Pulmonary blood flow and its distribution in highly trained endurance athletes and healthy control subjects

Pulmonary blood flow (PBF) is an important determinant of endurance sports performance, yet studies investigating adaptations of the pulmonary circulation in athletes are scarce. In the present study, we investigated PBF, its distribution, and heterogeneity at baseline and during intravenous systemic adenosine infusion in 10 highly trained male endurance athletes and 10 untrained but fit healthy controls, using positron emission tomography and [15O]water at rest and during adenosine infusion at supine body posture. Our results indicate that PBF at rest and during adenosine stimulation was similar in both groups (213 ± 55 and 563 ± 138 ml·100 ml−1·min−1 in athletes and 206 ± 83 and 473 ± 212 ml·100 ml−1·min−1 in controls, respectively). Although the PBF response to adenosine was thus unchanged in athletes, overall PBF heterogeneity was reduced from rest to adenosine infusion (from 84 ± 18 to 70 ± 19%, P < 0.05), while remaining unchanged in healthy controls (77 ± 16 to 85 ± 33%, P = 0.4). Additionally, there was a marked gravitational influence on general PBF distribution so that clear dorsal dominance was observed both at rest and during adenosine infusion, but training status did not have an effect on this distribution. Regional blood flow heterogeneity was markedly lower in the high-perfusion dorsal areas, both at rest and during adenosine, in all subjects, but flow heterogeneity in dorsal area tended to further decrease in response to adenosine in athletes. In conclusion, reduced blood flow heterogeneity in response to adenosine in endurance athletes may be a reflection of capillary reserve, which is more extensively recruitable in athletes than in matched healthy control subjects.

Phenotyping of left and right ventricular function in mouse models of compensated hypertrophy and heart failure with cardiac MRI

Background

Left ventricular (LV) and right ventricular (RV) function have an important impact on symptom occurrence, disease progression and exercise tolerance in pressure overload-induced heart failure, but particularly RV functional changes are not well described in the relevant aortic banding mouse model. Therefore, we quantified time-dependent alterations in the ventricular morphology and function in two models of hypertrophy and heart failure and we studied the relationship between RV and LV function during the transition from hypertrophy to heart failure.

Methods

MRI was used to quantify RV and LV function and morphology in healthy (n = 4) and sham operated (n = 3) C57BL/6 mice, and animals with a mild (n = 5) and a severe aortic constriction (n = 10).

Results

Mice subjected to a mild constriction showed increased LV mass (P<0.01) and depressed LV ejection fraction (EF) (P<0.05) as compared to controls, but had similar RVEF (P>0.05). Animals with a severe constriction progressively developed LV hypertrophy (P<0.001), depressed LVEF (P<0.001), followed by a declining RVEF (P<0.001) and the development of pulmonary remodeling, as compared to controls during a 10-week follow-up. Myocardial strain, as a measure for local cardiac function, decreased in mice with a severe constriction compared to controls (P<0.05).

Conclusions

Relevant changes in mouse RV and LV function following an aortic constriction could be quantified using MRI. The well-controlled models described here open opportunities to assess the added value of new MRI techniques for the diagnosis of heart failure and to study the impact of new therapeutic strategies on disease progression and symptom occurrence.

Abstract 28: In Vivo Knockdown of Mirna-15b Results in Increased Cardiac Hypertrophy and Fibrosis in Response to Pressure Overload of the Mouse Heart

MiRNAs play an important role in the control of diverse aspects of cardiac function. MiR-15b is highly expressed in the heart and is found consistently upregulated in hypertrophic and failing hearts. To investigate the function of miR-15b in the heart we set out two experiments. In the first experiment we generated two independent transgenic mouse lines that drive miR-15b expression under the αMHC-promotor and show a three and four fold overexpression of miR-15b. Strikingly, both lines show a decrease in heart weight/tibia length of 20% in adult and aged mice when compared to littermate controls. We investigated the response of these transgenic mice to thoracic aorta constriction (TAC) and found no differences in the hypertrophic response or in cardiac function measured by echocardiography between wild-type and transgenic mice. In a second experiment, we inhibited miR-15b using LNA-based antimiRs. In these mice, TAC resulted in an increased hypertrophic response and increased cardiac fibrosis when compared to a negative control antimiR.

