Myocardial Functional Changes in Heart Failure- From Clinical Image Studies to Animal Model

• Main Authors: Ho Yi-Lwun, 何奕倫
• Other Authors: Huang Por-Jau
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/91828142592201371857

博士 === 國立臺灣大學 === 臨床醫學研究所 === 92 === It has been known that total ischemia leads to a prompt cessation of contraction and eventually results in the appearance of cell damage and irreversible myocardial necrosis. Accordingly, in the mind of many cardiologists the discovery of an abnormal regional contraction in patients with coronary artery disease (CAD) has long been equated with the irreversible myocardial necrosis. With the advent of recanalization therapy, however, evidence progressively accumulated that prolonged regional ischemic dysfunction did not always arise from irreversible tissue damage and, to some extent, could be reversed by restoration of blood flow. The term ”hibernation” was first used by Diamond et al in 1978 to describe the chronic wall motion abnormalities of patients with CAD but no previous myocardial infarction and their reversibility after revascularization, and it was subsequently popularized by Rahimtoola and Braunwald and Rutherfold. The definition of hibernating myocardium, as formulated by Rahimtoola, thus implies that: (1) the heart can spontaneously adapt to chronic underperfusion (the “smart hear” hypothesis), (2) a new steady state between perfusion and contraction can be reached, and (3) this new equilibrium can be maintained for a long period of time.Clinical syndromes consistent with the existence of myocardial hibernation include unstable and stable angina, acute myocardial infarction, and left ventricular dysfunction and/or congestive heart failure. The concept of chronic hibernation bears important implication for the management of patients with CAD. Identifying areas of myocardium with depressed but potentially reversible contractile function helps to formulate the therapeutic strategy and to predict the prognosis of patients with CAD and chronic left ventricular dysfunction. Consequently, the non-invasive assessment of dyssynergy but viable myocardium, which may contribute to the overall improvement in the left ventricular function after revasculariztion, has generated great interest among cardiologist and cardiac surgeon. There are several aspects to evaluate the hibernating myocardium: (1) demonstration of a perfusion-contraction matching (i.e. decreased contraction in the face of decreased perfusion), (2) demonstration of a perfusion-metabolism mismatch (i.e. increased glycolytic metabolism in the face of decreased perfusion), (3) demonstration of an inotropic reserve at the expense of worsening of myocardial metabolism. Among the techniques used for this purpose, dobutamine stress echocardiography (DSE), cyclic variation of integrated backscatter (CVIBS), and thallium-201 scintigraphy (using stress-redistribution-reinjection protocols) have been shown to be useful methods. The clinical significance of stress-induced ST-segment elevation and T-wave pseudonormalization in infarct-related leads is still controversial. The possible mechanisms include ventricular asynergy, residual myocardial ischemia, and contractile reserve within infarct area. Since residual myocardial ischemia and viability within the infarct area is important for cardiologists to formulate the strategy of coronary intervention, the significance of these electrocardiographic changes need to be further validated. DSE and thallium-201 single-photon emission computed tomography (SPECT) are sensitive and specific in myocardial ischemia and viability detection. Both examinations also provide complementary information in the assessment of myocardial viability. However, there have been few reports about assessment of these electrocardiographic changes using simultaneous DSE and stress radionuclide imaging. The present study was designed to evaluate the functional significance of dobutamine-induced ST elevation and/or T pseudonormalization in patients with previous Q-wave myocardial infarction (MI) by simultaneous DSE and thallium-201 SPECT. A total of 119 patients with Q wave myocardial infarction were enrolled in this study. There were 58 patients with dobutamine-induced ST-T changes (group I) and 61 patients without (group II). The left ventricular ejection fraction was 43±13% in group I and 49±14% in group II (p<0.05). The baseline, low-dose and peak-dose global wall motion scores were similar between these 2 groups (26.2±6.1 vs 26.2±6.3 [p= non-significant];24.1±5.3 vs 23.5±5.7 [p = non-significant]; 26.4±5.7 vs 26.7±6.1 [p = non-significant]). The sensitivity, specificity, and accuracy of these ST-T changes for detecting residual myocardial viability and ischemia documented by DSE in total patients were 50%, 53%, and 51% (for viability); 47%, 48%, and 47% (for ischemia). The sensitivity, specificity, and accuracy of these ST-T changes for detecting reversible perfusion