M. Dan McKirnan

Cardiovascular Effects of Insulin-Like Growth Factor-1 and Growth Hormone in Chronic Left Ventricular Failure in the Rat

BACKGROUND Insulin-like growth factor-1 (IGF-1) appears to have favorable cardiac effects associated with left ventricular remodeling early after myocardial infarction in the rat. The present study was designed to determine whether IGF-1 combined with growth hormone would be beneficial later as well, when infarct healing and cardiac remodeling have occurred. METHODS AND RESULTS Four weeks after coronary occlusion, 36 rats were randomized to IGF-1 (3 mg.kg-1.d-1) plus growth hormone (0.1 mg BID) or to placebo for 4 weeks. Treated rats had significant increases in body weight (22%), while the ratio of heart weight to body weight was unchanged. Under anesthesia, cardiac output (fluorescent microspheres) increased 46%, and systemic vascular resistance decreased by 21% (P < .001) in the treated group; a significant (22%) increase of the cardiac index was limited to treated rats with large myocardial infarctions. Small increases in the reduced left ventricular ejection fractions and left ventricular dP/dt(max) values with treatment were not significant. Treated rats showed a borderline (16%) increase in left ventricular end-diastolic volume (angiography), whereas the ratio of left ventricular end-diastolic volume to body weight was reduced in the treated group. CONCLUSIONS IGF-1 plus growth hormone administered to rats with left ventricular failure starting 1 month after MI was associated with substantial body growth, decreased systemic vascular resistance, and increased cardiac output. The failing heart also underwent treatment-induced increases in left and right ventricular weights in proportion to body growth, but left ventricular remodeling was minor, and a decrease in the ratio of left ventricular end-diastolic volume to body weight reflected relatively less chamber dilation compared with controls. A significant interaction between size of the myocardial infarction and treatment was observed for several variables, and IGF-1 and growth hormone increased the cardia index (P < .035) in rats with a large myocardial infarction.

A Randomized Trial of Exercise Training in Patients With Coronary Heart Disease

In order to determine whether or not regular exercise could alter myocardial perfusion or function, we randomized 146 male volunteers with stable coronary heart disease to either a supervised exercise program (n = 72) or to a usual care program (n = 74). Subjects underwent exercise tests initially and one year later. Significant differences between the two groups included improved aerobic capacity, thallium ischemia scores, and ventricular function in the exercise intervention group. It was not possible to classify the conditions of patients as to the likelihood of improvement or deterioration. This study demonstrated changes in myocardial perfusion and function in a select group of middle-aged men with coronary heart disease who underwent a medically appropriate exercise program lasting one year, but these changes were relatively modest.

Intracoronary Delivery of Adenovirus Encoding Adenylyl Cyclase VI Increases Left Ventricular Function and cAMP-Generating Capacity

BackgroundWe tested the hypothesis that the intracoronary injection of a recombinant adenovirus encoding adenylyl cyclase type VI (ACVI) would increase cardiac function in pigs. Methods and ResultsLeft ventricular (LV) dP/dt and cardiac output in response to isoproterenol and NKH477 stimulation were assessed in normal pigs before and 12 days after the intracoronary delivery of histamine followed by the intracoronary delivery of an adenovirus encoding lacZ (control) or ACVI (1.4×1012 vp). Animals that had received ACVI gene transfer showed increases in peak LV dP/dt (average increase of 1267±807 mm Hg/s;P =0.0002) and cardiac output (average increase of 39±20 mL · kg−1 · min−1;P <0.0001); control animals showed no changes. Increased LV dP/dt was evident 6 days after gene transfer and persisted for at least 57 days. Basal heart rate, blood pressure, and LV dP/dt were unchanged, despite changes in cardiac responsiveness to catecholamine stimulation. Twenty-three hour ECG recordings showed no change in mean heart rate or ectopic beats and no arrhythmias. LV homogenates from animals receiving ACVI gene transfer showed increased ACVI protein content (P =0.0007) and stimulated cAMP production (P =0.0006), confirming transgene expression and function; basal LV AC activity was unchanged. Increased cAMP-generating capacity persisted for at least 18 weeks (P <0.0002). ConclusionsIntracoronary injection of a recombinant adenovirus encoding AC provides enduring increases in cardiac function.

