RESUMO
BACKGROUND: Cardiac resynchronization therapy (CRT) is the first clinical heart failure treatment that improves chamber systolic function in both the short-term and long-term yet also reduces mortality. The mechanical impact of CRT is immediate and well documented, yet its long-term influences on myocyte function and adrenergic modulation that may contribute to its sustained benefits are largely unknown. METHODS AND RESULTS: We used a canine model of dyssynchronous heart failure (DHF; left bundle ablation, atrial tachypacing for 6 weeks) and CRT (DHF for 3 weeks, biventricular tachypacing for subsequent 3 weeks), contrasting both to nonfailing controls. CRT restored contractile synchrony and improved systolic function compared with DHF. Myocyte sarcomere shortening and calcium transients were markedly depressed at rest and after isoproterenol stimulation in DHF (both anterior and lateral walls), and CRT substantially improved both. In addition, beta(1) and beta(2) stimulation was enhanced, coupled to increased beta(1) receptor abundance but no change in binding affinity. CRT also augmented adenylate cyclase activity over DHF. Inhibitory G-protein (Galpha(i)) suppression of beta-adrenergic stimulation was greater in DHF and reversed by CRT. Galpha(i) expression itself was unaltered; however, expression of negative regulators of Galpha(i) signaling (particularly RGS3) rose uniquely with CRT over DHF and controls. CRT blunted elevated myocardial catecholamines in DHF, restoring levels toward control. CONCLUSIONS: CRT improves rest and beta-adrenergic-stimulated myocyte function and calcium handling, upregulating beta(1) receptors and adenylate cyclase activity and suppressing G(i)-coupled signaling associated with novel RGS upregulation. The result is greater rest and sympathetic reserve despite reduced myocardial neurostimulation as components underlying its net benefit.
Assuntos
Insuficiência Cardíaca/fisiopatologia , Insuficiência Cardíaca/terapia , Marca-Passo Artificial , Receptores Adrenérgicos beta 1/fisiologia , Receptores Adrenérgicos beta 2/fisiologia , Adenilil Ciclases/metabolismo , Animais , Catecolaminas/metabolismo , Colforsina/farmacologia , Cães , Subunidades alfa Gi-Go de Proteínas de Ligação ao GTP/metabolismo , Insuficiência Cardíaca/metabolismo , Contração Miocárdica/fisiologia , Miócitos Cardíacos/efeitos dos fármacos , Miócitos Cardíacos/fisiologia , Proteínas RGS/fisiologia , Ensaio Radioligante , Sarcômeros/fisiologia , Transdução de Sinais/fisiologiaRESUMO
BACKGROUND: Cardiac dyssynchrony in the failing heart worsens global function and efficiency and generates regional loading disparities that may exacerbate stress-response molecular signaling and worsen cell survival. We hypothesized that cardiac resynchronization (CRT) from biventricular stimulation reverses such molecular abnormalities at the regional and global levels. METHODS AND RESULTS: Adult dogs (n=27) underwent left bundle-branch radiofrequency ablation, prolonging the QRS by 100%. Dogs were first subjected to 3 weeks of atrial tachypacing (200 bpm) to induce dyssynchronous heart failure (DHF) and then randomized to either 3 weeks of additional atrial tachypacing (DHF) or biventricular tachypacing (CRT). At 6 weeks, ejection fraction improved in CRT (2.8+/-1.8%) compared with DHF (-4.4+/-2.7; P=0.02 versus CRT) dogs, although both groups remained in failure with similarly elevated diastolic pressures and reduced dP/dtmax. In DHF, mitogen-activated kinase p38 and calcium-calmodulin-dependent kinase were disproportionally expressed/activated (50% to 150%), and tumor necrosis factor-alpha increased in the late-contracting (higher-stress) lateral versus septal wall. These disparities were absent with CRT. Apoptosis assessed by terminal deoxynucleotide transferase-mediated dUTP nick-end labeling staining, caspase-3 activity, and nuclear poly ADP-ribose polymerase cleavage was less in CRT than DHF hearts and was accompanied by increased Akt phosphorylation/activity. Bcl-2 and BAD protein diminished with DHF but were restored by CRT, accompanied by marked BAD phosphorylation, enhanced BAD-14-3-3 interaction, and reduced phosphatase PP1alpha, consistent with antiapoptotic effects. Other Akt-coupled modulators of apoptosis (FOXO-3alpha and GSK3beta) were more phosphorylated in DHF than CRT and thus less involved. CONCLUSIONS: CRT reverses regional and global molecular remodeling, generating more homogeneous activation of stress kinases and reducing apoptosis. Such changes are important benefits from CRT that likely improve cardiac performance and outcome.
