The metabolic demand and oxygen supply of the heart: physiologic and clinical considerations

Revolutionizing biomedical research: The imperative need for heart-kidney-connected organoids

Organoids significantly advanced our comprehension of organ development, function, and disease modeling. This Perspective underscores the potential of heart-kidney-connected organoids in understanding the intricate relationship between these vital organs, notably the cardiorenal syndrome, where dysfunction in one organ can negatively impact the other. Conventional models fall short in replicating this complexity, necessitating an integrated approach. By co-culturing heart and kidney organoids, combined with microfluidic and 3D bioprinting technologies, a more accurate representation of in vivo conditions can be achieved. Such interconnected systems could revolutionize our grasp of multi-organ diseases, drive drug discovery by evaluating therapeutic agents on both organs simultaneously, and reduce the need for animal models. In essence, heart-kidney-connected organoids present a promising avenue to delve deeper into the pathophysiology underlying cardiorenal disorders, bridging existing knowledge gaps, and advancing biomedical research.

Echocardiographic assessment of primary microvascular angina and primary coronary microvascular dysfunction

There is an increasing interest in the role of echocardiography in the evaluation of primary microvascular angina, which is attributed to primary coronary microvascular dysfunction. Valid echocardiographic techniques are expected to facilitate the diagnosis and follow-up of these patients and would be valuable for research purposes and therapy evaluation. However, adequate echocardiographic data are lacking, and the interpretation of the limited available literature is hindered by the previous addition of microvascular angina under more inclusive entities, such as cardiac syndrome X. In experienced hands, the assessment of primary coronary microvascular dysfunction in patients with suspected primary microvascular angina, using multiple echocardiographic techniques is feasible, relatively inexpensive, and safe. Exclusion of obstructive epicardial coronary artery disease is, however, a prerequisite for diagnosis. Two-dimensional transthoracic echocardiography, routine stress echocardiography, and speckle-tracking echocardiography indirectly assess primary coronary microvascular dysfunction by evaluating potential impairment in myocardial function and lack diagnostic sensitivity and specificity. Conversely, certain echocardiographic techniques, including Doppler-derived coronary flow velocity reserve and myocardial contrast echocardiography, assess some coronary microvascular dysfunction parameters and have exhibited diagnostic and prognostic potentials. Doppler-derived coronary flow velocity reserve is the best studied and only guideline-approved echocardiographic technique for documenting coronary microvascular dysfunction in patients with suspected microvascular angina. Myocardial contrast echocardiography, by comparison, can detect heterogeneous and patchy myocardial involvement by coronary microvascular dysfunction, which is an advantage over the common practice of coronary flow velocity reserve assessment in a single vessel (commonly the left anterior descending artery) which only reflects regional microvascular function. However, there is no consensus regarding the diagnostic criteria, and expertise performing this technique is limited. Echocardiography remains underexplored and inadequately utilized in the setting of microvascular angina and coronary microvascular dysfunction. Appraisal of the current echocardiographic literature regarding coronary microvascular dysfunction and microvascular angina is important to stay current with the progress in its clinical recognition and create a basis for future research and technological advancements.

Low Prevalence of Cardiomyopathy in Patients with Mitochondrial Disease and Neurological Manifestations

Patients with mitochondrial diseases can develop cardiomyopathy but with variable expressivity and penetrance. Our prospective study enrolled and evaluated a cohort of 53 patients diagnosed with chronic progressive ophthalmoplegia (CPEO, n = 34), Kearns-Sayre syndrome (KSS, n = 3), neuropathy ataxia and retinitis pigmentosa (NARP, n = 1), myoclonic epilepsy with ragged red fibers (MERRF, n = 1), Harel-Yoon Syndrome (HYS, n = 1) and 13 patients with undefined mitochondrial diseases, presenting primarily with neurological symptoms. Over a 4-year period, six patients in our study cohort were diagnosed with heart disease (11.3%), with only three patients having defined cardiomyopathy (5.7%). Cardiomyopathy was present in a 21-year-old patient with HYS and two CPEO patients having mild cardiomyopathy at an older age. Two CPEO patients had congenital heart disease, and a third CPEO had LV hypertrophy secondary to hypertension. In three patients, traditional risk factors for heart disease, including dyslipidemia, hypertension, and respiratory disease, were present. The majority of our adult cohort of patients have normal cardiac investigations with a median left ventricular (LV) ejection fraction of 59.0%, indexed LV mass of 67.0 g/m², and normal diastolic and valvular function at baseline. A 12-lead electrocardiogram showed normal cardiac conduction across the study cohort. Importantly, follow-up assessments showed consistent cardiac structure and function. Our study shows a low prevalence of cardiomyopathy and highlights the breadth of phenotypic variability in patients with mitochondrial disorders. The presence of cardiovascular risk factors and aging are important comorbidities in our cohort.

Intra-Aortic Balloon Pump for Patients with Cardiac Conditions: An Update on Available Techniques and Clinical Applications

In this paper, we present a review of the intra-aortic balloon pump, as well as the usage of it in the medical field today. An intra-aortic balloon pump (IABP) is a biomedical device that can assist the heart during unstable angina or after a heart attack. This pump is typically used in patients who suffer from ischemia of the heart tissue, due to an unbalanced level of myocardial oxygen supply or demand. Through counterpulsation, which is a technique to synchronize the external pumping of blood with the heart’s cycle, the device can balance the supply and demand of blood that is necessary for the heart to pump properly. The IABP is comprised of the following four components: a polyurethane balloon, a polyethylene or fiber-optic catheter, a transducer, and the intra-aortic balloon pump console. In the past, researchers have used other materials that have low biocompatibility and can cause complications within the body. This analysis will explain the complications and state changes that occurred due to them. Limitations of past designs and advantages of current designs will be acknowledged, for they can be used by researchers to enhance designs for the future. Consequently, the analysis of this device may lead to improved designs and treatment in the future for patients with cardiac conditions.

Radial Pulse Spectrum Analysis as Risk Markers to Improve the Risk Stratification of Silent Myocardial Ischemia in Type 2 Diabetic Patients

Diabetic patients with silent myocardial ischemia (SMI) have elevated rates of morbidity and mortality and need intensive care and monitoring. An early predictor of SMI may lead to early diagnosis and medical treatment to prevent progression and adverse clinical events. Therefore, this paper was aimed to evaluate the radial pulse spectrum as risk markers to improve the risk stratification of SMI in type-2 diabetic patients; 195 diabetic patients at high-risk of SMI were enrolled. All patients underwent myocardial perfusion imaging and radial pressure wave measurement. The spectrum analysis of the radial pressure wave was calculated and transformed into Fourier series coefficients Cns and Pns. The risk of SMI (odds ratio: 4.46, 95%, C.I. 1.61–12.4, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P<0.01$ \end{document}) was raised in diabetic patients classified high-risk group by C2. Multivariable regression analysis showed that C2 (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P<0.05$ \end{document}) and ankle–brachial index [(ABI) \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P<0.05$ \end{document})] were related to SMI (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$R=0.46$ \end{document} and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P<0.05$ \end{document}). The myocardial ischemic score (MIS), combining C2, C3, and P5, the albumin-to-creatinine ratio (ACR), and ABI, presented an excellent risk stratification performance in enrolled patients (odds ratio: 5.78, 95%, C.I. 2.29–14.6, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$P<0.01$ \end{document}). The area under receiver operating characteristic curves for C2, C3, P5, ABI, ACR, and MIS were 0.66, 0.60, 0.68, 0.51, 0.56, and 0.74, respectively, in identifying SMI. This paper demonstrated that C2 was independently associated with the extent of SMI in multivariable regression analysis. Odds ratio and chi-square tests reflected that C2 could be an important marker for the risk stratification of SMI. Furthermore, MIS, adding radial pulse spectrum analysis to ACR and ABI, could significantly improve the risk stratification of SMI in type-2 diabetic patients compared to any single risk factor.

