Stimulation of adult resident cardiac progenitor cells by durable myocardial expression of thymosin beta 4 with ultrasound-targeted microbubble delivery.

It has been proposed that thymosin beta 4 (TB4)-protein delivery stimulates differentiation of resident adult WT1-positive cardiac progenitor cells, but with very low efficiency. We determined whether gene therapy with human TB4 stimulates proliferation of resident adult cardiac progenitor cells in normal rat heart. Ultrasound-targeted microbubble destruction (UTMD) was used to deliver the human TB4 gene under a piggybac transposon plasmid to normal rat heart. The rat hearts were assayed by quantitative reverse transcription-PCR and immunohistology with a confocal microscope at 1, 2, 3, 4 and 12 weeks after UTMD. Exogenous TB4 stimulation resulted in the presence of WT1-positive cardiac progenitor cells from epicardium to endocardium. TB4 stimulated angiogenesis and arteriogenesis. One month after TB4 gene therapy by UTMD, the percentage of NKX2.5-positive cardiomyocytes was 5.5±1.0% and NKX2.5 mRNA was 24-fold higher than in the control groups (P<0.001). Similar results were found for ISL-1, BrDu, Ki-67, PHH3 and aurora B (P<0.001). Cardiac-specific delivery of exogenous human TB4 gene efficiently stimulates proliferation and differentiation of resident WT1-positive adult cardiac progenitor cells into three intact cardiac cell lineages-vascular endothelial cells, coronary artery smooth muscle cells and cardiac muscle cells in normal adult rat heart.

In vivo non-viral gene delivery of human vascular endothelial growth factor improves revascularisation and restoration of euglycaemia after human islet transplantation into mouse liver.

AIMS/HYPOTHESIS: Delivery of the gene for human vascular endothelial growth factor (VEGF, also known as VEGFA) to both the transplanted islets and the surrounding tissue may promote islet revascularisation and survival. We previously showed the effective delivery of VEGF gene to rat myocardium by an ultrasound-mediated gene-transfer method named ultrasound-targeted microbubble destruction (UTMD). Here we examined the effect of non-viral VEGF delivery using UTMD on transplanted islets in vivo. METHODS: A marginal number of human islets were transplanted into livers of mice which were a model for diabetes. Then, non-viral plasmid vectors encoding VEGF (VEGF group, n = 11) or the gene for green fluorescent protein (GFP) (GFP group, n = 7) were introduced into the host liver by UTMD. Transplantation without gene delivery was performed as a control (no-UTMD group, n = 8). Blood glucose, serum human insulin, C-peptide levels and the revascularisation in graft islets were evaluated. RESULTS: Restoration of euglycaemia occurred in 13% in the no-UTMD group and 14% in the GFP group, whereas 73% mice in the VEGF group became euglycaemic at day 30 (p < 0.05 in no-UTMD vs VEGF). Serum human insulin and C-peptide were significantly higher in the VEGF group at day 32 (insulin: no-UTMD, 17 +/- 8; GFP, 37 +/- 17; VEGF, 109 +/- 26 pmol/l, respectively, p < 0.05; C-peptide: no-UTMD, 68 +/- 38; GFP, 115 +/- 58; VEGF, 791 +/- 230 pmol/l, respectively, p < 0.05). Vessel density in graft islets was significantly higher in the VEGF group (no-UTMD, 169 +/- 36; GFP, 227 +/- 39; VEGF, 649 +/- 51 counts/mm(2), respectively, p < 0.05). CONCLUSIONS/INTERPRETATION: Delivery of VEGF gene to host liver using UTMD promoted islet revascularisation after islet transplantation and improved the restoration of euglycaemia.

Regeneration of pancreatic islets in vivo by ultrasound-targeted gene therapy.

