Background

Annually, ~80,000 Americans receive guideline-based primary prevention implantable cardioverter defibrillators (ICDs), but appropriate firing rates are low. Current selection criteria for ICDs rely on LVEF, which lacks sensitivity and specificity. Because scar-related, myocardial tissue heterogeneity is a substrate for life-threatening arrhythmias, we hypothesized that cardiac magnetic resonance (CMR) identification of myocardial heterogeneity improves risk stratification through: (1) its association with adverse cardiac events independent of clinical factors and biomarker levels; and (2) its ability to identify particularly high- and low-risk subgroups.

Methods and Results

In 235 ischemic and nonischemic patients with LVEF≤35%, undergoing clinically-indicated primary prevention ICD, gadolinium-enhanced CMR was prospectively performed to quantify the amount of heterogeneous myocardial tissue (gray zone-GZ) and dense core scar. Serum high sensitivity C-reactive protein (hsCRP) and other biomarkers were assayed. The primary endpoint was appropriate ICD shock for ventricular tachycardia/fibrillation or cardiac death, which occurred in 45 patients (19%) at 3.6 year median follow-up. On univariable analysis, only diuretics, hsCRP, GZ and core were associated with outcome. After multivariable adjustment, GZ and hsCRP remained independently associated with outcome (p<0.001). Patients in the lowest tertile for both GZ and hsCRP (n=42) were at particularly low risk (0.7%/year event rate) while those in the highest tertile for both GZ and hsCRP (n=32) had an event rate of 16.1%/year, p<0.001.

Conclusions

In a cohort of primary prevention ICD candidates, combining a myocardial heterogeneity index with an inflammatory biomarker identified a subgroup with a very low risk of adverse cardiac events, including ventricular arrhythmias. This novel approach warrants further investigation to confirm its value as a clinical risk stratification tool.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00181233.

Objectives

Our aim was to investigate the safety and efficacy of intravenous allogeneic human mesenchymal stem cells (hMSCs) in patients with myocardial infarction (MI).

Background

Bone marrow-derived hMSCs may ameliorate consequences of MI, and have the advantages of preparation ease, allogeneic use due to immunoprivilege, capacity to home to injured tissue, and extensive pre-clinical support.

Methods

We performed a double-blind, placebo-controlled, dose-ranging (0.5, 1.6, and 5 million cells/kg) safety trial of intravenous allogeneic hMSCs (Prochymal, Osiris Therapeutics, Inc., Baltimore, Maryland) in reperfused MI patients (n = 53). The primary end point was incidence of treatment-emergent adverse events within 6 months. Ejection fraction and left ventricular volumes determined by echocardiography and magnetic resonance imaging were exploratory efficacy end points.

Results

Adverse event rates were similar between the hMSC-treated (5.3 per patient) and placebo-treated (7.0 per patient) groups, and renal, hepatic, and hematologic laboratory indexes were not different. Ambulatory electrocardiogram monitoring demonstrated reduced ventricular tachycardia episodes (p = 0.025), and pulmonary function testing demonstrated improved forced expiratory volume in 1 s (p = 0.003) in the hMSC-treated patients. Global symptom score in all patients (p = 0.027) and ejection fraction in the important subset of anterior MI patients were both significantly better in hMSCs versus placebo subjects. In the cardiac magnetic resonance imaging substudy, hMSC treatment, but not placebo, increased left ventricular ejection fraction and led to reverse remodeling.

Conclusions

Intravenous allogeneic hMSCs are safe in patients after acute MI. This trial provides pivotal safety and provisional efficacy data for an allogeneic bone marrow-derived stem cell in post-infarction patients. (Safety Study of Adult Mesenchymal Stem Cells [MSC] to Treat Acute Myocardial Infarction; NCT00114452)

