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Perioperative Assessment of Diastolic Function
Case Study
A 75-year-old female presents for coronary artery bypass grafting (CABG) for treatment of unstable angina secondary to severe three-vessel coronary artery disease. The patient reports a history of hypertension, hyperlipidemia, and diabetes mellitus. Preoperative transthoracic echocardiogram demonstrated normal left ventricular (LV) and right ventricular (RV) systolic function, left atrial (LA) enlargement, mild mitral regurgitation (MR), and no evidence of pulmonary hypertension. Preoperative laboratory assessment is notable for a serum creatinine of 0.8 mg/dL and hemoglobin of 12.7 g/dL. The Society of Thoracic Surgeons risk calculator predicts a 1.3% risk of in-hospital or 30-day mortality.
Introduction
The assessment and utilization of diastolic function in the perioperative care of patients undergoing cardiac surgery remains controversial. The most recent American Society of Echocardiography/European Association of Cardiovascular Imaging (ASE/EACVI) guidelines on the evaluation of LV diastolic function cautions that diastolic assessment may not necessarily be applicable in the perioperative setting. Nevertheless there is a significant body of literature examining the utility of perioperative diastolic assessment, and a large percentage of cardiac anesthesiologists assess diastolic function as part of their standard perioperative transesophageal echocardiogram (TEE) exam. This chapter discusses the approach to the intraoperative assessment of diastolic function in patients undergoing cardiac surgery.
Current Guidelines for Diastolic Assessment
The intraoperative assessment of diastolic function largely mirrors that of the patient undergoing assessment outside of the surgical setting with some notable differences. Similar to the assessment of diastolic function in other settings, multiple measurement techniques should be utilized with underlying patient age, pathology, heart rate, ventricular loading conditions, and other factors (as discussed in the chapter) helping to contextualize the results of echocardiographic analysis.
The 2016 ASE/EACVI guidelines for the assessment of diastolic function in patients with normal ejection fraction (EF) advocate using annular e′ velocity, the E/e′ velocity (with e′ measured as an average of the septal and lateral annular velocities), the LA maximum volume index, and the peak velocity of the tricuspid regurgitation jet. Conservative cutoffs for diastolic dysfunction are used to try to improve diagnostic specificity ( Table 32.1 ). While assessment of transmitral flow, tricuspid regurgitation, and tissue Doppler velocities of the mitral annulus is readily accomplished via TEE, reliable assessment of LA volume is challenging given the proximity of the TEE probe to the left atrium, and TEE assessment typically underestimates the LA volume by ∼9% when compared to standardized assessment by transthoracic echocardiography.
Table 32.1
Measurements and Cutoff Values Used for Determination of Diastolic Function in Patients With a Normal Left Ventricular (LV) Ejection Fraction a
Adapted from Nagueh SF, et al. Recommendations for the evaluation of left ventricular diastolic function by cchocardiography: an update from the American Society of Echocardiography and the European Association of Cardiovascular Imaging. J Am Soc Echocardiogr . 2016;29(4):277–314.
| Measurement | Abnormal Cutoff | |
|---|---|---|
| 1 | Average E/e′ | >14 |
| 2 | Septal e′ velocity | <7 cm/sec |
| Lateral e′ velocity | <10 cm/sec | |
| 3 | Tricuspid regurgitation velocity | >2.8 m/sec |
| 4 | Left atrial volume index | >34 mL/m 2 |
a Patients meeting >2 of these criteria are categorized as having LV diastolic dysfunction.
In patients with reduced LV EF and myocardial pathology, determination of diastolic dysfunction can be accomplished using an algorithm that utilizes the E/e′ velocity, LA maximum volume index, and peak tricuspid regurgitation velocity, but also utilizes the ratio of transmitral E wave velocity to the transmitral A wave velocity (E/A ratio) and the maximum velocity of the transmitral E wave to help with additional characterization ( Fig. 32.1 ). The limited ability of TEE to optimally assess LA volume remains a barrier to directly applying this algorithm in the intraoperative setting.
The assessment of diastolic function in the perioperative period differs from other arenas in a number of ways. Perioperative diastolic assessment is performed almost exclusively via TEE. Additionally, hemodynamic factors, such as ongoing bleeding, positive pressure ventilation, and changing patient position, may complicate assessment. Anesthetic medications that alter contractility, heart rate, and afterload may also influence measures of diastolic function. An understanding of the influence of the perioperative period on echocardiographic assessment of diastolic function is important to allow for appropriate characterization of LV filling pressures that in turn influences hemodynamic management for optimizing cardiac output.
In the chapter-opening case study, intraoperative TEE assessment confirmed normal LV systolic function and mild mitral regurgitation (MR). Diastolic assessment was performed with the chest closed prior to surgical incision with the patient in the supine position ( Fig. 32.2 ). Transmitral flow demonstrated an E/A ratio of approximately 1.8. Tissue Doppler imaging (TDI) demonstrated a lateral e′ velocity of 9.5 cm/sec and an E/e′ ratio of 7.8 (see Fig. 32.2 ). Tricuspid regurgitation velocity was 2.0 m/sec. Given the patient’s normal E/e′ ratio and normal E/A ratio, she was judged to have normal LAP.
