Right Ventricular Pressure Flow Relationships and Intracardiac Venturi Effects in Fallot's Tetralogy

Recent studies of pressure flow relationships in isolated pulmonary valvular stenosis have demonstrated that, broadly speaking, they conform to certain well-known physical laws (Watson et al., 1960; Watson and Lowe, 1962), and a better understanding of right ventricular function in that condition has prompted us to make a similar study in patients with Fallot's tetralogy.Since there is still some disagreement about which cases should rightly be grouped under this title (Rosenblum et al., 1962;Coelho et al., 1961), we have considered only the so-called "classical" cases in our analysis: those with pulmonary stenosis, either valvular, infundibular, or both, and the characteristic ventricular septal defect that allows blood to pass freely from the right ventricle into an overriding aorta.When compared with those having a normal aortic root and an intact interven- tricular septum, it is obvious that the presence of this defect modifies the h1modynamic effects of obstruction to the outflow of blood from the right side of the heart.Because of it, the pressure in the right ventricle can never rise above that in the left in its attempt to force blood into the lungs, since at this level right-to-left shunting takes place and blood escapes into the systemic circulation.This affects the form as well as the height of the right ventricular pressure pulse and accounts for the difference between the peaked main cavity pulse waves of severe isolated pulmonary stenosis (Fine- berg and Wiggers, 1936) and the flat topped ones so often seen in Fallot's tetralogy.The other differences between the two conditions are due to the great variety and combination of stenotic lesions that may be present between the tricuspid valve and the pulmonary trunk in the tetralogy. NATURE OF OBSTRUCTIONA study of right ventricular pressure flow relations must take into account the types and sites of these obstructions, because such factors as the length/diameter ratio of the stenosis and the nature of the chamber distal to the constriction greatly influence the hemodynamics of the blood flowing through it.It is not yet easy to determine the true relative incidence of the various types of pul- monary stenosis found in Fallot's tetralogy, since it has only been possible to make an accarate anatomical assessment during open heart surgery for a relatively short time.Before this, such information as was available came from post-mortem studies, and as Keith, Rowe, and Vlad (1958) have pointed out in their review of earlier reports, there is considerable variation from series to series.Their averages of 13 per cent valvular, 60 per cent infundibular, and 27 per cent combined stenoses do not include pulmonary atresia which, it is generally agreed, accounts for about 1 case in 5, a figure that corresponds closely to Blalock's experience in a largely post-operative group (Johns, Williams, and Blalock, 1953).This high percentage of pulmonary atresia has, of course, been found amongst patients with the most severe Fallot's tetralogy who are least likely to surmount major 794 on July 17,