Coronary vessel distensibility is reduced with atherosclerosis and normal aging but direct measurements have historically required invasive measurements at cardiac catheterization. Therefore, we sought to assess coronary artery distensibility non-invasively with 3.0T coronary magnetic resonance imaging (MRI) and to test the hypothesis that this non-invasive technique can detect differences in coronary distensibility between healthy and coronary artery disease (CAD) subjects. Thirty-eight healthy, adult subjects (23 men, mean age 31±10 years) and 21 patients with CAD defined on X-ray angiography (11 men, mean age 57±6 years) were studied on a commercial whole-body MR imaging system (Achieva 3.0 T; Philips, Best, The Netherlands). In each subject, the proximal segment of a coronary artery was imaged for cross-sectional area measurements using cine spiral MRI. Distensibility (mmHg−1*103) was determined as: (end-systolic lumen area–end-diastolic lumen area) / (pulse pressure multiplied by the end-diastolic lumen area). Pulse pressure was calculated as the difference between the systolic and diastolic brachial blood pressures. Thirty-four healthy subjects and nineteen patients had adequate image quality for coronary area measurements. Coronary artery distensibility was significantly higher in healthy subjects, than in the CAD patients (mean ± 1 SD: 2.4 ± 1.7 mmHg−1*103 vs. 1.1 ± 1.1 mmHg−1*103 respectively, p=0.007); (median: 2.2 vs. 0.9 mmHg−1*103). In a subgroup of 10 CAD patients we found a significant correlation between coronary artery distensibility measurements assessed with MRI and X-ray coronary angiography (R=0.65; p=0.003). In a group of 10 healthy subjects repeated distensibility measurements demonstrated a significant correlation (R=0.80; p=0.006). In conclusion, 3.0T MRI, a reproducible non-invasive means to assess human coronary artery vessel wall distensibility, is able to detect significant differences in distensibility between healthy subjects and CAD patients.

An abnormally high ankle brachial index (ABI) is associated with increased all-cause and cardiovascular mortality. The relationship of obesity to incident high-ABI has not been characterized. We investigated the hypothesis that increased obesity—quantified by body weight, BMI, waist circumference, and waist-to-hip-ratio—is positively associated with a high-ABI (ABI ≥ 1.3) and with mean ABI increases over a four year follow-up. Prevalence and incidence ratios for a high-ABI were obtained for 6540 and 5045 participants respectively in the Multi-Ethnic Study of Atherosclerosis (MESA), using log-binomial regression models adjusted for demographic, cardiovascular, and inflammatory/novel risk factors. Linear regression was used to analyze mean ABI change. Both prevalence and incidence of a high-ABI were significantly higher for the highest versus the lowest quartile of every baseline measure of obesity, with weight and BMI demonstrating the highest incidence ratios (2.7 and 2.4, respectively). All prevalence and incidence ratios were positive and graded across obesity quartiles, and were persistent in the subpopulation without diabetes. Among those with normal baseline ABI values, one MESA-standard deviation increase in every baseline measure of obesity was associated with significant increases in mean ABI values. In conclusion, we observed an independent, positive and graded association of increasing obesity to both prevalent and incident high-ABI, and to mean increases in ABI values over time. Weight and BMI seemed to be at least as strongly, if not more strongly, associated with a high-ABI than were measures of abdominal obesity.

ATP is required for normal cardiac contractile function, and it has long been hypothesized that reduced energy delivery contributes to the contractile dysfunction of heart failure (HF). Despite experimental and clinical HF data showing reduced metabolism through cardiac creatine kinase (CK), the major myocardial energy reserve and temporal ATP buffer, a causal relationship between reduced ATP-CK metabolism and contractile dysfunction in HF has never been demonstrated. Here, we generated mice conditionally overexpressing the myofibrillar isoform of CK (CK-M) to test the hypothesis that augmenting impaired CK-related energy metabolism improves contractile function in HF. CK-M overexpression significantly increased ATP flux through CK ex vivo and in vivo but did not alter contractile function in normal mice. It also led to significantly increased contractile function at baseline and during adrenergic stimulation and increased survival after thoracic aortic constriction (TAC) surgery–induced HF. Withdrawal of CK-M overexpression after TAC resulted in a significant decline in contractile function as compared with animals in which CK-M overexpression was maintained. These observations provide direct evidence that the failing heart is “energy starved” as it relates to CK. In addition, these data identify CK as a promising therapeutic target for preventing and treating HF and possibly diseases involving energy-dependent dysfunction in other organs with temporally varying energy demands.