Inhibitors of soluble epoxide hydrolase minimize ischemia-reperfusion-induced cardiac damage in normal, hypertensive, and diabetic rats

AIM

We designed a study to evaluate the cardioprotective effect of two soluble epoxide hydrolase (sEH) inhibitors, 1-(1-propanoylpiperidin-4-yl)-3-(4-trifluoromethoxy)phenyl)urea (TPPU) and trans-4-{4-[3-(4-trifluoromethoxyphenyl)-ureido]cyclohexyloxy}benzoic acid (t-TUCB), in ischemia-reperfusion (IR) model.

METHODS

Cardioprotective effects of the sEH inhibitors were evaluated against IR-induced myocardial damage in hearts from normal, hypertensive, and diabetic rats using Langendorff's apparatus. In addition, the effect of sEH inhibitors on endothelial function was evaluated in vitro and ex vivo using isolated rat thoracic aorta.

RESULTS

Ischemia-reperfusion (IR) increased the myocardial damage in hearts from normal rats. IR-induced myocardial damage was augmented in hearts isolated from hypertensive and diabetic rats. Myocardial damage as evident from increase in the activities of lactate dehydrogenase (LDH) and creatine kinase-MB (CK-MB) in heart perfusate was associated with significant decrease in the heart rate and developed tension, and increase in the resting tension in isolated heart. Both sEH inhibitors protected the heart in normal, hypertensive, and diabetic rats subjected to IR injury. The sEH inhibitor t-TUCB relaxed phenylephrine precontracted aorta from normal rats. Relaxant effect of acetylcholine (ACh) was reduced in aortas from diabetic and hypertensive rats compared to normal rats. Pretreatment of sEH inhibitors to diabetic and hypertensive rats increased relaxant effect of ACh on aortas isolated from these rats.

CONCLUSIONS

Prophylactic treatment with sEH inhibitors decreased myocardial damage due to IR, hypertension and diabetes, and decreased endothelial dysfunction created by diabetes and hypertension. Therefore, inhibitors of sEH are useful probes to study cardiovascular pathology, and inhibition of the sEH is a potential approach in the management of IR-induced cardiac damage and endothelial dysfunction-related cardiovascular disorders.

Metabolic Modulation of Cardiac Metabolism in Heart Failure

Heart failure (HF) is associated with metabolic changes that cause a progressive impairment of cardiac and skeletal muscle high-energy phosphate production. As a consequence of the impaired cardiac metabolism, other processes are activated in the failing heart that further exacerbate the progression of HF. The reduced production of high-energy phosphates has important implications for both systole and diastole in HF with both preserved and reduced left ventricular function. The aim of this review is to summarise the state-of-the-art on metabolic therapy in HF with a particular focus on trimetazidine. Metabolic agents optimise cardiac substrate metabolism without exerting negative haemodynamic effects. In particular, as studies with metabolic agents modulating cardiac metabolism have consistently demonstrated, this approach is effective in improving symptoms, functional capacity and prognosis in people with HF when added to optimal medical therapy. Therefore, the modulation of cardiac metabolism is an important therapeutic approach to the treatment of HF, especially in patients where it is of ischaemic or metabolic origin. Although further studies are needed, metabolic agents might be a new, effective strategy for the treatment of HF.

Effects of dichloroacetate in patients with congestive heart failure

BACKGROUND

Conventional approaches to management of congestive heart failure (CHF) rely on drugs that increase myocardial contractility or reduce ventricular afterload. These approaches often improve cardiac symptoms and survival, but may be associated with significant deleterious effects. An alternative approach is to enhance myocardial energy production. Dichloroacetate (DCA) stimulates pyruvate dehydrogenase activity and accelerates aerobic glucose, pyruvate, and lactate metabolism in myocardial cells. These alterations would be expected to improve myocardial function.

HYPOTHESIS

The purpose of the investigation was to assess the efficacy of DCA in patients with left ventricular systolic dysfunction and to examine the mechanism by which improvement occurs.

METHODS

A total of 25 patients (16 men, 9 women; age range 31-72 years, mean 59) with CHF and ejection fraction < or = 40% received an intravenous infusion of 50 mg/kg DCA over 15 min. Indices of systolic and diastolic function were obtained by two-dimensional and Doppler echocardiography performed at baseline, 30 min, and 60 min following completion of DCA infusion.

RESULTS

Baseline ventricular ejection fraction was 27.3 +/- 9.1%; 17 patients (68%) had nonischemic cardiomyopathy. Heart rate increased after DCA infusion from 73.9 +/- 14.5 to 79.2 +/- 14.9 beats/min at 60 min; p = 0.02. Left ventricular diastolic and systolic volumes increased at 30 min compared with baseline (248.7 +/- 98.1 vs. 259.6 +/- 99.6; p = 0.04, and 180.1 +/- 80.4 vs. 192.2 +/- 84.9; p = 0.002, respectively), but stroke volume (49.2 +/- 19.1 vs. 48.9 +/- 18.1; p = 0.9) and ejection fraction (27.3 +/- 9.1 vs. 25.7 +/- 9.8; p = 0.2) were unchanged. Indices of diastolic function were also unchanged.

CONCLUSION

Dichloroacetate infusion in patients with CHF is not associated with improvement in noninvasively assessed left ventricular function.

Coronary risk factors and myocardial perfusion in asymptomatic adults: the Multi-Ethnic Study of Atherosclerosis (MESA)

OBJECTIVES

The purpose of this study was to determine the cross-sectional relation between myocardial perfusion and coronary heart disease (CHD) risk factors among adults with no clinical CHD.

BACKGROUND

Clinical studies suggest that myocardial perfusion is often abnormal in individuals without CHD but with risk factors. Epidemiologic study in asymptomatic populations is lacking.

METHODS

Two hundred twenty-two men and women, ages 45 to 84 years and free of a CHD diagnosis, in the University of Minnesota field center of the Multi-Ethnic Study of Atherosclerosis (MESA) had myocardial blood flow (MBF) determined using cardiac magnetic resonance imaging at rest and during adenosine-induced hyperemia. Perfusion reserve (PR) was calculated as the ratio of hyperemic to rest MBF.

RESULTS

Both resting and hyperemic MBF were lower in men than in women, even after considering age and menopause. Hyperemic MBF was also significantly lower in subjects who were older, and in those with higher blood pressure, higher fasting glucose, and lower low-density lipoprotein cholesterol. After adjusting for age, gender, and race, reduced PR was independently associated with hypertension, higher diastolic blood pressure, and higher total and low-density lipoprotein cholesterol, but was not associated with cigarette smoking, obesity, physical activity, or diabetes. Moreover, hyperemic MBF and PR were correlated strongly and inversely with estimated 10-year CHD risk based on Framingham equations (p for trends: <0.0001).

