David G. Rabkin

Correlation of the Tei index with invasive measurements of ventricular function in a porcine model.

BACKGROUND The Doppler myocardial performance (Tei) index has been reported to be clinically useful in assessing left ventricular systolic and diastolic function in both adults and children. However, there are limited data to compare the Tei index with invasive measurements of ventricular function. We used a porcine model to directly correlate the Tei index with invasive indices of systolic and diastolic function. METHODS Pressure volume loops were obtained from 10 pigs (32-45 kg). A micromanometer and a conductance catheter were placed in the left ventricle to record pressure and volume, respectively. A flow probe was placed around the ascending aorta to record cardiac output. Baseline pressure volume loops were generated during preload reduction through caval occlusion. Epicardial echocardiograms were performed just before the caval occlusion. Invasive indices including preload recruitable stroke work, ventricular stiffness constant, and cardiac output were assessed, as were noninvasive echocardiographic indices including Tei index and ejection fraction. An ischemic insult, ventricular fibrillation, was induced to alter ventricular function. After cardioversion and 40 minutes of reperfusion, echocardiographic and invasive measurements were repeated. RESULTS There was a statistically significant inverse relationship between the percent change in Tei and the percent change in preload recruitable stroke work after ventricular fibrillation (r = -0.70, P =.02), although the correlation between the actual values of Tei and preload recruitable stroke work were not statistically significant. There was a statistically significant inverse relationship between the percent change in Tei and the percent change in cardiac output (r = -0.65, P =.03). There was a direct correlation between the value of Tei and the ventricular stiffness constant at baseline (r = 0.63, P <.05). As anticipated, the value of Tei was inversely related to ejection fraction by epicardial echocardiogram at baseline (r = -0.85, P <.001). The percent change in Tei was inversely related to the percent change in ejection fraction as well (r = -0.69, P <.05). CONCLUSIONS This animal model is one of the first studies to demonstrate a direct correlation between the Tei index and systolic and diastolic invasive measurements of ventricular function. This supports the clinical use of this index as a measure of global ventricular function.

Load dependence of cardiac output in biventricular pacing

BACKGROUND The effect of biventricular pacing on stroke volume is believed to be dependent on right ventricular/left ventricular delay, but effects in individual patients are unpredictable. This variability may reflect relative right and left ventricular volume and/or pressure overloads. Accordingly, we tested the hypothesis that the relation of cardiac output to right ventricular/left ventricular delay is load dependent in a pig model of pulmonary stenosis. METHODS After median sternotomy in 6 anesthetized, domestic pigs, complete heart block was induced by ethanol ablation. During epicardial, atrial tracking DDD biventricular pacing, atrioventricular delay was varied between 60 and 180 ms in 30-ms increments. Right ventricular/left ventricular delay was varied at each atrioventricular delay from +80 ms (right ventricle first) to -80 ms (left ventricle first) in 20-ms increments. Aortic flow, right ventricular pressure, peripheral arterial pressure, and electrocardiogram were measured in the control state and during pulmonary stenosis, created by tightening a snare around the pulmonary artery until cardiac output decreased by 50%. RESULTS Atrioventricular and right ventricular/left ventricular delay had no effect on cardiac output during the control state, but during pulmonary stenosis there was a statistically significant (P =.0001, repeated-measures analysis of variance) right ventricular/left ventricular delay-related trend toward higher cardiac output with right ventricular pacing first. This effect was more pronounced when the optimal atrioventricular delay was determined first, resulting in a 20% increase in cardiac output when the optimal right ventricular/left ventricular delay was compared with simultaneous biventricular pacing. CONCLUSIONS Optimized biventricular pacing in swine is associated with increased cardiac output during acute pulmonary stenosis, but not during the control state. Further studies are needed to determine whether specific types of right ventricular and left ventricular overload predictably affect the relation between right ventricular/left ventricular delay and cardiac output.

Nitric oxide for the treatment of postpneumonectomy pulmonary edema

Inhaled nitric oxide, a selective pulmonary vasodilator, has been used to improve arterial oxygenation in adult respiratory distress syndrome. To our knowledge, it has not been successfully used to treat this syndrome after major lung resection. We used nitric oxide to treat postpneumonectomy pulmonary edema with immediate and sustained improvement in oxygenation. The patient was successfully weaned from nitric oxide and extubated after 3 days of supportive therapy.