While it is widely appreciated that volumetric blood flow rate (VFR) dynamics change with age, there has been no detailed characterization of the typical shape of carotid bifurcation VFR waveforms of older adults. Towards this end, retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms proximal and distal to the carotid bifurcations of 94 older adults (age 68±8 yrs) with little or no carotid artery disease, recruited from the BLSA cohort of the VALIDATE study of factors in vascular aging. Timings and amplitudes of well-defined feature points from these waveforms were extracted automatically, and averaged to produce representative common, internal and external carotid artery (CCA, ICA and ECA) waveform shapes. Relative to young adults, waveforms from older adults were found to exhibit a significantly augmented secondary peak during late systole, resulting in significantly higher resistance index (RI) and flow augmentation index (FAI). Cycle-averaged VFR at the CCA, ICA and ECA were 389±74, 245±61 and 125±49 mL min−1, respectively, reflecting a significant cycle-averaged outflow deficit of 5%, which peaked at around 10% during systole. A small but significant mean delay of 13 ms between arrivals of ICA versus CCA/ECA peak VFR suggested differential compliance of these vessels. Sex and age differences in waveform shape were also noted. The characteristic waveforms presented here may serve as a convenient baseline for studies of VFR waveform dynamics or as suitable boundary conditions for models of blood flow at the carotid arteries of older adults.

Long-term heat acclimation (AC, 30d/34°C) is a phenotypic adaptation leading to increased thermotolerance during heat stress (HS, 2 h 41°C). AC also renders protection against ischemic/reperfusion (I/R, 30′ global ischemia/40′ reperfusion) insult via cross-tolerance mechanisms. In contrast to the protected AC phenotype, the onset of acclimation (34°C, AC2d) is characterized by cellular perturbations, suggesting increased susceptibility to HS and I/R insults. In this investigation, we tested the hypothesis that apoptosis resistance is part of the AC repertoire and that, at the initial phase of acclimation (AC2d), cytoprotection is impaired. TUNEL staining and caspase 3 levels in HS and I/R insulted hearts affirmed this hypothesis. To examine the role of the mitochondria in life/death decision in AC2d and 30d AC settings vs. control hearts, we studied the Bcl-2 apoptotic cascade and found increased levels of the anti-apoptotic Bcl-XL and decreased levels of the pro-apoptotic death promoter Bad in hearts from AC2d and AC animals. In these groups, cytochrome c (cyt c) was elevated in the mitochondria and remained unchanged in the cytosol. This adaptation was insufficient to negate apoptosis in AC2d rats. At this early acclimation phase (and in controls), increased caspase 8 activity confirmed activation of the extrinsic (Fas ligand) apoptosis pathway. In conclusion, the elevated Bcl-XL/Bad ratio and decreased cyt c leakage to the cytosol are insufficient to protect the heart and interactions with additional cytoprotective pathways involved in acclimation (elevated HSP70, ROS, and sarcolemmal adaptations to abolish extrinsic apoptosis pathways) are required to induce the apoptosis-resistant AC phenotype.

Electronic supplementary material

The online version of this article (doi:10.1007/s12192-010-0178-x) contains supplementary material, which is available to authorized users.

Purpose. We evaluated the influence of the time between low-dose gadolinium (Gd) contrast administration and coronary vessel wall enhancement (LGE) detected by 3T magnetic resonance imaging (MRI) in healthy subjects and patients with coronary artery disease (CAD). Materials and Methods. Four healthy subjects (4 men, mean age 29 ± 3 years and eleven CAD patients (6 women, mean age 61 ± 10 years) were studied on a commercial 3.0 Tesla (T) whole-body MR imaging system (Achieva 3.0 T; Philips, Best, The Netherlands). T1-weighted inversion-recovery coronary magnetic resonance imaging (MRI) was repeated up to 75 minutes after administration of low-dose Gadolinium (Gd) (0.1 mmol/kg Gd-DTPA). Results. LGE was seen in none of the healthy subjects, however in all of the CAD patients. In CAD patients, fifty-six of 62 (90.3%) segments showed LGE of the coronary artery vessel wall at time-interval 1 after contrast. At time-interval 2, 34 of 42 (81.0%) and at time-interval 3, 29 of 39 evaluable segments (74.4%) were enhanced. Conclusion. In this work, we demonstrate LGE of the coronary artery vessel wall using 3.0 T MRI after a single, low-dose Gd contrast injection in CAD patients but not in healthy subjects. In the majority of the evaluated coronary segments in CAD patients, LGE of the coronary vessel wall was already detectable 30–45 minutes after administration of the contrast agent.

Background

Cardiosphere-derived cells (CDCs) isolated from human endomyocardial biopsies reduce infarct size and improve cardiac function in mice. Safety and efficacy testing in large animals is necessary for clinical translation.

