Milrinone Improves Diastolic Function in Coronary Artery Bypass Surgery as Assessed by Acoustic Quantification and Peak Filling Rate: A Prospective Randomized Study

Left Ventricular Diastolic Dysfunction in Cardiac Surgery: A Narrative Review

Cardiac relaxation is a complex process that involves various interconnected characteristics and, along with contractile properties, determines stroke volume. Perioperative ischemia-reperfusion injury and left ventricular diastolic dysfunction (DD) are characterized by the left ventricle's inability to receive a sufficient blood volume under adequate preload. Baseline DD and perioperative DD have an impact on postoperative complications, length of hospital stay, and major clinical outcomes in a variety of cardiac pathologies. Several baseline and perioperative factors, such as age, female sex, hypertension, left ventricle hypertrophy, diabetes, and perioperative ischemia-reperfusion injury, contribute to the risk of DD. The recommended diagnostic criteria available in guidelines have not been validated in the perioperative settings and still need clarification. Timely diagnosis of DD might be crucial for effectively treating postoperative low cardiac output syndrome. This implies the need for an individualized approach to fluid infusion strategy, cardiac rate and rhythm control, identification of extrinsic causes, and administration of drugs with lusitropic effects. The purpose of this review is to consolidate scattered information on various aspects of diastolic dysfunction in cardiac surgery and provide readers with well-organized and clinically applicable information.

Integration of longitudinal and circumferential strain predicts volumetric change across the cardiac cycle and differentiates patients along the heart failure continuum

BACKGROUND

Left ventricular (LV) circumferential and longitudinal strain provide important insight into LV mechanics and function, each contributing to volumetric changes throughout the cardiac cycle. We sought to explore this strain-volume relationship in more detail, by mathematically integrating circumferential and longitudinal strain and strain rate to predict LV volume and volumetric rates of change.

METHODS

Cardiac magnetic resonance (CMR) imaging from 229 participants from the Alberta HEART Study (46 healthy controls, 77 individuals at risk for developing heart failure [HF], 70 patients with diagnosed HF with preserved ejection fraction [HFpEF], and 36 patients with diagnosed HF with reduced ejection fraction [HFrEF]) were evaluated. LV volume was assessed by the method of disks and strain/strain rate were assessed by CMR feature tracking.

RESULTS

Integrating endocardial circumferential and longitudinal strain provided a close approximation of LV ejection fraction (EFStrain), when compared to gold-standard volumetric assessment (EFVolume: r = 0.94, P < 0.0001). Likewise, integrating circumferential and longitudinal strain rate provided a close approximation of peak ejection and peak filling rates (PERStrain and PFRStrain, respectively) compared to their gold-standard volume-time equivalents (PERVolume, r = 0.73, P < 0.0001 and PFRVolume, r = 0.78, P < 0.0001, respectively). Moreover, each integrated strain measure differentiated patients across the HF continuum (all P < 0.01), with the HFrEF group having worse EFStrain, PERStrain, and PFRStrain compared to all other groups, and HFpEF having less favorable EFStrain and PFRStrain compared to both at-risk and control groups.

CONCLUSIONS

The data herein establish the theoretical framework for integrating discrete strain components into volumetric measurements across the cardiac cycle, and highlight the potential benefit of this approach for differentiating patients along the heart failure continuum.

Effect of intravenous levosimendan or milrinone on left atrial pressure in patients undergoing off-pump coronary artery bypass grafting-A prospective double-blind, randomized controlled trial

Background

Maintaining a low left atrial pressure (LAP) in off-pump coronary artery bypass grafting (OPCAB) is desirable. This study was done to compare the effects of intravenous levosimendan or milrinone on LAP at different stages of OPCAB.

Materials and Methods

After institutional ethics committee clearance, this two-arm double-blind randomized control trial was done in 44 adult patients with triple vessel coronary artery disease undergoing OPCAB at cardiac OT of IPGME&R, Kolkata. The patients were randomly allocated into two groups receiving intraoperative either levosimendan or milrinone. Pulmonary capillary wedge pressure (PCWP) was compared as the primary outcome parameter, whereas other echocardiographic and hemodynamic parameters were also assessed during six stages of OPCAB, that is, after sternotomy, proximal(s), left anterior descending artery (LAD), obtuse marginal (OM), posterior descending artery (PDA) grafting, and before sternal closure. Numerical parameters were compared using Student's unpaired two-tailed t-test.