This study uses a novel approach to gene therapy in which plasmid DNA is targeted to the pancreas in vivo using ultrasound-targeted microbubble destruction (UTMD) to achieve islet regeneration. Intravenous microbubbles carrying plasmids are destroyed within the pancreatic microcirculation by ultrasound, achieving local gene expression that is further targeted to ß-cells by a modified rat insulin promoter (RIP3.1). A series of genes implicated in endocrine development were delivered to rats 2 days after streptozotocin-induced diabetes. The genes, PAX4, Nkx2.2, Nkx6.1, Ngn3 and Mafa, produced α-cell hyperplasia, but no significant improvement in ß-cell mass or blood glucose level 30 days after UTMD. In contrast, RIP3.1-NeuroD1 promoted islet regeneration from surviving ß-cells, with normalization of glucose, insulin and C-peptide levels at 30 days. In a longer-term experiment, four of six rats had a return of diabetes at 90 days, accompanied by ß-cell apoptosis on Tunel staining. Pretreatment with the JNK inhibitor SP600125 successfully blocked ß-cell apoptosis and resulted in restoration of ß-cell mass and normalization of blood glucose level for up to 90 days. This technique allows in vivo islet regeneration, restoration of ß-cell mass and normalization of blood sugar, insulin and C-peptide in rats without viruses.

Efficient, glucose responsive and islet-specific transgene expression by a modified rat insulin promoter.

This study was done to improve efficiency and islet specificity of the rat insulin promoter (RIP). Various RIP lengths were prepared and tested in vitro to drive luciferase reporter gene expression in INS1-cells, alpha-cells, acinar cells, ductal cells and fibroblasts. The CMV promoter was used as a positive control. In addition, the DsRed reporter gene was administered in vivo to rat pancreas by ultrasound-targeted microbubble destruction (UTMD). Confocal microscopy was used to detect the presence and distribution of DsRed within the pancreas after UTMD. A modified RIP3.1 promoter, which includes portions of the insulin gene after its transcription start site is fivefold more active in INS-1 cells than the full-length RIP promoter or the CMV promoter. RIP3.1 is regulated by glucose level and various islet transcription factors in vitro, and exhibits activity in alpha-cells, but not in exocrine cells. In vivo delivery of RIP3.1-DsRed resulted in expression of DsRed protein in beta-cells, and to a lesser extent in alpha-cells under normal glucose conditions. No DsRed signal was present in exocrine pancreas under RIP3.1. A modified RIP, RIP3.1, efficiently and specifically directs gene expression to endocrine pancreas.

Paradoxical withdrawal of reflex vasoconstriction as a cause of hemodialysis-induced hypotension.

Acute hypotension is an important complication of hemodialysis, but the underlying mechanisms remain poorly understood. Because hemorrhage-induced hypovolemia can trigger a sudden decrease in sympathetic activity resulting in bradycardia and vasodilation, we hypothesized that hemodialysis-induced hypovolemia also can trigger the same type of vasodepressor reaction, which would exacerbate the volume-dependent fall in blood pressure. We therefore measured blood pressure, vascular resistance, and sympathetic nerve activity (intraneural microelectrodes) during sessions of maintenance hemodialysis in 7 patients with and 16 patients without a history of hemodialysis-induced hypotension. During hemodialysis, blood pressure at first remained unchanged as calf resistance increased in both hypotension-resistant (from 37 +/- 4 to 49 +/- 5 U, P < 0.05) and hypotension-prone (from 42 +/- 6 to 66 +/- 12 U, P < 0.05) patients; sympathetic activity increased comparably in the subset of patients in whom it could be measured. With continued hemodialysis, calf resistance and sympathetic activity increased further in the hypotension-resistant patients, but in the hypotension-prone patients the precipitous decrease in blood pressure was accompanied by decreases in sympathetic activity, vascular resistance, and heart rate as well as symptoms of vasodepressor syncope. On an interdialysis day, both groups of patients increased vascular resistance normally during unloading of cardiopulmonary baroreceptors with lower body negative pressure and increased heart rate normally during unloading of arterial baroreceptors with infusion of nitroprusside. These findings indicate that in a group of hemodialysis patients without diabetes or other conditions known to impair autonomic reflexes, hemodialysis-induced hypotension is not caused by chronic uremic impairment in arterial or cardiopulmonary baroreflexes but rather by acute, paradoxical withdrawal of sympathetic vasoconstrictor drive producing vasodepressor syncope.

Effects of intranasal cocaine on sympathetic nerve discharge in humans.