Methods and Results

Mesenchymal stem cells, which resemble CDCs in size and thrombogenecity, have been associated with infarction following intracoronary infusion. To maximize CDC engraftment while avoiding infarction, we optimized the infusion protocol in 19 healthy pigs. A modified cocktail of CDCs in calcium-free PBS, 100U/mL heparin and 250μg/mL nitroglycerin eliminated infusion-related infarction. Subsequent infusion experiments in 17 pigs with post-infarct left ventricular dysfunction showed CDC doses ≥107 but <2.5×107 result in new myocardial tissue formation without infarction. In a pivotal randomized study, 7 infarcted pigs received 300,000 CDCs/kg (~107 total) and 7 received placebo (vehicle alone). Cardiac MRI 8 weeks later showed CDC treatment decreased relative infarct size (19.2% to 14.2% of left ventricle infarcted, p=0.01), while placebo did not (17.7% to 15.3%, p=0.22). End-diastolic volume increased in placebo, but not in CDC-treated animals. Hemodynamically, dP/dt max and dP/dt min were significantly better with CDC infusion. There was no difference between groups in the ability to induce ventricular tachycardia, nor was there any tumor or ectopic tissue formation.

Conclusions

Intracoronary delivery of CDCs in a pre-clinical model of post-infarct LV dysfunction results in formation of new cardiac tissue, reduces relative infarct size, attenuates adverse remodeling, and improves hemodynamics. The evidence of efficacy without obvious safety concerns at 8 weeks’ follow-up motivates human studies in post-MI patients and in chronic ischemic cardiomyopathy.

Background

Energy metabolism is essential for myocellular viability. The high-energy phosphates, ATP and phosphocreatine (PCr), are reduced in human myocardial infarction (MI), reflecting myocyte loss and/or decreased intracellular ATP generation by creatine kinase (CK), the heart's prime energy reserve. The pseudo-first-order CK rate-constant, k, measures intracellular CK reaction kinetics and is independent of myocyte number within sampled tissue. CK flux is defined as the product of [PCr] and k. CK flux and k have never been measured in human MI.

Methods and Results

Myocardial CK metabolite concentrations, k, and CK flux were measured noninvasively in fifteen patients 7-weeks to 16-years post-anterior MI using phosphorus magnetic resonance spectroscopy. In patients, mean myocardial [ATP] and [PCr] were 39-44% lower than in fifteen control subjects (PCr=5.4±1.2 in MI vs. 9.6±1.1 μmol/g.wet.wt. in controls, P<0.001; ATP=3.4±1.1 in MI vs. 5.5±1.3 μmol/g.wet.wt., P<0.001). The myocardial CK rate-constant, k, was normal in MI (0.31±0.08s-1) compared to controls (0.33±0.07 s-1), as was PCr/ATP (1.74±0.27 in MI vs. 1.87±0.45). However, CK flux was halved in MI (to 1.7±0.5 μmol[g.s]-1 vs. 3.3±0.8, P<0.001).

Conclusions

These first observations of CK kinetics in prior human MI demonstrate that CK ATP supply is significantly reduced due to substrate depletion, likely attributable to myocyte loss. That k and PCr/ATP are unchanged in MI, is consistent with the preservation of intracellular CK metabolism in surviving myocytes. Importantly, the results support therapies that primarily ameliorate the effects of tissue and substrate loss post-MI and that reduce energy demand, rather than those that increase energy transfer or workload in surviving tissue.

Background

Myocardial scarring from infarction (MI) or nonischemic fibrosis forms an arrhythmogenic substrate. The Selvester QRS-score has been extensively validated for estimating MI scar size in the absence of ECG confounders, but has not been tested to quantify scar in patients with hypertrophy, bundle branch/fascicular blocks or nonischemic cardiomyopathy. We assessed the hypotheses that (1) QRS-scores (modified for each ECG confounder) correctly identify and quantify scar in ischemic and nonischemic patients as compared to the reference standard of Cardiac Magnetic Resonance-Late Gadolinium Enhancement (CMR-LGE) and (2) QRS-estimated scar size predicts inducible sustained monomorphic ventricular tachycardia (MVT) during electrophysiologic (EP) testing.

Methods and Results

162 patients with left ventricular ejection fraction ≤35% (95 ischemic, 67 nonischemic) received 12-lead ECG and CMR-LGE before defibrillator (ICD) implantation for primary prevention of sudden cardiac death. QRS-scores correctly diagnosed CMR-scar presence with receiver operating characteristics area under the curve (AUC)=0.91 and correlation for scar quantification of r=0.74, p<0.0001, for all patients. Performance within hypertrophy, conduction defect and nonischemic subgroups ranged from AUC 0.81-0.94, r=0.60-0.80, p<0.001 for all. Among the 137 patients undergoing EP or device testing, each 3 point QRS-score increase (9% LV scarring) was associated with an odds ratio for inducing MVT of 2.2 [95% CI: 1.5-3.2, p<0.001] for all patients, 1.7 [1.0-2.7, p=0.04] for ischemics and 2.2 [1.0-5.0, p=0.05] for nonischemics.

