Guidelines for Complications of Cancer Treatment Vol VIII Part B

Radiation Induced Cardiac &Pulmonary ComplicationsCardiac ComplicationsPumping action of the heart is due to synchronized contractionof the myocytes which is the basic unit of cardiac musculature.Sinus node initiates electrical stimulus (action potential) whichpropagates through atrioventricular node and HIS-purkinjesystem to ventricular myocytes which causes contraction. Therelease of calcium from sarcoplasmic reticulum into thesarcoplasm which in turn catalyze the cross bridging of theactin and myosin filaments producing myocyte contraction.Cross bridging can only occur if the filaments are in theirnormal, relaxed state. If the myocytes are already stretched asin anthracycline-induced cardiomyopathy, then such crossbridging is impaired. Moreover, the myocytes must return totheir resting state to respond to the action potential for thenext contraction.The myocardial blood supply is a critical system. Rich capillarynetwork of the heart muscle is an important target because ofinherent sensitivity of the endothelial cells, which essentiallyconstitute the vessel wall. The endothelial lining of musculararteries ( epicardial and subepicardial) are also vulnerable to298