SUMMARY In 18 immature mongrel dogs (3-4 weeks of age), anesthetized with chloralose and morphine, the hearts were arrested with potassium chloride and excised. After reproducible curves relating pressure and volume in the left ventricle (LV) had been obtained, each LV was fixed by coronary perfusion with glutaraldehyde while pressure was maintained at a predetermined value between 0 and 30 mm Hg. Midwall sarcomere length in the LV free was determined by electron microscopy and was related to fixation pressure and to postfixation volume by silastic casts. Casts also were used to measure ventricular chamber dimensions. Results were compared with previous results for adult dogs. In the immature canine LV, the relation of sarcomere length and pressure is similar to that of the adult dog at physiological pressures. Above IS mm Hg, sarcomeres resist stretch significantly with immature LVs fixed between 15 and 30 mm Hg pressure with an average sarcomere length of 2.21 ± 0.05 fim in contrast to adult sarcomere length of 2.33 ± 0.01 Jim (P < 0.05). In the immature heart, electron microscopy demonstrated reduced cell size and evidence of assembly of immature sarcomeres from myofilaments. Compliance is reduced in the immature canine LV at pressures greater than 5 mm Hg as demonstrated in pressure-volume curves analyzed by exponential curve fitting. Measurements of silastic casts indicate a close geometric similarity between the immature and adult LV. Thus, whereas the ultrastructural limits on performance are similar in the adult and immature canine LV, the latter LV may be better protected against damage from volume overloads. Ore Res 44: 879-691, 1979

Recently, a compartment of c-kit positive cardiac progenitor cells (CPCs) has been identified in the adult mouse heart. Whether CPCs are restricted to the adult myocardium or are present throughout ontogenesis and contribute to heart development is unknown. For this purpose, a transgenic mouse in which EGFP was driven by the c-kit promoter was employed. C-kit-EGFP positive cells were present in the heart at all stages of embryonic and fetal development, and their number increased with time reaching 400 cells at E17. Symmetric and asymmetric division of c-kit-positive cells was identified respectively by the uniform and non-uniform localization of the endocytic proteins, Numb and α-adaptin. The presence of symmetric and asymmetric division was consistent with the rapid expansion of the pool of c-kit positive cells and the simultaneous generation of a committed progeny. A fraction of c-kit-EGFP positive cells expressed the myocyte transcription factors Nkx2.5 and MEF2C or specific sarcomeric proteins, α-sarcomeric actin, β-cardiac actinin, β-myosin heavy chain and troponin T. These findings demonstrated a linear relationship between CPCs and myocyte formation. Importantly, observations by two-photon microscopy showed that c-kit-EGFP positive cells in the forming heart exhibited morphogenic movements. Conversely, c-kit-EGFP positive cells from extracardiac regions or from the yolk sac did not translocate to the developing heart. Importantly, cardiac c-kit positive cells were negative for markers of hematopoietic stem cells CD34 and CD45. When c-kit-EGFP-positive cells were isolated from the embryonic heart and plated in vitro at limiting dilution, they formed single-cell derived clones. Almost all cells in the clones continued to express c-kit and EGFP. However, few cells located at the periphery of the clones were no longer positive for c-kit and EGFP and began to express sarcoplasmic proteins. In conclusion, c-kit positive cells in the developing myocardium exhibit the properties of stem cells; they are clonogenic and self-renewing and participate in the growth of the embryonic and fetal heart.

