Left ventricular mechanical efficiency in coronary artery disease

Myocardial mechano-energetic efficiency is not impaired in patients with metabolically healthy overweight and obesity

OBJECTIVE

Reduced myocardial mechano-energetic efficiency (MEE) was associated with BMI. Subgroups of individuals with increased BMI but favorable cardiovascular risk profile were identified as individuals with "metabolically healthy overweight" (MHOW) and "metabolically healthy obesity" (MHO), respectively. We aim to investigate whether those with MHOW/MHO, defined as those having none of the components of metabolic syndrome, exhibit impaired MEE compared with their unhealthy counterparts.

METHODS

Myocardial MEE per gram of left ventricular mass (MEEi) was assessed by echocardiography in 2190 nondiabetic individuals participating in the CATAnzaro MEtabolic RIsk factors (CATAMERI) study who were divided, according to BMI and metabolic status, into groups of individuals with metabolically healthy normal weight (MHNW), metabolically unhealthy normal weight (MUNW), MHOW, metabolically unhealthy overweight (MUOW), MHO, and metabolically unhealthy obesity (MUO).

RESULTS

After adjusting for age and sex, no differences in myocardial MEEi were observed among individuals with MHNW, MHOW, and MHO (p = 0.56). Myocardial MEEi was comparable among individuals with MUNW, MUOW, and MUO (p = 0.21). Individuals with MHNW, MHOW, and MHO displayed significantly higher myocardial MEEi compared with their unhealthy counterparts.

CONCLUSIONS

Increased BMI is not an obligate determinant for reduced myocardial MEEi. Other known components of metabolic syndrome rather than increased BMI contributed to reduced myocardial MEEi.

On Left Ventricle Stroke Work Efficiency in Children with Moderate Aortic Valve Regurgitation or Moderate Aortic Valve Stenosis

The optimal timing for management of pediatric patients with moderate aortic valve disease [moderate aortic stenosis (modAS) or moderate aortic regurgitation (modAR)] remains unknown and largely unexplored. Although usually asymptomatic, the risk of increased left ventricular (LV) wall stress, irreversible myocardial fibrosis and sudden death in untreated moderate conditions warrants clearer risk stratification for appropriate timely intervention. In this study, we explore the use of a patient-specific mathematical model to introduce a new evaluative parameter of LV performance in patients with moderate aortic valve disease. Synthetic patient data (N = 520) representing healthy patients, and patients with modAS or modAR were first generated. Then, data from twenty-five pediatric patients were included in this study (healthy = 9; moderate AS = 8; modAR = 8). The effect of modAS or modAR on LV performance was evaluated by LV stroke work (LVSW) efficiency, a new non-invasive parameter. The results demonstrate that healthy patients possess a very high LVSW efficiency (synthetic data: 91 ± 2%, in vivo data: 92 ± 3%). However, modAS patients have a significant reduction in LVSW efficiency (synthetic data: 78 ± 2%, in vivo data: 76 ± 5%, p < 0.05), whereas modAR patients had the lowest LVSW efficiency (synthetic data: 58 ± 3%, in vivo data: 66 ± 7%; p < 0.05). This highlights that patients with moderate aortic valve disease require careful myocardial assessment, regardless of onset of clinical symptoms as their LV performance is significantly reduced. The evaluation of LVSW efficiency offers a promising avenue for future stratification of mixed aortic valve disease for optimal timing of management and intervention.

Depressed Cardiac Mechanical Energetic Efficiency: A Contributor to Cardiovascular Risk in Common Metabolic Diseases-From Mechanisms to Clinical Applications

Cardiac mechanical energetic efficiency is the ratio of external work (EW) to the total energy consumption. EW performed by the left ventricle (LV) during a single beat is represented by LV stroke work and may be calculated from the pressure-volume loop area (PVLA), while energy consumption corresponds to myocardial oxygen consumption (MVO₂) expressed on a per-beat basis. Classical early human studies estimated total mechanical LV efficiency at 20-30%, whereas the remaining energy is dissipated as heat. Total mechanical efficiency is a joint effect of the efficiency of energy transfer at three sequential stages. The first step, from MVO₂ to adenosine triphosphate (ATP), reflects the yield of oxidative phosphorylation (i.e., phosphate-to-oxygen ratio). The second step, from ATP split to pressure-volume area, represents the proportion of the energy liberated during ATP hydrolysis which is converted to total mechanical energy. Total mechanical energy generated per beat-represented by pressure-volume area-consists of EW (corresponding to PVLA) and potential energy, which is needed to develop tension during isovolumic contraction. The efficiency of the third step of energy transfer, i.e., from pressure-volume area to EW, decreases with depressed LV contractility, increased afterload, more concentric LV geometry with diastolic dysfunction and lower LV preload reserve. As practical assessment of LV efficiency poses methodological problems, De Simone et al. proposed a simple surrogate measure of myocardial efficiency, i.e., mechano-energetic efficiency index (MEEi) calculated from LV stroke volume, heart rate and LV mass. In two independent cohorts, including a large group of hypertensive subjects and a population-based cohort (both free of prevalent cardiovascular disease and with preserved ejection fraction), low MEEi independently predicted composite adverse cardiovascular events and incident heart failure. It was hypothesized that the prognostic ability of low MEEi can result from its association with both metabolic and hemodynamic alterations, i.e., metabolic syndrome components, the degree of insulin resistance, concentric LV geometry, LV diastolic and discrete systolic dysfunction. On the one part, an increased reliance of cardiomyocytes on the oxidation of free fatty acids, typical for insulin-resistant states, is associated with both a lower yield of ATP per oxygen molecule and lesser availability of ATP for contraction, which might decrease energetic efficiency of the first and second step of energy transfer from MVO₂ to EW. On the other part, concentric LV remodeling and LV dysfunction despite preserved ejection fraction can impair the efficiency of the third energy transfer step. In conclusion, the association of low MEEi with adverse cardiovascular outcome might be related to a multi-step impairment of energy transfer from MVO₂ to EW in various clinical settings, including metabolic syndrome, diabetes, hypertension and heart failure. Irrespective of theoretical considerations, MEEi appears an attractive simple tool which couldt improve risk stratification in hypertensive and diabetic patients for primary prevention purposes. Further clinical studies are warranted to estimate the predictive ability of MEEi and its post-treatment changes, especially in patients on novel antidiabetic drugs and subjects with common metabolic diseases and concomitant chronic coronary syndromes, in whom the potential relevance of MEE can be potentiated by myocardial ischemia.

