Associate Professor, University of North Dakota School of Medicine and Health Sciences
Mean atrial pressures and ventricular end-diastolic pressures exceeding 14 mm Hg may reflect ventricular volume load states antibiotic resistance zone diameter generic colchicine 0.5 mg without prescription, decreased ventricular compliance antibiotics with anaerobic coverage order colchicine in india, or intermediate combinations of both hemodynamic conditions antibiotic resistance today order colchicine. Elevated filling pressures obligatorily result in elevated mean pulmonary artery pressures, but pulmonary arteriolar vascular resistance determinations also depend on pulmonary flow volume. Pulmonary Circulation Adequate demonstration of the pulmonary arterial system to delineate the central pulmonary artery size and to exclude distortion or stenoses of the central pulmonary arteries and the distal pulmonary arterial distribution remains a critical component of a complete preoperative assessment before definitive palliation. Angiographic study of Glenn shunts should be routinely obtained to detect the presence of venous collaterals, pulmonary artery stenoses, and pulmonary arteriovenous fistulae. Systemic Circulation Aortic arch anatomy should be adequately demonstrated by ventricular angiography or by selective injections to delineate the location of the aortic arch, to obtain the status of the brachiocephalic branches, and to exclude significant coarctation of the aorta. The progressive ventricular hypertrophy and decreased ventricular compliance secondary to the systemic hypertension and increased afterload associated with significant coarctation of the aorta are hemodynamic conditions that are poorly tolerated following modified Fontan operation. Preoperative assessment should include angiographic or catheter pressure measurements to exclude this associated lesion. Also, patency of surgically placed systemic pulmonary shunts, persistent ductus arteriosus, or systemic pulmonary collateral vessels should be determined preoperatively with aortic or selective arterial angiography. Treatment Rarely, unoperated patients with perfectly balanced circulation may survive into the sixth decade (24). Uncontrollable congestive heart failure, excessive pulmonary blood flow, and severe pulmonary hypertension should prompt pulmonary artery banding in early infancy. Patients after pulmonary artery banding should be monitored carefully to determine that the reduction of the pulmonary blood flow reduces the pulmonary pressure to normal levels. Even mild elevations of pulmonary vascular resistance (3 U/m2) will preclude successful Fontan operation. One option is to interrupt the pulmonary outflow tract and place a systemic-to-pulmonary artery shunt large enough to provide adequate pulmonary blood flow. It is preferred because it does not require ligation of the subclavian artery and the length of the graft is not limited. Beyond the first 4 to 6 months of life, the bidirectional cavopulmonary connection (bidirectional Glenn shunt) is an effective means of providing mediumterm palliation for patients with univentricular connection. The bidirectional cavopulmonary shunt includes anastomosis of the cardiac end of the superior vena cava to the right pulmonary artery but leaves the pulmonary arteries confluent. The bidirectional Glenn shunt provides effective pulmonary blood flow by directing desaturated blood directly into the pulmonary circuit. It does not increase the ventricular volume load as does a systemic-to-pulmonary shunt. Previously, the classic Glenn shunt was the preferred technique, consisting of anastomosing the superior vena cava to the right pulmonary artery resulting in nonconfluent pulmonary arteries. Other significant disadvantages include loss of confluence between right and left pulmonary arteries, distortion or stenosis of the superior vena cava or the right pulmonary artery, right pulmonary artery thrombosis, abnormal right pulmonary blood flow distribution, and failure of the right pulmonary artery to develop normally. Although the bidirectional cavopulmonary shunt produces excellent palliation in the first 2 to 3 years of life, progressive cyanosis and secondary erythrocytosis usually prompt further palliative efforts to improve pulmonary flow. If the pulmonary arteries remain hypoplastic, an additional systemic-to-pulmonary shunt may provide greater pulmonary blood flow for relief of cyanosis and promote growth of the pulmonary vascular bed. In 1956, Kirklin performed a septation operation in a 12-year-old patient who had a single ventricle with a small ridge of apical ventricular septum. However, early mortality rates were high, approximately 38% to 40%, and subsequent reports noted similar results (27,28). Also, the bidirectional caval pulmonary anastomosis and an added external or internal conduit from the inferior vena cava to the right pulmonary artery are optional methods for surgical repair.
