Site Of Shunt Research Articles

Quantitation of left-to-right cardiac shunts with radionuclide angiography.

A quantitative radionuclide angiogram technique using an intravenous injection of technetium-99m (Tc-99m) pertechnetate is described for quantitation of left-to-right shunts in the central circulation. Data analysis assumes exponential indicator clearance from normal cardiac chambers by dilution. A late prolongation of tracer disappearance compared to the initial clearance rate indicates an abnormally early return of indicator to the cardiac chamber. Patients with left-to-right shunts demonstrate prolonged clearance of radioactivity from all cardiac chambers distal to the site of shunt. The magnitude of curve distortion is quantitatively related to the size of shunt, and counts recorded from the right lung are used for shunt quantitation. Quadratic regression analysis of data from 21 patients with left-to-right shunts and eight normal subjects demonstrated a correlation coefficient of 0.951 between measurements of left-to-right shunts by the radionuclide and by the Fick method. Observations on 14 patients with aortic or mitral valve disease revealed this method of shunt evaluation to be of limited value in the presence of severe cardiac valvular disease. However, the method permits detection of left-to-right shunts that are too small to be diagnosed by the Fick method and accurately quantitates shunts which are not at either extreme in size and flow. This technique appears to be potentially useful for the initial diagnosis and serial evaluation of patients with these disorders.

Alveolar-arterial oxygen gradients in infants and children with left-to-right shunts

Studies of alveolar-arterial oxygen differences and intrapulmonary venous admixture and shunting were undertaken in 144 children with congenital heart disease; 37 had insignificant lesions and were considered control subjects. Of the remaining 107 patients, there were 104 with intracardiac or great vessel left-to-right shunts and 3 with primary pulmonary hypertension. Of the total, 25 were under 1 year of age. Those presenting in cardiac failure were well compensated at the time of study. The data revealed that patients with left-to-right interventricular and great vessel shunts have an abnormally high venous admixture and aa DO 2 at both room air and while breathing 100 per cent oxygen. The increase in aa DO 2 is related to increased pulmonary vascular resistance and is due to intrapulmonary shunting. Patients with atrial septal defects have normal aa DO 2 values except for minor variations. The discrepancy in data between these two groups is probably related to increase in pulmonary arterial resistance found in ventricular septal defects and patent ductus arteriosus. This rarely occurs in atrial septal defects despite large increases in pulmonary blood flow. The site of intrapulmonary shunting remains undefined, but presumably is in areas that are unventilated but perfused (i.e., areas with a low ventilation-perfusion ratio).

Bleeding from dialysis shunt sites.

Bleeding from dialysis shunt sites.

Large vessel appliqué arteriovenous shunt for hemodialysis: A new concept

<h2>Summary</h2> A high-flow arteriovenous shunt has been developed which is attached to the common femoral artery and vein. This large vessel "appliqué" shunt resulted from the vexations of repeated cannulations in aging patients receiving dialysis using the standard peripheral arm or leg arteriovenous shunt. Thirty-nine patients have been operated on for a total of forty shunts and these patients have been followed up for from four to eighteen and a half months, with satisfactory results to date. Complications other than infection have been negligible and readily handled without rehospitalization and reoperation. Forty per cent of the patients are receiving anticoagulation therapy for repetitive minor shunt thromboses and heavy fibrin formation on the artificial kidney. Infection remains a serious problem and has caused the death of two patients. Further follow-up studies will ultimately make it possible to ascertain whether or not this concept, with continuing changes in the prosthesis, will be adequate for all patients. As it stands currently, it is a readily satisfactory back-up and support shunt when all other available shunt sites have been used. Acceptance by the patient of this femoral shunt, with its position, high-flow characteristics and ease of handling, is high.

Radiological contrast study of arteriovenous dialysis cannulae.

Radiographic contrast studies of shunts are helpful in defining the causes of cannula dysfunction. X -ray examination has confirmed the presence of thrombi and revealed the adequacy of declotting procedures, indicating circumstances under which such techniques should be avoided. Radiographic studies provide a sound anatomical basis for the selection of shunt sites. Dilute contrast media are recommended.

Effect of site of shunt on left heart-volume characteristics in children with ventricular septal defect and patent ductus arteriosus.