Myocardial High-Energy Phosphate and Substrate Metabolism in Swine With Moderate Left Ventricular Hypertrophy

BACKGROUND Although left ventricular hypertrophy (LVH) is frequently associated with impaired coronary vasodilator reserve, it is uncertain whether this leads to myocardial ischemia under physiological conditions. The goal of the present study was to determine whether swine with moderate LVH exhibit metabolic evidence of ischemia when myocardial oxygen requirements are increased. METHODS AND RESULTS Myocardial metabolism was evaluated in an open-chest anesthetized preparation at baseline and during dobutamine infusion in 13 adolescent pigs with moderate LVH induced by supravalvular aortic banding and 12 age-matched control pigs. Transmural myocardial blood flow was quantified with radioactive microspheres; the ratio of phosphocreatine to ATP (PCr/ATP) in the anterior LV free wall was measured by 31P-nuclear magnetic resonance; and anterior wall lactate release was quantified from the arterial-coronary venous difference in 14C- or 13C-labeled lactate. In a subset of 5 animals from each group, the metabolic fate of exogenous glucose was determined from the transmyocardial difference in 6-14C-glucose and its metabolites 14C-lactate and 14CO2. Coronary reserve, as assessed by the ratio of blood flow during adenosine infusion to baseline blood flow, was significantly lower in the LVH pigs compared with controls (3.5 +/- 0.4 versus 5.5 +/- 0.4 mL/g.min, P < .05); however, transmural myocardial blood flow was similar in both groups of pigs, both at baseline and with dobutamine stimulation, probably reflecting the higher coronary perfusion pressure in the LVH pigs. At baseline, PCr/ATP tended to be lower in the LVH pigs (P = .09) but decreased similarly with dobutamine infusion in both groups. Isotopically measured anterior wall lactate release did not differ between the groups at baseline, nor did the increase in lactate release differ during dobutamine stimulation. The uptake of glucose, lactate, and free fatty acids did not differ between the groups in the basal state. However, during dobutamine stimulation, glucose uptake was greater in the LVH group (0.84 +/- 0.09 mumol/g.min versus 0.59 +/- 0.08 mumol/g.min, P < .05). In a subset of animals, 14C-glucose was used to assess glucose oxidation. These data showed that the LVH animals had a greater rate of glucose oxidation (0.6 +/- 0.10 versus 0.28 +/- 0.08 mumol/g.min, P < .05) and a greater rate of glucose conversion to lactate (0.20 +/- 0.04 versus 0.09 +/- 0.02 mumol/g.min, P < .05) compared with the control pigs. CONCLUSIONS These results suggest that despite their reduced coronary vasodilator reserve and the absence of a greater rise in myocardial blood flow to compensate for a substantially higher LV double product, pigs with this model of moderate LVH do not exhibit a greater susceptibility to myocardial ischemia during dobutamine stress. However, LVH pigs exhibit significantly greater use of exogenous glucose during dobutamine stress, as evidenced by increases in both glucose oxidation and anaerobic glycolysis.

Angiogenic gene therapy for heart disease: a review of animal studies and clinical trials

The current published clinical literature on angiogenic gene therapy for the treatment of myocardial ischemia does not include a single randomized, placebo-controlled trial. Based on current clinical literature, it is an unproven therapy. Successful animal studies combined with published reports of good outcomes in patients enrolled in uncontrolled trials has led to the expectation that angiogenic gene therapy will ultimately become a clinical reality. The next important landmark in the field will be the publication of data showing a favorable effect of angiogenic gene transfer in placebo-controlled, blinded clinical trials.