Myocardial Efficiency: A Fundamental Physiological Concept on the Verge of Clinical Impact

Myocardial external efficiency is the relation of mechanical energy generated by the left (or right) ventricle to the consumed chemical energy from aerobic metabolism. Efficiency can be calculated invasively, and, more importantly, noninvasively by using positron emission tomography, providing a single parameter by which to judge the adequacy of myocardial metabolism to generated mechanical output. This parameter has been found to be impaired in heart failure of myocardial or valvular etiology, and it changes in a characteristic manner with medical or interventional cardiac therapy. The authors discuss the concept, strengths, and limitations, known applications, and future perspectives of the use of myocardial efficiency.

Depressed myocardial energetic efficiency is associated with increased cardiovascular risk in hypertensive left ventricular hypertrophy

BACKGROUND AND PURPOSE

Myocardial mechano-energetic efficiency (MEE) can be easily approximated by the ratio of stroke work [i.e. SBP times stroke volume (SV)] to a rough estimate of energy consumption, the 'double product' [SBP times heart rate (HR)], which can be simplified as SV/HR. We evaluated whether MEE is associated with adverse prognosis in relation to the presence of left ventricular hypertrophy (LVH).

METHODS

Hypertensive participants of the Campania Salute Network (n = 12 353) without prevalent coronary or cerebrovascular disease and with ejection fraction more than 50% were cross-sectionally and longitudinally analyzed, over a median follow-up of 31 months. MEE was estimated by echocardiographic SV (z-derived)/(HR × 0.6).

RESULTS

Due to the close relation with left ventricular mass (LVM) (P < 0.0001), MEE was normalized for LVM (MEEi) and divided into quartiles. The lowest quartile of MEEi (<0.29 ml/s per g) was considered 'low MEEi'. MEEi was greater in women than in men (P < 0.0001). Progressively lower MEEi was associated with older age, male sex, obesity, diabetes, LVH, concentric geometry, inappropriate LVM and diastolic dysfunction, more use of antihypertensive therapy, and higher BP (all P < 0.002). In Cox regression, after controlling for LVH, age, sex, and average follow-up SBP, low MEEi exhibited increased hazard of composite fatal and nonfatal cardiovascular end-points (P < 0.01), independently of antihypertensive therapy and associated cardiovascular risk factors.

CONCLUSION

A simple estimate of low myocardial mechano-energetic efficiency is associated with altered metabolic profile, LVH, concentric left ventricular geometry, and diastolic dysfunction and predicts cardiovascular end-points, independently of age, sex, LVH antihypertensive therapy, and cardiovascular risk factors.

Effects of exenatide on cardiac function, perfusion, and energetics in type 2 diabetic patients with cardiomyopathy: a randomized controlled trial against insulin glargine

BACKGROUND

Multiple bloodglucose-lowering agents have been linked to cardiovascular events. Preliminary studies showed improvement in left ventricular (LV) function during glucagon-like peptide-1 receptor agonist administration. Underlying mechanisms, however, are unclear. The purpose of this study was to investigate myocardial perfusion and oxidative metabolism in type 2 diabetic (T2DM) patients with LV systolic dysfunction as compared to healthy controls. Furthermore, effects of 26-weeks of exenatide versus insulin glargine administration on cardiac function, perfusion and oxidative metabolism in T2DM patients with LV dysfunction were explored.