A wide range of predicted targets of miR-15 belong to the pathways of the TGFβ-superfamily and using a smad-dependent reporter we show that miR-15b inhibits TGFβ-induced Smad activity in HepG2 cells. One of the predicted targets in the TGFβ pathway is TGFβ receptor 1 (TGFβR1), of which the 3’UTR contains six predicted miR-15 binding sites. This suggests that the phenotype in the transgenic mice and after knockdown of miR-15b may be (partly) mediated by repression of TGFβR1. Indeed, in the adult miR-15b transgenic hearts we found a downregulation of TGFβR1 mRNA and protein and we confirmed binding of miR-15 to the TGFβR1 3’UTR by luciferase assays.

In conclusion, miR-15b causes a cardiac hypotrophic phenotype at baseline in transgenic mice and inhibition of miR-15b leads to a stronger hypertrophic and fibrotic response after TAC. Furthermore miR-15b inhibits the TGFβ pathway by targeting the TGFβR1 and possibly other targets in this pathway.

This research is funded by the Dutch Heart Foundation (NHF grant #2007B077).

Apelin enhances cardiac neovascularization after myocardial infarction by recruiting aplnr+ circulating cells

RATIONALE

Neovascularization stimulated by local or recruited stem cells after ischemia is a key process that salvages damaged tissue and shows similarities with embryonic vascularization. Apelin receptor (Aplnr) and its endogenous ligand apelin play an important role in cardiovascular development. However, the role of apelin signaling in stem cell recruitment after ischemia is unknown.

OBJECTIVE

To investigate the role of apelin signaling in recruitment after ischemia.

METHODS AND RESULTS

Aplnr was specifically expressed in circulating cKit+/Flk1+ cells but not in circulating Sca1+/Flk1+ and Lin+ cells. cKit+/Flk1+/Aplnr+ cells increased significantly early after myocardial ischemia but not after hind limb ischemia, indicative of an important role for apelin/Aplnr in cell recruitment during the nascent biological repair response after myocardial damage. In line with this finding, apelin expression was upregulated in the infarcted myocardium. Injection of apelin into the ischemic myocardium resulted in accelerated and increased recruitment of cKit+/Flk1+/Aplnr+ cells to the heart. Recruited Aplnr+/cKit+/Flk1+ cells promoted neovascularization in the peri-infarct area by paracrine activity rather than active transdifferentiation, resulting into cardioprotection as indicated by diminished scar formation and improved residual cardiac function. Aplnr knockdown in the bone marrow resulted in aggravation of myocardial ischemia-associated damage, which could not be rescued by apelin.

CONCLUSIONS

We conclude that apelin functions as a new and potent chemoattractant for circulating cKit+/Flk1+/Aplnr+ cells during early myocardial repair, providing myocardial protection against ischemic damage by improving neovascularization via paracine action.

Nucleotide excision DNA repair is associated with age-related vascular dysfunction

BACKGROUND

Vascular dysfunction in atherosclerosis and diabetes mellitus, as observed in the aging population of developed societies, is associated with vascular DNA damage and cell senescence. We hypothesized that cumulative DNA damage during aging contributes to vascular dysfunction.

METHODS AND RESULTS

In mice with genomic instability resulting from the defective nucleotide excision repair genes ERCC1 and XPD (Ercc1(d/-) and Xpd(TTD) mice), we explored age-dependent vascular function compared with that in wild-type mice. Ercc1(d/-) mice showed increased vascular cell senescence, accelerated development of vasodilator dysfunction, increased vascular stiffness, and elevated blood pressure at a very young age. The vasodilator dysfunction was due to decreased endothelial nitric oxide synthase levels and impaired smooth muscle cell function, which involved phosphodiesterase activity. Similar to Ercc1(d/-) mice, age-related endothelium-dependent vasodilator dysfunction in Xpd(TTD) animals was increased. To investigate the implications for human vascular disease, we explored associations between single-nucleotide polymorphisms of selected nucleotide excision repair genes and arterial stiffness within the AortaGen Consortium and found a significant association of a single-nucleotide polymorphism (rs2029298) in the putative promoter region of DDB2 gene with carotid-femoral pulse wave velocity.

CONCLUSIONS

Mice with genomic instability recapitulate age-dependent vascular dysfunction as observed in animal models and in humans but with an accelerated progression compared with wild-type mice. In addition, we found associations between variations in human DNA repair genes and markers for vascular stiffness, which is associated with aging. Our study supports the concept that genomic instability contributes importantly to the development of cardiovascular disease.

