Effects of acute, transient coronary occlusion on global and regional right ventricular function in humans

New method for calculating right ventricular ejection fraction using gated myocardial perfusion studies

BACKGROUND

Quantification of right ventricular ejection fraction (RVEF) is important in patients who have right heart failure or cor pulmonale. When Tl-201 was the primary radiotracer used to evaluate myocardial perfusion, the outline of the right ventricle could vary and was not visualized in most patients. However, visualization of the right ventricle has become easier with the use of Tc-99m-labeled myocardial perfusion agents.

PURPOSE

This study describes a new method for quantifying RVEF using gated stress myocardial perfusion (GMP) slices. The results are compared with those of first-pass radionuclide ventriculography (FPRNA) in the same patients.

METHODS

Fifty-two consecutive patients referred for routine GMP imaging were included. After administration of Tc-99m tetrofosmin, all patients underwent FPRNA using a single crystal gamma camera and a GMP study. Regions of interest (ROI) were drawn to outline the right ventricular cavity at end diastole and end systole from three pairs of GMP slices. The RVEF was calculated from the number of pixels within the ROIs. The mean RVEF obtained using FPRNA and GMP imaging was 51.8 +/- 10.8% and 51.9 +/- 12.3%, respectively. The two methods showed good correlation with r = 0.81. In addition, there was no significant difference in the RVEFs calculated using these methods (P = 0.85). Bland-Altman analysis also showed good agreement between the two methods (limits of agreement +14.4% to -14.0%, slope = 0.19). Intraobserver and interobserver correlation were evaluated by reanalyzing 12 patients using the new RVEF quantification method and were good at r = 0.87 and 0.82, respectively. Therefore, this is a new convenient method for evaluating RVEF as part of a routine tomographic gated myocardial perfusion study.

Evaluation of the biocompatibility of titanium-tantalum alloy versus titanium

To evaluate the biocompatibility of a new titanium-tantalum alloy, with qualities superior to titanium alone, for use in oral implantology, fibroblast and epithelial cell lines were grown on plastic, titanium, copper, and titanium-tantalum supports. Studies using scanning electron microscopy, flow cytometry, and cytotoxicity assays were conducted to compare the different supports. Scanning electron microscopic observations showed high densities of fibroblasts and epithelial cells with well-developed attachment systems in the form of cytoplasmic projections. Cell densities were lower on titanium and titanium-tantalum surfaces than on plastic. Cell numbers, as determined by cytotoxicity assays, were significantly higher on plastic than on titanium or titanium-tantalum surfaces while fibroblasts proliferated better than epithelial cells on both metal surfaces. Flow cytometric analyses of cell cycles did not reveal any significant variations in the distribution of cells among the cycle phases on the three materials. We found no differences with regard to the parameters studied between titanium and the titanium-tantalum alloy.

Influence of exercise induced myocardial ischemia on right ventricular dP/dt: potential implications for rate responsive pacing

BACKGROUND

Right ventricular (RV) dP/dtmax has been used as a simple parameter for rate responsive pacing to simulate the normal sinus node function. However, the effect of acute myocardial ischemia on RV dP/dtmax has not yet been evaluated.

METHODS

RV high fidelity pressure was measured in 21 patients at rest and during supine bicycle exercise. Nine patients (Group 1 = controls) had no or only minimal alterations of the coronary arteries and 12 (Group 2 = CAD) had significant coronary artery disease with exercise induced left ventricular (LV) wall-motion abnormalities (n = 10) and/or angina pectoris (n = 6). RV pressure and its first derivative (RV dP/dt) were determined by an 8 French micromanometer catheter. The time constant of RV pressure decay (Tau) was calculated from the negative reciprocal of RV pressure versus negative dP/dt during isovolumic relaxation. RV volumes and ejection fraction were calculated from RV biplane angiograms (multiple slice method) at rest and during exercise.