Chapter 22 Conclusions – Future Directions Piero Anversa MD, Piero Anversa MDSearch for more papers by this authorEdmund H. Sonnenblick MD, Edmund H. Sonnenblick MDSearch for more papers by this authorWilliam H. Frishman MD, William H. Frishman MDSearch for more papers by this author Piero Anversa MD, Piero Anversa MDSearch for more papers by this authorEdmund H. Sonnenblick MD, Edmund H. Sonnenblick MDSearch for more papers by this authorWilliam H. Frishman MD, William H. Frishman MDSearch for more papers by this author Book Editor(s):Annarosa Leri MD, Annarosa Leri MD Professor of Medicine, Department of Medicine, Cardiovascular Research Institute, New York Medical College, Valhalla, NYSearch for more papers by this authorPiero Anversa MD, Piero Anversa MD Professor of Medicine and Vice Chairman, Department of Medicine, Director, Cardiovascular Research Institute, New York Medical College, Valhalla, NYSearch for more papers by this authorWilliam H. Frishman MD, William H. Frishman MD Rosenthal Professor and Chairman, Department of Medicine, New York Medical College, Director of Medicine, Westchester Medical Center, Valhalla, NYSearch for more papers by this author First published: 01 January 2007 https://doi.org/10.1002/9780470988909.ch23 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onEmailFacebookTwitterLinkedInRedditWechat References Orlic D, Kajstura J, Chimenti S, et al. Bone marrow cells regenerate infarcted myocardium. Nature 2001; 420: 701–705. 10.1038/35070587 Web of Science®Google Scholar Wollert KC, Drexler H. Clinical applications of stem cells for the heart. Circ Res 2005; 96: 151–163. 10.1161/01.RES.0000155333.69009.63 CASPubMedWeb of Science®Google Scholar Laflamme MA, Murry CE. Regenerating the heart. Nat Biotechnol 2005; 23: 845–856. 10.1038/nbt1117 CASPubMedWeb of Science®Google Scholar Chien KR. Stem cells: lost in translation. 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In the last decade, apoptosis has gained recognition as an important event determining the structure and function of the myocardium. The purpose of this review is to provide insights into the mechanisms controlling programmed cell death of myocytes. In this regard, the role of the local renin–angiotensin system and oxidative stress is emphasized. Moreover, the effect of cell death on ventricular remodeling and performance is analyzed. The impact of the identification of apoptosis in the heart on the current view of myocardium as a dynamic organ is discussed.

The recognition that the heart can replace old dying myocytes by activation of resident cardiac stem cells raises the possibility that organism, organ and cell age do not coincide and that the myoc...

Cytoplasmic overexpression of Akt in the heart results in a myopathy characterized by organ and myocyte hypertrophy. Conversely, nuclear-targeted Akt does not lead to cardiac hypertrophy, but the cellular basis of this distinct heart phenotype remains to be determined. Similarly, whether nuclear-targeted Akt affects ventricular performance and mechanics, calcium metabolism, and electrical properties of myocytes is unknown. Moreover, whether the expression and state of phosphorylation of regulatory proteins implicated in calcium cycling and myocyte contractility are altered in nuclear-targeted Akt has not been established. We report that nuclear overexpression of Akt does not modify cardiac size and shape but results in an increased number of cardiomyocytes, which are smaller in volume. Additionally, the heart possesses enhanced systolic and diastolic function, which is paralleled by increased myocyte performance. Myocyte shortening and velocity of shortening and relengthening are increased in transgenic mice and are coupled with a more efficient reuptake of calcium by the sarcoplasmic reticulum (SR). This process increases calcium loading of the SR during relengthening. The enhanced SR function appears to be mediated by an increase in SR Ca2+-ATPase2a activity sustained by a higher degree of phosphorylation of phospholamban. This posttranslational modification was associated with an increase in phospho-protein kinase A and a decrease in protein phosphatase-1. Together, these observations provide a plausible biochemical mechanism for the potentiation of myocyte and ventricular function in Akt transgenic mice. Therefore, nuclear-targeted Akt in myocytes may have important implications for the diseased heart.

