopulmonary bypass; heart, myocardial function; monitoring, echocardiography
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Introduction |
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In cardiovascular surgery, the perioperative left ventricular (LV) systolic function is frequently assessed by the echocardiographic measurement of ejection indexes. As these parameters are load-dependent, their utility remains questionable in patients suffering from severe mitral regurgitation (MR). Moreover, an overestimation of systolic function by ejection indexes is commonly admitted in these patients.1 Indeed, in the presence of MR, LV loading conditions are markedly modified2 3 with a decrease in LV afterload. This phenomenon is undoubtedly related to the bidirectional ventricular ejection both towards the low impedance left atrium and the aorta. Therefore, the availability of a load-independent index could be helpful in detecting an unsuspected systolic dysfunction before operation and anticipate a difficult weaning from cardiopulmonary bypass (CPB). Tei index is a simple Doppler-derived index of global myocardial function.4 Although it seems to be unaffected by changes in heart rate,5 its proposed load-independence remains to be a subject of controversy. While Tei index is unaffected by the decrease in preload, Lutz and colleagues6 found that this index can be influenced by an increase in preload in mechanically ventilated patients. Moreover, Moller and colleagues7 reported that the Tei index is only affected by changes in load conditions in healthy volunteers. Conversely, several experimental studies have shown that Tei index is affected by acute and large changes in loading conditions.8–10 Finally, a recent clinical study reported that Tei index is unchanged before and after MR.11 We tested the hypothesis that Tei index could be less affected in the perioperative period than fractional area change (FAC) in patients undergoing mitral valve repair (MVR). Therefore, we simultaneously measured FAC and Tei index in anaesthetized patients before and after MVR. This surgical procedure was favoured because it preserves the mitral apparatus, which is involved in the maintenance of LV architecture by avoiding LV dilation and preserving LV function by actively participating in its contraction.12–14 Indeed, previous clinical studies have clearly demonstrated that mitral valvuloplasty provides superior postoperative LV systolic performance than conventional mitral valve replacement.15
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Methods |
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This prospective study was approved by our Ethical Committee (Comité de Protection des Personnes, CPP Pitié-Salpêtrière, Paris, France). Authorization was granted to waive the informed consent for the study as care for patients conformed to the standard procedures currently used in our surgical unit. Twenty-five consecutive patients scheduled for MVR were prospectively enrolled. Non-inclusion criteria were as follows: the presence of a supraventricular arrhythmia or coronary artery disease, coexisting valvular disease with the exception of tricuspid regurgitation and any contradiction for transoesophageal echocardiography (TOE).
After the induction of anaesthesia, a TOE probe (Ultrasound Transducer, Philips, Bothell, WA, USA) was carefully introduced. TOE examinations (SONOS 5500, Hewlett-Packard, Andover, MA, USA) were performed by experienced operators after sternotomy and was repeated after weaning from CPB but before any inotropic support. Any interventions that might affect the echocardiographic variables (vasopressors infusion, fluid loading, or changes during deep anaesthesia) were not performed during the measurements. All the echocardiographic images were recorded during a period of brief apnoea and under haemodynamic monitoring on an optical disk for offline measurements later. For each echocardiographic parameter, a mean of three retrospective offline measurements were obtained from consecutive beats. Furthermore, all the echocardiographic views were acquired in a similar order. First, the mid-oesophageal four-chamber view enabled recording of the pulse-wave Doppler of mitral inflow. The Doppler cursor was positioned at the tip of the mitral leaflets during diastole allowing the calculation of the interval between cessation and onset of mitral inflow. This interval corresponds to the sum of isovolumetric contraction time, ejection time, and isovolumetric relaxation time. Secondly, the deep transgastric long-axis view permitted recording of the pulsed-wave Doppler of the LV outflow signal and measurement of the ejection time. The Tei index is defined as the sum of isovolumetric contraction and relaxation times divided by the ejection time (Fig. 1). Thirdly, LV end-diastolic and end-systolic areas were obtained through the transgastric mid short-axis view to calculate FAC, defined as the difference between the end-diastolic and end-systolic areas of the LV, divided by the LV end-diastolic area expressed as a percentage. The recording of these three consecutive views never exceeded 6 min. Data were analysed independently by two observers each of whom reviewed the data twice. Inter- and intra-observer reproducibilities were assessed by the analysis of 10 randomly selected recordings for each measured echocardiographic parameter. Reproducibility was expressed as a percentage of the error (SD) and calculated as the absolute difference between two sets of measurements divided by the mean value of the measurements.