Results

PCWP was found to be significantly lower (P < 0.05) in the levosimendan group during proximal (P = 0.047), LAD (P = 0.018), OM (P < 0.0001), PDA grafting (P = 0.028), and before sternal closure (P = 0.015). Other parameters indicate LAP, that is, from mitral early diastolic inflow velocity to mitral annular early diastolic velocity ratio (E/e'), which indicated significantly lower LAP in levosimendan group during LAD, OM, and PDA grafting and before sternal closure. Conclusion: Levosimendan may be used as a primary inotrope in terms of better reduction in left atrial pressure during different stages of OPCAB, translating to a decrease in left ventricular end-diastolic pressure, therefore maintaining optimum coronary perfusion pressure, which is the primary goal of the surgery.

Model-Based Quantification of Left Ventricular Diastolic Function in Critically Ill Patients with Atrial Fibrillation from Routine Data: A Feasibility Study

Introduction

Left ventricular diastolic dysfunction (LVDD) and atrial fibrillation (AF) are connected by pathophysiology and prevalence. LVDD remains underdiagnosed in critically ill patients despite potentially significant therapeutic implications since direct measurement cannot be performed in routine care at the bedside, and echocardiographic assessment of LVDD in AF is impaired. We propose a novel approach that allows us to infer the diastolic stiffness, β, a key quantitative parameter of diastolic function, from standard monitoring data by solving the nonlinear, ill-posed inverse problem of parameter estimation for a previously described mechanistic, physiological model of diastolic filling. The beat-to-beat variability in AF offers an advantageous setting for this.

Methods

By employing a global optimization algorithm, β is inferred from a simple six parameter and an expanded seven parameter model of left ventricular filling. Optimization of all parameters was limited to the interval ]0, 400[ and initialized randomly on large intervals encompassing the support of the likelihood function. Routine ECG and arterial pressure recordings of 17 AF and 3 sinus rhythm (SR) patients from the PhysioNet MGH/MF Database were used as inputs.

Results

Estimation was successful in 15 of 17 AF patients, while in the 3 SR patients, no reliable estimation was possible. For both models, the inferred β (0.065 ± 0.044 ml⁻¹ vs. 0.038 ± 0.033 ml⁻¹ (p=0.02) simple vs. expanded) was compatible with the previously described (patho) physiological range. Aortic compliance, α, inferred from the expanded model (1.46 ± 1.50 ml/mmHg) also compared well with literature values.

Conclusion

The proposed approach successfully inferred β within the physiological range. This is the first report of an approach quantifying LVDF from routine monitoring data in critically ill AF patients. Provided future successful external validation, this approach may offer a tool for minimally invasive online monitoring of this crucial parameter.

Inotropic and lusitropic effects of levosimendan and milrinone assessed by strain echocardiography-A randomised trial

BACKGROUND

We compared the direct inotropic and lusitropic effects of two inodilators, milrinone and levosimendan in patients after aortic valve replacement for aortic stenosis.

METHODS

In this randomised, blinded study, 31 patients with normal LV function, were randomised to either levosimendan (0.1 and 0.2 μg/kg/min, n = 15) or milrinone (0.4 and 0.8 μg/kg/min, n = 16) after aortic valve replacement. The effects on LV performance, LV strain, systolic (SR-S) and early diastolic (SR-E) strain rate were assessed by a pulmonary artery catheter and transoesophageal two-dimensional speckle tracking echocardiography of the LV inferior wall. To circumvent the inodilator-induced hemodynamic changes on LV systolic and diastolic deformation, central venous pressure (CVP), systolic artery pressure (SAP), and heart rate were maintained constant by colloid infusion, phenylephrine-induced vasoconstriction and atrial pacing, respectively, during drug infusion.

RESULTS

Both inotropic agents induced a dose-dependent increase in cardiac index and stroke volume index by approximately 20% at the highest infusion rates with no differences between groups (P = .139 and .249, respectively). CVP, pulmonary capillary wedge pressure, SAP and heart rate were maintained constant in both groups. LV strain and SR-S increased with both agents, dose-dependently, by 17%-18% and 25%-30%, respectively, at the highest infusion rates, with no difference between groups (P = .434 and .284, respectively). Both agents improved early LV relaxation with no differences between groups (P = .637). At the higher doses, both agents increased SR-E by 30%.

CONCLUSIONS

At clinically relevant infusion rates and a certain increase in LV performance the direct inotropic and lusitropic of milrinone and levosimendan were comparable.

