Describe Pathophysiology of tetralogy of fallots ?
The PS causes concentric hypertrophy of right ventricle without enlargement. The right ventricular pressure are equal to or higher than left ventricular / aortic systolic pressure to maintain forward blood flow to lungs. Hence an increase in PS results in right to left shunt across large unrestrictive VSD, which is non - turbulent and silent on auscultation. The pulmonary stenosis results in an ejection systolic murmur (ESM), the intensity of which is directly proportional to pulmonary blood flow across the valve. Cyanosis is thus directly proportional and ESM is inversely proportional to the severity of PS. The PS causes a delayed and soft pulmonary component of second sound, which is inaudible in most patients. Hence on bedside examination second sound is single since only aortic component is audible. The VSD, by decompressing the right ventricle, limits the severity of right ventricular hypertrophy unlike in pure PS, The left parasternal impulse is, therefore, mild and generally without thrill. The hypercyanotic spells (also known as 'Cyanotic spells' or 'tet' spells)