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The variables are expressed as mean (SD). Comparison of two means was performed using a paired Student's t-test. Correlation between two variables was performed using the least-square method. We used the Tei index to predict the postoperative FAC. Then, we compared the predicted and observed FAC using the Bland-Altman method and by calculating the bias, precision, and proportion of outliers, a priori defined as a difference between predicted and observed FAC greater than 10%. P<0.05 was required to rule out the null hypothesis. Statistical analysis was performed with NCSS (Statistical Solutions Ltd, Cork, Ireland).
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Results |
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Twenty-five patients who underwent MVR were prospectively included in our study; two patients lacked suitable acoustic windows and were excluded. The perioperative characteristics of the patients are summarized in Table 1. A tricuspid regurgitation was diagnosed in eight patients before operation. Three patients (13%) required inotropic support for CPB weaning and this was introduced only after the postoperative TOE measurements were completed. Minor residual MR was found in six patients. No systolic anterior movement of the anterior mitral valve was observed. The inter- and intra-observer reproducibilities of the TOE measurements are shown in Table 2. During echocardiographic measurements, haemodynamic profile of the patients was stable (Table 3).
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Changes in haemodynamic and echocardiographic variables before and after the surgical procedure are summarized in Table 4. After surgical correction of MR, FAC significantly decreased while the Tei index was not significantly altered (Table 4, Fig. 2).
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As the Tei index was not found to be influenced by the correction of MR, we studied whether the preoperative determination of Tei index could be used to predict postoperative FAC. As shown in Figure 3, a significant relationship between these two parameters was found (R=–0.64, P<0.001). According to this mathematical model, the relation between preoperative Tei index and postoperative predicted FAC is: FACp (%)=61–41xTei (Fig. 3). When comparing the predicted and observed postoperative FAC (Fig. 4), we observed that the bias was 0.1 (7.7) % (NS), precision was 6.3 (4.2) %, and the proportion of outliers was 20%. As shown in Figure 4, a significant relationship was also found between these two parameters (R=0.64, P<0.001). Finally, despite this trend, we could not observe any significant difference in the mean value of the Tei index of patients requiring inotropic support from those who did not require any drugs [0.58 (0.11) vs 0.44 (0.16), P=0.17].
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Discussion |
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The major findings of the present study are that: (i) the LV FAC decreased after MVR, whereas the Tei index remained unaffected by the surgical procedure; (ii) the preoperative value of the Tei index allowed estimation of the postoperative value of FAC after the correction of MR.
In the presence of MR, LV loading conditions are modified with a trend to increased preload and decreased afterload.2 3 Under these haemodynamic conditions, the assessment of myocardial contractility by ejection phase measurements is inappropriate, as these are well-known to be influenced by acute changes in loading conditions.16 It has been demonstrated that ejection fraction decreases after surgical correction of MR.17 18 During mitral valve replacement, this reduction in ejection fraction may in part be explained by myocardial depression related to the removal of the mitral apparatus in addition to the changes in loading conditions.15 For this reason, only patients undergoing MVR have been included in our study. Conversely, the decline in ejection fraction observed during the correction of MR using valvuloplasty can certainly be attributed to changes in LV loading conditions.19 20 We hypothesized that this surgical procedure preserves the systolic performance of the LV, thus illustrating the preoperative overestimation and unreliability of ejection fraction or FACs as measures of ejection phase.1 18 21
We assumed that the Tei index would be a useful tool in the assessment of systolic function in the presence of MR. The LV load independence of this myocardial global index remains to be a subject of controversy in the literature. Some authors clearly reported that Tei index is weakly influenced by changes in loading conditions and heart rate in clinical settings.5 22 23 Lutz and colleagues6 found that Tei index is only affected by the increase in preload in mechanically ventilated patients. Similarly, Moller and colleagues7 reported that Tei index is only affected by changes in load conditions in healthy volunteers. Under experimental conditions, in which a large magnitude of loading changes may be induced, other authors have clearly demonstrated the load-dependence of the Tei index.8–10 We have compared the ability of FAC and the Tei index to assess the systolic function in patients with MR, by analysing the influence of MVR. As previously reported,17 18 a significant