Uncoupling protein-2 expression and effects on mitochondrial membrane potential and oxidant stress in heart tissue

Myocardial uncoupling protein (UCP)-2 is increased with chronic peroxisome proliferator-activated receptor γ (PPARγ) stimulation, but the effect on membrane potential and superoxide is unclear. Wild-type (WT) and UCP-2 knockout (KO) mice were given a 3-week diet of control (C) or the PPARγ agonist pioglitazone (PIO; 50 μg/g-chow per day). In isolated mitochondria, UCP-2 content by Western blots, membrane potential (ΔΨm) by tetraphenylphosphonium (TPP), and relative superoxide levels by dihydroethidium (DHE) were measured. Oxygen respiration was determined at baseline and after 10 min anoxia-reoxygenation. PIO induced a 2-fold increase in UCP-2 and nuclear-bound PGC1α in WT mice with no UCP-2 expression in KO mice. Mitochondrial ΔΨm from WT mice on C and PIO diets was -166±4 mV and -147±6 mV, respectively (P<0.05). These values were lower than in UCP-2 KO mice on C and PIO (-180±4 mV and -180±4 mV, respectively; P<0.05). Maximal complex III inhibitable superoxide from WT mice on C and PIO diets was 22.5±1.3 and 17.8±1.1 AU, respectively (P<0.05), and were lower than UCP-2 KO on C and PIO (32.9±2.3 and 29.2±1.9 AU, respectively; P<0.05). Postanoxia, the respiratory control index (RCI) in mitochondria from WT mice with and without PIO was 2.5±0.3 and 2.4±0.2, respectively, and exceeded that of UCP-2 KO mice on C and PIO (1.2±0.1 and 1.4±0.1, respectively; P<0.05). In summary, chronic PPARγ stimulation leads to depolarization of the inner membrane and reduced superoxide of isolated heart mitochondria, which was critically dependent on increased expression of UCP-2. Thus, UCP-2 expression affords resistance to brief anoxia-reoxygenation.

Initiation of ventricular contraction as reflected in the aortic pressure waveform

Prior to aortic valve opening, aortic pressure is perturbed by ventricular contraction. The onset of this pressure perturbation coincides with the onset of the left ventricular (LV) isovolumic contraction, and hence will be referred to as the start of the arterially detected isovolumic contraction (AIC(start)). In the present study we test the hypothesis that the pressure perturbation indeed has a cardiac origin. In ten Yorkshire-Landrace swine, waveform intensity analysis demonstrated that AIC(start) was followed by a positive intensity wave (0.3 × 10(5) ± 0.3 × 10(5) W (m(2) s(2))(-1)). Timing analysis of LV and aortic pressure waveform showed that AIC(start) was preceded by a LV pressure perturbation (3.8 ± 1.8 ms, p < 0.001). These novel cardiac timing and aortic wave intensity findings reveal the cardiac origin of the pressure perturbation. In 15 Yorkshire-Landrace swine, myocardial motion analysis showed a significantly higher rate of segment shortening during the first part of the LV pressure perturbation. Therefore, both the LV and aortic pressure perturbation are most likely caused by the early phase of myocardial contraction, which also causes mitral valve closure. Consequently, AIC(start) is useful in the determination of the isovolumic contraction period, a well-known marker to quantify cardiac dysfunction.

Altered expression of mitochondrial electron transport chain proteins and improved myocardial energetic state during late ischemic preconditioning

Altered expression of mitochondrial electron transport proteins has been shown in early preconditioned myocardial tissue. We wished to determine whether these alterations persist in the Second Window of Protection (SWOP) and if so, whether a favorable energetic state is facilitated during subsequent ischemia. Fourteen pigs underwent a SWOP protocol with ten 2-minute balloon inflations in the LAD artery, each separated by 2 minutes reperfusion. Twenty-four hours later, mitochondria were isolated from SWOP and SHAM pig hearts and analyzed for uncoupling protein (UCP)-2 content by western blot analysis, proteomic changes by iTRAQ(®) and respiration by an oxygen electrode. In parallel in vivo studies, high-energy nucleotides were obtained by transmural biopsy from anesthetized SWOP and SHAM pigs at baseline and during sustained low-flow ischemia. Compared with SHAM mitochondria, ex vivo SWOP heart tissue demonstrated increased expression of UCP-2, Complex IV (cytochrome c oxidase) and Complex V (ATPase) proteins. In comparison with SHAM pigs during in vivo conditions, transmural energetics in SWOP hearts, as estimated by the free energy of ATP hydrolysis (ΔG(0)), were similar at baseline but had decreased by the end of low-flow ischemia (-57.0 ± 2.1 versus -51.1 ± 1.4 kJ/mol; P < 0.05). In conclusion, within isolated mitochondria from preconditioned SWOP hearts, UCP-2 is increased and in concert with enhanced Complex IV and V proteins, imparts a favorable energetic state during low-flow ischemia. These data support the notion that mitochondrial adaptations that may reduce oxidant damage do not reduce the overall efficiency of energetics during sustained oxygen deprivation.