Assuntos
Apoptose , Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Estimulação Cardíaca Artificial/métodos , Insuficiência Cardíaca/terapia , Processamento de Proteína Pós-Traducional , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Proteínas 14-3-3/metabolismo , Animais , Bloqueio de Ramo/complicações , Cães , Ativação Enzimática , Fatores de Transcrição Forkhead/metabolismo , Quinase 3 da Glicogênio Sintase/metabolismo , Glicogênio Sintase Quinase 3 beta , Insuficiência Cardíaca/enzimologia , Insuficiência Cardíaca/etiologia , Insuficiência Cardíaca/patologia , Fosforilação , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Distribuição Aleatória , Volume Sistólico , Taquicardia Atrial Ectópica/complicações , Taquicardia Atrial Ectópica/enzimologia , Taquicardia Atrial Ectópica/patologia , Taquicardia Atrial Ectópica/terapia , Taquicardia Ventricular/complicações , Taquicardia Ventricular/enzimologia , Taquicardia Ventricular/patologia , Taquicardia Ventricular/terapia , Fator de Necrose Tumoral alfa/biossíntese , Proteína de Morte Celular Associada a bcl/metabolismoRESUMO
BACKGROUND: The efficacy of cardiac resynchronization therapy (CRT) depends on placement of the left ventricular lead within the late-activated territory. The geographic extent and 3-dimensional distribution of left ventricular (LV) locations yielding optimal CRT remain unknown. METHODS AND RESULTS: Normal or tachypacing-induced failing canine hearts made dyssynchronous by right ventricular free wall pacing or chronic left bundle-branch ablation were acutely instrumented with a nonconstraining epicardial elastic sock containing 128 electrodes interfaced with a computer-controlled stimulation/recording system. Biventricular CRT was performed using a fixed right ventricular site and randomly selected LV sites covering the entire free wall. For each LV site, global cardiac function (conductance catheter) and mechanical synchrony (magnetic resonance imaging tagging) were determined to yield 3-dimensional maps reflecting CRT impact. Optimal CRT was achieved from LV lateral wall sites, slightly more anterior than posterior and more apical than basal. LV sites yielding > or = 70% of the maximal dP/dtmax increase covered approximately 43% of the LV free wall. This distribution and size were similar in both normal and failing hearts. The region was similar for various systolic and diastolic parameters and correlated with 3-dimensional maps based on mechanical synchrony from magnetic resonance imaging strain analysis. CONCLUSIONS: In hearts with delayed lateral contraction, optimized CRT is achieved over a fairly broad area of LV lateral wall in both nonfailing and failing hearts, with modest anterior or posterior deviation still capable of providing effective CRT. Sites selected to achieve the most mechanical synchrony are generally similar to those that most improve global function, confirming a key assumption underlying the use of wall motion analysis to optimize CRT.
Assuntos
Estimulação Cardíaca Artificial/métodos , Animais , Cães , Eletrocardiografia , Imageamento Tridimensional , Imageamento por Ressonância Magnética , Análise de RegressãoRESUMO
The purpose of this study was to establish reference ranges for magnetic resonance imaging (MRI) measurements of the adult right ventricle stratified by gender. Cardiovascular MRI is increasingly used for evaluating the right ventricle in congenital and acquired heart disease, but gender-specific normative values are currently unavailable. Study participants included 500 subjects free of clinical cardiovascular disease who were participants in the Multi-Ethnic Study of Atherosclerosis (MESA). All subjects underwent MRI according to a standard protocol. The endocardial margins of the right ventricle were manually contoured on short-axis images, and right ventricular (RV) volumes were calculated using a summation-of-disks method. RV dimensions were measured on 4-chamber gradient-echo images and in the short-axis plane. Except for the ejection fraction, all unadjusted RV parameters were significantly greater in men than in women (p <0.001). In the entire study population, RV volumes and linear dimensions each correlated significantly with height (r = 0.38 to 0.64, p = 0.001 for all) and body surface area (r = 0.41 to 0.64, p = 0.001 for all). Gender differences persisted after adjustment for subject height. After adjustment for body surface area, volumetric variables remained significantly greater (p = 0.001) in men than in women. Even after adjusting for body surface area and height, Chinese participants had significantly lower RV volumes compared with Caucasians. In conclusion, gender-specific normal values for the adult right ventricle by MRI are presented. Cardiovascular MRI measures of RV volumes and linear dimensions differ significantly according to gender and body size. These values will be useful to differentiate RV health from diseases that result in abnormal RV structure and function.
Assuntos
Ventrículos do Coração/anatomia & histologia , Imageamento por Ressonância Magnética , Adulto , Idoso , Idoso de 80 Anos ou mais , Estatura , Superfície Corporal , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Grupos Raciais , Valores de Referência , Caracteres Sexuais , Volume SistólicoRESUMO
The first known descriptions regarding the basic aspects of circulation was probably in 500 B.C., by the Greek thinker Alcmaeon of Croton who observed arteries and veins to be dissimilar in animal dissection, and this was followed by the description of the human heart as a three chambered organ by Aristotle in 350 B.C. Herophilus of Chalcedon, a Greek anatomist, confirmed the findings of dissimilarity between arteries and veins in human cadaver dissections in 300 B.C., and determines that arteries were thicker than veins and contained blood. The advancement by far in the learning of human circulation was made possible first by significant contribution of Galen followed by observations of Ibn al-Nafis, Servetus, Colombo, Cesalpino, Vesalius and Fabricius. In 17th century William Harvey, an English physician, made important advancements into the understanding of this important area of medicine, advancements that continued with the observations of Malpighi.