Cocaine-induced cardiovascular emergencies are mediated by excessive adrenergic stimulation. Animal studies suggest that cocaine not only blocks norepinephrine reuptake peripherally but also inhibits the baroreceptors, thereby reflexively increasing sympathetic nerve discharge. However, the effect of cocaine on sympathetic nerve discharge in humans is unknown. In 12 healthy volunteers, we recorded blood pressure and sympathetic nerve discharge to the skeletal muscle vasculature using intraneural microelectrodes (peroneal nerve) during intranasal cocaine (2 mg/kg, n = 8) or lidocaine (2%, n = 4), an internal local anesthetic control, or intravenous phenylephrine (0.5-2.0 microg/kg, n = 4), an internal sympathomimetic control. Experiments were repeated while minimizing the cocaine-induced rise in blood pressure with intravenous nitroprusside to negate sinoaortic baroreceptor stimulation. After lidocaine, blood pressure and sympathetic nerve discharge were unchanged. After cocaine, blood pressure increased abruptly and remained elevated for 60 min while sympathetic nerve discharge initially was unchanged and then decreased progressively over 60 min to a nadir that was only 2+/-1% of baseline (P < 0.05); however, plasma venous norepinephrine concentrations (n = 5) were unchanged up to 60 min after cocaine. Sympathetic nerve discharge fell more rapidly but to the same nadir when blood pressure was increased similarly with phenylephrine. When the cocaine-induced increase in blood pressure was minimized (nitroprusside), sympathetic nerve discharge did not decrease but rather increased by 2.9 times over baseline (P < 0.05). Baroreflex gain was comparable before and after cocaine. We conclude that in conscious humans the primary effect of intranasal cocaine is to increase sympathetic nerve discharge to the skeletal muscle bed. Furthermore, sinoaortic baroreflexes play a pivotal role in modulating the cocaine-induced sympathetic excitation. The interplay between these excitatory and inhibitory neural influences determines the net effect of cocaine on sympathetic discharge targeted to the human skeletal muscle circulation.

Assessment of myocardial perfusion by harmonic power Doppler imaging at rest and during adenosine stress: comparison with (99m)Tc-sestamibi SPECT imaging.

BACKGROUND: Harmonic power Doppler imaging (HPDI) is a novel technique for assessing myocardial perfusion by contrast echocardiography in humans. The purpose of this study was to compare myocardial perfusion by HPDI with that obtained by (99m)Tc-sestamibi single photon emission computed tomography (SPECT) during rest and pharmacological stress. METHODS AND RESULTS: HPDI was performed on 123 patients who were referred for SPECT imaging for known or suspected coronary artery disease. Images were obtained at baseline and during adenosine infusion (0.14 mg. kg(-)(1). min(-)(1)x6 minutes) in 3 apical views. Myocardial perfusion by HPDI was graded for each coronary territory as absent, patchy, or full. The persistence of absent or patchy myocardial perfusion by HPDI between rest and adenosine was interpreted as a fixed defect, whereas any decrease in perfusion grade was interpreted as a reversible defect. Overall concordance between HPDI and SPECT was 83 (81%) of 103 for normal versus abnormal perfusion. Agreement between the 2 methods for each of the 3 coronary territories was 81% (kappa=0.57) for the left anterior descending artery, 76% (kappa=0.52) for the right coronary artery, and 72% (kappa=0.40) for the left circumflex artery. Discrepancies between the 2 techniques were most notable in the circumflex territory, where fixed defects were observed in 33% by HPDI but in only 14% by SPECT (chi(2)=15.8, P=0.0001). CONCLUSIONS: This study demonstrates that HPDI can reliably detect myocardial perfusion during pharmacological stress, although there was a significantly higher number of falsely abnormal results in the circumflex territory.

Echocardiographic destruction of albumin microbubbles directs gene delivery to the myocardium.

