Ali Salahieh

Effect of clonidine on cardiovascular morbidity and mortality after noncardiac surgery.

Background:Perioperative myocardial ischemia occurs in 20–40% of patients at risk for cardiac morbidity and is associated with a ninefold increase in risk of cardiac morbidity. Methods:In a prospective, double-blinded, clinical trial, we studied 190 patients with or at risk for coronary artery disease in two study groups with a 2:1 ratio (clonidine, n = 125 vs. placebo, n = 65) to test the hypothesis that prophylactic clonidine reduces the incidence of perioperative myocardial ischemia and postoperative death in patients undergoing noncardiac surgery. Clonidine (0.2 mg orally as well as a patch) or placebo (tablet and patch) was administered the night before surgery, and clonidine (0.2 mg orally) or placebo (tablet) was administered on the morning of surgery. The patch or placebo remained on the patient for 4 days and was then removed. Results:The incidence of perioperative myocardial ischemia was significantly reduced with clonidine (intraoperative and postoperative, 18 of 125, 14% vs. placebo, 20 of 65, 31%; P = 0.01). Prophylactic clonidine administration had minimal hemodynamic effects. Clonidine reduced the incidence of postoperative mortality for up to 2 yr (clonidine, 19 of 125 [15%] vs. placebo, 19 of 65 [29%]; relative risk = 0.43 [confidence interval, 0.21–0.89]; P = 0.035). Conclusions:Perioperative administration of clonidine for 4 days to patients at risk for coronary artery disease significantly reduces the incidence of perioperative myocardial ischemia and postoperative death.

The effect of ventricular volume reduction surgery in the dilated, poorly contractile left ventricle: a simple finite element analysis.

OBJECTIVES Ventricular volume reduction surgery has been proposed by Batista to improve cardiac function in patients with dilated cardiomyopathy. However, limited clinical data exist to determine the efficacy of this operation. A finite element simulation is therefore used to determine the effect of volume reduction surgery on left ventricular end-systolic elastance, diastolic compliance, stroke work/end-diastolic volume (preload recruitable stroke work), and stroke work/end-diastolic pressure (Starling) relationships. METHODS End-diastole and end-systole were represented by elastic finite element models with different unloaded shapes and nonlinear material properties. End-systolic elastance, diastolic compliance, preload recruitable stroke work, and Starling relationships, as well as energy expenditure per gram of unresected myocardium, were calculated. Two different types of volume reduction surgery (apical and lateral) were simulated at 10% and 20% left ventricular mass reduction. RESULTS Ventricular volume reduction surgery causes diastolic compliance to shift further to the left on the pressure-volume diagram than end-systolic elastance. Volume reduction surgery increases the slope of the preload recruitable stroke work relationship (dilated cardiomyopathy 0.006 J/mL; 20% lateral volume reduction surgery 0.009 J/mL) but decreases the slope of the Starling relationship (dilated cardiomyopathy 0.028 J/mm Hg; 20% lateral volume reduction 0.023 J/mm Hg). For a given amount of resection, lateral volume reduction has a greater effect than apical volume reduction. Ten-percent and 20% lateral volume reduction reduces energy expenditure by 7% and 17%, respectively. CONCLUSION Ventricular volume reduction surgery shifts end-systolic elastance and diastolic compliance to the left on the pressure-volume diagram. The net effect on ventricular function is mixed. Volume reduction surgery increases the slope of preload recruitable stroke work, but increased diastolic compliance causes a small decrease in the Starling relationship (3 mm Hg difference between dilated cardiomyopathy and volume reduction surgery at stroke work = 0.5 J).

Ventricular volume, chamber stiffness, and function after anteroapical aneurysm plication in the sheep ☆ ☆☆ ★

OBJECTIVE The success of left ventricular aneurysm plication depends on how the procedure affects both end-systolic elastance and diastolic compliance and how those changes affect ventricular function (stroke work/end-diastolic volume [PRSW] and stroke volume/end-diastolic pressure [Starling] relationships). METHODS Five male Dorsett sheep were surgically instrumented with coronary artery snares, an inferior vena caval occluder, and an ascending aortic ultrasonic flow probe. One week later an anteroapical myocardial infarction was produced by tightening the coronary snares. Ten weeks after myocardial infarction, the left ventricular aneurysm was plicated. Absolute left ventricular volume was measured by long-axis transdiaphragmatic echocardiography, and relative changes in left ventricular volume were measured with a conductance catheter. End-systolic elastance, diastolic compliance, PRSW, and Starling relationships were measured immediately before myocardial infarction, 10 weeks after myocardial infarction (immediately before plication), and immediately after and 6 weeks after aneurysm plication. RESULTS After plication, end-diastolic and end-systolic left ventricular volumes return to preinfarction values. The slopes of end-systolic elastance, diastolic compliance, and PRSW decrease 10 weeks after myocardial infarction, increase with aneurysm plication, and then decrease 6 weeks after aneurysm plication. The Starling relationship undergoes a downward parallel shift with aneurysm plication. CONCLUSION Aneurysm plication abruptly decreases left ventricular volume and diastolic compliance, increases end-systolic elastance and PRSW, but decreases the Starling relationship. The net effect on left ventricular function is mixed. Furthermore, left ventricular remodeling 6 weeks after aneurysm plication causes left ventricular volume, end-systolic elastance, diastolic compliance, PRSW, and the Starling relationship to return to preplication values.