CONCLUSIONS

Coronary vasoreactivity is reduced in asymptomatic individuals with a greater coronary risk factor burden. Our study results imply that changes in coronary vascular reactivity, in response to risk factors, may be detected in adults without symptomatic CHD.

Bosentan, the mixed ETA–ETB endothelin receptor antagonist, attenuated oxidative stress after experimental myocardial ischemia and reperfusion

Endothelin-1 has been shown to be associated with greater myocardial ischemia and reperfusion injury in which oxidative stress plays a key role. The efficacy of bosentan, a mixed ETA-ETB endothelin receptor antagonist, in protecting the myocardium from ischemia-reperfusion injury and oxidative stress was studied in open-chest Wistar rats. Anesthetized adult male rats (175-250 g b wt) underwent sham operation (SHAM group) or were subjected to 40 min of myocardial ischemia (MI) induced by temporary occlusion of the left anterior descending coronary artery (LAD) followed by 2 h reperfusion (R). Rats submitted to the MI-R protocol were administered bosentan at a dose of 3 mg/kg i.v. 20 min (BOS group) or saline (CON group) 20 min post-occlusion of LAD. After the 2 h reperfusion period the animals were euthanized and the heart rapidly excised. Cardiac tissue samples were snap frozen in liquid nitrogen for biochemical assay and were fixed in 10% formalin solution for histologic evaluation. Myocardial I-R resulted in a significant increase (p < 0.05) in the myocardial malondialdehyde levels and a decrease (p < 0.01) in the myocardial reduced glutathione content. These changes were associated with significant decreases in the myocardial activity of antioxidant enzymes superoxide dismutase (p < 0.05) and catalase (p < 0.01) and severe tissue damage in the jeopardized myocardium in the CON group as compared with the non-myocardial ischemia-reperfusion (NMI-R) SHAM group. Bosentan exerted marked tissue protective effect as assessed by histologic evaluation of the myocardium. The drug significantly (p < 0.05) attenuated myocardial oxidative stress and restored the cellular antioxidant defense mechanisms as compared with the saline-treated controls subjected to the MI-R protocol. Furthermore, bosentan also exerted a marked effect on peripheral hemodynamics and heart rate during the reperfusion phase (data reported elsewhere). These results are consistent with the concept that endothelin-1 may be involved in the pathogenesis of myocardial ischemia and infarction. This study demonstrates the antioxidant effect of non-selective endothelin receptor antagonism elucidating that, part of the aetiology of ischemia and reperfusion induced myocardial injury involves impaired antioxidant defenses.

Rate‐Dependent AV Delay Optimization in Cardiac Resynchronization Therapy

BACKGROUND

During cardiac resynchronization therapy (CRT), cardiac performance is dependent on an optimized atrioventricular delay (AVD). However, the optimal AVD at different heart rates has not been defined yet during CRT.

METHOD

The effects of an increase in heart rate by pacing or physical exercise on optimal AVD were studied in 36 patients with biventricular pacemakers/defibrillators. The velocity time integral (VTI) in the left ventricular outflow tract (LVOT) was measured with pulsed Doppler either at three different paced heart rates in the supine position or in seated position before and after physical exercise.

RESULTS

The baseline AVD was optimized to 99 +/- 19 ms in the supine and 84 +/- 22 ms in the seated position. When the heart rate was increased by DDD pacing, there was a positive linear relationship between an increase in heart rate, in AVD and in VTI (LVOT-VTI + 0.047 cm/s per 10 beats per minute (bpm) heart rate increase per 20 ms increase in AVD, P = 0.007). A similar but more pronounced relationship was found after physical exercise in the seated position (LVOT-VTI + 0.146 cm/s per 10 bpm heart rate increase per 20 ms increase of AVD, P = 0.013). This effect was observed in patients with and without AV block and mitral regurgitation.

CONCLUSIONS

In conclusion, the systolic performance of the dilated ventricle, which depends on an elevated preload, is critically affected by the appropriate timing of the AVD during exercise. In contrast to normal pacemaker patients, in CRT the relatively short baseline AVD should be prolonged at increased heart rates. Further studies with other means of measuring exercise cardiac performance are needed to confirm these unexpected findings.

Can the premises of the spasm of resistance vessel concept permit improvement in the treatment and prevention of ischemic heart disease?

In this communication, the spasm of resistance vessel (S-RV) concept of ischemic heart disease (IHD) and other ischemic will be reviewed and updated, and evidence will be presented that principles of the hypothesis might improve the treatment and prevention of IHD. The S-RV concept provides a different basic pathogenetic framework for IHD, and suggestions for treatment and prevention stem from its different basic conceptualization of this disorder. The concept asserts that S-RV directly induces symptoms in IHD, and this position challenges the accepted pathogenetic mechanism for this disorder, i.e., that symptoms in IHD are due directly to obstructive occlusions of epicardial arteries secondary to coronary artery disease. The S-RV concept avers that ischemia-induced S-RV is a major factor in IHD, and evidence supporting this position is provided. Another major position of the hypothesis is that no-reflow (reduced flow after infarction and severe myocardial ischemia in the absence of infarction) is due to ischemic injury-induced S-RV, and a variety of evidences to support this position are offered.Proposed improvement in the treatment of IHD is based mainly on treating ischemia-induced S-RV. alpha-Adrenergic sympathetic blockade reverses ischemia-induced S-RV, and alpha-adrenergic blockade is suggested as therapy for acute coronary syndromes and to prevent complications of percutaneous coronary interventions. Also, angiotensin-converting enzyme inhibition, which has actions similar to alpha-adrenergic blockade, is also suggested. Proposals for the prevention of IHD are based the prevention of S-RV, and special emphasis is given to preventing exercise- and stress-related IHD.

Intermediate coronary artery stenosis: evidence-based decisions in interventions to avoid the oculostenotic reflex

The prevalence of intermediate coronary artery stenosis (defined as a diameter stenosis of 40% to 70%) is quite large in patients undergoing PTCA. The coronary angiogram is considered the 'gold standard' for the definition of coronary anatomy, in spite of various limitations associated with its use. In recent years, sensor tipped guidewire based methods of physiologic assessment of stenosis severity, like myocardial fractional flow reserve, and poststenotic coronary flow reserve had established their role in the decision making in catheterization laboratory. The decision making should combine morphologic and physiologic assessment as better evidence based approach in guiding therapy to avoid the 'oculostenotic reflex'.

Occlusions of epicardial arteries might not directly induce symptoms in ischemic heart disease

It is accepted that primary occlusions of epicardial arteries by thromboses, stenotic coronary artery disease (CAD), and spasm directly induce symptoms in ischemic heart disease (IHD). Because of this acceptance, there has been little interest in alternate mechanisms for IHD--as the spasm of resistance vessel (S-RV) concept of IHD, which asserts that S-RV directly induces symptoms in IHD. To stimulate interest in the S-RV concept, evidence against the primacy of occlusions of epicardial arteries was presented, as well as evidence for this position to provide a balanced discussion; while the evidence was mixed, overall findings appeared to weigh significantly against the primacy of occlusions of epicardial arteries. Also, the S-RV concept was discussed; the discussion included presenting the theory's explanations for events in epicardial arteries, with the aim of demonstrating that the concept provides more consistent explanations than the standard position. It is suggested that there is sufficient information to warrant renewed consideration of the S-RV concept.