METHODS AND RESULTS

Twenty-six T2DM patients with LV systolic dysfunction (cardiac magnetic resonance (CMR) derived LV ejection fraction (LVEF) of 47 ± 13%) and 10 controls (LVEF of 59 ± 4%, P < 0.01 as compared to patients) were analyzed. Both myocardial perfusion during adenosine-induced hyperemia (P < 0.01), and coronary flow reserve (P < 0.01), measured by [¹⁵O]H₂O positron emission tomography (PET), were impaired in T2DM patients as compared to healthy controls. Myocardial oxygen consumption and myocardial efficiency, measured using [¹¹C]acetate PET and CMR derived stroke volume, were not different between the groups. Eleven patients in the exenatide group and 12 patients in the insulin glargine group completed the trial. Systemic metabolic control was improved after both treatments, although, no changes in cardiac function, perfusion and metabolism were seen after exenatide or insulin glargine.

CONCLUSIONS

T2DM patients with LV systolic dysfunction did not have altered myocardial efficiency as compared to healthy controls. Exenatide or insulin glargine had no effects on cardiac function, perfusion or oxidative metabolism. Trial registration NCT00766857.

Impaired myocardial oxygen availability contributes to abnormal exercise hemodynamics in heart failure with preserved ejection fraction

BACKGROUND

Hypertension is a frequent risk factor for the development of heart failure with preserved ejection fraction (HFPEF). Progressive extracellular matrix accumulation has been presumed to be the fundamental pathophysiologic mechanism that leads to the transition to impaired diastolic reserve. However, the contribution of other mechanisms affecting active and passive components of diastolic function has not been comprehensively assessed. In this study, we investigated the potential role of impaired myocardial oxygen delivery in the pathophysiology of HFPEF.

METHODS AND RESULTS

Patients with HFPEF, those with controlled hypertension, and healthy controls underwent simultaneous right-heart catheterization, echocardiography, and paired arterial and coronary sinus blood gas sampling at rest and during supine-cycle ergometry. Despite a lower workload (HFPEF vs control, hypertension: 43±8 versus 114±12, 87±14 W; P<0.001 and P<0.05, respectively), peak exercise pulmonary capillary wedge pressure was markedly higher in HFPEF patients compared with healthy and hypertensive controls (32±2 versus 16±1 and 17±1 mm Hg, both P<0.001). During exercise, the transcardiac oxygen gradient increased significantly in all groups; however, the peak transcardiac oxygen gradient was significantly lower in HFPEF patients (P<0.05). In addition, the left ventricular-work corrected transcardiac oxygen gradient remained significantly lower in HFPEF patients compared with controls (P<0.001).

CONCLUSION

The current study provides unique data suggesting that the abnormal diastolic reserve observed during exertion in HFPEF patients may, in part, be explained by impaired myocardial oxygen delivery due possibly to microvascular dysfunction. Further studies are required to confirm the structural and functional basis of these findings and to investigate the influence of potential therapies on this abnormality.

Modulation of cardiac A1-adenosine receptors in rats following treatment with agents affecting heart rate

Effects of chronic treatment affecting heart rate on A1 adenosine receptor levels and their functions were studied. Treatment of rats with isoproterenol for 10 days accelerated heart rate and increased the level of adenosine receptors, in both the atria and ventricles. Negative dromotropic response of isolated heart to adenosine was enhanced in isoproterenol-treated rats. Similar results were obtained following treatment with atropine sulfate, or swimming training but not after treatment with thyroxine. On the other hand, treatment with amiodarone, which normally causes a decrease in heart rate, also increased the level of adenosine receptors in both atria and ventricles. The sensitivity of the isolated heart to the negative dromotropic and chronotropic effects of adenosine was not enhanced in the amiodarone treated rats. Similar results were obtained following treatment with propranolol, while treatment with PTU (6-n-propyl-2-thiouracil) increased adenosine sensitivity in the isolated heart. It was concluded that the levels of A1 adenosine receptors in the heart correspond to heart rate, and to cardiac efficiency. While an increase in heart rate was followed by up-regulation of A1 adenosine receptors, a decrease in heart rate caused a moderate elevation of these receptors.

Ventriculoarterial coupling and left ventricular efficiency in heart transplant recipients

BACKGROUND

In heart transplants, left ventricular function may be impaired in the absence of rejection or graft atherosclerosis. Matching between left ventricle and arterial receptor, i.e., ventriculoarterial coupling, and left ventricular efficiency have never been studied.

METHODS

Left ventricular pressure-volume loops and single beat analysis were used to determine effective arterial elastance (Ea) and the slope of the end-systolic pressure-volume relation (end-systolic elastance; Ees). Left ventricular efficiency was evaluated by determination of external work (EW), pressure-volume area (PVA), coronary blood flow (continuous thermodilution), and myocardial oxygen consumption (MVO2). Measurements were made at baseline in 11 control subjects and 9 heart transplant recipients (HTX) without rejection and were repeated after phenylephrine in the latter group.

RESULTS

At baseline, Ees, Ees/Ea, and work efficiency (EW/PVA) were lower in HTX than in control subjects (2.51+/-0.87 vs. 3.70+/-1.15 mmHg/ml/m2, P<0.01; 0.96+/-0.21 vs. 1.47+/-0.31, P<0.001; and 0.53+/-0.08 vs. 0.59+/-0.09, P<0.01, respectively). Energy conversion efficiency (PVA/MVO2) and mechanical efficiency (EW/ MVO2) were higher in HTX (0.58+/-0.08 vs. 0.45+/-0.14, P<0.001; and 0.31+/-0.05 vs. 0.26+/-0.06, P<0.001, respectively). In HTX, phenylephrine infusion increased Ees, Ea, EW, PVA, and MVO2 without modifying Ees/Ea, EW/PVA, PVA/MVO2, and EW/MVO2.