Coronary perfusate composition influences diastolic properties, myocardial water content, and histologic characteristics of the rat left ventricle

BACKGROUND Recent studies found that edema, histology, and left ventricular diastolic compliance exhibit quantitative relationships in rats. Edema due to low osmolarity coronary perfusates increases myocardial water content and histologic edema score and decreases left ventricular filling. The present study examined effects of perfusate osmolarity and chemical composition on rat hearts. METHODS Arrested American Cancer Institute (ACI) rat hearts (4 degrees C) were perfused with different cardioplegia solutions, including Plegisol (289 mOsm/L), dilute Plegisol (172 mOsm/L), Stanford solution (409 mOsm/L), and University of Wisconsin solution (315 mOsm/L). Controls had blood perfusion (310 mOsm/L). Postmortem left ventricular pressure-volume curves and myocardial water content were measured. After glutaraldehyde or formalin fixation, dehydration, and paraffin embedding, edema was graded subjectively. RESULTS Myocardial water content reflected perfusate osmolarity, being lowest in Stanford and University of Wisconsin solutions (p<0.05 versus other groups) and highest in dilute Plegisol (p<0.05). Left ventricular filling volumes were smallest in dilute Plegisol and Plegisol (p<0.05). Osmolarity was not a major determinant of myocardial edema grade, which was highest with University of Wisconsin solution and dilute Plegisol (p<0.05 versus other groups). CONCLUSIONS Perfusate osmolarity determined myocardial water content and left ventricular filling volume. However, perfusate chemical composition influenced the histologic appearance of edema. Pathologic grading of edema can be influenced by factors other than osmolarity alone.

Mechanisms of optimized biventricular pacing in pulmonary stenosis: effects on left ventricular geometry in swine.

We tested the hypothesis that optimized biventricular pacing (BiVP) enhances cardiac output (CO) during critical pulmonary stenosis (PS) by attenuating distortions in left ventricular (LV) geometry. Following median sternotomy in six anesthetized pigs, heart block was induced by ethanol ablation. During epicardial, DDD BiVP, atrioventricular delay (AVD) was varied from 60 ms to 180 ms in 30 ms increments. At the AVD with the highest CO right‐left delay (RLD) was varied from (+) 80 ms (RV first) to (−) 80 ms (LV first) in 20 ms increments. At each pacing setting, aortic flow, ECG, and LV diameter were measured in the control state (CON) and during PS, created by snaring the pulmonary artery until CO decreased 50%. Short axis LV echocardiograms were obtained at (+) and (−) 80 ms. In CON, RLD had no effect on function or geometry. During PS optimum BiVP resulted in significant increases in CO (1.12 L/min ± 0.13 SEM at RLD =+ 40 ms versus 0.92 ± 0.12 at RLD = 0 and 0.73 ± 0.08 at RLD =−80), and LV fractional shortening (8.97%± 0.51% at RLD =+ 40 ms versus 7.34%± 0.58% at RLD = 0 and 6.21%± 0.66% at RLD =−80). In addition, LV eccentricity with (−) RLD was significantly different versus CON at both end‐diastole (0.79 ± 0.07 vs 1.02 ± 0.03, P = 0.011 Students t‐test) and end‐systole (0.83 ± 0.05 vs 1.00 ± 0.02, P = 0.017). However, with (+) RLD differences versus CON were not significant at either end‐diastole (0.88 ± 0.06 vs 0.99 ± 0.03) or end‐systole (0.92 ± 0.03 vs 1.01 ± 0.03). In swine hearts with PS, optimized BiVP increases CO, fractional shortening, and LV symmetry. BiVP warrants further study as treatment for acute postoperative heart failure.

Unconventional approaches to cardiac pacing in patients with inaccessible cardiac chambers

BACKGROUND Transvenous endocardial implantation can be impossible or contraindicated in patients with inaccessible right cardiac chambers. These patients usually undergo epicardial implantation, which has been associated with frequent rising thresholds and limited lead survival. We have used the following two alternative approaches in these patients: (1) transatrial puncture and passage of pacing leads for patients with no access to the right atrium and (2) ventricular pacing from the coronary sinus or its tributaries for patients with inaccessible ventricles. METHODS. We retrospectively reviewed our experience in 9 patients who had those procedures. Five patients had pacing from the coronary sinus, and 4 by transatrial puncture. RESULTS Seven of the 9 patients had DDD pacing. Low acute pacing thresholds and satisfactory sensing levels were obtained with both approaches. One instance of high stimulation threshold (20%) occurred in the coronary sinus group and none in the transatrial puncture group. One patient in the transatrial puncture group died from unrelated causes. No malignant arrhythmias, pneumothorax, diaphragmatic pacing, or infectious complications have been observed. CONCLUSION These unconventional approaches are safe, relatively simple, and reliable. Although the short-term follow-up is favorable, long-term follow-up is necessary to ascertain the relative merit of these approaches.

Spontaneous popliteal artery dissection: a case report and review of the literature.

Spontaneous arterial dissection of a peripheral artery involving an extremity is a rare event. We report a case of atraumatic, nonaneurysmal dissection of the popliteal artery that occurred in a 62-year-old man who was admitted with progressive right lower-extremity claudication. Preoperative arteriography was suggestive of arterial dissection, and surgical treatment was undertaken before irreversible ischemia developed. Intraoperatively, a dissection of the popliteal artery was observed, and the patient underwent femoral-popliteal bypass grafting with the ipsilateral, greater saphenous vein and the popliteal artery was ligated distal to the dissection. Spontaneous dissection limited to the popliteal artery has not previously been reported in the literature. Successful management depends on consideration of the diagnosis, particularly when other, more common diseases have been excluded.