Mechanisms of coronary flow reserve impairment in human hypertension. An integrated approach by transthoracic and transesophageal echocardiography

The purpose of this study was to investigate the different mechanisms responsible for an impairment of coronary vasodilator capacity in hypertensive subjects by an integrated echocardiographic approach, including transesophageal Doppler echocardiography, which allows noninvasive monitoring of coronary flow velocity in the left anterior descending artery during pharmacological vasodilation. The study population consisted of 17 healthy control subjects and 33 hypertensive subjects: 10 without hypertrophy, 16 with mild to moderate hypertrophy, and 7 with severe left ventricular hypertrophy. Mean systolic and diastolic flow velocities were monitored basally (together with indexes of myocardial oxygen demand, such as heart rate, myocardial inotropism, and left ventricular wall stress) and during infusion of low-dose (0.56 mg/kg per 4 minutes) and high-dose (0.84 mg/kg per 9 minutes) dipyridamole. Coronary reserve was assessed as the ratio of mean diastolic velocity after high-dose dipyridamole and basal diastolic velocity, and minimum coronary resistance as the ratio of diastolic blood pressure and diastolic velocity after high-dose dipyridamole. Compared with the control group, in all hypertensive groups, coronary reserve was similarly decreased (3.54 +/- 0.84 versus 2.59 +/- 0.42, 2.29 +/- 0.46, and 2.43 +/- 0.71; P < .01) and minimum resistance increased (0.56 +/- 0.15 versus 0.75 +/- 0.31, 0.75 +/- 0.19, and 0.78 +/- 0.21 mm Hg.s-1.cm-1; P = NS). These results confirm that coronary reserve in hypertensive individuals is reduced even before the occurrence of left ventricular hypertrophy. The reduction in coronary reserve depends on both an increase in resting coronary flow and an impairment in maximal vasodilator capacity. An increase in resting flow is dependent on higher heart rate and wall stress in hypertensive subjects without ventricular hypertrophy and on increased myocardial mass in hypertensive subjects with hypertrophy. Hypertensive subjects with ventricular hypertrophy also demonstrated a significantly blunted response to low-dose dipyridamole.

Regional fibre stress-fibre strain area as an estimate of regional blood flow and oxygen demand in the canine heart

1. In the present study the relation between regional left ventricular contractile work, regional myocardial blood flow and oxygen uptake was assessed during asynchronous electrical activation. 2. In analogy to the use of the pressure-volume area for the estimation of global oxygen demand, the fibre stress-fibre strain area, as assessed regionally, was used to estimate regional oxygen demand. The more often used relation between the pressure-sarcomere length area and regional oxygen demand was also assessed. 3. Experiments were performed in six anaesthetized dogs with open chests. Regional differences in mechanical work were generated by asynchronous electrical activation of the myocardial wall. The ventricles were paced from the right atrium, the left ventricular free wall, the left ventricular apex or the right ventricular outflow tract. Regional fibre strain was measured at the epicardial anterior left ventricular free wall with a two-dimensional video technique. 4. Regional fibre stress was estimated from left ventricular pressure, the ratio of left ventricular cavity volume to wall volume, and regional deformation. Total mechanical power (TMP) was calculated from the fibre stress-fibre strain area (SSA) and the duration of the cardiac cycle (tcycle) using the equation: TMP = SSA/tcycle. Regional myocardial blood flow was measured with radioactive microspheres. Regional oxygen uptake was estimated from regional myocardial blood flow values and arteriovenous differences in oxygen content. 5. During asynchronous electrical activation, total mechanical power, pressure-sarcomere length area, myocardial blood flow and oxygen uptake were significantly lower in early than in late activated regions (P < 0.05). 6. Within the experiments, the correlation between the pressure-sarcomere length area and regional oxygen uptake was not significantly lower than the one between total mechanical power (TMP) and regional oxygen uptake (VO2,reg). However, variability of this relation between the experiments was less for total mechanical power. Pooling all experimental data revealed: VO2,reg = k1 TMP+k2, with k1 = 4.94 +/- 0.31 mol J-1 k2 = 24.2 +/- 1.9 mmol m-3 s-1 (means +/- standard error of the estimate). 7. This relation is in quantitative agreement with previously reported relations between the pressure-volume area and global oxygen demand. The results indicate that asynchronous electrical activation causes a redistribution of mechanical work and oxygen demand and that regional total mechanical power is a better and more general estimate of regional oxygen demand than the regional pressure-sarcomere length area.

Improved hemodynamic function and mechanical efficiency in congestive heart failure with sodium dichloroacetate

OBJECTIVES

The purpose of this study was to determine whether sodium dichloroacetate improves hemodynamic performance and mechanical efficiency in congestive heart failure.

BACKGROUND

Congestive heart failure is associated with impaired hemodynamic performance and reduced mechanical efficiency. Dichloroacetate stimulates pyruvate dehydrogenase activity by inhibition of pyruvate dehydrogenase kinase, which results in inhibition of free fatty acid metabolism and stimulation of high respiratory quotient glucose and lactate consumption by the heart. Facilitation of glucose and lactate consumption with dichloroacetate should improve mechanical efficiency of the failing ventricle.

METHODS

Ten patients with New York Heart Association functional class III to IV congestive heart failure were studied. Dichloroacetate (50 mg/kg body weight) was administered intravenously for 30 min, with measurements of hemodynamic variables, coronary sinus blood flow and blood gas, glucose and lactate levels for 2 h. The same patients were also given dobutamine (5 to 12.5 micrograms/kg per min) for comparison.

RESULTS

Therapeutic levels of dichloroacetate were achieved (100 to 160 micrograms/liter of plasma). Myocardial consumption of lactate was stimulated from 29% to 37.4%. Forward stroke volumes increased (+5.3 ml/beat, p < 0.02), as did left ventricular stroke work (+1.8 g-m/m2 per beat, p < 0.02) and left ventricular minute work (from 1.38 to 1.55 kg-m/m2 per min, p < 0.01). Myocardial oxygen consumption decreased (from 19.3 to 16.5 ml/min, p = 0.06) as left ventricular minute work increased. Left ventricular mechanical efficiency thus improved from 15.2% to 20.6% (p = 0.03). Dobutamine administration resulted in the opposite trend with respect to myocardial lactate extraction (from 34% to 15.3%, p < 0.02). Stroke volume increased (+7.4 ml/beat, p = NS vs. dichloroacetate), as did left ventricular minute work (from 1.29 to 1.59 g-m/m2 per min, p < 0.01 vs. dichloroacetate) and myocardial oxygen consumption (from 18.6 to 21.0 ml/min, p = 0.06 vs. dichloroacetate). Left ventricular mechanical efficiency did not change with dobutamine administration (from 16.4% to 15.8%, p = NS).

CONCLUSIONS

Dichloroacetate administration stimulates myocardial lactate consumption and improves left ventricular mechanical efficiency. Forward stroke volume and left ventricular minute work increase significantly, with a simultaneous reduction in myocardial oxygen consumption. Dobutamine administration results in similar hemodynamic improvements but with no change in left ventricular mechanical efficiency and with opposite effects on lactate metabolism. The opposing metabolic actions, yet similar hemodynamic responses, of dichloroacetate and dobutamine suggest that these agents may be complementary in the treatment of congestive heart failure.