RESULTS

Heart rate (HR), RV dP/dtmax and dP/dtmin increased significantly during exercise, whereas Tau decreased. There were no significant differences between the two groups, although RV ejection fraction increased from 67% to 72% in the control group but decreased from 63% to 51% in the CAD group (P < 0.05). An exponential relationship was found between HR and dP/dtmax with a correlation coefficient of 0.82 (P < 0.01; SEE = 7% of the mean value).

CONCLUSIONS

Acute exercise induced myocardial ischemia does not significantly influence RV dP/dtmax during sinus rhythm. Consequently, this index of RV contractility may be used in patients with coronary artery disease as a simple parameter for rate responsive pacing.

Beneficial cumulative role of both nitroglycerin and dobutamine on right ventricular systolic function in congestive heart failure patients awaiting heart transplantation

End-stage idiopathic dilated cardiomyopathy or ischemic heart disease usually present with very low cardiac output and severe ventricular dysfunction which may require pharmacological support before heart transplantation. Right ventricular ejection fraction might be an important factor of functional capacity and survival in congestive heart failure. In order to test the immediate response of right ventricular hemodynamic parameters to nitroglycerin and dobutamine usually used to treat severe left ventricular dysfunction, we studied 17 congestive heart failure patients (15 men, two women; mean age 55 +/- 13 years) with end-stage idiopathic dilated cardiomyopathy (n = 10) or end-stage ischemic heart disease (n = 7), left ventricular ejection fraction < 35% (mean 22 +/- 8%), and sinus rhythm. A well validated thermodilution technique using a dedicated catheter with a fast catheter-computer response, permitting instantaneous measurements of right ventricular ejection fraction, was used. Right ventricular hemodynamic parameters were recorded at baseline, after an intravenous bolus injection of 3 mg nitroglycerin and after an intravenous infusion of dobutamine administered after nitroglycerin until normalization of cardiac index or a maximal dose of 15 micrograms/kg/min. Pulmonary artery mean pressure significantly decreased after nitroglycerin (43 +/- 9 mmHg at baseline vs. 31 +/- 10 mmHg after nitroglycerin, P < 0.0001) and did not subsequently change after dobutamine (32 +/- 10 mmHg after dobutamine, ns). Cardiac index was not affected by nitroglycerin (1.7 +/- 0. l/min/m2 at baseline vs. 2.0 +/- 0.3 l/min/m2 after nitroglycerin, ns), but dramatically increased after dobutamine (3.0 +/- 1.0 l/min/m2 after dobutamine, P < 0.0001). Concomitantly to the changes of these two parameters, right ventricular ejection fraction progressively increased (14 +/- 8% at baseline vs. 20 +/- 10% after nitroglycerin (P < 0.0006) vs. 28 +/- 13% after dobutamine (P < 0.0001)). Progressive increase of right ventricular ejection fraction after administration of nitroglycerin followed by administration of dobutamine suggests the beneficial cumulative role of both medications on right ventricular systolic function in severe congestive heart failure.

Serial changes in left and right ventricular systolic and diastolic dynamics during the first year after an index left ventricular Q wave myocardial infarction

OBJECTIVES

This study quantified serially biventricular emptying and filling after infarction and related these to changes in volume, muscle mass, wall stress and contractility.

BACKGROUND

There are limited data on serial changes in ventricular dynamics after infarction.

METHODS

Forty patients had serial electron beam computed tomographic examinations during the first year after index Q wave infarction (21 anterior, 19 inferior), and global biventricular volumes, peak rates of emptying and filling and left ventricular muscle masses were quantified. Mean mid-left ventricular end-systolic wall stresses, rate-corrected velocities of circumferential shortening and two indexes of left ventricular contractility--the end-systolic wall stress/volume ratio and the end-systolic wall stress/rate-corrected velocity of circumferential shortening relation--were estimated in each instance.