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Systemic outflow obstruction may take the form of functional and/or true aortic valve atresia as well as obstructive anomalies of the aortic arch (27 treatment for distemper dogs cheap colchicine 0.5mg with visa,28 bacteria listeria order genuine colchicine on-line,29) virus 0f2490 buy colchicine 0.5 mg on-line. The defects are most often perimembranous and a consequence of the atrial and ventricular septal malalignment (16). The defects are often large with anterior extension and therefore suitable for intraventricular tunneling. In general, the coronary arteries originate from the posterior-facing sinuses of the aortic valve. In a 14-specimen study (34), investigators observed the persistent origin of the sinus node artery from the circumflex artery. In that same report, a correlation between commissural malalignment and eccentric coronary ostia P. Rare cases of an isolated origin of the sinus node artery from a coronary sinus have also been reported (36). Anomalies were found in 11 specimens and a single coronary artery was the most common in four (two originating from the right and two from the left facing sinuses). A main coronary branch coursing anterior to the pulmonary trunk was found in 96% of the specimens, and a large infundibular branch supplying the right ventricular outflow tract was found in 61% of the specimens. The posterior descending artery was supplied by the morphologic right coronary artery in 59% of specimens. From their study of 62 patients, they concluded that the proximal coronary pattern at the aortic sinus depends on the aortopulmonary rotation, and the peripheral coronary pattern depends on the atrial situs and apical position (apicocaval ipsilaterality), as well as ventricular looping (37). Several investigators have helped elucidate the presence of normal and abnormal conduction tissues (17,38,39,40,41). The bundle then courses onto the anatomic right side of the upper interventricular septum from which it descends and branches. The bundle branches remain associated with the morphologic ventricles, with the left bundle on the right and the right bundle on the left side of the septum. Others may not present until adulthood when right ventricular dysfunction, heart block, or other arrhythmias become apparent (3). On the other hand, patients with associated lesions will have a variable presentation. Characteristically patients have an accentuated, often palpable, single second heart sound reflecting the anteriorly positioned aortic valve. The electrical activation of the ventricles in the normal heart begins in the interventricular septum P. The absence of Q waves in the left precordial leads is seldom observed in normal children, but 25% of normal neonates may not demonstrate a Q wave in V6. With ventricular inversion, both its surfaces and ventricular bundle branches are inverted, thus the sequence of initial activation is oriented from right to left and usually in a more superior and anterior direction. This results in a reversal of the normal Q-wave pattern in the precordial leads: Q waves are present in the right precordial leads but are absent in the left precordial leads. This pattern of reversal is appreciated less commonly when the heart is right sided or when there are confounding associated lesions producing pressure or volume overload (15). Despite the development of surgical techniques to reduce the incidence of complete heart block at surgery, this problem continues to be significant and progressive (49). This is manifested in the plain chest radiograph in the frontal projection as a deformity of the left upper mediastinal border characterized by a convex prominence at its middle and upper portions with a mild convexity in the anticipated position of the pulmonary trunk. In some patients, despite an ambiguous atrial situs, the atria may be relatively well lateralized.
