Atrial contractile protein content and function are preserved in patients with coronary artery disease and atrial fibrillation.

OBJECTIVES: Atrial fibrillation (AF) causes atrial contractile dysfunction. The focus of this study was to determine whether the contractile deficit of human AF is the result of altered contractile protein abundance and/or function. METHODS: Atrial tissue from patients with chronic AF undergoing open-heart surgery was compared with the tissue from patients in normal sinus rhythm (NSR). Myosin isoform composition and content were determined. Intact native thin filament and cardiac myosin contractile protein performance were independently assessed in an in-vitro motility assay. RESULTS: Myosin isoform expression and total myosin content were not different between AF and NSR. Calcium-activated native thin filament function was similar between AF and NSR as measured by calcium sensitivity and maximal activation. Myosin isolated from the atria of AF and NSR groups showed similar unloaded shortening speeds and isometric force generation. CONCLUSION: Unlike human ventricular dysfunction where contractile protein function is directly affected, the contractile deficit of AF is not the result of alterations in myosin content or contractile protein function.

Atypical presentation of anomalous origin of the left main coronary artery from the pulmonary artery.

Anomalous origin of the left main coronary artery from the pulmonary artery (ALCAPA) is a rare congenital anomaly that usually presents in childhood. Ninety percent of the patients with ALCAPA die within the first year of life without surgical intervention. In adults, ALCAPA is associated with left ventricular dysfunction, mitral regurgitation, and sudden death. The present report describes the case of an adult patient who presented with an abnormal stress test and ALCAPA was diagnosed during cardiac catheterization.

Valves of the deep venous system: an overlooked risk factor.

Deep venous valves are frequent sites of deep venous thrombosis initiation. However, the possible contribution of the valvular sinus endothelium has received little attention in studies of thrombosis risk. We hypothesized that the endothelium of valve sinus differs from that of vein lumen with up-regulation of anticoagulant and down-regulation of procoagulant activities in response to the local environment. In pursuit of this hypothesis, we quantified endothelial protein C receptor (EPCR), thrombomodulin (TM), and von Willebrand factor (VWF) by immunofluorescence in great saphenous veins harvested at cardiac bypass surgery. We found significantly increased expression of EPCR and TM in the valvular sinus endothelium as opposed to the vein lumenal endothelium, and the opposite pattern with VWF (paired t test for TM and EPCR, each P < .001; for VWF, P = .01). These data support our hypothesis and suggest that variation in valvular sinus thromboresistance may be an important factor in venous thrombogenesis.

Matrix metalloproteinase and tissue inhibitor expression in atherosclerotic and nonatherosclerotic thoracic aortic aneurysms.

OBJECTIVES: The altered expression of matrix metalloproteinases and their inhibitors influences the formation of atherosclerotic abdominal aortic aneurysms. Their association with thoracic aneurysms is less clear. This study describes the expression of metalloproteinases and their inhibitors in atherosclerotic and nonatherosclerotic thoracic aneurysms, and compares these with age-matched controls. METHODS: Matrix metalloproteinase-2 and 9 activity were measured by antibody capture, and tissue inhibitor-1 and 2 levels were measured by enzyme-linked immunosorbent assay in 24 patients with atherosclerotic aneurysms and in 63 patients with nonatherosclerotic aneurysms. Gene expression was assessed with reverse transcriptase polymerase chain reaction. The results were compared with 17 controls. RESULTS: Data are in nanograms per milligram of protein. Matrix metalloproteinase-2 activity was greater in controls than in the atherosclerotic and nonatherosclerotic groups (80 +/- 67 vs 49 +/- 50 and 35 +/- 44, P = .002). Matrix metalloproteinase-9 activity was greater in the atherosclerotic group than in the nonatherosclerotic group and controls (11.7 +/- 15.7 vs 2.5 +/- 2.2 and 1.7 +/- 1.9, P = .001). Tissue inhibitor-1 and 2 levels were greater in controls than in either aneurysm group (tissue inhibitor of metalloproteinase-1: 376 +/- 192 vs 234 +/- 233 and 174 +/- 148, P = .003; tissue inhibitor of metalloproteinase-2: 143 +/- 74 vs 14 +/- 13 and 27 +/- 43, P < .001). Atherosclerotic aneurysms expressed more matrix metalloproteinase mRNA than controls. CONCLUSIONS: The metalloproteinase/tissue inhibitor phenotype of atherosclerotic thoracic aneurysms is similar to that of abdominal aneurysms. The diminished expression of metalloproteinases and tissue inhibitors in nonatherosclerotic thoracic aneurysms relative to aged controls may represent a loss of smooth muscle cells.

