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Cardio pharmacologyAngina
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angina
Causes
Atheroma
Others: Aortic stenosis, aberrant coronary circulation, severe anaemia, arteritis
Prevention
Decrease metabolic demands of the heart
Increase coronary blood flow
Decrease cardiovascular risk factors
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decrease cardiovascular risk factors
BP
Cholesterol
Smoking
LVH
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Decrease metabolic demands of the heart
1. Decrease HR
2. Decrease arterial pressure
3. Decrease ventricular dimensions
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1. Decrease HR
Beta adrenoreceptor blockers
Decrease sympathetic response
Not for HF
B1
Atenolol
B2
Propranolol
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Detail 1. Drugs that ⇓ HR:
§ β-adrenoreceptor blockers – atenolol (β1) - , propranolol (β2). Block β receptors ∴ attenuate the sympathetic response of the heart → slow heart rate & improve capacity for exercise. Good if cardiac function is preserved, not for HF
§ Mode of action:
— ⇓ HR ⇑ with exercise etc.
— ⇓ contractility & arterial P
— ∴ ⇓ O2 demands of myocardium during exercise
§ Side effects:
— ⇑ LV dimensions∴ ⇑ LV work offsetting benefits
— Slow HR
— Heart failure
— Cold peripheries - Raynaud’s
§ Alternatives = Ca channel blockers – verapamil & diltiazem also slow HR due to effect on calcium channels in cardiac pacemaker cells
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2. decrease arterial pressure
Calcium channel blockers
Dihydropyridines
Nifedipine
Non-dihydropyridines
Diltiazem, verapamil
Mainly relax resistance arteries BP falls
Some effect on heart with...
...Diltiazem and Verapamil?
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Details2. Drugs that ⇓ Arterial Pressure
§ Ca channels blockers – verapamil, diltiazem & nifedipine (short acting)
§ Mode of action:
— Diltiazem (small effects) / Verapamil (large effects) - ⇓ Ca entry into cardiac pacemaker cells → HR ⇓. ⇓ Ca entry into myocytes ∴ ⇓ force of contraction
— Side effects: bradycardia & heart failure (oedema)
— All - ⇓ Ca influx thru L-type voltage-gated Ca channels in peripheral vasculature ∴⇓ peripheral resistance
— All - ⇓ Ca entry into vascular myocytes → relex at arteries, TPR ⇓, BP ⇓
Side effects:
§ reflex tachycardia (Nifedipine only) in response to peripheral vasodil
§ Flushing
§ Headaches
§ Ankle swelling
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3. Decrease ventricular size
Nitrovasodilators
GTN & isosorbide mononitrate/ dinitrate
Active in 1-2 mins
Lasts for 15-20
Metabolised to NO
Increase venous capacitance
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Details3. Drugs that ⇓ Ventricular Dimensions:
§ Nitrovasodilators – glyceryl trinitrate (GTN), isosorbide mononitrate, dinitrate relax vascular & other types of smooth muscle with preferential effect on veins
— ⇑ venous capacitance (& small ⇓ in arterial resistance) ⇓ central venous P → ⇓ in ventricular dimensions & CO. The ⇓ in cardiac size & small ⇓ in TPR = ⇓ in LV work. They also dilate coronary arteries → relief from angina
§ Mode of action: – nirtovasodilators metabolised to NO → activates vsmc guanylate cyclase in vascular smooth muscle → ⇑ in cGMP → ⇓ in IC free Ca → vascular relaxation
§ GTN – when swallowed is inactive until metabilsed in liver. If sucked under tongue absorbed rapidly, works within 1-2 mins & effects last for 15-20 mins
§ Isosorbide dinitrate ISDN– converted to ISMN in liver ∴ long acting orally active form of GTN (prophylactic)
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Details cont.§ Side effects:
— development of tolerance, resistance of vsm:· In withdrawal constriction of coronary arteries may
develop· Blood vessels may become insensitive to NO· Stable NO metabolite pool may become depleted Solution = give intermittently — Headaches due to dilation of muscular intracranial
arteries— Reflex ⇑ in HR— Limited potential for dilating sites of atheroma,
risk of steal syndrome – if one artery stenosed dilation of other = they take all the blood & leave that artery further depleted
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GTN ----> NO
GTN is a prodrug for NO
NO activates GC
GC converts GTP ----> cGMP
cGMP leads to smooth muscle relaxation...
...by decrease Ca
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Potassium channel openers
Nicorandil
Vasodilator due to hyperpolarising of cells
Ivabradine
Acts selectively on SA node to slow HR
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DetailsPotassium channel Openers
· Nicorandil – ⇓ ICK+ ∴ cells become hyperpolarised - vasodilator
§ Side effects:
— Severe headache
— Flushing
— Dizziness & low BP
· Ivabradine:
§ Selective action on SA node → slows HR
§ Protects endothelium dependant relaxation → relax coronary arteries
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Combinations
Increase in heart size caused by B-blockers can be offset by...
...nitrovasodilators
Tachycardia of nitrovasodilators or nifedipine can be prevented by giving...
...B-blockers
Aspirin good for stopping platelets sticking
Given to everyone unless...
...they are bleeding