Coronary Artery Disease Flashcards
Coronary Arteries
- length of Left main - 2cm; LAD - 8cm; RCA - 10cm; Cx - 6cm
- if divided into 5mm segments = 2 segments for LM; 20 LAD; 20 RCA; 12 Cx; TOTAL of 54 segments
Coronary Arteries
Roberts et al: in patients with fatal MI, ~35% of the 54 segments have >75% narrowed in x-sectional area;
- 50% diameter reduction (stenosis) by angiogram = 75% narrowing of x-sectional area (CSA)
- IVUS uses CSA to report disease
- patients with unstable angina have shown to have the worse coronary narrowing (~48% of the 54-segments with >75% narrowing of CSA);
- in acute MI, stable angina, healed myocardial infarction, only 35% of the 54-segments had >75% narrowing
Coronary arteries
75% narrowing in CSA (50% diameter narrowin) = important bc coronary flow is decreased at this point; narroing < 75%, causes no flow issues;
- so if there is decrease in coronary flow = severe narrowing in coronary artery
- amount of severe CSA narrowing at death from MI is similar to when the first event occurred
- (ie. occurrence of coronary event = severe and extensive atherosclerosis)
Common areas of severe narrowing
RCA - distal third
LAD - proximal third
Cx - proximal third
Composition of atherosclerotic plaque
- Fibrous tissue (70%)
- lipids 10%
- calcium 10%
- other things 10%
- multiluminal channels (common in unstable angina) - suggest thrombi were present and have reoorganized
- such high amount of fibrosus suggests that thrombosis plays a role in plaque formation
Acute Plaque Composition
Seen in patients who died within 6hrs of chest pain
- thrombi is not major (only in 15% of plaques and is attached onto the plaque not limiting flow)
- cause of sudden death is unclear
- occlusive thrombi usually occurs with acute MI (70% of patients)
- in the other 30%, the thrombus likely lysed but was initially present at the onset of acute MI
- a study from MtSinai NY, showed that all occluded thrombus lyse after MI (patients who receive thrombolysis, lyses faster)
- also, on average, the amoung of thrombus present at site of infarction was 20% with underlying plaque which was about 80%;
- the range of thrombus present was from 2 to 67%; this explains why in some patients thrombolysis is more successful or less preferred;
Cardiac Meds
Beta blockers: first line for chronic angina; reduce BP and HR –>reduce myocardial oxygen demand by reducing cardiac workload
- decrease MACE and death in patients with previous MI; no survival benefit in angina;
- B1 selective (metoprolol, atenolol) better than B2 selective (causes bronchospasm, depression, hyperglycemia); Improve survival in low EF, prior MI, CHF; no benefit in stable CAD, no MI or normal EF;
CCBs: no survival benefit at all. similar symptom reduction in angina like BB;
- dihydropyridine = peripheral and coronary dilation (amlodipine, felodipine)
- non-dihydro = negative chronoptrope and inotrope (verapamil, diltiazem) - avoid with LVD patients
Nitrates = coronary and peripheral vasodilation; tachyphylaxis can occur as a s/e
Cardiac Meds - secondary prevention
Lifestyle Modification can reduce morbidity and mortality.
Flu vaccines should be administered regularly.
Lipids: patients with history of CAD, LDL target = 2mmol/L using statins. Role of other LDL reducing agents like ezetimibe is unclear.
-HDL increasing agents like niacin is effective but has side effects and no convincing survival data;
-lowering of TG with fibrates, or niacin is effective but less than statins (fenofibrate best)
Cardiac Meds- Antiplatelets
Aspirin - All CHD patients should be on this; reduce MACE by 25-30% in secondary prevention patients. Dose: 75-162mg/d
Plavix: Give if ASA intolerant; ideal upto 1 year after MI
BB: Improve survival in low EF, prior MI, CHF; no benefit in stable CAD, no MI or normal EF;
ACE/ARB: survival benefit in low EF, prior MI; no benefit in stable CAD, and normal EF.
Aldosterone Antagonists (spirinolactone) - improves survival in EF<40%, prior MI, or mod to severe CHF; monitor K and renal function; should only be used be Cr is normal;
Coumadin: no role unless other conditions present (afib, LV thrombus, recent ant MI)
No role in vitamins;
Myocardial Protection
Monitor venous O2 and lactate
Modify cardiolegia based on:
-pressure, flow, oxygen saturation, lactate
-adenosine - during induction, with folow contant, increase adenosine dose until pressure falls;
-insulin - during rewarming, measure coronary venous glucose; increase insulin dose until glucose falls; oxygen saturation increases; lactate decreases;
O2 deman of heart
at 37dc - baseline (10); off-loaded (6);