Myocardial oxygenation in dogs during partial and complete coronary artery occlusion

Regional myocardial oxygenation was assessed during partial and complete coronary artery occlusion using near infrared spectroscopy. In eight open-chest dogs, partial occlusions resulting in an approximately 42% decrease in left anterior descending coronary artery (LAD) blood flow produced an approximately 21% decrease in tissue O2 stores (tissue oxyhemoglobin plus oxymyoglobin) and no change in the oxidation level of mitochondrial cytochrome aa3. An approximately 81% reduction in LAD blood flow produced nadir levels of tissue oxyhemoglobin plus oxymyoglobin, maximal levels of deoxyhemoglobin plus deoxymyoglobin, a decline in tissue blood volume, and an approximately 39% decrease in cytochrome aa3 oxidation level. These changes were associated with an approximately 52% decrease from the preischemic baseline in mean transmural myocardial blood flow, measured by radiolabeled microspheres, and an approximately 41% decrease in myocardial O2 consumption. Complete occlusion resulted in further decreases in myocardial blood flow, O2 consumption, tissue blood volume, and cytochrome aa3 oxidation state but also produced increases in tissue O2 stores to above the nadir levels noted during partial occlusion. These results indicate that decreases in O2 delivery during partial coronary occlusion increase O2 extraction to sustain mitochondrial O2 availability, but as little as a 52% reduction in myocardial blood flow produces maximal O2 extraction and depletion of tissue O2 stores. Mitochondrial O2 availability is restricted further during complete occlusion because of limited O2 delivery and, possibly, decreases in tissue blood volume and O2 extraction.

Tedisamil (KC 8857) is a new specific bradycardic drug: does it also influence myocardial contractility? Analysis by the conductance (volume) technique in coronary artery disease

To determine whether inotropism influences the bradycardic action of tedisamil, hemodynamic assessment was performed in 13 patients with ischemic coronary artery disease including analysis of end-systolic pressure-volume relationships after an infusion of tedisamil, 0.3 mg/kg, at rest, and during paced tachycardia stress. Slope Emax fell by 14% at rest (13 patients) and by 10% during tachycardia (6/13 patients), whereas loops of end-systolic pressure-volume relationships moved rightward; all parameter changes indicated a lack of significant inotropism loss with tedisamil (p > 0.05). Although the mean heart rate decreased from 77.5 to 64.7 beats/min and QTc duration increased by 14% (p < 0.05), filling pressure and dp/dtmin remained unchanged and vascular resistance increased by 30%. Parameters of left ventricular pump function (ejection fraction, stroke volume, left ventricular efficiency) decreased slightly (between 3% and 13%), whereas left ventricular volumes increased (end-diastolic volume by 6%, end-systolic volume by 23%). The respective parameter changes during tachycardia were comparable in tendency, and angina could no longer be induced during postdrug pacing stress. We concluded that the bradycardic effects of tedisamil are selectively generated without impairing either ventricular pump function or contractility in a clinically relevant fashion, whereas the postdrug anginal threshold appears elevated. Thus tedisamil can be used safely in ischemic coronary artery disease.

A haemodynamic comparison of intrathecal morphine and sufentanil supplemented with general anaesthesia for abdominal aortic surgery

The haemodynamic changes associated with intrathecal morphine (IM) compared to intrathecal sufentanil (IS) as a supplement to general anaesthesia for elective bypass grafting in patients with aortoiliac occlusive disease were studied. Thirty-six, ASA Grade 2, patients randomly received morphine hydrochloride (0.1%) 50 micrograms kg-1 (n = 18) or undiluted sufentanil, 150 micrograms (n = 18) intrathecally at T12-L1, combined with light general anaesthesia. Haemodynamics were measured before and after endotracheal intubation, abdominal incision, aortic cross-clamping and the first revascularisation. The major differences were recorded after abdominal incision. Heart rate, systemic blood pressure and coronary perfusion pressure were significantly lower in the IS group. The probable cause was greater systemic absorption of sufentanil and its faster binding to the specific opiate receptors, resulting in a more efficacious supraspinal and spinal blockade during the first surgical period. However, both opioids provided adequate analgesia during the whole surgical procedure.

Myocardial oxygen supply under critical conditions, the effects of hemodilution and fluorocarbons

This article reviews the factors influencing myocardial oxygen supply and demand. The regulative mechanisms in coronary blood flow, especially in critical conditions, are explained. Myocardial oxygenation in coronary artery disease is discussed with special reference to pharmacological intervention. An extensive evaluation of the effects of hemodilution on both the healthy and diseased heart is presented. Effects of hemodilution with fluorocarbons for the treatment or prevention of myocardial ischemia are shown with the aid of intramyocardial oxygen partial pressure measurements.

A physiological approach to drug therapy in dilated cardiomyopathy. Echo-Doppler evaluation of cardiac mechanics, myocardial energetics, and ventriculo-vascular coupling

Cardiac ultrasound imaging can be used in conjunction with calibrated external pulse recordings to provide detailed information regarding cardiovascular hemodynamics. This review establishes a physiological framework for the echo-Doppler assessment of cardiac mechanics, left ventricular energetics, and ventriculo-systemic vascular coupling in patients with dilated cardiomyopathy. The section on cardiac mechanics concerns the evaluation of overall cardiac performance and its individual determinants. Particular emphasis is placed upon the use of noninvasive methodology to identify the relative contributions of altered loading conditions and intrinsic myocardial contractility to cardiac performance. The noninvasive evaluation of left ventricular energetics is based on the physiological premise that myocardial oxygen consumption is a function of three major determinants, i.e., heart rate, contractility, and the integral of left ventricular systolic load (or wall stress). Following a brief discussion of the vascular properties that determine the relationship between pressure and flow in the systemic circulation, noninvasive methods for determination of systemic vascular resistance and arterial compliance are described. At the end of each section, practical clinical applications of these techniques to the evaluation and management of patients with dilated cardiomyopathy are presented.

Computer simulation of the mechanically-assisted failing canine circulation

A model of the cardiovascular system is presented. The model includes representations of the left and right ventricles, a nonlinear multielement model of the aorta and its main branches, and lumped models of the systemic veins and the pulmonary circulation. A simulation of the intra-aortic balloon pump and representations of physiological compensatory mechanisms are also incorporated in the model. Parameters of the left ventricular model were set to simulate either the normal or failing canine circulation. Pressure and flow waveforms throughout the circulation as well as ventricular pressure and volume were calculated for the normal, failing, and assisted failing circulation. Cardiac oxygen supply and consumption were calculated from the model. They were used as direct indices of cardiac energy supply and utilization to assess the effects of cardiac assistance.

