Cardiology USMLE step 1 right coronary a perfuses - Answer: SA, AV node posterior descending branch--> inferior LV (Right dominant, if left dominant, PD is derived from the circumflex artery) marginal a. --> right ventricle left coronary perfuses - Answer: LAD --> anterior LV MOST COMMON SITE OF OCCLUSION circumflex a. --> posterior LV coronary arteries fill during - Answer: diastole most posterior part of the heart - Answer: LA enlargement --> dysphagia, hoarseness CO - Answer: = SVxHR = rate O2 consumed/(PaO2-PvO2) = EDV - ESV Cardiology USMLE step 1 MAP - Answer: COxTPR exercise - Answer: initially, incr in CO via incr HR later, incr SV and incr contractility play a big role incr symp stim: incr venous return contracts arterioles EXCEPT in working muscle and dumps volume into the muscle --> local mediators in muscle: adenosine, K, ATP, CO2, lactate this DECREASE in SYSTEMIC VASCULAR RESISTANCE by dilating muscle vessels allows for BP to be relatively stable during exercise despite incr CO CO variables - Answer: SV - affected by contractility, afterload, + preload SV incr with: anxiety, exercise, pregnancy Contractility/SV incr with: catecholamines (incr Ca pump in SR) incr intracellular Ca decr extracellular Na (decr Ca/Na exchange) Cardiology USMLE step 1 Digitalis - incr intracellular Na-->incr Ca Contractility/SV decr with: beta block (decr cAMP) systolic heart fail acidosis hypoxia/hypercapnea non-dihydropyridine Ca channel blockers these incr myocardial O2 demands - Answer: incr afterload/arterial pressure incr contractility incr HR incr heart size incr wall tension preload/afterload - Answer: preload = ventricular EDV afterload = MAP ~ PR venodilators decr preload (nitro) vasodilators decr afterload (hydralazine) incr preload with exercise, blood volume, sympathetic/excitement starling curve (CO) + venous return graphs - Answer: basically CO (SV) incr with preload - from fiber stretch Cardiology USMLE step 1 force of contraction ~ initial length of cardiac muscle fiber ~ preload ejection fraction - Answer: = SV/EDV = (EDV - ESV)/ EDV EF is an index of VENTRICULAR CONTRACTILITY NORMAL ≥ 55?CR EF WITH HEART FAILURE resistance, pressure, flow - Answer: P = QxR R ~ (viscosity x length)/radius^4 ARTERIOLES account for most of the TPR, regulate capillary flow resistance of vessels in series= R1 + R2 1/total resistance in parallel=1/R1 + 1/R2 ...remember that if youre adding 1/Rn then you have to flip sum to get Rtotal viscosity ~ hematocrit incr viscosity in POLYCYTHEMIA, HYPERPROTEIN