reduction in the ejection phase measurement after MVR was observed in the present study. This finding may be explained by numerous factors. First, a decrease in preload was induced by the absence of regurgitating volume after MVR. Secondly, an increase in LV afterload occurs after hermetic closure of the mitral leaflets induced by surgical repair.24 This significantly enhances LV systolic wall tension and provokes a decrease in FAC. Thirdly, the myocardial dysfunction after CPB could be involved in the decrease in FAC. However, this mechanism is unlikely because of the brief duration of aortic clamping, and the fact that in MR valvular–ventricular interaction preserves LV contractility.14 Conversely, we could observe a significant increase in heart rate and a lower systolic arterial blood pressure after surgical procedure, both factors which should tend to increase FAC. In the present study, the Tei index remains unchanged after MVR. This finding is consistent with the results of other authors demonstrating that the Tei index is not influenced by valve dysfunction.11 25 Our results strongly suggest that the Tei index is not significantly influenced by perioperative changes in LV loading conditions and these findings are consistent with those previously published by other groups.23 26 The absence of change in Tei index immediately after MVR may be explained by the fact that a simultaneous change in preload and afterload occurred and that the magnitude of these changes in this clinical setting are relatively moderate. Although heart rate could be increased after surgical procedure, this haemodynamic change did not affect the Tei index.5 The mean value of preoperative Tei index observed in our study is higher than in healthy adults. This finding is consistent with the previously reported values in patients with MR.11 Several reasons can be given to explain the increased Tei index in our patients. First, probable systolic dysfunction in these patients related to the chronic evolution of their valvular disease. Secondly, even if we had no patients with major chronic myocardial failure in our series, we cannot exclude that the patients included did not suffer from diastolic dysfunction. Thirdly, a negative inotropic effect of anaesthetic drugs cannot be ruled out. Many attempts have been made to predict systolic function after the correction of MR.21 27–29 In the present study, we found a significant relationship between the preoperative Tei index and the postoperative FAC: postoperative FAC=61–41xpreoperative Tei index. Interestingly, a similar correlation was previously established by Lax and colleagues30 between ejection fraction and Tei index in 55 patients with previous myocardial infarction, ejection fraction=60–34xTei index. The prediction of the postoperative FAC presents several advantages. First, to date, FAC remains an easy parameter to assess and is widely used in the perioperative period. Secondly, the prediction of postoperative FAC allows us to anticipate a probably difficult weaning from CPB. Currently, it may not be feasible to replace FAC by the preoperative Tei index as this parameter is still not widely used in clinical practice despite the abundant literature available.
The following points must be considered in the assessment of the clinical relevance of our study. First, the current literature has for the most part focused on late postoperative LV function after valve surgery,11 whereas, we have studied the early postoperative period to provide data at this critical stage. Secondly, TOE measurements were performed under general anaesthesia with opened chest and do not enable generalization of our results to conscious, spontaneously breathing patients with MR. Thirdly, the Tei index was calculated from pulse wave Doppler. However, further investigation should consider the measurement of Tei index from tissue Doppler imaging, which is apparently less variable as recently reported.31 Fourth, in our study, FAC has been evaluated. Among the ejection indexes, Simpson ejection fraction is the current gold standard. However, the relation between FAC and ejection fraction is usually quite good.32 Fifth, one can argue that the choice of the MVR model may have induced a selection bias, as this surgery is often proposed to patients with MR at an early stage of the disease, when their systolic function is still preserved. However, the range of FAC in our patients was large enough to reflect a realistic sampling of the population, and to establish an accurate correlation between Tei index and the postoperative FAC. Finally, although the preoperative determination of Tei index allowed us to predict postoperative FAC, we were unable to predict patients requiring inotropes for weaning from CPB. Consequently, it remains necessary to investigate the impact of preoperative Tei index in predicting the weaning management from CPB in future studies.
To conclude, in contrast to FAC, the Tei index remains unchanged after MVR, suggesting that this parameter is less sensible to changes in LV loading conditions. In addition, its preoperative determination allows us to predict postoperative FAC and offers the opportunity to identify patients in whom a severe unsuspected systolic dysfunction could render difficult the weaning from CPB.
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