Assuntos
Circulação Sanguínea , Fisiologia/história , História do Século XVI , História do Século XVII , História Antiga , HumanosRESUMO
Vascular malformations of the mediastinum including mediastinal lymphangioma are exceedingly rare in adults. A resected case of mediastinal cystic lymphangioma (cystic hygroma) that presented with acute onset of retrosternal chest pain is reported in a 45-year-old man. Cystic hygromas are benign cysts frequently discovered incidentally on chest radiograph. Although computed tomography scan provides helpful information about the size, density, and site of the cysts, it cannot establish a precise diagnosis concerning its nature. Complete removal of the cyst is the treatment of choice and allows precise diagnosis on histologic examination. However, surgical excision is sometimes difficult, owing to the size and extension of the cysts, infiltrating mediastinal planes, enveloping great vessels, and displacing mediastinal organs without invasion. The difficulty of completely eradicating certain cysts explains cases of insidious progression with compressive recurrence. The subject is succinctly reviewed.
Assuntos
Dor no Peito/etiologia , Linfangioma Cístico , Neoplasias do Mediastino , Seguimentos , Humanos , Linfangioma Cístico/complicações , Linfangioma Cístico/diagnóstico por imagem , Linfangioma Cístico/patologia , Linfangioma Cístico/cirurgia , Masculino , Neoplasias do Mediastino/complicações , Neoplasias do Mediastino/diagnóstico por imagem , Neoplasias do Mediastino/patologia , Neoplasias do Mediastino/cirurgia , Mediastino/patologia , Pessoa de Meia-Idade , Radiografia Torácica , Síndrome , Fatores de Tempo , Tomografia Computadorizada por Raios XRESUMO
Essential thrombocythemia is a clonal disorder of the myeloid stem cell that causes pathologic expansion of the megakaryocytic elements in the bone marrow, with a persistent increase in the platelet count. The disease is associated with an elevated risk of thrombosis, hemorrhage, and vasomotor symptoms. The presenting features of essential thrombocythemia can range from being asymptomatic to thrombohemorrhagic complications including acute myocardial infarction. Acute ST-segment elevation myocardial infarction due to left main trunk and ostial left anterior descending coronary artery lesions was diagnosed in a young 31-year-old man. Platelet count was markedly increased and essential thrombocythemia was also diagnosed. Because of left main disease, primary coronary intervention was not feasible and an emergent coronary artery bypass grafting was performed along with pharmacologic management of essential thrombocythemia. The early postoperative period was complicated by acute pulmonary embolism. Hydroxyurea and anagrelide were administered postoperatively, resulting in the decrease of platelet count. A succinct review of myocardial infarction in patients with essential thrombocythemia is presented, and therapeutic strategies in such patients are discussed.
Assuntos
Eletrocardiografia , Infarto do Miocárdio/etiologia , Trombocitemia Essencial/complicações , Adulto , Angiografia Coronária , Trombose Coronária/diagnóstico por imagem , Trombose Coronária/etiologia , Humanos , Masculino , Infarto do Miocárdio/diagnóstico , Infarto do Miocárdio/diagnóstico por imagem , Infarto do Miocárdio/cirurgia , Trombocitemia Essencial/terapiaRESUMO
Left ventricular free wall rupture is an uncommon complication after a myocardial infarction that is associated with a high mortality rate from pericardial tamponade, especially in the elderly. Early recognition and management of this clinical entity affects the outcome; therefore, a high index of suspicion is imperative. We present a case of an 80-year-old man admitted with myocardial infarction, who had subsequent findings of left ventricular free wall rupture complicated by pericardial tamponade. Emergent surgical repair led to successful recovery. A brief overview of the clinical presentation, diagnosis, and management of this challenging and potentially fatal complication is presented.
Assuntos
Ruptura Cardíaca Pós-Infarto/cirurgia , Ventrículos do Coração/patologia , Infarto do Miocárdio/complicações , Ruptura/etiologia , Fatores Etários , Idoso , Idoso de 80 Anos ou mais , Ventrículos do Coração/cirurgia , Humanos , MasculinoRESUMO
Torsade de pointes is a polymorphic form of ventricular tachycardia associated with prolongation of the QT interval, which may be either congenital or acquired. Etiologies for the acquired forms include drug effects, hypokalemia, hypomagnesemia, hypocalcemia, starvation, sick sinus syndrome, and atrioventricular block. We present a 76-year-old man with acute on chronic renal failure, hypocalcemia, on ciprofloxacin, and a prolonged QT interval with torsade de pointes triggered by hemodialysis. The QT prolongation was corrected by treating the hypocalcemia. Hypocalcemia and ciprofloxacin are known to independently cause prolonged QT interval and torsade de pointes; our case illustrates that dialysis can trigger torsade on a background of this risk factor combination.