Myocardial energetics and efficiency in patients with idiopathic cardiomyopathy: response to dobutamine and amrinone

Nine consecutive patients having severe idiopathic dilated cardiomyopathy were studied for their response in ventricular function, coronary sinus blood flow and myocardial oxygen consumption, lactate extraction and efficiency following incremental doses of dobutamine, followed by the combination of dobutamine and the phosphodiesterase inhibitor amrinone. Results, presented as baseline and the response to the peak dose (15 micrograms/kg/min) of dobutamine and to the combination of dobutamine and amrinone (each at 15 micrograms/kg/min) (differences compared with baseline) were: wedge pressure decreased from 28 +/- 7 to 26 +/- 8 mm Hg (p = NS) and to 20 +/- 6 mm Hg (p less than 0.01); cardiac index rose from 1.47 +/- 0.44 L/min/m2 to 2.89 +/- 1.1 L/min/m2 (p less than 0.01) and to 3.64 +/- 1.05 L/min/m2 (p less than 0.001); myocardial oxygen consumption remained invariant (18 +/- 8, 17 +/- 5, and 19 +/- 5 ml/min) despite progressive increments in minute work from 2.96 +/- 1.1 to 6.98 +/- 3.9 kg - m/min (p less than 0.01) and to 9.38 +/- 4.3 kg - m/min (p less than 0.001); myocardial lactate extraction rose from 21 +/- 10% to 30 +/- 15% (p = NS) and to 35 +/- 10% with the addition of amrinone (p less than 0.01). No patient had net lactate efflux into the coronary sinus, and myocardial efficiency improved from 9.5 +/- 5% to 21.7 +/- 13.0% (p less than 0.01) and to 28.0 +/- 18.0% (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Computer simulation of the hemodynamic determinants of myocardial oxygen supply and demand

A computer program was developed that uses a mathematical model of the cardiovascular system to predict myocardial oxygen supply and demand as well as cardiac hemodynamics. This model combines the time-varying elastance model of the left ventricle, the modified Windkessel model of the arterial system, and the left ventricular pressure-volume area prediction of myocardial oxygen demand. The computer simulation permits independent control of variables, thus providing the opportunity to design "experiments" and to observe the results. The model predicts that tachycardia leads to reduced myocardial oxygen supply and increased demand. Hypertension caused by increased systemic vascular resistance increases supply more than it increases demand. On the other hand, increased contractility or left ventricular end-diastolic pressure increases demand more than supply, and may cause ischemia in the presence of coronary artery stenosis. The model is an aid in understanding how hemodynamic variables affect the balance between myocardial oxygen supply and demand. It can be used for education and to analyze study protocols prior to animal experimentation.

Effects of long-term xamoterol therapy on the left ventricular mechanical efficiency in patients with ischemic heart disease

Myocardial oxygen uptake and an index of mechanical left ventricular efficiency were determined in basal conditions or during prolonged therapy with the new beta 1-adrenoceptor partial agonist xamoterol in 16 patients with mild to moderate ischemic heart failure. During xamoterol therapy, left ventricular end-diastolic pressure decreased from 24.4 +/- 6.5 to 17.8 +/- 8.6 mm Hg (P less than 0.01) and the isovolumic index of inotropic state (dP/dt)/DP40 increased by 14% (P less than 0.01). The heart rate increased slightly and the mean systolic and peak systolic wall stress also tended to increase (+ 7%; NS) but myocardial oxygen uptake (14.1 vs 14.7 ml/min; NS) and the index of efficiency (8.77 +/- 3.44 to 8.82 +/- 4.27; NS) were not significantly modified. In conclusion, prolonged therapy with xamoterol was not accompanied by a deterioration in the mechanical efficiency of the ventricle, even in patients with ischemic heart disease.

Dobutamine: ten years later

Dobutamine is a commonly used positive inotrope for the short-term management of heart failure. It is commercially available as a 50:50 mixture of two isomers with unique effects on alpha- and beta adrenergic receptors. In dosages of 2-15 micrograms/kg/minute, dobutamine has been shown to increase cardiac output (mainly through stroke volume), reduce systemic vascular resistance, lower central venous and pulmonary artery wedge pressures, improve renal blood flow, and relieve signs and symptoms of congestive heart failure. At higher dosages it can increase heart rate and induce arrhythmias. Recent evidence indicates that effects of dobutamine last long after the drug has been eliminated from the plasma, and some work has been done on ambulatory use of this agent. Dobutamine has been used successfully in several circumstances, such as after cardiac surgery, in patients with myocardial infarction, and in various shock states. An understanding of the pathophysiology of the underlying disorder is important in deciding which catecholamine to use. With this in mind, monotherapy or combination therapy with inodilators such as dobutamine, or inopressors like dopamine will follow logically.

Metabolic and hemodynamic consequences of sodium bicarbonate administration in patients with heart disease

PURPOSE

The use of sodium bicarbonate (NaHCO3) in cardiopulmonary arrest has been questioned, but the effects of NaHCO3 in patients with heart disease are not known. We therefore prospectively evaluated the effects of NaHCO3 in patients with congestive heart failure.

PATIENTS AND METHODS

Ten patients received NaHCO3 and control infusions of equimolar sodium chloride (NaCl). Measurements were made of blood gases, 2,3-diphosphoglyceric acid (2,3-DPG), glucose, lactate, cardiac hemodynamics, and oxygen consumption.

RESULTS

The arterial oxygen tension (pO2) fell an average of 10 mm Hg after NaHCO3 administration in patients with congestive heart failure, whereas it rose with NaCl (p less than 0.005). Myocardial oxygen consumption decreased by 17% (p less than 0.002) without an accompanying change in oxygen demand. Systemic oxygen consumption fell by 21%. Red blood cell 2,3-DPG levels were elevated at baseline, but did not change with NaHCO3 administration. The oxygen pressure at 50% hemoglobin saturation (P50) was correspondingly elevated at baseline in these patients and decreased significantly with NaHCO3 (Bohr effect) (p less than 0.003). The arterial and mixed venous carbon dioxide tensions increased with NaHCO3 but decreased with NaCl administration (p less than 0.05). Blood glucose concentrations fell by 1.7 mmol/L with NaHCO3 (p less than 0.003) and blood lactate concentrations increased uniformly (p less than 0.001). Three patients developed net myocardial lactate generation during NaHCO3 administration; two of these three developed symptoms of angina. Coronary blood flow did not change with NaHCO3 but increased with NaCl (p less than 0.04). Two patients developed transient pump failure.

CONCLUSION

These data demonstrate that NaHCO3 impairs arterial oxygenation and reduces systemic and myocardial oxygen consumption. The decrease in oxygen utilization is associated with anaerobic metabolism, enhanced glycolysis, and elevation of the blood lactate level, and may lead to transient myocardial ischemia in some patients. Thus, the use of NaHCO3 in such patients warrants re-evaluation.

Effect of phosphodiesterase inhibition on myocardial oxygen consumption and coronary blood flow

The phosphodiesterase inhibitors (amrinone, milrinone and enoximone) can cause major improvement in the performance of the failing heart without increasing myocardial oxygen consumption. This appears to be the result of a reduction in left ventricular systolic wall stress due to peripheral arteriolar vasodilatation, which offsets the increase in myocardial oxygen consumption that would otherwise result from an enhanced inotropic state. In comparison, catecholamine agents such as dobutamine, given at doses that achieve the same level of inotropic enhancement or improved left ventricular performance, produce less associated arteriolar vasodilatation and a significant (approximately 30%) increase in myocardial oxygen consumption. This difference between the phosphodiesterase inhibitors and the conventional catecholamine agents may be of clinical importance in patients with limited coronary flow reserve due to severe congestive heart failure.