Resting left ventricular ejection fraction (LVEF) and functional capacity do not correlate in chronic heart failure patients treated with digitalis, diuretics, and angiotensin-converting enzyme inhibitors. We sought to determine whether substantial improvement in LVEF, as may occur during long-term beta-blockade or after coronary artery bypass graft (CABG) surgery, leads consistently to improvement in functional class. Doppler echocardiogram and assessment of functional class were obtained at baseline and 12 months after initiation of beta-blockade (87 patients) or CABG surgery (51 patients). At 12 months the effects of beta-blockade were variable: LVEF increased greatly by >or=11% (median value) in 45 patients (52%) and by <11% in 19 (22%), but it decreased or remained unchanged in 23 patients (26%). In contrast, functional class was unchanged or worsened in 59 patients (68%) and improved in only 28 (32%). Similarly, surgery had variable effects on LVEF. LVEF increased by >or=12% (median) in 28 patients (55%) and by <12% in 14 (27%), whereas it decreased or remained unchanged in 9 patients (18%). Functional class was unchanged or worsened in 41 patients (80%) and improved in only 10 (20%). Changes in functional class and LVEF were unrelated for both interventions. Both beta-blockade and CABG surgery improve LVEF in the majority of patients. However, significant improvement in LVEF does not enhance functional capacity consistently in chronic heart failure.

sponse to exercise in patients with chest pain and normnal coronary arteriogram. Circulation 64: 952, 1981 17. Williams RS, Behar VS, Peter RH: Left bundle branch block: angiographic segmental wall motion abnormalities. Am J Cardiol 44: 1046, 1979 18. Abbasi AS, Eber LM, MacAlpin RN, Kattus AA: Paradoxical motion of interventricular septum in left bundle branch block. Circulation 49: 423, 1974 19. Rowe DW, DePuey EG, Sonnemaker RG, Hall RJ, Burdine JA: Left ventricular performance during exercise in patients with LBBB. (abstr) Circulation 62 (suppl III): 111-147, 1980 20. McGowan RL, Welch TG, Zaret BL, Bryson AL, Martin WD, Flamm MD: Noninvasive myocardial imaging with potassium-43 and rubidium-81 in patients with left bundle branch block. Am J Cardiol 38: 422, 1976 21. Borer JS, Bacharach SL, Green MV, Kent KM, Epstein SE, Johnston GS: Real-time radionuclide cineangiography in the noninvasive evaluation of global and regional left ventricular function at rest and during exercise in patients with coronary-artery disease. N Engl J Med 296: 839, 1977

To determine whether acute left ventricular failure associated with myocardial infarction leads to architectural changes in the spared nonischemic portion of the ventricular wall, large infarcts were produced in rats, and the animals were killed 2 days after surgery. Left ventricular end-diastolic pressure was increased, whereas left ventricular dP/dt and systolic pressure were decreased, indicating the presence of severe ventricular dysfunction. Absolute infarct size, determined by measuring the fraction of myocyte nuclei lost from the left ventricular free wall, averaged 63%. Transverse midchamber diameter increased by 20%, and wall thickness diminished by 33%. The mural number of myocytes in this spared region of the left ventricular free wall decreased by 36% and the capillary profiles by 40%o. The combination of these functional abnormalities and structural rearrangement of the wall resulted in a 7.8-fold increase in diastolic wall stress. A comparable analysis of the interventricular septum demonstrated a 24% reduction in the number of cells across the septal thickness, whereas capillaries were diminished by 26%. Moreover, a 7.2-fold elevation in diastolic stress was computed in this region of the ventricle. The augmentation in diastolic stress was associated with a 22% and a 16% myocyte cellular hypertrophy in the wall and septum, respectively. In conclusion, side-to-side slippage of myocytes in the myocardium occurs in association with ventricular dilatation after a large myocardial infarction and contributes to ventricular remodeling and the occurrence of decompensated eccentric hypertrophy. (Circulation Research 1990;67:23-34)