Nitroso-redox balance in control of coronary vasomotor tone

Reactive oxygen species (ROS) are essential in vascular homeostasis but may contribute to vascular dysfunction when excessively produced. Superoxide anion (O(2)(·-)) can directly affect vascular tone by reacting with K(+) channels and indirectly by reacting with nitric oxide (NO), thereby scavenging NO and causing nitroso-redox imbalance. After myocardial infarction (MI), oxidative stress increases, favoring the imbalance and resulting in coronary vasoconstriction. Consequently, we hypothesized that ROS scavenging results in coronary vasodilation, particularly after MI, and is enhanced after inhibition of NO production. Chronically instrumented swine were studied at rest and during exercise before and after scavenging of ROS with N-(2-mercaptoproprionyl)-glycine (MPG, 20 mg/kg iv) in the presence or absence of prior inhibition of endothelial NO synthase (eNOS) with N(ω)-nitro-L-arginine (L-NNA, 20 mg/kg iv). In normal swine, MPG resulted in coronary vasodilation as evidenced by an increased coronary venous O(2) tension, and trends toward increased coronary venous O(2) saturation and decreased myocardial O(2) extraction. These effects were not altered by prior inhibition of eNOS. In MI swine, MPG showed a significant vasodilator effect, which surprisingly was abolished by prior inhibition of eNOS. Moreover, eNOS dimer/monomer ratio was decreased after MI, reflecting eNOS uncoupling. In conclusion, ROS exert a small coronary vasoconstrictor influence in normal swine, which does not involve scavenging of NO. This vasoconstrictor influence of ROS is slightly enhanced after MI. Since inhibition of eNOS abolished rather than augmented the vasoconstrictor influence of ROS in swine with MI, while eNOS dimer/monomer ratio was decreased, our data imply that uncoupled eNOS may be a significant source of O(2)(·-) after MI.

Endothelial dysfunction enhances the pulmonary and systemic vasodilator effects of phosphodiesterase-5 inhibition in awake swine at rest and during treadmill exercise

Cardiovascular disease is characterized by impaired exercise capacity and endothelial dysfunction, i.e. reduced bioavailability of nitric oxide (NO). Phosphodiesterase-5 (PDE5) inhibition is a promising vasodilator therapy, but its effects on pulmonary and systemic hemodynamic responses to exercise in the absence, and particularly in the presence, of endothelial dysfunction have not been studied. We investigated the effects of PDE5 inhibitor EMD360527 in chronically instrumented swine at rest and during exercise with and without NO synthase inhibition (N(ω)-nitro-l-arginine; NLA). PDE5 inhibition caused a 19 ± 3% decrease in systemic vascular resistance (SVR) and a 24 ± 4% decrease in pulmonary vascular resistance (PVR) at rest. At maximal exercise, PDE5 inhibition caused a 13 ± 1% decrease in SVR and a 29 ± 3% decrease in PVR. NLA enhanced PDE5-inhibition-induced pulmonary (decrease in PVR 32 ± 12% at rest and 41 ± 3% during exercise) and systemic (decrease in SVR 24 ± 5% at rest and 18 ± 3% during exercise) vasodilation. Similarly, NLA increased the pulmonary and systemic vasodilation to nitroprusside and 8-bromo-cyclic guanosine monophosphate (cGMP), indicating that inhibition of NO synthase increases responsiveness to stimulation of the NO/cGMP pathway. Thus, PDE5 inhibition causes pulmonary and systemic vasodilation that is, respectively, maintained and slightly blunted during exercise. The degree of dilation in both the pulmonary and systemic beds were paradoxically enhanced in the presence of reduced bioavailability of NO, suggesting that this vasodilator therapy is most effective in patients with cardiovascular disease.