Conclusions

QRS-scores identify and quantify scar in ischemic and nonischemic cardiomyopathy patients despite ECG confounders. Higher QRS-estimated scar size is associated with increased arrhythmogenesis and warrants further study as a risk-stratifying tool.

There is significant regional variability in the quality of care provided in the United States. This article compares regional performance for three measures that focus on transitions in care, and the care of patients with multiple conditions. Admissions for people with ambulatory care-sensitive conditions, hospital readmissions within 30 days of discharge, and compliance with practice guidelines for people with three chronic conditions (congestive heart failure, chronic obstructive pulmonary disease, and diabetes) were analyzed using data drawn from the Centers for Medicare & Medicaid Services’ Standard Analytic Files for 5% of a 2004 national sample of Medicare beneficiaries which was divided by hospital referral regions and regional performance. There were significant regional differences in performance which we hypothesize could be improved through better care coordination and system management.

Structured Abstract

Objectives

We examined whether the presence and extent of late gadolinium enhancement (LGE) by CMR predict adverse outcomes in nonischemic cardiomyopathy (NICM) patients.

Background

Morbidity and mortality is high in NICM patients. However, the clinical course of an individual patient is unpredictable and current risk stratification approaches are limited. Cardiovascular magnetic resonance (CMR) detects myocardial fibrosis, which appears as LGE after contrast administration and may convey prognostic importance.

Methods

In a prospective cohort study, 65 NICM patients with LVEF ≤35% underwent CMR before placement of an internal cardioverter defibrillator (ICD) for primary prevention of sudden cardiac death. CMRs were analyzed for the presence and extent of LGE, and for LV function, volumes, and mass. Patients were followed for an index composite endpoint of three cardiac events: hospitalization for heart failure, appropriate ICD firing, and cardiac death.

Results

42% (n=27) of patients had CMR LGE, averaging 10±13% of LV mass. During a 17 month median follow-up, 44% (n=12) of patients with LGE had an index composite outcome event, versus only 8% (n=3) of those without LGE (p<0.001 for Kaplan-Meier survival curves). After adjustment for LV volume index and functional class, patients with LGE had an eight-fold higher risk of experiencing the primary outcome (hazard ratio 8.2, 95% CI 2.2–30.9, p=0.002).

Conclusions

CMR LGE in NICM patients strongly predicts adverse cardiac outcomes. CMR LGE may represent the end-organ consequences of sustained adrenergic activation and adverse LV remodeling, and its identification may significantly improve risk stratification strategies in this high risk population.

Condensed Abstract

Predicting prognosis in nonischemic cardiomyopathy patients is challenging and current risk stratification approaches are limited. Cardiovascular magnetic resonance (CMR) detects myocardial fibrosis, which appears as late gadolinium enhancement (LGE). The presence of LGE predicts an eight-fold increased risk of an adverse cardiac outcome (HR 8.1, 95% CI 1.9–33.7, p=0.004), after controlling for baseline variables. CMR LGE may reflect the transition from compensated to decompensated state resulting from long-term stressors such as sustained adrenergic activation and/or the mechanical disadvantages caused by LV remodeling leading to increasing fibrosis. Identifying CMR LGE may significantly improve risk stratification strategies in this high risk population.

Background

The extent of the peri-infarct zone by magnetic resonance imaging (MRI) has been related to all-cause mortality in patients with coronary artery disease. This relationship may result from arrhythmogenesis in the infarct border. However, the relationship between tissue heterogeneity in the infarct periphery and arrhythmic substrate has not been investigated. In the present study, we quantify myocardial infarct heterogeneity by contrast-enhanced MRI and relate it to an electrophysiological marker of arrhythmic substrate in patients with left ventricular (LV) systolic dysfunction undergoing prophylactic implantable cardioverter defibrillator placement.