BACKGROUND: The noninvasive, tissue-specific delivery of therapeutic agents to the heart would be a valuable clinical tool. This study addressed the hypothesis that albumin-coated microbubbles could be used to effectively deliver an adenoviral transgene to rat myocardium by ultrasound-mediated microbubble destruction. METHODS AND RESULTS: Recombinant adenovirus containing beta-galactosidase and driven by a constitutive promoter was attached to the surface of albumin-coated, perfluoropropane-filled microbubbles. These bubbles were infused into the jugular vein of rats with or without simultaneous echocardiography. Additional controls included ultrasound of microbubbles that did not contain virus, virus alone, and virus plus ultrasound. One group underwent ultrasound-mediated destruction of microbubbles followed by adenovirus infusion. Rats were killed after 4 days and examined for beta-galactosidase expression. The hearts of all rats that underwent ultrasound-mediated destruction of microbubbles containing virus showed nuclear staining with 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside substrate, indicating expression of the transgene. None of the control animals showed myocardial expression of the beta-galactosidase transgene. By quantitative analysis, beta-galactosidase activity was 10-fold higher in the treated group than in controls (P<0.0001). CONCLUSIONS: Ultrasound-mediated destruction of albumin-coated microbubbles is a promising method for the delivery of bioactive agents to the heart.

Accuracy of dobutamine echocardiography for detection of myocardial viability in patients with an occluded left anterior descending coronary artery.

OBJECTIVES: We studied the accuracy of dobutamine echocardiography for the detection of myocardial viability in patients with an occluded left anterior descending coronary artery and regional ventricular dysfunction. BACKGROUND: Contractile reserve during dobutamine echocardiography is an accurate marker of myocardial viability in patients with coronary stenoses and ventricular dysfunction. However, its accuracy in patients with an occluded vessel has not been evaluated. METHODS: We studied 41 patients with > 50% stenosis of the left anterior descending coronary artery and regional ventricular dysfunction who underwent dobutamine echocardiography for detection of viable myocardium. Contractile reserve was defined as improvement in wall motion score of two or more contiguous septal or anterior segments during doubutamine echocardiography. Recovery of function was defined as improvement in rest wall motion score of two or more contiguous segments after revascularization. RESULTS: Patients were classified into two groups according to the presence (n = 20) or absence (n = 21) of left anterior descending coronary artery occlusion. Contractile reserve was detected in 40% of patients with an occluded and 43% with a nonoccluded artery (p = 0.8). Of 41 patients, 27 underwent revascularization, 12 with and 15 without an occluded vessel. Recovery of function occurred in 6 (50%) of 12 patients in the occluded artery group and in 5 (33%) of 15 in the nonoccluded artery group (p = 0.4). Among patients with an occluded artery, the positive and negative predictive values of dobutamine echocardiography for recovery of function were 100% (95% confidence interval [CI] 48% to 100%) and 86% (95% CI 42% to 100%), respectively. CONCLUSIONS: Our results indicate that contractile reserve during dobutamine echocardiography can be detected in patients with an occluded vessel and may be useful for predicting recovery of function after revascularization.

Prognosis after valve replacement in patients with severe aortic stenosis and a low transvalvular pressure gradient.

OBJECTIVES: This study was conducted to determine the risks and benefits of valve replacement in patients with severe aortic stenosis and a low transvalvular pressure gradient. BACKGROUND: There is uncertainty regarding the appropriate management of adults with severe aortic stenosis and a transvalvular pressure gradient < or = 30 mm Hg. With only six such patients reported, one study suggested that these subjects have a prohibitive operative risk and little symptomatic improvement if they survive surgical treatment, whereas another showed that they can survive an operation and improve symptomatically. METHODS: In an attempt to clarify the risks and benefits of valve replacement in these patients, we reviewed the records of 18 patients (15 men and 3 women, aged 49 to 81 years) with severe aortic stenosis (valve area < or = 0.4 cm2/m2 body surface area), a mean transvalvular pressure gradient < or = 30 mm Hg and limiting symptoms (New York Heart Association functional class III or IV) who underwent valve replacement. RESULTS: Six patients (33%) (95% confidence interval 13% to 59%) died perioperatively, whereas 10 patients (56%) (95% confidence interval 31% to 78%) improved symptomatically to functional class I (n = 8) or II (n = 2) (p = NS in comparison with the 6 who died). No clinical or hemodynamic variable was predictive of survival or improvement in functional class. CONCLUSIONS: Valve replacement in patients with severe aortic stenosis and a transvalvular pressure gradient < or = 30 mm Hg is accompanied by a considerable operative risk. Although there were no significant differences in this small series between the fraction of patients who died and those who exhibited improvement, we still recommend the procedure because many patients survive the operation and most of the survivors show an improved symptomatic status.