Acto-myosin crossbridge kinetics in humans with coronary artery disease: influence of sex and diabetes mellitus.

Risk of heart failure (HF) is influenced by sex and diabetes mellitus (DM). To better understand these interactions, sub-epicardial myocardium from 26 patients with coronary artery disease (CAD) undergoing coronary bypass surgery was examined in vitro using sinusoidal length perturbation analysis at varying [Ca(2+)] to determine the viscoelastic properties of myofilaments related to acto-myosin crossbridge kinetics. Half of the patients had CAD only (four female, F-CAD; nine male, M-CAD), while the other half had both CAD and Type 2 DM (six F-DM; seven M-DM). At maximal and sub-maximal myofilament Ca(2+) activation there was a significant effect of sex and disease on frequency of maximum oscillatory work output during sinusoidal perturbation (P<0.05). Myofilaments from F-CAD produced oscillatory work at significantly higher frequencies compared with M-CAD, while myofilaments from F-DM and M-DM produced work at similar frequencies. Correspondingly, minimum viscoelastic stiffness at maximum Ca(2+) activation occurred at significantly higher frequencies in F-CAD (5.0+/-0.3 Hz) than M-CAD (3.3+/-0.3 Hz), but at similar frequencies in F-DM (3.7+/-0.3 Hz) and M-DM (4.3+/-0.2 Hz). Thus, sex influences acto-myosin crossbridge kinetics in myofilaments isolated from CAD patients. These sex-related differences were absent in DM, suggesting that differences in the properties of cardiac muscle contribute to reported sex differences in the incidence and mortality of HF in DM.

Regional differences in the force-frequency relation of human left ventricular myocardium in mitral regurgitation: implications for ventricular shape.

Sphericalization of the left ventricular (LV) chamber shape in patients with mitral regurgitation (MR) contributes to increased LV wall stress and energy consumption. On the basis of previous observations, we hypothesized the existence of regional differences in the force-frequency relation (FFR) within the LV that may contribute to its shape. Accordingly, in the present study, we assessed regional variation in the FFR in patients undergoing surgery for chronic, nonischemic MR with class II-III heart failure symptoms and related our findings to the in vivo LV shape. FFRs (steady-state isometric twitches, 0.2-3.4 Hz, 37 degrees C) were evaluated in MR myocardium from the LV subepicardial free wall (MR-FW) and papillary muscle (MR-PM) and from the subepicardial free wall in coronary artery bypass graft patients with normal LV contraction patterns [nonfailing (NF)]. Ascending slope, optimal stimulation frequency, and maximal twitch tension of the FFR were depressed in MR-FW and MR-PM compared with NF (P < 0.05). FFR depression was greater in MR-PM than in MR-FW. Between 107 and 134 beats/min, twitch tension became weaker in MR-PM, whereas it increased in MR-FW. Elevation of intracellular cAMP with forskolin eliminated FFR depression in MR-FW but not in MR-PM. MR-PM also had a 35% lower myosin heavy chain content and slowed twitch kinetics. In MR patients, the echocardiographic end-diastolic LV shape (end-diastolic eccentricity index = long axis/short axis) correlated with the ratio of ascending FFR slopes such that the end-diastolic eccentricity index increased 10% per 15% increase in slope ratio (r = 0.88, P = 0.01). These regional differences in the frequency dependence of contractility between the free wall and papillary myocardium may contribute to changes in LV shape in MR as well as during exercise.

Thin-filament-based modulation of contractile performance in human heart failure.