CONCLUSIONS

In heart transplants, (1) left ventricular contractility is moderately depressed; (2) elevation of energy conversion efficiency compensates for the decrease in work efficiency, allowing normal mechanical efficiency; and (3) alpha 1 adrenergic stimulation does not impair ventriculoarterial coupling and mechanical efficiency.

Mechanical efficiency in hypertrophic cardiomyopathy assessed by positron emission tomography with carbon 11 acetate

This study was performed to assess the relation between the regional work and oxidative metabolism in hypertrophic cardiomyopathy (HCM). By using carbon 11 acetate as a tracer of myocardial blood flow (%A(0)) and oxygen consumption (k value), 12 patients with HCM with asymmetric septal hypertrophy and 10 normal subjects were studied. Regional work rate (RWR) of the left ventricle was estimated by wall stress and wall thickness. %A(0) in hypertrophied septum was similar to that in nonhypertrophied free wall (92.6% +/- 2.8% vs 93.5% +/- 3.8%; p = not significant). However, oxygen consumption was significantly lower in hypertrophied septum than in nonhypertrophied free wall (0.043 +/- 0.011 vs 0.057 +/- 0.013 min(-1); p < 0.001). The k value in nonhypertrophied free wall was similar to the value observed in normal subjects (0.062 +/- 0.013). Average values for RWR in hypertrophied septum, nonhypertrophied free wall, and normal subjects were 0.26 +/- 0.07,0.62 +/- 0.02,and 1.98 +/- 0.15 J/cm3/ min, respectively. Furthermore, the analysis of covariance, in which the effect of RWR was removed as a covariate, revealed that the overall RWR-corrected k value was much larger in patients with HCM (0.109 vs 0.062, p < 0.0001) than expected from the decreased regional myocardial work, suggesting that there was a diffused inefficiency in oxygen consumption. We concluded, therefore, that the relative value of oxidative metabolism in patients with HCM is significantly higher than that of the normal subjects, suggesting the presence of reduced mechanical efficiency.

Effects of heart rate on coronary circulation and external mechanical efficiency in elderly hypertensive patients with left ventricular hypertrophy

BACKGROUND AND HYPOTHESIS

Mechanisms of heart failure in elderly hypertensive patients with hypertrophy have not been studied sufficiently. We hypothesized that impaired increment of coronary blood flow in response to increases in heart rate could be responsible for the occurrence or aggravation of heart failure.

METHODS

To test this hypothesis, we measured coronary hemodynamics and lactate balance during basal conditions and atrial pacing in 21 elderly patients aged > or = 65 years (mean 74 +/- 6 years) without coronary arterial disease: 7 normotensive control patients (Group 1), 7 hypertensive hypertrophic patients without a history of congestive heart failure (Group 2), and 7 patients with such history (Group 3). Coronary sinus blood flow (CSBF) was measured in coronary sinus using a thermodilution catheter.

RESULTS

During basal conditions, heart rate did not differ among the three groups (67 +/- 3 in Group 1, 65 +/- 11 in Group 2, and 63 +/- 6 beats/ in Group 3). CSBF was significantly higher in the two hypertrophic groups than in the control group, but CSBF normalized by left ventricular mass was significantly lower in both hypertrophic groups. External mechanical efficiency (EME) obtained as left ventricular work divided by myocardial oxygen consumption did not differ among groups during basal conditions (36 +/- 9% in Group 1, 35 +/- 8% in Group 2, and 29 +/- 9% in Group 3, NS). During atrial pacing to increase heart rate by 25 +/- 5% (lower) and 54 +/- 6% (higher), the increases in CSBF were markedly limited in both hypertrophic groups, and the response in Group 3 was more depressed than that in Group 2. EME did not change in the control group or in Group 2, but did decrease to 21 +/- 5% in Group 3 during the higher pacing rate (p < 0.01 vs. basal conditions). In this group, the relationship between EME and heart rate showed a significant negative correlation (r = -0.56, p = 0.02). Lactate balance in coronary sinus blood showed a tendency to production in Group 3 during the higher pacing rate, suggesting myocardial ischemia.

CONCLUSION

These findings suggest that in hypertensive hypertrophic patients with a history of heart failure, the coronary circulation system is vulnerable to increasing heart rate. In medical treatment of elderly hypertensive patients, control of heart rate in addition to blood pressure control should be considered to minimize the occurrence or aggravation of heart failure.

A preliminary study of growth hormone in the treatment of dilated cardiomyopathy

BACKGROUND

Cardiac hypertrophy is a physiologic response that allows the heart to adapt to an excess hemodynamic load. We hypothesized that inducing cardiac hypertrophy with recombinant human growth hormone might be an effective approach to the treatment of idiopathic dilated cardiomyopathy, a condition in which compensatory cardiac hypertrophy is believed to be deficient.