Demonstration of an imbalance between coronary perfusion and excessive load as a mechanism of ischemia during stress in patients with aortic stenosis

Patients with aortic stenosis are susceptible to myocardial ischemia during hemodynamic stress, which may be caused by two mechanisms. First, vascular abnormalities inherent in myocardial hypertrophy may impair coronary vasodilation, limiting the ability to increase coronary blood flow to meet increased metabolic demands. Second, aortic stenosis itself may cause an imbalance between oxygen supply and demand during hemodynamic stress by decreasing aortic pressure (decreasing coronary perfusion or oxygen supply) and increasing left ventricular pressure (increasing oxygen demand). By decreasing aortic valve gradient without immediately altering ventricular hypertrophy, aortic balloon valvuloplasty offers the opportunity to distinguish these mechanisms. We hypothesized that aortic valvuloplasty would improve the balance between myocardial oxygen supply and demand, especially during isoproterenol infusion. Nine patients undergoing aortic balloon valvuloplasty were assessed at baseline and during isoproterenol infusion (5 +/- 2 micrograms/min, mean +/- SD) before and after valvuloplasty. Valvuloplasty increased myocardial oxygen supply. After valvuloplasty, isoproterenol decreased diastolic pressure time index (DPTI) less and increased coronary sinus blood flow more than before valvuloplasty (-630 +/- 367 vs. -292 +/- 224 mm Hg.sec/min, p = 0.02 and 53 +/- 137 vs. 179 +/- 145 ml/min, p = 0.001, respectively). Valvuloplasty also decreased oxygen demand, decreasing systolic pressure time index (SPTI) from 4,135 +/- 511 to 3,021 +/- 492 mm Hg.sec/min (p = 0.0002). Valvuloplasty improved the balance between myocardial oxygen supply and demand, increasing baseline DPTI:SPTI, decreasing aortocoronary sinus oxygen content difference (0.51 +/- 0.15 to 0.68 +/- 0.14, p = 0.005 and 96 +/- 14 to 78 +/- 15 ml O2/l, p = 0.002, respectively), and decreasing myocardial lactate production during isoproterenol infusion (mean lactate extraction fraction, -0.26 +/- 0.40 to 0.14 +/- 0.17; p = 0.01). We conclude that aortic valvuloplasty improves the balance between myocardial oxygen supply and demand during hemodynamic stress induced by isoproterenol infusion. We speculate that the clinical improvement, which often occurs in these patients after valvuloplasty despite persistence of hemodynamically "critical" aortic stenosis, is in part attributable to immediate improvement in the myocardial oxygen supply:demand ratio.

Combining transmural left ventricular mechanics and energetics to predict oxygen demand

This study relates to our earlier study which predicts the transmural distribution as well as the global left ventricular (LV) function and oxygen demand, based on the LV structure, geometry and sarcomere function. Here, we test the predicted global oxygen demand against experimental data in anesthetized, open chest dogs under changing working conditions. The experimental oxygen demand was calculated from the arterio-venous difference in oxygen content times the measured coronary flow. LV load was manipulated by a combination of a pressurized chamber connected to the femoral artery, phenylephrine infusion and an adjustable arteriovenous shunt. The heart was paced in two present heart rates. The study demonstrates that the global predictions, based on the local distributed oxygen demand model, are comparable to those obtained by other methods of global metabolic predictions. However, unlike other global methods, the distributed model gives spatial information and predicts an endo/epi ratio of oxygen demand ranging between 1.05 to 1.14, depending on the loading conditions, which is comparable to available experimental data. For the experimental conditions studied here (stroke volume, heart rate, aortic pressure), the theoretical analysis shows that only the end diastolic volume is significantly correlated to the endo/epi ratio of the transmural oxygen demand.

Clinical utility of exercise, pacing, and pharmacologic stress testing for the noninvasive determination of myocardial contractility and reserve

The ability of the left ventricle to modulate its performance is an important and integral component in the cardiovascular system's adaptive response to increased workload. Abnormalities in ventricular contractility can blunt this response and thus significantly limit the patient's functional capacity. The accurate determination and quantitation of cardiac contractility and reserve is a difficult task in the symmetrically contracting ventricle and more so when regional contraction abnormalities are present. Moreover, derangements in other physiologic variables, such as ventricular loading conditions, heart rate, systemic vascular tone, cardiac autonomic function, and pulmonary gas exchange, can diminish cardiopulmonary reserve. This report relates the determinants of myocardial oxygen demand and efficiency to the currently available forms of exercise, pacing, and pharmacologic stress testing. Within this framework, commonly used as well as newer approaches to the noninvasive assessment of stress-induced changes in left ventricular performance and contractility are addressed. In addition, several examples are presented in which noninvasive techniques for assessing intracardiac structures, pressures, and flows (eg, echo/Doppler, radionuclide angiography, rapid acquisition computed tomography, and magnetic resonance imaging) are combined with various cardiovascular stress tests to achieve more reliable measures of myocardial contractility and reserve.

Improved myocardial efficiency in the working perfused heart of the spontaneously hypertensive rat

We assessed the relationship between determinants of myocardial oxygen demand--wall stress, peak rate of change of pressure and heart rate--and measured myocardial oxygen consumption over a range of loading conditions in the perfused, working heart of 6-month-old spontaneously hypertensive rats (SHR) and control Wistar-Kyoto rats (WKY). Two isolated heart preparations, an aortic-ejecting heart and an isovolumically contracting preparation with and without isoproterenol (10(-7)M) added, were employed. Under a constant perfusion pressure of 110 mm Hg, the heart rate, developed wall stress, and peak rate of change of pressure were not different between the two groups, but coronary flow and myocardial oxygen consumption were significantly lower in the SHR. Systolic values of myocardial high energy phosphate compounds (adenosine 5'-triphosphate, phosphocreatine) and myocardial lactate in the two preparations were not significantly different between SHR and WKY. Following adenosine infusion at maximum developed pressure (isovolumic preparation), both SHR and WKY demonstrated preservation of coronary reserve. These results indicate that cardiac hypertrophy represents a compensatory adaptation with improved mechanical efficiency in the 6-month-old SHR when maximally stressed and may be related to the shift from V1 to V2 and V3 isomyosin phenotypes that was observed in the hypertensive animals.

Newer positive inotropic agents in the treatment of chronic cardiac failure. Current status and future directions

Heart failure is a serious worldwide health problem of major proportions. For many physicians, digitalis (an inotropic agent of limited proportions) and diuretics have proven the standard of treatment for heart failure. Vasodilators have also gained acceptance in recent years. Nevertheless, many patients remain symptomatic and therefore attention has been given to the development of pharmacological agents with mechanisms of action targeted to cardiac and vascular smooth muscle. The newer generation of inotropic agents have clearly been shown to improve the pumping function of the failing heart in patients who remain symptomatic despite digitalis, diuretics and vasodilators, while myocardial oxygen consumption is not enhanced. Several uncontrolled trials with the phosphodiesterase inhibitors enoximone, milrinone and piroximone have concluded that these agents improve exercise capacity and thereby hold promise to enhance quality of life. Large scale controlled trials currently in progress will determine the ultimate efficacy, as well as safety, of these agents. Results to date with several orally active beta-adrenoceptor agonists suggest that their efficacy may be limited by the induction of ventricular arrhythmias.