defect documented by thallium-201 SPECT were 51%, 54% and 52%, respectively. In conclusion, dobutamine-induced ST elevation and/or T-wave pseudonormalization is associated with poor resting left ventricular function. These ST-T changes are not associated with residual myocardial ischemia and viability in infarct area. Therefore, these electrocardiographic changes alone cannot be reliably considered as distinctive markers in the formulation of the therapeutic strategy of coronary intervention. Apoptosis has been reported to be one of the possible mechanisms for the hemodynamic deterioration of congestive heart failure. There have been several studies exploring the existence of apoptosis in patients with heart failure. Although available data supports the above findings, studies about the relation between myocardial functional reserve and apoptosis-related proteins (bcl-2, bax, and p53) are lacking. Changes in left ventricular systolic performance during low dose dobutamine infusion are useful markers to predict the recovery of systolic function in patients with dilated cardiomyopathy (DCM). Therefore, we conducted this prospective study to evaluate the apoptosis-related proteins (bcl-2, bax, and p53) and apoptosis in myocardium of patients with DCM and to correlate these proteins with the dobutamine-induced myocardial contractile reserve. A total of 81 segments of left ventricles (from 6 patients with DCM) were collected in this study. Another 5 patients who had died of non-cardiac causes were used as the control group. Apoptosis related proteins (bax, bcl-2, and p53) and apoptosis were evaluated in these segments by immunocytochemical stain and terminal deoxynucleotidyl transferase-mediated DNA nick end-labeling assay (TUNEL). There were 26 segments with dobutamine-induced contractile reserve. There were significant differences in numbers of segments with over-expression of bcl-2 and bax in the study and control groups. However, p53 was not found in either group. The total TUNEL-positive nuclei in explanted hearts of DCM were 0.73%. The myocardial contractile reserve was inversely associated with an over-expression of bcl-2 (p<0.01) rather than bax. In conclusions, the expression of bax and bcl-2 proteins in patients with DCM is enhanced and independent of p53. Loss of contractile reserve is associated with over-expression of bcl-2 protein in failing myocardium. Several studies have reported that cardiac allografts undergo some cardiomyocyte hypertrophy after heart transplantation. These histological alterations may contribute to the functional changes of the transplanted hearts, particularly myocardial stiffness, diastolic dysfunction, and, to a certain extent, systolic dysfunction. On the other hand, interstitial fibrin deposition in biopsies of transplanted hearts has been reported to identify patients at high risk for developing coronary artery disease or graft failure. Therefore, noninvasive detection of these myocardial changes has clinical significance. Ultrasonic tissue characterization with integrated backscatter (IBS) mode has been used to detect acute cardiac allograft rejection, myocardial ischemia and viability. The changes in IBS are caused by variations in myocardial collagen or water content, myofibril orientation relative to the incident ultrasound beam and myocardial contractile performance. Therefore, we hypothesized that IBS could assess cardiomyocyte hypertrophy and interstitial fibrin deposition in heart transplant recipients without evident acute myocardial rejection. The aims of this study were: (1) to evaluate the IBS of heart transplant recipients without or with minimal acute myocardial rejection (International Society of Heart and Lung Transplantation grade 0 or IA); (2) to compare the results of IBS with those of simultaneous DSE and thallium-201 perfusion imaging; and (3) to compare the results of IBS with pathology of endomyocardial biopsy. A total of 32 heart transplant recipients with either no or mild acute rejection (International Society of Heart and Lung Transplantation grade IA) were enrolled in this study. IBS data of myocardium were collected immediately prior to simultaneous DSE and thallium-201 imaging. Coronary angiography and endomyocardial biopsy were also performed. Coronary angiography showed diffuse narrowing in 1 patient who also had abnormal results of IBS, DSE and thallium results. In the other 31 patients with patent coronary arteries, there were 3 patients (10%) with abnormal DSE results, 19 patients (61%) with abnormal IBS patterns and 16 patients (52%) with reversible thallium perfusion defects. There were 44% patients with cardiomyocyte hypertrophy and 56% with interstitial fibrin deposition. There were significant differences in the prevalence of thallium-201 perfusion defects and serum cyclosporine levels between patients with and without abnormal IBS patterns. Pathological changes were also associated with abnormal IBS patterns (p = 0.01). However, there