RESULTS

Patients with anterior infarction had an increase in biventricular chamber volume of 15% to 35% by 1 year. Global biventricular peak rates of emptying and filling were decreased by 20% to 30% from hospital discharge to 6 weeks but thereafter remained unchanged. Despite a significant increase in mean wall stresses, the end-systolic wall stress/volume ratio remained unchanged during the year. The rate-corrected velocities of circumferential shortening declined serially after anterior infarction but did so in proportion to the increase in mean wall stresses, consistent with no net change in left ventricular contractility. Patients with inferior infarction showed a trend toward similar changes, but the magnitudes did not reach significance.

CONCLUSIONS

Left (and right) ventricular global peak rates of emptying and filling during the first year after infarction can be altered in the absence of additional ischemic injury but are more consistent with responses to changes in left ventricular afterload than changes in intrinsic ventricular performance or contractility. Serial changes in left ventricular afterload after infarction are largely due to progressive chamber enlargement and limited development of compensatory hypertrophy during the first year. Intrinsic global left ventricular contractile performance was not altered by postinfarction cardiac remodeling in the patients examined.

Comparison of right ventricular systolic function in idiopathic dilated cardiomyopathy and healed anterior wall myocardial infarction associated with atherosclerotic coronary artery disease

A case-controlled study assessed right ventricular (RV) systolic function in 10 patients with idiopathic dilated cardiomyopathy (IDC) and in 10 with healed anterior wall myocardial infarction associated with atherosclerotic coronary artery disease (CAD). Each patient was matched for sex, left ventricular ejection fraction +/- 5% and pulmonary artery mean pressure +/- 5 mm Hg. All patients had sinus rhythm and a left ventricular ejection fraction < 45%. A new, well-validated thermodilution technique was used to assess RV ejection fraction and volumes. RV ejection fraction was lower in the IDC than in the CAD group (25 +/- 14% vs 36 +/- 11%; p < 0.02). Linear correlations between RV parameters and pulmonary artery pressure were significantly present in both groups. However, the slopes of the equations were not statistically different. In comparison with healed anterior wall myocardial infarction with CAD and for similar levels of left ventricular dysfunction, RV systolic function appeared to be more altered in IDC.

Myocardial perfusion and ventricular function measurements during total coronary artery occlusion in humans. A comparison with rest and exercise radionuclide studies

BACKGROUND

The purpose of this investigation was to compare the magnitude of change in myocardial perfusion and function during exercise with that obtained during total coronary artery occlusion. Radionuclide studies are widely used for the diagnosis and determination of prognosis in patients with suspected or known coronary artery disease. These studies are based on the premise that the relative deficit of coronary blood flow, which is induced by exercise and recognized as increased demand, relates to the jeopardy experienced by the decrease or sudden absolute interruption of coronary blood flow that is recognized as decreased supply and is associated with coronary stenosis or total coronary artery occlusion. The magnitude of exercise-induced perfusion and function abnormalities compared with those induced by total coronary artery occlusion in humans has not been previously reported.

METHODS AND RESULTS

We prospectively studied 20 patients with > or = 50% diameter stenosis documented by quantitative coronary angiography in at least one vessel. A same-day rest/exercise sestamibi myocardial function and perfusion study was performed within 24 hours before percutaneous transluminal coronary angioplasty. At 1 minute after balloon inflation, while the vessel was occluded, sestamibi was injected, and a myocardial perfusion and function study was performed. Perfusion defect size was greater during occlusion (28 +/- 3%) than during exercise (13 +/- 2%) (P < .01). Ejection fraction was greater during exercise (53 +/- 3%) compared with values measured during occlusion (41 +/- 2%) (P < .01).

CONCLUSIONS

Physiological abnormalities induced by coronary occlusion are greater than those that occur during exercise, thereby indicating that stress-induced ischemia may not reflect the total potential myocardium in jeopardy from a stenotic lesion, if sudden occlusion occurs.