METHODS

Seven patients with idiopathic dilated cardiomyopathy and moderate-to-severe heart failure were studied at base line, after three months of therapy with human growth hormone, and three months after the discontinuation of growth hormone. Standard therapy for heart failure was continued throughout the study. Cardiac function was evaluated with Doppler echocardiography, right-heart catheterization, and exercise testing.

RESULTS

When administered at a dose of 14 IU per week, growth hormone doubled the serum concentrations of insulin-like growth factor I. Growth hormone increased left-ventricular-wall thickness and reduced chamber size significantly. Consequently, end-systolic wall stress (a function of both wall thickness and chamber size) fell markedly (from a mean [+/-SE] of 144+/-11 to 85+/-8 dyn per square centimeter, P<0.001). Growth hormone improved cardiac output, particularly during exercise (from 7.4+/-0.7 to 9.7+/-0.9 liters per minute, P=0.003), and enhanced ventricular work, despite reductions in myocardial oxygen consumption (from 56+/-6 to 39+/-5 ml per minute, P=0.005) and energy production (from 1014+/-100 to 701+/-80 J per minute, P=0.002). Thus, ventricular mechanical efficiency rose from 9+/-2 to 21+/-5 percent (P=0.006). Growth hormone also improved clinical symptoms, exercise capacity, and the patients' quality of life. The changes in cardiac size and shape, systolic function, and exercise tolerance were partially reversed three months after growth hormone was discontinued.

CONCLUSIONS

Recombinant human growth hormone administered for three months to patients with idiopathic dilated cardiomyopathy increased myocardial mass and reduced the size of the left ventricular chamber, resulting in improvement in hemodynamics, myocardial energy metabolism, and clinical status.

Reduced left ventricular mechanical efficiency in elderly patients with coronary artery disease

We evaluated left ventricular (LV) mechanical efficiency in 23 elderly patients (mean age 67 +/- 2) with coronary artery disease (CAD) and in 22 patients younger than 65 years (mean age 49 +/- 8) with similar severity of CAD (2.4 +/- 0.8 and 2.2 +/- 0.8 vessels per patient, respectively) and history of myocardial infarction (34% and 41%, respectively). LV mechanical efficiency was calculated as the ratio of LV work per minute and myocardial O2 consumption. LV stroke volume was calculated from left ventriculography. Coronary blood flow was measured by thermodilution. Older patients had lower values of LV stroke volume (49 +/- 16 vs 73 +/- 16 mL, p < 0.005), ejection fraction (41 +/- 17 vs 58 +/- 17%, p < 0.05), LV stroke work (93 +/- 26 vs 131 +/- 41 g.m., p < 0.02) and LV work per minute (6.7 +/- 2.6 vs 9.3 +/- 2.7 kg.m./min, p < 0.05). Since myocardial O2 consumption was similar in the two groups, LV mechanical efficiency was lower in older CAD patients (16.2 +/- 15 vs 23.8 +/- 12%, p < 0.05). Thus, elderly patients with CAD show a reduced LV mechanical pump performance and efficiency, compared with younger patients with similar disease severity and history of myocardial infarction. These observations may contribute to understanding the higher frequency of congestive heart failure in elderly patients with CAD.

A new methodology for non-invasive clinical assessment of cardiovascular system performance and of ventricular-arterial coupling during stress

The objective of the study was to develop a non-invasive method for the quantitative evaluation of cardiovascular performance and ventricular-arterial (VA) coupling during varying physiological states. VA-coupling was represented by the ratio between the arterial and ventricular elastances-Ea/Ees. Approximate indices of the relative change of Ees and VA-coupling during stress were developed and tested. These indices can be evaluated directly from non-invasive measurements of ejection fraction values (for VA-coupling) and measurements of stroke volumes and systolic and diastolic arterial pressures (for Ees). Additional relative indices can be evaluated from these data (e.g., stroke work, cardiac output) to yield a complete representation of the cardiovascular response to stress. The present methodology was applied to assess the exercise stress response in healthy subjects (H, n = 8) and in patients with left ventricular dysfunction (n = 24). Left ventricular volumes were determined by nuclear angiography and arterial pressures were measured non-invasively by a new, validated method. Using published data obtained invasively, we found that the relative indices of Ees and VA-coupling showed a high correlation with the invasive ones (r > 0.8, P < 0.01). The patients were subgrouped by their maximal exercise capacitance (P2-50W, P3-75W). At rest, the two patient groups had similar ejection fraction values (45 +/- 15% and 48 +/- 16%), which were significantly different from those of the healthy subjects (66 +/- 7%, P < 0.05). During stress, a larger increase in stroke work and cardiac output was found in the healthy subjects. All three groups showed similar relative increases in Ees and heart rate, but relative Ea increased in P2 and decreased in H, while the opposite was found for the end-diastolic volume. The relative VA-coupling index in P2 was significantly larger than that in P3 and H (P < 0.05). The present non-invasively based indices can be used to quantitatively monitor the individual cardiovascular response to stress testing or drug interventions and to evaluate the importance of VA-coupling in the clinical setting.