Additional assessment to further characterize the patient’s diastolic function was performed, including LV inflow propagation velocity (Vp) and pulmonary vein pulse wave Doppler assessment. Vp was 57 cm/sec and pulmonary vein flow assessment showed an S wave to D wave ratio greater than 1. Both measurements were consistent with normal LV filling pressures, confirming normal diastolic function.
The Effect of the Perioperative Period on the Assessment of LV Diastolic Dysfunction
Perioperative hemodynamic perturbations can have a significant effect on the assessment of diastolic function. Changes associated with general anesthesia may complicate the accurate assessment and classification of diastolic dysfunction in this patient population.
Intravascular Volume Status
Cardiac surgery typically involves substantial fluctuations in intravascular volume status, with bleeding, ongoing resuscitation, and surgical manipulation of the heart or chest wall resulting in rapid and variable shifts in myocardial preload. Changes in preload are known to have a significant effect on measures of diastolic function, including transmitral E wave velocities and the e′ value.
The response of the transmitral E wave velocity and E/A ratio to changes in ventricular preload is dependent on the underlying degree of diastolic dysfunction. In patients with diastolic dysfunction, increases in preload increase the peak E wave velocity (thus increasing the E/A ratio), and decreases in preload tend to decrease the velocity (decreasing the E/A ratio). In healthy patients with normal diastolic function, E wave velocity also increases with increasing preload, but the E/A ratio is not significantly affected as the A wave velocity simultaneously increases. A similar pattern is seen with the mitral annular e′ velocity, with increases in the e′ with a concurrent rise in preload and decreases in e′ with a decline in preload. Notably, the E/e′ ratio does not appear to be significantly altered by preload changes. Though propagation velocity appears to be mostly unaffected by changes in preload, the utility of this measurement in quantifying diastolic function is limited by technical challenges in obtaining the measurement and its inability to effectively discriminate between grades of diastolic dysfunction.
Mechanical Ventilation and Patient Position
Patients undergoing general anesthesia almost always require invasive mechanical ventilation to maintain oxygenation and ventilation. Evidence suggests that patient position and the level of positive end-expiratory pressure (PEEP) both have a significant effect on indices of diastolic function. Two prior studies have evaluated the influence of incremental PEEP application on diastolic assessment in patients undergoing cardiac surgery. Increasing PEEP is associated with a significant decrease in the lateral mitral annular e′ velocity with a concomitant reduction in transmitral E wave velocity . Notably, this study did not find a major difference in the ratio of E/e′ (with e′ assessed using either the lateral mitral annulus alone or as an average of the lateral and septal mitral annulus e′ values) with changes in PEEP. Similarly, Trendelenburg position was associated with an increase in the septal and lateral e′ values as well as transmitral E wave velocity with no significant change in the E/e′ ratio.
Anesthetic Agents
Anesthetic agents appear to have different degrees of influence on the measurement of indices of diastolic function. Unfortunately, direct comparison of these agents is difficult, as studies examining the influence of anesthetic agents on diastolic function have focused on heterogeneous diastolic indices and have examined a diverse population, ranging from healthy volunteers to patients with known diastolic dysfunction.
The effect of inhaled anesthetic gas and propofol on diastolic function was previously investigated in both healthy volunteers and patients with preexisting diastolic dysfunction undergoing aortic valve replacement. Both studies evaluated the effect on mitral annular e′ velocity, and the study examining healthy patients also assessed isovolumic relaxation time (IVRT). In patients without preexisting diastolic dysfunction, halothane and sevoflurane did not have a significant effect on the e′ velocity, whereas propofol caused a small but statistically significant decrease in e′ (18.0 cm/sec vs. 16.8 cm/sec). Patients with impaired diastolic function showed an increase in e′ during spontaneous ventilation, which returned to baseline following the initiation of positive pressure ventilation and did not differ from the propofol group. These findings have not been consistently replicated in other studies examining the effects of volatile anesthetics and propofol on diastolic function. Houltz et al. previously described both isoflurane and halothane as having a detrimental effect on LV diastolic function, whereas Gare et al. described no significant change in LV diastolic function with either propofol or midazolam sedation, in contrast to the findings of Filipovic (discussed earlier).
The effect of remifentanil on systolic and diastolic function was assessed in healthy patients with no known diastolic dysfunction undergoing minor surgery. In this study, remifentanil was not associated with worsening of transmitral E wave velocity or e′ and did not appear to affect systolic function. In contrast, the administration of dexmedetomidine appears to significantly worsen indices of both LV diastolic and systolic performance. A study examining the impact of dexmedetomidine in patients with preexisting diastolic dysfunction demonstrated a significant increase in the LV and RV E/e′ ratios as well as an increase in myocardial performance index.
In summary, the effect of anesthetic agents on diastolic function remains poorly defined, and data on any effect, either positive or negative, are inconclusive. It is unclear whether the changes in indices of diastolic function observed in patients under anesthesia represent a true physiologic decline in diastolic function or are simply a result of transient alterations in loading conditions or other influences. The echocardiographer should be aware of the potential influence of anesthetic agents on diastolic function to contextualize diastolic assessment.
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