REVERSAL OF IATROGENIC MYOCARDIAL EDEMA AND RELATED ABNORMALITIES OF DIASTOLIC PROPERTIES IN THE PIG LEFT VENTRICLE

OBJECTIVE This study examines the resolution of iatrogenic edema and related changes in systolic and diastolic properties in the intact pig left ventricle. METHODS The coronary arteries were perfused for 50 to 60 seconds with diluted blood (hematocrit value 10% +/- 1%, edema group, n = 5) or whole blood (hematocrit value 28% +/- 1%, control group, n = 6) infused into the aortic root during aortic crossclamping in conditioned, anesthetized pigs. After whole blood reperfusion, preload reduction by vena caval occlusion was used to define systolic and diastolic properties at 15-minute intervals. Left ventricular pressure and conductance, aortic flow, and two-dimensional echocardiography were recorded. RESULTS Left ventricular mass (wall volume) in the edema group increased significantly compared with that in control pigs after crossclamp removal. Mass returned to preperfusion levels after 45 minutes. The ventricular stiffness constant (beta) increased significantly in the edema group versus the control group, returning to baseline by 30 minutes. The diastolic relaxation constant (tau) and base constant (alpha) did not differ between groups. There was no significant change in contractility. CONCLUSION Increases in left ventricular mass and diastolic stiffness induced by coronary perfusion with hemodiluted blood resolve after 45 minutes of whole blood perfusion in pigs. This study defines physiologic effects of edema in the normal heart while eliminating most common confounding experimental errors.

Aortic regurgitation in the heterotopic rat heart transplant: effect on ventricular remodeling and diastolic function

OBJECTIVES Use of the heterotopic rat cardiac isograft model is limited by ventricular atrophy attributable to the left ventricles non-working state. Previous studies indicate that increased left ventricular pressure-volume work minimizes atrophy. We used a simpler approach to increase ventricular work, imposing aortic regurgitation on the transplant. We hypothesized that this would prevent atrophy and preserve left ventricular compliance. METHODS We analyzed heterotopic transplants with aortic valvotomy and without aortic valvotomy (controls). Recipient native hearts served as separate controls. After 15 to 25 days, we measured cardiac wet weight, dry weight, and water content of all groups and measured echocardiographic left ventricular wall thickness and end-diastolic and end-systolic diameters in both transplant groups. Left ventricular volume infusions yielded pressure-volume data that we analyzed using regression methods. RESULTS Aortic regurgitant transplants weighed more than control transplants (dry weight, 0.109 +/- 0.013 g vs 0.097 +/- 0.016 g; p = 0.020, 2-way analysis of variance), but all transplants weighed less than native hearts weighed (p = 0.001). Control transplants were less compliant than regurgitant transplants (p = 0.002), but the latter were similar to their own native hearts (p = 0.34). Wall thickness decreased in regurgitant vs control transplants (p = 0.020, Students t-test), but end-diastolic and end-systolic diameters increased (p < or = 0.001). CONCLUSIONS Aortic regurgitation in heterotopic transplants improves left ventricular compliance through chamber dilatation without preventing atrophy. Moderate acute aortic regurgitation affects ventricular remodeling more than it stimulates myocardial hypertrophy. Smaller end-diastolic diameter, greater wall thickness, and myocardial edema may explain decreased compliance in non-working transplants.

Retrograde Coronary Perfusion: Effects on Iatrogenic Edema and Diastolic Properties

BACKGROUND The relative merits of antegrade infusion and retrograde infusion of cardioplegic solution in terms of heart weight, myocardial water content, and ventricular diastolic properties are undefined. Accordingly, we compared antegrade and retrograde flow of hemodiluted blood in isolated, hypothermic porcine hearts. METHODS After cardiectomy, 1 L of cold heparinized blood diluted with lactated Ringers solution to concentrations ranging from 100% lactated Ringers to 50% lactated Ringers and 50% blood was perfused in an antegrade (n = 6) or retrograde (n = 6) fashion at mean pressures of 62 +/- 2 mm Hg (+/- standard error of the mean) and 49 +/- 2 mm Hg, respectively. Heart weight, myocardial water content, and left ventricular pressure-volume relationships were obtained before and after perfusion. RESULTS In the comparison of measurements before and after perfusion, changes in heart weight (36 +/- 4 g versus 5 +/- 2 g; p < 0.05), myocardial water content (6.9% +/- 1.0% versus 2.5% +/- 0.4%; p < 0.01), and ventricular filling measured by normalized left ventricular volume at 10, 15, and 20 mm Hg were greater in the antegrade group. CONCLUSIONS In the isolated porcine heart, retrograde flow is distinguished from antegrade flow by less change in heart weight and myocardial water content and no diastolic dysfunction.