An approach to ventricular efficiency by use of carbon 11-labeled acetate and positron emission tomography

BACKGROUND

Positron emission tomography-derived 11C-labeled acetate kinetics have been shown to reflect myocardial oxidative metabolism. The objective of the study was to use this metabolic imaging technique in combination with an evaluation of left ventricular work as an index of ventricular mechanical efficiency.

METHODS AND RESULTS

The effects of ventricular ejection fraction and loading on this index were studied quantitatively in a canine experimental model. There was a curvilinear relationship between efficiency and the end-diastolic volume per unit mass (r = 0.84), which appeared to integrate the main determinants of left ventricular mechanical performance successfully and allowed the detection of a decreased ventricular efficiency in acute experimental heart failure.

CONCLUSIONS

This approach appears to have the potential to assess the energetic working point of the ventricle in clinical heart disease and follow the effects of therapy. The data demonstrate the feasibility of an estimate of ventricular efficiency that relies on noninvasive data-acquisition techniques.

Cardiac efficiency

Efficiency is defined as the ratio of the energy delivered by a system to the energy supplied to it. Depending on the particular question being addressed, there exist a plethora of definitions of efficiency in medical texts, thus hampering their comparison. If only the ventricular work seen by the arterial system is under investigation, pressure-volume work will serve as a useful numerator. If, on the other hand, external and internal work together, i.e. the total mechanical work, is of interest, the pressure-volume area might be employed. Total myocardial oxygen consumption (MVO2) will be a useful denominator in the case of aerobic energy production. The MVO2 for the unloaded contraction must be assessed if, as in other energy transfer systems, net efficiency is to be addressed. If even smaller steps in the chain of energy transfer are to be investigated MVO2 for the arrested heart must be assessed. With an appropriate therapy, hemodynamic determinants can be varied, to improve cardiac efficiency. Nonetheless, measurement of all variables necessary for the calculation of efficiency remains a challenge, in particular in the clinical setting. Separation of the direct effects of drugs on efficiency is even more difficult, since hemodynamic conditions can hardly be controlled throughout the observation period, and changes in efficiency might be secondary to changes in hemodynamics. Whether the heart by itself employs mechanisms to improve its efficiency is still a matter of discussion: there is evidence that when oxygen supply decreases, the heart can switch from one substrate to a less costly one, or possibly can improve efficiency through better use of oxygen. Moreover, the heart seems to "sense" an even more decreased oxygen supply and reduce function in response. Myocardial stunning could be regarded as a protective mechanism as well, with function remaining depressed and the oxygen supply being normal or close to normal. One may conclude from the decreased efficiency that the excess oxygen consumption is used up for repair processes. The improved efficiency found in hypertrophied hearts represents another adaptive process. The underlying mechanism is unclear: a shift towards isomyosin V3 or some undefined shift in metabolic pathway is discussed. It is also still a moot question towards which objective the efficiency of the heart is adjusted. It has been described that under physiologic conditions, the efficiency of both the left and the right ventricle ought to be maximized.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiovascular applications of laser technology

Laser technology has been evaluated for the treatment of coronary artery disease, ventricular and supraventricular arrythmias, hypertrophic cardiomyopathy, and congenital heart disease. Developments in laser angioplasty, laser thrombolysis, transmyocardial laser revascularization, photochemotherapy, laser treatment of arrhythmias and/or laser diagnostics are directed at improving upon conventional non-laser approaches, and providing new therapeutic and diagnostic options. This review will summarize the current status of the multiple applications of laser technology for cardiovascular diagnosis and therapy.

The effects of afterload reduction on myocardial carbon 11-labeled acetate kinetics and noninvasively estimated mechanical efficiency in patients with dilated cardiomyopathy

METHODS AND RESULTS

With echocardiography and dynamic carbon 11-labeled acetate (C-11 acetate) positron emission tomographic imaging, C-11 acetate kinetics and a parameter that estimates mechanical ventricular efficiency (the work metabolic index) were defined in eight patients with dilated cardiomyopathy. The effect of afterload reduction with nitroprusside on these parameters was evaluated in six of these patients. Nitroprusside increased stroke work index but decreased the C-11 clearance rate. The work metabolic index determined noninvasively increased and correlated well with an invasive approach. The work metabolic index was inversely correlated with systemic vascular resistance. Nitroprusside shifted this relationship upward and to the left.

CONCLUSION

This method of estimating efficiency is feasible and may represent a unique noninvasive approach for the evaluation of cardiac performance and responses to therapy.

Effect of enoximone alone and in combination with metoprolol on myocardial function and energetics in severe congestive heart failure: improvement in hemodynamic and metabolic profile