Quantitative cineangiocardiographic technics have been utilized to determine left ventricular (LV) and left atrial (LA) volumes and LV muscle mass in 58 patients with isolated ventricular septal defect, 14 of whom were infants less than 2 years old, and in 25 patients with isolated patent ductus arteriosus, 13 of whom were infants. Patients were divided according to the degree of left-to-right shunt into small (&lt;35%), moderate (35 to 50%), and large (&gt;50%) shunt groups. Data obtained in both the VSD and the PDA groups were compared with normal values. Left ventricular end-diastolic volume and mass and LA maximal volumes in the patients of both groups who had shunts of 35% or more were greater than normal and showed a linear increase with increasing left-to-right shunt. The LV ejection fraction was decreased from normal in infants with either VSD or PDA and a shunt of more than 50%. This variable was normal in older children with either VSD or PDA. Patients with an aortic or a ventricular defect and equivalent shunts did not differ significantly in terms of LV end-diastolic volume, LV mass, LV ejected fraction, or LA maximal volume, normalized for body surface area. Patients with a patent ductus demonstrated the following differences when compared with patients with ventricular septal defect: (1) elevated LV end-diastolic pressure, (2) elevated LV end-diastolic stress, and (3) elevated value for LV mass (/m 2 BSA) per degree of shunt in children over 2 years of age with a patent ductus ( P &lt;0.05). These results indicate that left ventricular distensibility is decreased in patients with aortic left-to-right shunts compared to that in patients with ventricular left-to-right shunts of equivalent magnitude.

Hemodynamic and metabolic changes associated with bacterial peritonitis

Hemodynamic and metabolic studies of ten patients critically ill with diffuse bacterial peritonitis have been presented. The cardiac output and velocity of blood flow were normal. Total peripheral arterial resistance was markedly reduced in patients in whom systolic blood pressure was reduced to 75 mm. Hg or less despite normal cardiac output. Blood lactate levels were greatly elevated in these patients, indicative of a critical reduction in blood flow necessary to sustain normal metabolism of vital tissues. Our data indicate that an abnormal variation in distribution of blood flow is an outstanding circulatory alteration in patients with diffuse bacterial peritonitis. This hemodynamic effect may be explained by arteriovenous shunting in the systemic vascular bed. The site of such shunting is as yet unidentified, but presumably occurs in the area of peritoneal inflammation. Decreases in alveolar oxygen exchange also indicate the coexistence of arteriovenous shunting in the pulmonary circulation. Ventilatory failure and profound alterations in pulmonary function appear to be significant factors in the lethality of diffuse bacterial peritonitis.

The eisenmenger syndrome

The authors review the plain radiographs of 81 patients with the Eisenmenger syndrome in an attempt to localise the site of the shunt. It is concluded that the site of shunt can generally be predicted by assessment of the cardiac silhouette and of the pulmonary vascular pattern. The largest hearts and the biggest proximal pulmonary arteries were found in association with atrial septal defects. The aortic arch-pulmonary artery complex was abnormal in all patients with patent ductus. The plain radiographic appearance in ventricular septal defect was often almost normal.

PERSISTENCE OF FETAL DUCTUS FUNCTION AFTER BIRTH. THE DUCTUS ARTERIOSUS AS AN AVENUE OF ESCAPE

Within recent years there has been increasing interest in the presence of reversed flow through the ductus arteriosus. Most reported cases have been in older children and young adults. There is a group of cases in which the ductus serves as a site of a veno-arterial shunt in infancy, and thus continues to perform its fetal function. The conditions under which veno-arterial shunting persists after birth are illustrated and analyzed, and an effort is made to clarify the common features of these lesions.

Persistence of fetal ductus function after birth; the ductus arteriosus as an avenue of escape.

Within recent years there has been increasing interest in the presence of reversed flow through the ductus arteriosus. Most reported cases have been in older children and young adults. There is a group of cases in which the ductus serves as a site of a veno-arterial shunt in infancy, and thus continues to perform its fetal function. The conditions under which veno-arterial shunting persists after birth are illustrated and analyzed, and an effort is made to clarify the common features of these lesions.

Pulmonary arteriovenous fistula located by indicator dilution studies

Two cases of pulmonary arteriovenous fistula are described in which thoracotomy was performed and the lesion resected. In both patients the site of the venoarterial shunt and the absence of significant lesions in the opposite lung were demonstrated by indicator-dilution curves. During cardiac catheterization, peripheral arterial unsaturation was demonstrated and venoarterial shunts of 32 per cent of systemic flow and 53 per cent of systemic flow, respectively, were calculated.