Observer variability in the quantitation of Doppler color flow jet areas for mitral and aortic regurgitation.

Early studies using Doppler color flow imaging have suggested that measurement of the regurgitant jet area provides information regarding the severity of valvular insufficiency. This study was performed to assess the observer variability of mitral and aortic regurgitant jet area measurements using the Doppler color technique. Color Doppler recordings from 45 patients were reviewed: 23 patients had aortic regurgitation and 22 had mitral regurgitation. To assess interobserver variability, the largest definable mitral regurgitant jets from three cardiac cycles were independently chosen and measured by planimetry by two observers who were unaware of other patient information. Measurements were repeated by both observers at a separate time to obtain intraobserver data. Videotapes from 23 patients with aortic regurgitation were similarly analyzed. Each observer measured the isovolumic aortic jet (before mitral valve opening) and the maximal aortic regurgitant jet (at any time during diastole) using computer-assisted planimetry. Both intraobserver and interobserver correlations were excellent for mitral regurgitant jet areas (r = 0.97 and r = 0.93, respectively). The intraobserver correlation for isovolumic aortic regurgitant jet was r = 0.73; the interobserver correlation for this measurement was only fair (r = 0.57). For the maximal aortic regurgitant jet area, intraobserver correlation was good (r = 0.86) and interobserver correlation was fair (r = 0.72). These findings suggest that intraobserver and interobserver reproducibility are acceptable for the measurement of mitral regurgitant jet area.(ABSTRACT TRUNCATED AT 250 WORDS)

Endothelium-dependent vasorelaxation is impaired in cocaine arteriopathy.

OBJECTIVES: This study sought to assess endothelium-dependent vasorelaxation in long-term users of cocaine. BACKGROUND: Cocaine use has been associated with myocardial infarction, stroke and intestinal infarction. Previously demonstrated effects of the drug, including increased heart rate and blood pressure and increased vascular tone, do not explain the sporadic nature of these vascular events or the occurrence of ischemia remote from acute administration. Abnormal endothelial function could contribute to focal vasospasm and thrombosis and predispose to premature atherosclerosis, all of which have been demonstrated in cocaine users with myocardial infarction. METHODS: Using plethysmography, we studied the change in forearm blood flow in response to intraarterial acetylcholine and nitroprusside in 10 long-term cocaine users and 13 control subjects of similar age who had not used cocaine; sample size was based on a 70% power to detect a 20% reduction in flow with acetylcholine between subjects and control subjects. Using graded doses of intracoronary acetylcholine (from 10(-9) to 10(-6) mol/liter), we studied a second group of 10 cocaine users with angiographically normal or near-normal arteries. RESULTS: Mean forearm blood flow during acetylcholine infusion was significantly lower in cocaine users than in control subjects (p = 0.02). During nitroprusside infusion, there was no difference (p = 0.2) between cocaine users and control subjects. Cigarette smoking did not explain the differences between cocaine users and control subjects. Acetylcholine elicited coronary vasoconstriction in 8 of 10 subjects. CONCLUSIONS: We conclude that endothelium-dependent vasorelaxation is impaired in long-term users of cocaine.

Time course of improvement in left ventricular function, mass and geometry in patients with congestive heart failure treated with beta-adrenergic blockade.

OBJECTIVES: We examined the time course of ventricular functional improvement in patients with dilated cardiomyopathy who received beta-blockade and the long-term effects of beta-blockade on ventricular mass and geometry in these patients. BACKGROUND: Previous studies have shown that beta-adrenergic blocking agents when administered long term improve ventricular function in patients with heart failure. However, the time course of improvement in ventricular function and the long-term effects of beta-blockade on ventricular mass and geometry are not known. METHODS: Twenty-six men with dilated cardiomyopathy underwent serial echocardiography on days 0 and 1 and months 1 and 3 of either metoprolol (n = 16) or standard therapy (n = 10). At 3 months all patients on standard therapy were crossed over to metoprolol, and late echocardiograms were obtained after 18 +/- 5 (mean +/- SD) months of metoprolol therapy. All echocardiograms were read in blinded manner. RESULTS: Patients treated with metoprolol had an initial decline (day 1 vs. day 0) in ventricular function (increase in end-systolic volume and decrease in ejection fraction). Ventricular function improved between months 1 and 3 (p = 0.013, metoprolol vs. standard therapy). Left ventricular mass regressed at 18 months (333 +/- 85 to 275 +/- 53 g, p = 0.011) but not at 3 months. Left ventricular shape became less spherical and assumed a more normal elliptical shape by 18 months (major/minor axis ratio 1.5 +/- 0.2 to 1.7 +/- 0.2, p = 0.0001). CONCLUSIONS: Patients with heart failure treated with metoprolol do not demonstrate an improvement in systolic performance until after 1 month of therapy and may have a mild reduction in function initially. Long-term therapy with metoprolol results in a reversal of maladaptive remodeling with reduction in left ventricular volumes, regression of left ventricular mass and improved ventricular geometry by 18 months.