The hemodynamic and myocardial metabolic effects of enoximone (phosphodiesterase III inhibitor), alone or in combination with metoprolol (beta-adrenergic blocker), were studied in patients with congestive heart failure. Ten patients (New York Heart Association Class III-IV) underwent right heart and coronary sinus catheterization, and parameters were assessed at basal condition, at peak enoximone response (mean intravenous loading dose = 2.2 mg/kg), and after the combination with metoprolol (mean intravenous dose = 8.5 mg). Heart rate tended to increase during enoximone administration (from 102 +/- 16 to 107 +/- 16 min-1, ns) and was reduced during enoximone plus metoprolol (to 88 +/- 15 min-1, p < 0.05 vs. basal). Cardiac index was increased during enoximone (from 2.2 +/- 0.2 to 3.8 +/- 0.5 1/min/m2, p < 0.05) and decreased during enoximone plus metoprolol (to 2.8 +/- 0.5 1/min/m2, p < 0.05 vs. enoximone). Mean pulmonary wedge pressure fell during enoximone and remained reduced during enoximone plus metoprolol (from 27 +/- 9 to 9 +/- 3 and to 13 +/- 4 mmHg, respectively, both p < 0.05). Myocardial oxygen consumption did not change during enoximone (from 27 +/- 8 to 25 +/- 13 ml/min, ns) and was reduced during enoximone plus metoprolol (to 19 +/- 8 ml/min, p < 0.05 vs. basal). Myocardial lactate extraction tended to be lower during enoximone and during enoximone plus metoprolol conditions (from 38 +/- 17% to 26 +/- 20% and to 29 +/- 24%, respectively), but no statistical significance was found. Myocardial efficiency was increased during enoximone and during enoximone plus metoprolol (from 9 +/- 3% to 15 +/- 6% and to 14 +/- 6%, respectively, both p < 0.05). Thus in patients with congestive heart failure enoximone improves hemodynamics and, in most cases, it does not influence energetics. The addition of metoprolol to enoximone reduces heart rate, cardiac index, and myocardial oxygen consumption without any other major changes, producing a more physiologic hemodynamic and metabolic profile.

Oxygen cost of stress development in hypertrophied and failing hearts from the spontaneously hypertensive rat

Left ventricular isovolumic stress development and metabolic parameters were studied in 18-24-month-old spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rat controls using the isolated, isovolumic (balloon in left ventricle) buffer-perfused rat heart preparation. After WKY rats and all SHRs were compared, SHRs were divided into two groups: those animals with (SHR-F) and without (SHR-NF) evidence of heart failure. Hearts were perfused at 100 mm Hg using a constant pressure system at a temperature of 37 degrees C. In the baseline state, peak systolic pressure was greatest in the SHR-NF group and lowest in the SHR-F group. Peak midwall stress was greatest in the WKY group and, again, lowest in the SHR-F group. Oxygen consumption was lowest in the SHR-F group. When the oxygen cost of stress development was estimated by normalizing myocardial oxygen consumption by peak developed midwall stress, values were lowest in the WKY, greater in the SHR-NF, and greatest in the SHR-F group. Lactate production did not occur in the baseline state in any of the groups. Functional and metabolic responses to graded hypoxia, induced by changing the gas mixture of the perfusate from 95% to 50%, 25%, and 0% oxygen at perfusion pressures of 100 and 130 mm Hg, were studied. Increasing perfusion pressure generally resulted in small increases in peak systolic pressure and myocardial oxygen consumption but did not substantially reverse the contractile or metabolic deficit present in the SHR-F group.(ABSTRACT TRUNCATED AT 250 WORDS)

Energy conversion efficiency in human left ventricle

BACKGROUND

Left ventricular mechanical efficiency is one of the most important measures of left ventricular pump performance. Several clinical studies, however, have shown that mechanical efficiency does not fall substantially as the heart fails. To clarify the insensitivity of mechanical efficiency to the change in pump performance, we analyzed human left ventricular mechanical efficiency, applying the concept of left ventricular systolic pressure-volume area (PVA).

METHODS AND RESULTS

PVA correlates linearly with myocardial oxygen consumption per beat (MVO2): MVO2 = a.PVA+b, and represents the total mechanical energy of contraction. We determined MVO2-PVA relation and external work in 11 patients with different contractile states. We also calculated the energy transfer from MVO2 to PVA (PVA/MVO2 efficiency), that from PVA to external work (work efficiency), and mechanical efficiency (external work/MVO2). Left ventricular pressure-volume loops were constructed by plotting the instantaneous left ventricular pressure against the left ventricular volume at baseline and during pressure loading. The contractile properties of the ventricle were defined by the slope of the end-systolic pressure-volume relation (Ees). Pressure elevation raised external work by 41.4%, PVA by 71.2%, and MVO2 by 54.5%. These changes were associated with a decrease in work efficiency and an increase in PVA/MVO2 efficiency. The opposite directional changes in these two efficiencies rendered the mechanical efficiency constant. The slope, a, of the relation between MVO2 and PVA was relatively constant (2.46 +/- 0.33) over the range of 0.8-8.8 mm Hg/ml of Ees, but the oxygen axis intercept, b, tended to decrease with the reduction in Ees. PVA/MVO2 efficiency correlated inversely (r = -0.66, p less than 0.05) with Ees, whereas work efficiency correlated linearly with Ees (r = 0.91, p less than 0.01).

CONCLUSIONS

Mechanical efficiency is not appreciably affected by changes in loading and inotropic conditions as long as the left ventricular contractility is not severely depressed.