BACKGROUND: The contribution of the sarcomere's thin filament to the contractile dysfunction of human cardiomyopathy is not well understood. METHODS AND RESULTS: We have developed techniques to isolate and functionally characterize intact (native) thin filaments obtained from failing and nonfailing human ventricular tissue. By use of in vitro motility and force assays, native thin filaments from failing ventricular tissue exhibited a 19% increase in maximal velocity but a 27% decrease in maximal contractile force compared with nonfailing myocardium. Native thin filaments isolated from human myocardium after left ventricular assist device support demonstrated a 37% increase in contractile force. Dephosphorylation of failing native thin filaments resulted in a near-normalization of thin-filament function, implying a phosphorylation-mediated mechanism. Tissue expression of the protein kinase C isoforms alpha, beta1, and beta2 was increased in failing human myocardium and reduced after left ventricular assist device support. CONCLUSIONS: These novel findings demonstrate that (1) the thin filament is a key modulator of contractile performance in the failing human heart, (2) thin-filament function is restored to near normal levels after LVAD support, and (3) the alteration of thin-filament function in failing human myocardium is mediated through phosphorylation, most likely through activation of protein kinase C.

Matrix metalloproteinase activity in thoracic aortic aneurysms associated with bicuspid and tricuspid aortic valves.

OBJECTIVE: Matrix metalloproteinases are endopeptidases that function in cell matrix turnover. Abnormal matrix metalloproteinase activity has been implicated in the formation of atherosclerotic abdominal aortic aneurysms. Recent studies suggest that abnormal matrix metalloproteinase activity may also be associated with the formation of atherosclerotic and nonatherosclerotic thoracic aortic aneurysms. Bicuspid aortic valves are associated with an intrinsic aortic pathology that predisposes to formation of proximal thoracic aneurysms while tricuspid aortic valves are not. The objective of this study was to compare the activities of matrix metalloproteinases and levels of their inhibitors in thoracic aneurysms of patients with bicuspid and tricuspid aortic valves. METHODS: Endogenous and total activity of matrix metalloproteinase-2 and matrix metalloproteinase-9 were measured in proximal nonatherosclerotic thoracic aortic aneurysms of 16 patients with bicuspid aortic valves and 12 patients with tricuspid aortic valves. Levels of tissue inhibitor metalloproteinase-1 and -2 were also measured. Results were standardized to total protein (mg). RESULTS: Total matrix metalloproteinase-2 activity was greater in aneurysms associated with bicuspid valves when compared with those from tricuspid valves (43 +/- 11 ng/mg vs 14 +/- 2 ng/mg, P =.02). Total matrix metalloproteinase-9 activity was also greater in aneurysms associated with bicuspid aortic valves (4.0 +/- 0.9 vs 1.5 +/- 0.3, P =.02). There was no meaningful difference between groups in levels of tissue inhibitor-1 and -2. CONCLUSION: The increased activity of matrix metalloproteinases in the walls of aneurysms associated with bicuspid aortic valves may partly explain the predilection to aneurysm formation in these patients.

Myosin from failing and non-failing human ventricles exhibit similar contractile properties.

In non-failing human myocardium, V1 myosin comprises a small amount (<10%) of the total myosin content, whereas end-stage failing hearts contain nearly 100% V3 myosin. It has been suggested that this shift in V1 myosin isoform content may contribute to the contractile deficit in human myocardial failure. To test this hypothesis, myosin was isolated from human failing and non-failing ventricles, and non-failing atria. Performance was assessed in in vitro motility and isometric force assays. Consistent with prior reports, a small amount of V1 myosin was present in both non-failing (6.2 +/- 1.0%) and failing (3.5 +/- 1.4%) ventricular tissues. No difference in isometric force or unloaded shortening velocity was observed for failing and non-failing ventricular myosin irrespective of myosin isoform content. Atrial tissue expressing predominantly V1 myosin (66.7 +/- 4.1%) generated half the force but greater velocity compared with ventricular tissue, expressing predominantly V3 myosin. In additional experiments, rabbit cardiac myosin was used in a calcium regulated assay system to determine if V1 and V3 isoforms differentially affect thin filament activation. Half-maximal calcium activation was similar for the two cardiac isoforms. A 1:9 mixture of V1/V3 myosin, simulating isoform composition in non-failing human myocardium, was indistinguishable from 100% V3 myosin (simulating the failing state) with regard to velocity of shortening and average force. These data suggest that the myosin isoform shift reported in human myocardial failure does not significantly contribute to the contractile deficit of this disease.