It is noteworthy that none of the drugs shown to have a survival benefit in chronic heart failure in adults have had similar effects demonstrated in children (196) antimicrobial news buy 0.5mg colchicine with mastercard. The reasons for this are numerous and complex zinc antibiotic resistance order colchicine online from canada, but include the relative rarity of heart failure in children and the difficulty recruiting subjects to perform adequately powered clinical trials antibiotic resistance research topics purchase colchicine 0.5 mg with amex, the use of surrogate end points. As such, the evidence base for much of chronic heart failure therapy in children is derived from the experience in the adult literature, combined with a limited number of randomized studies, uncontrolled studies, consensus opinion, and accumulated experience. The symptoms of chronic heart failure exist along a continuum and therapies are available that can be tailored on an individual basis according to the severity of illness. A proposed schema for heart failure medical management with escalating disease severity is shown in Figure 73. For asymptomatic outpatients with only imaging evidence of ventricular dysfunction or for those with mild symptoms of chronic heart failure, introduction of oral medication therapy alone may be appropriate. The evidence base for these medications and major issues associated with these medications will be discussed below. Diuretics Diuretics are frequently employed to control symptoms and/or signs of extravascular volume overload, such as orthopnea, dyspnea, peripheral edema, hepatomegaly, or ascites. With the exception of aldosterone antagonists, conventional diuretics (loop diuretics, thiazide diuretics) block specific ion transport proteins in renal tubular cells and thereby inhibit the reabsorption of solutes (198). In doing so, free water is retained in the convoluted tubule and collecting duct, allowing the reduction of systemic and pulmonary venous pressures (199). They may be used in acute exacerbations of chronic heart failure or as part of a chronic medical regimen in patients who are dependent on their administration for maintenance of a euvolemic state. Loop diuretics (furosemide, bumetanide) are typically used as first-line agents, with thiazide diuretics (chlorothiazide, metolazone) added for refractory fluid retention, although there is no clear evidence to support superiority of one class over the other. In the acute decompensated state, loop diuretics may be given in bolus or continuous doses, with equivalent effect on symptom relief (200). In adult practice, it has traditionally been held that diuretics provide symptomatic benefit and improved exercise capacity only, without survival benefit. A recent meta-analysis of diuretic regimens in adults with heart failure suggests a survival benefit, albeit from trials with small numbers of participants (201). To circumvent this undesired effect in diuretic-dependent patients, ultrafiltration has been proposed (203); however, this has limited application in pediatric patients outside of extracorporeal support due to practical considerations. Diuretic resistance is also a concern with long-term use, which may be caused by noncompliance, concomitant use of nonsteroidal anti-inflammatory drugs, and diminished renal natriuretic effect owing to compensatory hypertrophy and hyperplasia of epithelial cells of the distal convoluted tubule leading to increased reabsorption of sodium (204). Once noncompliance has been excluded, strategies to alleviate diuretic resistance include increasing diuretic dose and frequency, adding an additional class of diuretic (usually a thiazide), and considering the specific diuretics metolazone (205) and tolvaptan (206,207), which may be successful at effecting diuresis in edematous or diuretic-resistant patients (208). However, there are no data available regarding the use of metolazone or tolvaptan in pediatric patients. Angiotensin-Converting Enzyme Inhibitors and Angiotensin-Receptor Blockers Since the mid-1980s, afterload reduction of the left ventricle through systemic vasodilation has been a basic therapeutic premise of heart failure. The secondary composite outcome of death and/or hospitalization for heart failure was not different between groups, but all-cause mortality was significantly lower in the losartan group. For example, in a small study of pediatric patients with idiopathic dilated and restrictive cardiomyopathy, increases in stroke volume and cardiac index with a corresponding decrease in systemic vascular resistance were seen after administration of captopril (223). Administration of a single dose of enalapril to children with asymptomatic chronic mitral regurgitation was reported to reduce the degree of mitral regurgitation and increase left ventricular ejection fraction by echocardiography in another small study (224). In fact, in this study, cardiac index was decreased at peak exercise compared to resting conditions in the enalapril group compared to the placebo group. These results are difficult to reconcile with other published studies, but must be viewed in light of small sample size and the use of surrogate endpoints such as exercise capacity as a primary endpoint, which has been shown to be problematic in heart failure trials (226). In a recent double-blind, placebo-controlled trial infants with single ventricle physiology who received enalapril during the first year of life, there were no differences between enalapril and placebo groups with respect to ventricular function, serum brain natriuretic peptide concentration, heart failure class, somatic growth, or mortality at 14 months of age (227).
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