Drugs Used in Chronic IHD Flashcards
Classic angina
Occlusion of coronary aa. resulting from atherosclerotic plaque
Variant (Prinzmetal) angina
Episodes of vasoconstriction of coronary aa.
Angina def:
Imbalance between oxygen demand of the heart and oxygen supply via the coronary aa.
Why does angina occur during exercise or stress?
Oxygen demand of the heart increases significantly, which is greater than the supply of oxygen through the partially blocked coronary a.
3 approaches to treating angina pectoris
- Decrease cardiac work
- Increase blood flow through coronary aa.
- Reduce myocardial oxygen demand
What is the best way to treat vasospastic (Prinzmetal) angina?
Is it helpful in classic angina?
Increase coronary blood flow using vasodilators.
No.
What is the “coronary steal” phenomenon?
The redistribution of blood to non-ischemic areas associated w/ dilation of small arterioles. This is the reason vasodilators don’t work well in classic angina.
3 phases of phasic coronary flow
- Isovolumetric contraction
- Ejection
- Diastole
3 drug classes used in chronic IHD
Nitrates
Ca++ channel blockers
Beta-blockers
How do organic nitrates work?
Once ingested, the nitrates are activated and lead to SM relaxation and vasodilation.
3 Nitrovasodilators (nitrates)
Nitroglycerin
Isosorbide dinitrate
Isosorbide mononitrate
What is the first-pass metabolism of nitrates?
It is significant, meaning the oral bioavailability is low. Other routes that avoid the GI tract are used mostly.
What nitrate is a poor substrate of nitrate reductase and has a greater bioavailability?
Isosorbide mononitrate
What is needed to release NO from nitrates?
Thiols
What does NO dilate?
Veins and large arteries (higher conc. needed for aa.)
NO dilates veins and arteries. What is the effect of dilating them?
Veins:
- increased venous capacitance
- reduced ventricular preload
Arteries:
-reduce afterload
*there is no substantial increase in coronary blood flow into the ischemic area in classic angina.
MOA of nitrates to treat variant angina
Vascular SM relaxation -> coronary a. dilation -> coronary spasm relief
MOA of nitrates to treat classic angina
Venous dilation -> reduced preload -> decrease oxygen demand
4 ways to develop tolerance to nitrates
Depletion of thiol components
Increased generation of superoxide radicals (leads to depletion of NO)
Reflex activation of SNS
Salt and water retention
What is the use of short-acting nitrates vs. long-acting nitrates?
Short-acting: relieve angina attack
Long-acting: prevent future attacks
S/E of nitrates
HA
Orthostatic hypoTN
Tachy/inotropy
Increased Na+ and water reabsorption
3 Non-cardioactive (Dihydropines) Ca++ channel blockers
Amlodipine (long-acting)
Nifedipine (short-acting)
Nicardipine (short-acting)
2 Cardioactive Ca++ channel blockers
Diltiazem
Verapamil
Ca++ channel blockers MOA
Ca++ enters via voltage-dependent Ca++ channels to cause SM contraction, so by blocking it, it is inhibited.