Use of exercise Doppler echocardiography to evaluate cardiac drugs: effects of propranolol and verapamil on aortic blood flow velocity and acceleration.

This study evaluated the ability of exercise Doppler echocardiography to identify hemodynamic changes due to cardiac medication. Twenty young healthy volunteers (mean age 30 years) underwent continuous wave Doppler examination from the suprasternal notch at rest, during each stage of a standard exercise protocol and immediately after exercise. On completion of the control test, each subject received either 60 to 80 mg of propranolol or 120 mg of verapamil orally, and the same exercise protocol was repeated after 90 min. During the control test, values for modal velocity, acceleration and flow velocity integral all increased significantly from baseline (p less than 0.0002 for each). When exercise was repeated after propranolol administration, values for all Doppler measurements were significantly altered. Modal velocity at baseline was significantly lower after propranolol when compared with control (0.53 +/- 0.11 versus 0.63 +/- 0.17 m/s; p less than 0.0001). Similarly, modal velocity at maximal exercise was significantly lower after propranolol (1.11 +/- 0.2 versus 1.25 +/- 0.21 m/s; p less than 0.0001). The effect of propranolol on acceleration was even greater, with blunting of baseline (11.4 +/- 2 versus 15.4 +/- 5 m/s per s; p less than 0.0005) and exertional (33.4 +/- 10 versus 56.3 +/- 15 m/s per s; p less than 0.0001) acceleration. The flow velocity integral during exercise was greater after propranolol (14.1 +/- 3.1 versus 10.1 +/- 3.2 cm; p less than 0.0005) than during the control test. Verapamil failed to influence any Doppler-measured index of aortic blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Quantitative assessment of the hemodynamic consequences of aortic regurgitation by means of continuous wave Doppler recordings.

The purpose of this study was to evaluate the ability of continuous wave Doppler ultrasound recordings to reflect the magnitude and hemodynamic effects of aortic regurgitation. Forty-five patients with angiographically proved aortic regurgitation had Doppler studies performed within 24 hours of cardiac catheterization. High quality spectral recordings of the regurgitant jet were obtained in 31 patients, whereas 14 patients exhibited dropout of high velocity signals precluding measurement of maximal velocities. The slope of the peak to end-diastolic velocity decrease measured by Doppler examination was compared with the decay in the aortic to left ventricular diastolic pressure gradient by catheterization and was found to correlate well (r = 0.86). The Doppler velocity decay slope was generally higher in patients with angiographically severe rather than mild or moderate aortic regurgitation, but considerable overlap was present among groups. However, a diastolic velocity decay slope of greater than 3 m/s2 was seen only in those patients with advanced (3 or 4+) aortic regurgitation. Left ventricular end-diastolic pressure was estimated from the Doppler recordings by subtracting the end-diastolic pressure gradient obtained by the modified Bernoulli equation from the cuff diastolic blood pressure. A correlation was observed (r = 0.84) between Doppler and catheterization left ventricular end-diastolic pressure in the 31 patients with high quality spectral data, although the SEE was substantial (5.5 mm Hg). These data demonstrate that continuous wave Doppler recordings of the regurgitant jet can be useful in assessing the angiographic severity and hemodynamics of aortic regurgitation.

Peripheral intravenous myocardial contrast echocardiography using a 2% dodecafluoropentane emulsion: identification of myocardial risk area and infarct size in the canine model of ischemia.