Effect of beta-adrenergic blockade on myocardial function and energetics in congestive heart failure. Improvements in hemodynamic, contractile, and diastolic performance with bucindolol

The hemodynamic effects of beta-adrenergic blockade with bucindolol, a nonselective beta-antagonist with mild vasodilatory properties, were studied in patients with congestive heart failure. Fifteen patients (New York Heart Association class I-IV) underwent cardiac catheterization before and after 3 months of oral therapy with bucindolol. The left ventricular ejection fraction increased from 0.23 +/- 0.12 to 0.29 +/- 0.14 (p = 0.007), and end-systolic elastance, a relatively load-independent determinant of contractility, increased from 0.60 +/- 0.40 to 1.11 +/- 0.45 mm Hg/ml (p = 0.0049). Both left ventricular stroke work index (34 +/- 13 to 47 +/- 19 g-m/m2, p = 0.0059) and minute work (5.5 +/- 2.2 to 7.0 +/- 2.6 kg-m/min, p = 0.0096) increased despite reductions in left ventricular end-diastolic pressure (19 +/- 8 to 15 +/- 5 mm Hg, p = 0.021). There was an upward shift in the peak + dP/dtmax-end-diastolic volume relation (p = 0.0005). These data demonstrate improvements in myocardial contractility after beta-adrenergic blockade with bucindolol. At a matched paced heart rate of 98 +/- 15 min-1, the time constant of left ventricular isovolumic relaxation was significantly reduced by bucindolol therapy (92 +/- 17 versus 73 +/- 11 msec, p = 0.0013), and the relation of the time constant to end-systolic pressure was shifted downward (p = 0.014) with therapy. The slope of the logarithm left ventricular end-diastolic pressure-end-diastolic volume relation was unchanged (p = 0.51) after bucindolol. These data suggest that chronic beta-adrenergic blockade with bucindolol improves diastolic relaxation but does not alter myocardial chamber stiffness. Myocardial oxygen extraction, consumption, and efficiency were unchanged despite improvement in contractile function and mechanical work. Thus, in patients with congestive heart failure, chronic beta-adrenergic blockade with bucindolol significantly improves myocardial contractility and minute work, yet it does not do so at the expense of myocardial oxygen consumption. Additionally, bucindolol improves myocardial relaxation but does not affect chamber stiffness.

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.

Characterisation of the normal right ventricular pressure-volume relation by biplane angiography and simultaneous micromanometer pressure measurements

The normal right ventricular pressure-volume relation was studied by recording biplane right ventriculograms with simultaneous high fidelity pressure recordings in 10 adults found to have normal coronary arteries and haemodynamic function at diagnostic cardiac catheterisation. Right ventricular volume was measured frame by frame from digitised ventriculograms by a modification of Simpson's rule. The accuracy of this method was tested in a study of 22 human and animal right ventricular casts. There was excellent agreement between calculated volumes and those measured by fluid displacement. The derived regression equations were used to correct right ventricular volumes calculated from in vivo studies. The mean (SD) end diastolic volume index for the group was 62 (13) ml/m2, the stroke volume index was 43 (8) ml/m2, and the ejection fraction was 62 (6)%. Right ventricular pressure-volume loops were generated by combining simultaneous volume and pressure curves. The normal right ventricular pressure-volume loop was triangular, departing significantly from the square or rectangle of the normal left ventricular pressure-volume loop. Ejection from the right ventricle began early during the pressure rise and continued as right ventricular pressure fell. As a result phases of isovolumic contraction and relaxation were difficult to define. These observations show that normal right ventricular pressure-volume relations differ considerably from those of the normal left ventricle, presumably reflecting the different loading conditions of the two ventricles.

Quantitative analysis of coronary arteriograms by microprocessor cinevideodensitometry

A rapid microprocessor technique for measuring the cross-sectional area, diameter, and relative percentage stenosis of coronary atherosclerotic lesions by cinevideodensitometric analysis was developed and validated. Video images of projected 35-mm coronary arteriographic cine frames were analyzed from cinevideodensitometric profile curves recorded for the catheter shaft, normal artery, and stenotic segment. In radiographic phantom studies of calibrated, contrast-filled, plexiglass cylinders, cinevideodensitometric measurements correlated linearly with percentage relative stenosis (r = 0.98; SEE = 4.1%), diameter (r = 0.99; SEE = 0.12 mm), and cross-sectional area (r = 0.99; SEE = 0.32 mm2). In postmortem studies of two patients dying after coronary arteriography, cross-sectional areas of arterial segments measured by cinevideodensitometry correlated well (r = 0.99; SEE = 0.71 mm) with areas of acrylic resin casts of the coronary arteries. Intraobserver variability (r = 0.99; SEE = 2.6%) and interobserver variability (r = 0.96; SEE = 5.3%) of cinevideodensitometric measurements of coronary arteriograms were low. Additionally, percentage relative stenosis measured in the right anterior oblique projection correlated well with measurements in the left anterior oblique projection (r = 0.98; SEE = 0.11 mm2) of patients with eccentric stenotic lesions. Lastly, cinevideodensitometric measurements were significantly (p less than 0.05) more reproducible than caliper measurements. This inexpensive dedicated microprocessor system provides rapid cinevideodensitometric measurements of coronary arterial dimensions, without requiring manual tracing of arterial segments or the major expense of a main-frame computer system.