Cytochrome P-450 2C9 exerts a vasoconstrictor influence on coronary resistance vessels in swine at rest and during exercise

A significant endothelium-dependent vasodilation persists after inhibition of nitric oxide synthase (NOS) and cyclooxygenase (COX) in the coronary vasculature, which has been linked to the activation of cytochrome P-450 (CYP) epoxygenases expressed in endothelial cells and subsequent generation of vasodilator epoxyeicosatrienoic acids. Here, we investigated the contribution of CYP 2C9 metabolites to regulation of porcine coronary vasomotor tone in vivo and in vitro. Twenty-six swine were chronically instrumented. Inhibition of CYP 2C9 with sulfaphenazole (5 mg/kg iv) alone had no effect on bradykinin-induced endothelium-dependent coronary vasodilation in vivo but slightly attenuated bradykinin-induced vasodilation in the presence of combined NOS/COX blockade with N(ω)-nitro-L-arginine (20 mg/kg iv) and indomethacin (10 mg/kg iv). Sulfaphenazole had minimal effects on coronary resistance vessel tone at rest or during exercise. Surprisingly, in the presence of combined NOS/COX blockade, a significant coronary vasodilator response to sulfaphenzole became apparent, both at rest and during exercise. Subsequently, we investigated in isolated porcine coronary small arteries (∼250 μm) the possible involvement of reactive oxygen species (ROS) in the paradoxical vasoconstrictor influence of CYP 2C9 activity. The vasodilation by bradykinin in vitro in the presence of NOS/COX blockade was markedly potentiated by sulfaphenazole under control conditions but not in the presence of the ROS scavenger N-(2-mercaptoproprionyl)-glycine. In conclusion, CYP 2C9 can produce both vasoconstrictor and vasodilator metabolites. Production of these metabolites is enhanced by combined NOS/COX blockade and is critically dependent on the experimental conditions. Thus production of vasoconstrictors slightly outweighed the production of vasodilators at rest and during exercise. Pharmacological stimulation with bradykinin resulted in vasodilator CYP 2C9 metabolite production when administered in vivo, whereas vasoconstrictor CYP 2C9 metabolites, most likely ROS, were dominant when administered in vitro.

The coronary circulation in exercise training

Exercise training (EX) induces increases in coronary transport capacity through adaptations in the coronary microcirculation including increased arteriolar diameters and/or densities and changes in the vasomotor reactivity of coronary resistance arteries. In large animals, EX increases capillary exchange capacity through angiogenesis of new capillaries at a rate matched to EX-induced cardiac hypertrophy so that capillary density remains normal. However, after EX coronary capillary exchange area is greater (i.e., capillary permeability surface area product is greater) at any given blood flow because of altered coronary vascular resistance and matching of exchange surface area and blood flow distribution. The improved coronary capillary blood flow distribution appears to be the result of structural changes in the coronary tree and alterations in vasoreactivity of coronary resistance arteries. EX also alters vasomotor reactivity of conduit coronary arteries in that after EX, α-adrenergic receptor responsiveness is blunted. Of interest, α- and β-adrenergic tone appears to be maintained in the coronary microcirculation in the presence of lower circulating catecholamine levels because of increased receptor responsiveness to adrenergic stimulation. EX also alters other vasomotor control processes of coronary resistance vessels. For example, coronary arterioles exhibit increased myogenic tone after EX, likely because of a calcium-dependent PKC signaling-mediated alteration in voltage-gated calcium channel activity in response to stretch. Conversely, EX augments endothelium-dependent vasodilation throughout the coronary arteriolar network and in the conduit arteries in coronary artery disease (CAD). The enhanced endothelium-dependent dilation appears to result from increased nitric oxide bioavailability because of changes in nitric oxide synthase expression/activity and decreased oxidant stress. EX also decreases extravascular compressive forces in the myocardium at rest and at comparable levels of exercise, mainly because of decreases in heart rate and duration of systole. EX does not stimulate growth of coronary collateral vessels in the normal heart. However, if exercise produces ischemia, which would be absent or minimal under resting conditions, there is evidence that collateral growth can be enhanced. While there is evidence that EX can decrease the progression of atherosclerotic lesions or even induce the regression of atherosclerotic lesions in humans, the evidence of this is not strong due to the fact that most prospective trials conducted to date have included other lifestyle changes and treatment strategies by necessity. The literature from large animal models of CAD also presents a cloudy picture concerning whether EX can induce the regression of or slow the progression of atherosclerotic lesions. Thus, while evidence from research using humans with CAD and animal models of CAD indicates that EX increases endothelium-dependent dilation throughout the coronary vascular tree, evidence that EX reverses or slows the progression of lesion development in CAD is not conclusive at this time. This suggests that the beneficial effects of EX in CAD may not be the result of direct effects on the coronary artery wall. If this suggestion is true, it is important to determine the mechanisms involved in these beneficial effects.