OBJECTIVES: This study assessed the accuracy of 2% dodecafluoropentane (EchoGen), an intravenous echocardiographic contrast agent, in identifying myocardial area at risk and infarct size in the canine model of myocardial ischemia. BACKGROUND: Myocardial contrast echocardiography allows determination of myocardial area at risk and infarct size but requires intracoronary injection in humans. The development of agents that can be delivered by peripheral intravenous injection could enable bedside myocardial contrast echocardiographic assessment of risk area, infarct size and reperfusion. METHODS: Two protocols were used. Protocol 1 assessed the accuracy of myocardial contrast echocardiography using intravenous dodecafluoropentane in defining myocardial area at risk and infarct size in the canine model of regional myocardial ischemia versus gross pathologic specimens stained with monastral blue to determine area at risk and triphenyltetrazolium chloride to determine the area of necrosis. Protocol 2 assessed the effects of repeated injections of dodecafluoropentane (0.5 ml/kg body weight, four doses 30 min apart or eight doses 10 min apart) on myocardial blood flow and hemodynamic variables. RESULTS: Myocardial contrast echocardiography accurately defined area at risk and infarct size (r = 0.96 vs. triphenyltetrazolium chloride). Myocardial blood flow remained stable after multiple serial injections of dodecafluoropentane. However, a significant increase in pulmonary artery pressure and pulmonary vascular resistance, along with a decrease in arterial oxygen saturation and cardiac output, was seen in dogs that received eight injections at 10-min intervals. CONCLUSIONS: Myocardial contrast echocardiography using intravenous dodecafluoropentane accurately defined myocardial area at risk and infarct size. Hemodynamic variables and regional myocardial blood flows remained stable when dodecafluoropentane was injected at 30-min intervals for up to four doses; more frequent administration led to cardiopulmonary deterioration. Dodecafluoropentane offers the potential for reliable, noninvasive assessment of reperfusion after therapeutic interventions.

Quantitation of aortic regurgitation by computer analysis of digital subtraction angiography.

Digital subtraction angiography provides the potential to determine aortic regurgitant fraction by computer analysis of time-intensity curves generated from regions of interest positioned over the aorta and left ventricle after aortography. To validate this ability, we studied six dogs instrumented with an electromagnetic flow probe on the ascending aorta. Aortic regurgitation of varying severity was produced by a basket catheter introduced through the right carotid artery. Aortograms were performed using continuous fluoroscopy at 30 frames/s and stored in digital format in a 256 x 256 pixel matrix. An image-processing computer was utilized to plot summated pixel intensity versus time for both the aortic and the left ventricular regions of interest. Regurgitant fraction was calculated from the time-intensity curves using an algorithm analogous to that employed by dye-dilution methods. Regurgitant fraction determined from digital angiography was compared with that obtained by electromagnetic flow and was found to correlate well (r = 0.94, SEE = 7.4%) over a wide range of values. Thus, these data indicate that aortic regurgitant fraction can be accurately determined from computer analysis of digitally acquired aortograms in an animal model of acute aortic regurgitation.

Administration of an intravenous perfluorocarbon contrast agent improves echocardiographic determination of left ventricular volumes and ejection fraction: comparison with cine magnetic resonance imaging.

OBJECTIVES: The purpose of this study was to determine whether contrast-enhanced transthoracic echocardiography improves the evaluation of left ventricular (LV) volumes and ejection fraction (EF). BACKGROUND: Echocardiographic assessment of LV volumes and EF is widely used but may be inaccurate when the endocardium is not completely visualized. Recently the intravenous (i.v.) administration of perfluorocarbon microbubbles has been shown to enhance opacification of the LV cavity, but the utility of these agents to improve the echocardiographic assessment of LV systolic function is unknown. METHODS: In 40 subjects (29 men and 11 women, aged 24 to 81 years) an assessment of LV volumes and EF was performed with a magnetic resonance imaging examination, followed immediately by a transthoracic echocardiogram before and after the intravenous administration of 2% dodecafluoropentane emulsion (EchoGen; Sonus Pharmaceuticals, Bothell, Washington). RESULTS: Contrast enhanced the echocardiographic assessment of LV end diastolic volume (p < 0.02), end systolic volume (p < 0.01) and LVEF (p < 0.03). The percentage of subjects in whom the correct echocardiographic classification EF was normal, mild to moderately depressed or severely reduced improved significantly after contrast enhancement (from 71% before contrast to 94% after, p < 0.03). These findings were most striking in the subjects with two or more adjacent endocardial segments not visualized at baseline. CONCLUSIONS: Administration of an intravenous contrast agent improves the ability to accurately assess LV volumes and EF in humans. Contrast enhancement is most useful in subjects with two or more adjacent endocardial segments not seen at baseline.