Methods and Results

Before implantable cardioverter defibrillator implantation for primary prevention of sudden cardiac death, 47 patients underwent cine and contrast-enhanced MRI to measure LV function, volumes, mass, and infarct size. A method for quantifying the heterogeneous infarct periphery and the denser infarct core is described. MRI indices were related to inducibility of sustained monomorphic ventricular tachycardia during electrophysiological or device testing. For the noninducible versus inducible patients, LV ejection fraction (30±10% versus 29±7%, P=0.79), LV end-diastolic volume (220±70 versus 228±57 mL, P=0.68), and infarct size by standard contrast-enhanced MRI definitions (P=NS) were similar. Quantification of tissue heterogeneity at the infarct periphery was strongly associated with inducibility for monomorphic ventricular tachycardia (noninducible versus inducible: 13±9 versus 19±8 g, P=0.015) and was the single significant factor in a stepwise logistic regression.

Conclusions

Tissue heterogeneity is present and quantifiable within human infarcts. More extensive tissue heterogeneity correlates with increased ventricular irritability by programmed electrical stimulation. These findings support the hypothesis that anatomic tissue heterogeneity increases susceptibility to ventricular arrhythmias in patients with prior myocardial infarction and LV dysfunction.

Background

The progression of pressure-overload left ventricular hypertrophy (LVH) to chronic heart failure (CHF) may involve a relative deficit in energy supply and/or delivery.

Methods and Results

We measured myocardial creatine kinase (CK) metabolite concentrations and adenosine triphosphate (ATP) synthesis through CK, the primary energy reserve of the heart, to test the hypothesis that ATP flux through CK is impaired in patients with LVH and CHF. Myocardial ATP levels were normal, but creatine phosphate levels were 35% lower in LVH patients (n= 10) than in normal subjects (n= 14, P< 0.006). Left ventricular mass and CK metabolite levels in LVH were not different from those in patients with LVH and heart failure (LVH+CHF, n= 10); however, the myocardial CK pseudo first-order rate constant was normal in LVH (0.36±0.04 s−1 in LVH versus 0.32±0.06 s−1 in normal subjects) but halved in LVH+CHF (0.17±0.06 s−1, P < 0.001). The net ATP flux through CK was significantly reduced by 30% in LVH (2.2 ± 0.7 μmol · g−1 · s−1, P < 0.011) and by a dramatic 65% in LVH+CHF (1.1±0.4 μmol · g−1 · s−1, P< 0.001) compared with normal subjects (3.1 ± 0.8 μmol · g−1 · s−1).

Conclusions

These first observations in human LVH demonstrate that it is not the relative or absolute CK metabolite pool sizes but rather the kinetics of ATP turnover through CK that distinguish failing from nonfailing hypertrophic hearts. Moreover, the deficit in ATP kinetics is similar in systolic and nonsystolic heart failure and is not related to the severity of hypertrophy but to the presence of CHF. Because CK temporally buffers ATP, these observations support the hypothesis that a deficit in myofibrillar energy delivery contributes to CHF pathophysiology in human LVH.

Conventional approaches for the treatment of myocardial ischemia increase coronary blood flow or reduce myocardial demand. To determine whether a rightward shift in the hemoglobin–oxygen saturation curve would reduce the metabolic and contractile effects of a myocardial oxygen-supply imbalance, we studied the impact of a potent synthetic allosteric modifier of hemoglobin–oxygen affinity, a 2-[4-[[(3,5-disubstituted anilino)carbonyl]methyl] phenoxy] -2-methylproprionic acid derivative (RSR13), during low-flow ischemia. Changes in myocardial high-energy phosphate levels and pH were studied by 31P nuclear magnetic resonance (NMR) spectroscopy in 12 open-chest dogs randomized to receive RSR13 or vehicle control during a reversible reduction of left anterior descending (LAD) coronary artery blood flow. Changes in cardiac metabolites and regional ventricular function studied by pressure segment–length relations were also investigated in additional animals before and after RSR13 administration during low-flow LAD ischemia. The intravenous administration of RSR13 before ischemia resulted in a substantial increase in the mean hemoglobin p50 and attenuated the decline in cardiac creatine phosphate/adenosine triphosphate (PCr/ATP), percent PCr, and pH during ischemia without a change in regional myocardial blood flow, heart rate, or systolic blood pressure. RSR13 given after the onset of low-flow ischemia also improved cardiac PCr/ATP ratios and regional function as measured by fractional shortening and regional work. Thus, synthetic allosteric reduction in hemoglobin–oxygen affinity may be a new and important therapeutic strategy to ameliorate the metabolic and functional consequences of cardiac ischemia.

J. Clin. Invest. 103:739–746 (1999)