Sunitinib-Induced Systemic Vasoconstriction in Swine Is Endothelin Mediated and Does Not Involve Nitric Oxide or Oxidative Stress

Angiogenesis inhibition with agents targeting tyrosine kinases of vascular endothelial growth factor receptors is an established anticancer treatment, but is, unfortunately, frequently accompanied by systemic hypertension and cardiac toxicity. Whether vascular endothelial growth factor receptor antagonism also has adverse effects on the pulmonary and coronary circulations is presently unknown. In chronically instrumented awake swine, the effects of the vascular endothelial growth factor receptor antagonist sunitinib on the systemic, pulmonary, and coronary circulation were studied. One week after sunitinib (50 mg PO daily), mean aortic blood pressure (MABP) had increased from 83±5 mm Hg at baseline to 97±6 mm Hg ( P <0.05) because of a 57±20% increase in systemic vascular resistance as cardiac output decreased. In contrast, sunitinib had no discernible effects on pulmonary and coronary hemodynamics or cardiac function. We subsequently investigated the mechanisms underlying the sunitinib-induced systemic hypertension. Intravenous administration of NO synthase inhibitor N G -nitro- l -arginine increased MABP by 24±1 mm Hg under baseline conditions, whereas it increased MABP even further after sunitinib administration (32±3 mm Hg; P <0.05). Reactive oxygen species scavenging with a mixture of antioxidants lowered MABP by 13±2 mm Hg before but only by 5±2 mm Hg ( P <0.05) after sunitinib administration. However, intravenous administration of the dual endothelin A/endothelin B receptor blocker tezosentan, which did not lower MABP at baseline, completely reversed MABP to presunitinib values. These findings indicate that sunitinib produces vasoconstriction selectively in the systemic vascular bed, without affecting pulmonary or coronary circulations. The sunitinib-mediated systemic hypertension is principally attributed to an increased vasoconstrictor influence of endothelin, with no apparent contributions of a loss of NO bioavailability or increased oxidative stress.

Different algorithms for quantitative analysis of myocardial infarction with DE MRI: comparison with autopsy specimen measurements

RATIONALE AND OBJECTIVES

To compare two semiautomated methods for measurement of infarcted myocardium area on delayed contrast enhanced magnetic resonance imaging, with histopathology findings as standard of reference.

MATERIALS AND METHODS

Percentage area of myocardial infarction was measured in 10 Yorkshire landrace pigs manually and using two semiautomated methods. The first (standard deviation method) used two operator-selected regions of interest (ROIs) and nine different cutoff values (one to nine times the standard deviation of signal intensity in normal myocardium) to identify infarction. The second (threshold method) used threshold values based on percentages of maximum signal intensity to identify infarction. Results were compared with histopathology findings.

RESULTS

Difference between percentage area of infarction obtained with standard deviation method and autopsy specimens was in the range: -13.5% to +13.2%. With threshold method (thresholds from 30% to 90% of signal intensity), difference was -15% to +23%. Manual contouring underestimated infarcted area by 2% comparing to autopsy results. The best agreement between histopathology and semi-automated software was achieved for 4 standard deviations with standard deviation method: difference -0.45%, and for a percentage threshold of 70% (difference +0.67%) with threshold method. However, with standard deviation method, there was statistically significant difference between ROIs based on their location in viable myocardium: mean difference 1.7 ± 4%, P < .0001.

CONCLUSION

Semiautomated measurement of myocardial infarcted area on delayed enhanced magnetic resonance images performs well compared to autopsy. The threshold method, based on percentages of maximum signal intensity is preferable over standard deviation method, which is more susceptible to variability from location of ROIs within viable myocardium.