Myocardial viability during dobutamine echocardiography predicts survival in patients with coronary artery disease and severe left ventricular systolic dysfunction.

OBJECTIVES: The purpose of this study was to assess whether the presence or absence of myocardial viability during dobutamine echocardiography (DE) predicts survival in patients with coronary artery disease (CAD) and severe left ventricular (LV) dysfunction. BACKGROUND: In patients with CAD, the presence of myocardial viability during DE identifies viable myocardium and predicts recovery of LV systolic function after revascularization. However, there is little data on the relation between myocardial viability and clinical outcome in patients with CAD and severe LV dysfunction. METHODS: We studied 318 patients with CAD and a LV ejection fraction (EF) < or =35% who underwent DE and were followed for 18+/-10 months. Patients were classified into four groups. Group I (n=85) consisted of patients who had evidence of myocardial viability and subsequently underwent revascularization. Group II (n=119) consisted of patients with myocardial viability who did not undergo revascularization. Group III (n=30) consisted of patients who did not have myocardial viability and underwent revascularization. Finally, group IV (n=84) patients lacked myocardial viability and did not undergo revascularization. RESULTS: The four groups had similar baseline characteristics and rest LVEF. During follow-up there were 51 deaths (16%). The mortality rate was 6% in group I, 20% in group II, 17% in group III and 20% in group TV (p=0.01, group I vs. other groups). CONCLUSIONS: In patients with CAD and severe LV dysfunction who demonstrated myocardial viability during DE, revascularization improved survival compared with medical therapy.

Effects of afterload reduction on vena contracta width in mitral regurgitation.

OBJECTIVES: We used color Doppler flow mapping to determine whether vena contracta width (VCW) is a load-independent measure of the severity of mitral regurgitation. BACKGROUND: VCW has been proposed to be a relatively load-independent measure of mitral regurgitation severity in flow models using a fixed orifice. However, in patients with mitral regurgitation, VCW may not be load independent because of a dynamic regurgitant orifice. METHODS: VCW, effective regurgitant orifice area and regurgitant volume were measured by quantitative Doppler mapping in 31 patients with chronic mitral regurgitation at baseline and during nitroprusside infusion. Patients with rheumatic heart disease, annular calcification or endocarditis were considered to have a fixed regurgitant orifice, whereas patients with mitral valve prolapse, dilated cardiomyopathy or ischemia were considered to have a dynamic regurgitant orifice. RESULTS: Systolic blood pressure (148 +/- 27 to 115 +/- 25 mm Hg) and end-systolic wall stress (121 +/- 50 to 89 +/- 36) decreased with nitroprusside (p < 0.05). Although nitroprusside did not significantly change mean values for VCW (0.5 +/- 0.2 to 0.5 +/- 0.2 cm), regurgitant volume (69 +/- 47 to 69 +/- 56 ml) or effective regurgitant orifice area (0.5 +/- 0.4 to 0.5 +/- 0.6 cm2), individual patients exhibited marked directional variability. Specifically, VCW decreased in 16 patients (improved mitral regurgitation), remained unchanged in 7 patients and increased in 8 patients (worsened mitral regurgitation) with nitroprusside. Also, the VCW response to nitroprusside was concordant with changes in effective regurgitant orifice area and regurgitant volume, and was not different between dynamic and fixed orifice groups. CONCLUSIONS: Contrary to the results from in vitro studies, VCW is not load independent in patients with mitral regurgitation caused by dynamic changes in the regurgitant orifice. The origin of mitral regurgitation does not predict accurately whether the regurgitant orifice is fixed or dynamic. Finally, short-term vasodilation with nitroprusside may significantly worsen the severity of mitral regurgitation in some patients.