Relation between myocardial substrate utilization, oxygen consumption and regional oxygen balance in the dog heart in vivo

The interaction between myocardial function, oxygen consumption and energy production was examined in the left ventricular myocardium during various physiological conditions. Myocardial function was measured by both LV dP/dTmax and by local contractile tension. Coronary blood flow was measured from the coronary sinus; regional coronary blood supply was recorded using a thermistor placed on the epicardial surface. Intracellular oxygen balance was estimated using NADH fluorescence. Myocardial oxygen consumption and utilization of glucose, pyruvate, lactate and free fatty acids were calculated from their concentrations in the arterial and coronary sinus blood. The effects of tachycardia at 180 and 240 bpm, noradrenaline infusion (25 micrograms kg-1 min-1), and increased coronary blood flow caused by hypopneic respiration were examined. During pacing, contractile force, coronary flow and NADH fluorescence increased. At 240 bpm, the lactate/pyruvate ratio increased from 5.98 +/- 0.92 to 8.76 +/- 1.41 and NADH fluorescence increased from 50 to 71.7 +/- 3.73 (as compared to control), indicating impairment of myocardial oxygenation. Hypopneic respiration produced a marked elevation of coronary blood flow. Both noradrenaline infusion and hypopnea produced a decrease in both NADH fluorescence and the lactate/pyruvate ratio. No significant difference was found between the FORCE/ATP, FORCE/MVO2 and ATP/MVO2 ratios during pacing and noradrenaline. However, during hypopnea, the amount of ATP apparently formed (as calculated by substrate utilization assuming the formation of 3 ATP molecules per oxygen) was disproportionately greater than contractile force and oxygen consumption. It is suggested that this discrepancy may be due to the uncoupling of oxidative phosphorylation.

Spatial energy balance within a structural model of the left ventricle

A model describing the local instantaneous energetic needs within the left ventricle (LV) myocardium is presented. The model, which combines the myocardial oxygen consumption (MVO2) with the mechanical activity of the cardiac muscle, is based on the theory of cross bridge kinetics between the actin and myosin fibers within the sarcomere. The microscale relationship between the stress, stress development, strain rate and basal metabolism demand is incorporated into the LV model which describes the mechanical activities of different layers within the myocardium. The model shows a significant increase in the oxygen consumption in the endocardial layers as compared with the epicardial layers. Integrating the spatial and temporal oxygen consumption distribution within the myocardium yields the total myocardial oxygen consumption. The quantitative relationships between the heat rate, stress, contractility and external work and the MVO2 are in agreement with known data. The model thus offers a tool to assess the local instantaneous as well as the time averaged overall energy consumption, over a wide range of loading conditions of the LV.

Left ventricular mechanics related to the local distribution of oxygen demand throughout the wall

The complex interactions between left ventricular mechanics and the oxygen demand is studied by relating the left ventricular transmural oxygen demand to the myocardial structural and dynamic characteristics. The study utilizes a recent model of left ventricular contraction, which is based on a nested shell spheroidal geometry, a fan-like fibrous structure, the twisting motion of the left ventricle over its long axis, a transmural electrical activation propagation and the basic laws of sarcomere dynamics. The local "axial" stress (in the direction of the fibers) and the instantaneous sarcomere length are used to calculate the spatial distribution of the intramural oxygen demand per beat Vo2(y), where y is the distance from the endocardium. The normalized local sarcomere stress-length area SLAn(y) is related linearly to Vo2(y) by: Vo2(y) = K1 X SLAn(y) + K2, where K1 and K2 are constants. The calculations show a transmural metabolic gradient which is characterized by higher values of Vo2(y) in the endocardial layers than in the epicardial layers. Shorter endocardial sarcomeres and the twisting motion of the left ventricle around the long axis decrease the metabolic gradient across the wall, while a slow transmural electrical propagation wave as well as a wider angle of distribution of the fan-like fiber architecture increases the transmural metabolic gradient. Integration of the local oxygen demand across the left ventricular wall yields global values in agreement with those based on Suga's pressure-volume area approach. The model thus provides a qualitative and quantitative tool to assess the relation of the local and global oxygen demand to the complex left ventricular structure, fiber mechanics, and the dynamics of contraction.

The effects of milrinone (Win 47203) on the coronary blood flow and oxygen consumption of the dog heart-lung preparation

Milrinone is a new bipyridine-positive inotropic agent that is closely related to amrinone. In the nonfailing heart, coronary blood flow was increased and coronary bed resistance was decreased by milrinone, most probably by a direct action of milrinone on the coronary vasculature. Oxygen consumption was increased at the lower workloads. In the failing heart milrinone (0.1 to 0.5 mg/L of blood) increased cardiac output and coronary blood flow and reduced coronary vascular resistance. With the 0.1 mg dose oxygen consumption was reduced, especially at the high workloads, and was not significantly changed at the low work levels. With higher doses of milrinone oxygen consumption of the heart was not changed significantly while external work was increased. These data show that milrinone can increase the work of the heart with a decrease or no significant change in oxygen consumption of the isolated failing heart. The use of this drug in heart failure accompanied by restricted blood flow may thus be indicated.

Shock following generalized hypoxic-ischemic injury in previously healthy infants and children

Eighteen previously healthy patients with hypoxic-ischemic shock were observed longitudinally by means of data measured or derived from systemic arterial and pulmonary artery catheters. Shock was characterized by low cardiac index, elevated right and left heart filling pressures, elevated systemic and pulmonary vascular resistances, decreased oxygen consumption, and elevated oxygen extraction indices. Oxygen consumption was significantly correlated with oxygen delivery (r = 0.74, P less than 0.0001). This pattern fits that of cardiogenic shock. Cardiopulmonary data were not significantly different in survivors (n = 10) and nonsurvivors (n = 8). Outcome was determined by neurologic injury.

Study on myocardial contractility after cardiopulmonary bypass versus cardioplegic arrest in an air-ejecting in vivo heart model

Cardiac function was assessed in a working in vivo canine heart preparation. Minute work and myocardial oxygen consumption (MVo2) were measured after a two-hour period of hypothermic hyperkalemic crystalloid cardioplegic arrest in one group of dogs (Group 1, N = 6) and in another group of dogs on cardiopulmonary bypass (CPB) alone (Group 2, N = 6). Results indicate that at an afterload of 50 cm H2O, minute work was the same in all hearts but MVo2 was significantly higher in Group 1 hearts at all levels of preload. At higher afterloads, both minute work and MVo2 were significantly greater in Group 1 hearts over the range of preloads tested. Ventricular compliance was decreased in Group 1 over the range of preloads studied. These results suggest that hearts undergoing cardioplegic arrest had better left ventricular contractility than hearts undergoing CPB alone.

Effects of diltiazem during tachycardia-induced angina pectoris

To investigate the mechanism of relief of angina pectoris by diltiazem administration, 14 patients with effort angina were studied using a protocol to control heart rate. Coronary, systemic and left ventricular (LV) hemodynamic function was assessed at rest and during tachycardia stress (atrial pacing)-induced angina before and during diltiazem infusion. Angina occurred in all patients during tachycardia stress before diltiazem administration. During tachycardia stress at the heart rate that produced angina after diltiazem infusion, pressure-rate product, coronary sinus flow and resistance and ST-segment depression were all similar to findings before diltiazem. Although at the onset of angina, systolic pressure was usually slightly lower after diltiazem infusion (138 +/- 11 vs 128 +/- 11 mm Hg, p less than 0.05), the pacing rate at onset of angina was higher in only 3 patients and the pressure-rate product was higher in only 1 patient. After diltiazem, left ventricular end-diastolic pressure increased less frequently after interruption of pacing. The results suggest that diltiazem favorably alters the relation between myocardial oxygen demand and supply at rest, but during tachycardia, anginal threshold and coronary reserve do not change. Diltiazem's potent antianginal action, shown in previous investigations using exercise-induced angina, is not prominent when heart rate is controlled. The major benefit of diltiazem in patients with stress-induced angina is related to reduction of myocardial oxygen demand rather than improved myocardial oxygen delivery.