Myocardial gene transfer and long-term expression following intracoronary delivery of adeno-associated virus.

Adeno‐associated viral vectors (AAV) can direct long‐term gene expression in post‐mitotic cells. Previous studies have established that long‐term cardiac gene transfer results from intramuscular injection into the heart. Cardiac gene transfer after direct intracoronary delivery of AAV in vivo, however, has been minimal in degree, and indirect intracoronary delivery, an approach used in an increasing number of studies, appears to be receiving more attention. To determine the utility of indirect intracoronary gene transfer of AAV, we used aortic and pulmonary artery cross clamping followed by proximal aortic injection of AAV encoding enhanced green fluorescent protein (AAV.EGFP) at 1011 DNase resistant particles (drp; high‐performance liquid chromatography (HPLC)‐purified) per rat. Gene expression was quantified by fluorescent microscopy at four time points up to 1 year after vector delivery, revealing 20–32% transmural gene expression in the left ventricle at each time point. Histological analysis revealed little or no inflammatory response and levels of transgene expression were low in liver and undetectable in lung. In subsequent studies in pigs, direct intracoronary delivery into the left circumflex coronary artery of AAV.EGFP (2.64–5.28 × 1013 drp; HPLC‐purified) resulted in gene expression in 3 of 4 pigs 8 weeks following injection with no inflammatory response in the heart. PCR analysis confirmed AAV vector presence in the left circumflex perfusion bed. These data indicate that intracoronary delivery of AAV vector is associated with transgene expression in the heart, providing a means to obtain long‐term expression of therapeutic genes. Copyright

Effects of dobutamine and arbutamine on regional myocardial function in a porcine model of myocardial ischemia.

OBJECTIVES The present study was performed to determine the mechanisms for catecholamine-induced wall motion abnormalities and to compare the diagnostic efficacy of two catecholamines: arbutamine and dobutamine. BACKGROUND Catecholamine stress echocardiography is used to induce regional wall motion abnormalities for the detection of coronary artery disease, but the mechanism by which these abnormalities occur is unknown. METHODS Ten pigs were instrumented with left circumflex coronary artery ameroid constrictors, sonomicrometers to measure transmural wall thickening in the left circumflex (ischemic) and left anterior descending (control) coronary artery beds and a pressure gauge to measure left ventricular pressure and its first derivative (dP/dt). Myocardial blood flow was measured by microspheres. RESULTS At 38 +/- 6 days (mean +/- SEM) after surgery, percent wall thickening was normal at rest in both beds but abnormal in the left circumflex coronary artery bed during atrial pacing. These findings were associated with reduced myocardial blood flow in the ischemic bed during atrial pacing. Dobutamine infusion increased percent wall thickening, with no differences between the two beds (p = 0.63). In contrast, arbutamine infusion increased percent wall thickening only in the nonischemic bed, with no effect on percent wall thickening in the ischemic bed (p = 0.03). Although the endocardial/epicardial blood flow ratio tended to be reduced in the left circumflex artery bed during catecholamine infusion (p = 0.07), both agents were similar in this effect. Despite differences in function between the beds, there was no difference in transmural myocardial blood flow between the two beds during catecholamine infusion. When examined at matched metabolic demands, arbutamine elicited greater differences in percent wall thickening than dobutamine between the two beds (p < 0.01). CONCLUSIONS Arbutamine was able to provoke regional differences in function in a manner superior to dobutamine. This occurred independently of altered transmural myocardial blood flow or differences in hemodynamic effects between the agents. Differences in their inotropic properties may be important in explaining their different effects on ischemic myocardium.