Effects of Combined Milrinone and Levosimendan Treatment on Systolic and Diastolic Function During Postischemic Myocardial Dysfunction in a Porcine Model

It is not known whether there are positive or negative interactions on ventricular function when a calcium-sensitizing inotrope is added to a phosphodiesterase inhibitor in the clinical setting of acute left ventricular (LV) dysfunction. We hypothesized that when levosimendan is added to milrinone treatment, there will be synergetic inotropic and lusitropic effects. This was tested in an anesthetized porcine postischemic global LV injury model, where ventricular pressures and volumes (conductance volumetry) were measured. A global ischemic injury was induced by repetitive left main stem coronary artery occlusions. Load-independent indices of LV function were assessed before and after ventricular injury, after milrinone treatment, and finally after addition of levosimendan to the milrinone treatment. Nonparametric, within-group comparisons were made. The protocol was completed in 12 pigs, 7 of which received the inotrope treatment and 5 of which served as controls. Milrinone led to positive lusitropic effects seen by improvement in tau after myocardial stunning. The addition of levosimendan to milrinone further increased lusitropic state. The latter effect could however not be attributed solely to levosimendan, since lusitropic state also improved spontaneously in time-matched controls at the same rate during the corresponding period. When levosimendan was added to milrinone infusion, there was no increase in systolic function (preload recruitable stroke work) compared to milrinone treatment alone. We conclude that in this model of postischemic LV dysfunction, there appears to be no clear improvement in systolic or diastolic function after addition of levosimendan to established milrinone treatment but also no negative effects of levosimendan in this context.

Incremental value of the preoperative echocardiogram to predict mortality and major morbidity in coronary artery bypass surgery

BACKGROUND

Although echocardiography is commonly performed before coronary artery bypass surgery, there has yet to be a study examining the incremental prognostic value of a complete echocardiogram.

METHODS AND RESULTS

Patients undergoing isolated coronary artery bypass surgery at 2 hospitals were divided into derivation and validation cohorts. A panel of quantitative echocardiographic parameters was measured. Clinical variables were extracted from the Society of Thoracic Surgeons database. The primary outcome was in-hospital mortality or major morbidity, and the secondary outcome was long-term all-cause mortality. The derivation cohort consisted of 667 patients with a mean age of 67.2±11.1 years and 22.8% females. The following echocardiographic parameters were found to be optimal predictors of mortality or major morbidity: severe diastolic dysfunction, as evidenced by restrictive filling (odds ratio, 2.96; 95% confidence interval, 1.59-5.49), right ventricular dysfunction, as evidenced by fractional area change <35% (odds ratio, 3.03; 95% confidence interval, 1.28-7.20), or myocardial performance index >0.40 (odds ratio, 1.89; 95% confidence interval, 1.13-3.15). These results were confirmed in the validation cohort of 187 patients. When added to the Society of Thoracic Surgeons risk score, the echocardiographic parameters resulted in a net improvement in model discrimination and reclassification with a change in c-statistic from 0.68 to 0.73 and an integrated discrimination improvement of 5.9% (95% confidence interval, 2.8%-8.9%). In the Cox proportional hazards model, right ventricular dysfunction and pulmonary hypertension were independently predictive of mortality over 3.2 years of follow-up.

CONCLUSIONS

Preoperative echocardiography, in particular right ventricular dysfunction and restrictive left ventricular filling, provides incremental prognostic value in identifying patients at higher risk of mortality or major morbidity after coronary artery bypass surgery.

The effect of milrinone on the intraoperative hemodynamics during off-pump coronary bypass surgery in patients with an elevated echocardiographic index of the ventricular filling pressure

BACKGROUND

Hemodynamic derangement during off-pump coronary artery bypass surgery (OPCAB) is mainly attributed to impaired filling and diastolic dysfunction. An elevated ratio of the mitral velocity to the early-diastolic velocity of the mitral annulus (E/e' > 15) is a relatively new indicator of diastolic function, and this was reported to be associated with impaired hemodynamics during OPCAB. We investigated the efficacy of milrinone on the perioperative hemodynamics and short term outcomes of patients with an E/e' > 15 and who underwent OPCAB.

METHODS

The patients were randomly allocated into either group C (control, n = 31) or group M (n = 31) and they were treated with the same amount of either normal saline or milrinone (0.5 µg/kg/min) without bolus loading after completion of internal mammary artery harvest until the end of operation. Hemodynamic measurements were recorded after the induction of anesthesia (T1), 5 min after starting each distal anastomosis of the left anterior descending artery (T2), left circumflex artery (T3) and right coronary artery (T4), and 5 min after sternum closure (T5).

RESULTS

The mixed venous oxygen saturation (SvO(2)) was lower through T2-T4 compared to the baseline value in both groups, while the degree of the decrease was significantly less in group M than that in group C. The other hemodynamic variables, the operative data and the postoperative outcomes were similar between the two groups.

CONCLUSIONS

Intraoperative infusion of milrinone did not significantly improve the perioperative hemodynamics and the subsequent short term outcomes for the patients with preexisting diastolic dysfunction as represented by an elevated E/e' value, although it reduced the degree of decrease of the SvO(2) during OPCAB.