was no association between abnormal IBS and DSE results. By multiple logistic regression analysis, the abnormal IBS patterns were associated inversely with serum cyclosporine level (p = 0.028). In conclusion, abnormal IBS patterns are associated significantly with perfusion heterogeneity and pathological changes in heart transplant recipients without evident acute myocardial rejection. There is no association between abnormal IBS patterns and dobutamine-induced dyssynergy in these patients. IBS provides a noninvasive approach for detection of myocardial changes in transplanted hearts without evident acute rejection. The zebrafish (Danio rerio) is a new animal model for cardiac researches. The zebrafish heart contains 4 components (sinus venosus, atrium, ventricle and bulbus arteriosus). Although it has a prototypic vertebrate heart, the studies of genetic control for zebrafish development can reveal some hints to solve human problems. On the other hand, the zebrafish mutations which principally disturb cardiac contractility fall into two broad phenotypic categories, 'dilated' and 'hypertrophic'. These correspond to the two primary types of heart failure in humans. The disorders of cardiac function provided candidate genes to be examined in complex human heart diseases, including arrhythmias and heart failure). Despite the simplicity of zebrafish heart, the objective parameters of cardiac performance are not easily available except morphological description. A lack of functional evaluation by either echocardiography or pressure tracing makes the diagnosis of heart failure phenotype in zebrafish less convincing than that in human. As the zebrafish reached maturity (3 months post-fertilization), its atrial wall increased to 2 to 3 cells layers and the ventricle wall increased to 4 cells layers. The ventricle-to-body ratio decreased to 0.02 in adult fishes. The body length of adult zebrafish is around 5 cm. Therefore, the size of the ventricle is around 1.0 mm. These factors make the pressure tracing and two-dimension echocardiography for zebrafish hearts not easily feasible. Power Doppler imaging has become a popular ultrasonic angiography due to its high sensitivity. The frequency spectrum analysis also provides useful information about flow disturbance. Since the 4 components of a zebrafish heart are connected in series, we hypothesized that ultrasonic imaging methods for vascular system analysis could be used for the study of zebrafish hearts. The routine Doppler echocardiography, power angiography and the frequency spectrum analysis were used to evaluate the cardiac performance of the zebrafish by a clinical instrument. A total of 20 fishes that aged 3-4 months were studied. Their mean body weight and height were 562 ±173 mg and 4.6 ±0.7 cm, respectively. Power angiography and routine Doppler echocardiography were used to evaluate the cardiac performance of zebrafish at 25℃ and 15℃. The zebrafish hearts could be easily identified with color-Doppler (8.5 MHz) or power angiography (7 MHz). The ventricular filling flow contained 2 components (E and A-flow). The E-flow velocities were lower than the A-flow velocities at both 25 and 15℃. The cycle length was prolonged (p<0.05) and the velocities of ventricular filling and bulbus arteriosus decreased significantly at 15℃ (p<0.05). Significant decrease in early diastolic acceleration slope and significant prolongation in early-diastolic and late-diastolic acceleration times were found at a lower temperature (15℃). The acceleration/deceleration ratio for early and late diastole also showed significant difference at 15℃. In conclusion, the cardiac performance of the zebrafish could be approached using commercially available clinical instruments equipped with Doppler echocardiography and power angiography. Green fluorescent protein (GFP) has been reported to cause dilated cardiomyopathy in mice. We tested the possible cardiac toxicity of GFP in zebrafish. Two lines with different GFP expression were breed (A26 and A277). The luminance of A277 was higher than A26 (1.7 folds). The short and long diameters of ventricle, ejection fraction and heart rates were all similar between these two groups. Under such luminance of GFP, the cardiac toxicity can be excluded. We added doxycycline to cardiac troponin C (cTnC) anti-sense zebrafish 12 hours post fertilization. T cTnC anti-sense zebrafish showed dilated atrium, ventricle and impaired contractility. The ejection fraction decreased from 48% to 25%. Arrhythmia was observed 8 days post fertilization. There were 3 types of arrhythmia：The first type was bradycardia without affecting ventricular contractility. The second type was intra-ventricular conduction delay. The third type was complete atrio-ventricular block. Calcium channel may play a role in electric conduction in zebrafish. Cardiac diseases are the main cause of death in Taiwan. We hope we can open a new window for basic research of heart failure in Taiwan.