Regional Deficits of Myocardial Blood Flow and Function in Left Ventricular Pacing–Induced Heart Failure

BACKGROUND Pacing-induced congestive hear, failure has become a preferred model for the study of the pathogenesis of dilated cardiomyopathy. However, little is known regarding regional myocardial blood flow and function during the development of heart failure in this model. METHODS AND RESULTS To determine whether regional differences in myocardial blood flow are associated with regional dysfunction in ventricular pacing-induced heart failure, regional myocardial blood flow (radioactive microspheres) and regional wall thickening (transthoracic echocardiography) were measured in pigs studied at weekly intervals during the progression of heart failure induced by rapid pacing from the lateral wall of the left ventricle (220 +/- 9 bpm for 26 +/- 4 days). Echocardiography and hemodynamic measurements with the pacemaker off showed progressive, severe global left ventricular dysfunction. During pacing over the 3- to 4-week period, a progressive decrease in systolic wall thickening in the lateral wall occurred compared with the interventricular septum (IVS; P = .001); at 21 to 28 days, the difference was 50% (lateral wall, 14 +/- 6%; IVS, 28 +/- 6%; P = .0001). A difference in subendocardial blood flow per beat between the left ventricular lateral wall (the site of stimulation) and the IVS was found immediately on the initiation of pacing (IVS, 0.009 +/- 0.002 mL.min-1.g-1.beat-1; lateral wall, 0.005 +/- 0.001 mL.min-1.g-1.beat-1; P = .001), a difference that was sustained during pacing throughout the study. Subendocardial blood flow per beat was normal in both regions with the pacemaker off throughout the study. CONCLUSIONS These data indicate that regional myocardial ischemia is associated with the development of contractile dysfunction of the paced wall during prolonged rapid left ventricular pacing and that regional stunning contributes to persistent global left ventricular dysfunction when pacing is discontinued.

Errors in predicting functional capacity for postmyocardial infarction patients using a modified Bruce protocol

Clinically, the modified Bruce protocol is widely used to predict functional capacity in postmyocardial infarction (post-MI) patients. However, it has been suggested that post-MI patients have lower oxygen uptakes for standard workloads. In order to study this, we measured oxygen uptake (VO2) and venous blood lactic acid concentration in 12 post-MI patients and 12 normal male subjects during a modified Bruce treadmill protocol. During the first four stages of the protocol, mean oxygen uptake was significantly lower (1.0 to 6.2 cc X kg-1 X min-1; p less than 0.001) for the post-MI patients than for the normal male subjects. Venous blood lactic acid concentrations were different only at stage 4. However, a higher respiratory exchange ratio was observed for post-MI patients (p less than 0.001 at stage 3), suggesting an increased anaerobic metabolism and adequate buffering of lactic acid. The post-MI patients measured VO2 for three stages of the protocol ranged from 1.8 to 7.3 cc X kg-1 X min-1 lower than the Bruce prediction for cardiac patients. In addition, maximal measured VO2 for the post-MI patients ranged from 3.7 to 11.2 cc X kg-1 X min-1 lower than predicted VO2 derived from the normal subjects. These data suggest myocardial damage may slow oxygen uptake kinetics, thus increasing the oxygen deficit at standard workloads during progressive exercise. An increased respiratory exchange ratio secondary to the buffering of lactic acid suggests that anaerobic metabolism may compensate for this oxygen deficit.

Improvement in ventricular function during exercise studied with radionuclide ventriculography after cardiac rehabilitation

A heterogeneous group of 19 consecutive patients with coronary artery disease were studied with radionuclide ventriculography before and after a mean of 6 months of exercise training. Ejection fraction was measured at rest, at matched submaximal supine work loads and during maximal supine bicycle exercise. After training there was no change in mean ejection fraction at rest or during maximal exercise, but a higher maximal mean systolic blood pressure, heart rate and work load were achieved. At equivalent submaximal work loads after training, similar levels of mean heart rate and systolic blood pressure were reached but a statistically greater mean ejection fraction was obtained. These preliminary results suggest that exercise training may improve cardiac function during exercise in selected patients with coronary disease. A randomized study using similar techniques has been initiated.