Improved global or segmental wall motion following revascularization suggests potential reversibility of ischemic left ventricular dysfunction in coronary artery disease (CAD). This study evaluates the effectiveness of post-extra systolic potentiation (PESP) to detect latent residual contractile function. Quantitative left ventriculography was performed in 15 patients with CAD (including seven with significant asynergy) and in three normal controls. During the ventriculogram, a single extra-systole was introduced by an R-wave coupled stimulator (R-stimulus interval averaged 398 msec, with an average mA of 2.4). PESP improved segmental axis shortening in 51 of 55 normal axes and 15 of 17 hypokinetic or akinetic axes. It also increased both ejection fraction and mean rate of circumferential fiber shortening in 17 of 18 patients. No significant arrhythmia occurred with this technique. A single interposed beat with PESP in one ventriculogram is a safe, effective method to detect residual potential contractile function in myocardium that may be hypokinetic or akinetic under conditions of the study.

This review questions the old paradigm that describes the heart as a post-mitotic organ and introduces the notion of the heart as a self-renewing organ regulated by a compartment of multipotent cardiac stem cells (CSCs) capable of regenerating myocytes and coronary vessels throughout life. Because of this dramatic change in cardiac biology, the objective is to provide an alternative perspective of the aging process of the heart and stimulate research in an area that pertains to all of us without exception. The recent explosion of the field of stem cell biology, with the recognition that the possibility exists for extrinsic and intrinsic regeneration of myocytes and coronary vessels, necessitates reevaluation of cardiac homeostasis and myocardial aging. From birth to senescence, the mammalian heart is composed of non-dividing and dividing cells. Loss of telomeric DNA is minimal in fetal and neonatal myocardium but rather significant in the senescent heart. Aging affects the growth and differentiation potential of CSCs interfering not only with their ability to sustain physiological cell turnover but also with their capacity to adapt to increases in pressure and volume loads. The recognition of factors enhancing the activation of the CSC pool, their mobilization, and translocation, however, suggests that the detrimental effects of aging on the heart might be prevented or reversed by local stimulation of CSCs or the intramyocardial delivery of CSCs following their expansion and rejuvenation in vitro. CSC therapy may become, perhaps, a novel strategy for the devastating problem of heart failure in the old population.

Cardiac performance and mitral regurgitation were measured by Doppler echocardiography and right heart catheterization in 12 patients with severe congestive heart failure who performed isometric exercise during control and intravenous administration of dobutamine and nitroglycerin. During control isometric exercise, mitral regurgitant volume increased from 18±13 to 31±17 ml (p<0.01), while forward stroke volume, by both thermodilution and Doppler echocardiography, substantially decreased. At rest, dobutamine decreased mitral regurgitant volume from 18± 13 to 11± 10 ml (p<0.05), while forward stroke volume increased from 46±13 to 55±15 ml (p <0.05). During isometric exercise, dobutamine tended to decrease mitral regurgitant volume (24±12 vs. 31±17 ml; NS) when compared with control exercise. At rest, nitroglycerin decreased mitral regurgitant volume from 18±13 to 11±11 ml (p<0.05), while forward stroke volume, by both thermodilution and Doppler echocardiography, substantially increased. Similarly, during isometric exercise, nitroglycerin decreased mitral regurgitant volume from 31±17 to 20±14 ml (p<0.05), while significantly increasing forward stroke volume. At control rest, the median mitral regurgitant fraction was 24% for the 12 patients. Neither dobutamine nor nitroglycerin changed significantly forward stroke and mitral regurgitant volumes at rest and during isometric exercise in the six patients with resting mitral regurgitant fraction below the median. In contrast, dobutamine and nitroglycerin significantly decreased mitral regurgitant volume and increased forward stroke volume both at rest and during isometric exercise in the six patients with mitral regurgitant fraction greater than the median. Thus, aggravation of mitral regurgitation contributes substantially to the fall in forward stroke volume noted during isometric exercise in patients with severe congestive heart failure. The presence and severity of functional mitral regurgitation appears to be an important determinant of the hemodynamic response to acute therapy with dobutamine and nitroglycerin in these patients. (Circulation 1989;80:306-313)