Myosplint decreases wall stress without depressing function in the failing heart: a finite element model study.

BACKGROUND The Myocor Myosplint is a transcavitary tensioning device designed to change left ventricular (LV) shape and reduce wall stress. Regional wall stress cannot be measured in the intact heart and LV function after surgical remodeling is often confounded by inotropic agents and mitral repair. We used a realistic mathematical (finite element) model of the dilated human LV to test the hypothesis that Myosplint decreased regional ventricular fiber stress and improved LV function. METHODS A finite element model was used to simulate the effects of Myosplint on the LV stroke volume/end-diastolic pressure (Starling) relationship and regional distributions of stress in the local muscle fiber direction (fiber stress) for a wide range of diastolic and end-systolic material properties. The nonlinear stress-strain relationship for the diastolic myocardium was anisotropic with respect to the local muscle fiber direction. An elastance model for active fiber stress was incorporated in an axisymmetric geometric model of the globally dilated LV wall. RESULTS Both diastolic compliance and end-systolic elastance shifted to the left on the pressure-volume diagram. LV end-diastolic volume and end-systolic volumes were reduced by 7.6% and 8.6%, respectively. Mean end-diastolic and end-systolic fiber stress was decreased by 24% and 16%, respectively. Although the effect of Myosplint on the Starling relationship was not significant, there were trends toward an improvement in this relationship at low diastolic stiffness, C, high peak intracellular calcium concentration, Ca(0), and high arterial elastance, E(A). Of note, the effect of C was twice that of Ca(0) and E(A). Diastolic function would, therefore, be expected to be the prime determinant of success with Myosplint. CONCLUSIONS Myosplint reduces fiber stress without a decrement in the Starling relationship. Myosplint should be much more effective than partial ventriculectomy as a surgical therapy for patients with dilated cardiomyopathy and end-stage congestive heart failure.

Endotracheal cardiac output monitor

Background The endotracheal cardiac output monitor (ECOM) is a new device that uses an endotracheal tube with multiple electrodes to measure cardiac output (CO). It measures the changes in electrical impedance caused by pulsatile blood flow in the aorta. The system was tested for safety and efficacy in 10 swine. Methods Swine (60–80 kg) were chronically instrumented with a transit time flow probe on the ascending aorta and vascular occluders on the vena cava and pulmonary artery. After a minimum recovery of 4 days, the animals were anesthetized and intubated with an ECOM endotracheal tube. CO measurements from the ECOM system were compared to transit time flow probe measurements using linear regression and Bland–Altman analysis. Three different inotropic states were studied: (1) baseline; (2) increased (dobutamine); and (3) decreased (esmolol). CO was changed at each inotropic state by impeding left ventricular filling with the vena cava or pulmonary artery occluders. CO values between 0 and 15 l/min were studied. Pigs were studied for 24 h consecutively. Results There was no deterioration of the impedance signal with time and no tracheal injury from the ECOM electrodes. There is a linear relationship between the ECOM and transit time flow probe CO between 0 and 15 l/min (slope = 0.94; intercept = 0.15 l/min; R2= 0.77). The mean difference between the two measures (bias) is 0.15 l/min and the SD is 1.34 l/min. The limits of agreement are −2.53 to 2.82 l/min. Conclusion Endotracheal CO monitor is a promising technology that needs further evaluation in clinical trials.

The effect of diastolic stiffness on ventricular function after partial ventriculectomy: a finite element simulation.

Partial ventriculectomy (PV) has been proposed by Batista and colleagues to improve cardiac function in patients with dilated cardiomyopathy (DCM); however, results have been mixed. We tested the hypothesis that preoperative diastolic function affects the stroke volume/end-diastolic pressure (Starling) relationship after PV. A previously described finite element simulation of DCM and PV was used. Diastole and end systole were represented by separate elastic finite element models with different unloaded shapes and nonlinear material properties. Left ventricular (LV) end-systolic elastance (E(ES)), diastolic compliance (DC), and Starling relationships were calculated. DC was varied by changing Ogden material property alpha(i) from 12 (compliant) to 20 (stiff). PV was simulated at 20% LV mass reduction. The slope of the Starling relationship increased from 1.82 to 1.21 as alpha(i) increased from 12 to 20. Partial ventriculectomy increased the Starling relationship in each case from 1.34 to 1.01 respectively. However, the net result in each case is a decrement in the Starling relationship with resection, and the smallest decrement was associated with the highest diastolic stiffness (alpha(i) = 20). Partial ventriculectomy depressed the Starling relationship for all values of diastolic compliance. It is expected that patients with a higher diastolic stiffness should do better.