Angina
Pectoris
·
Pathophysiology.
·
Principles of drug therapy.
·
Individual drugs.
Pathophysiology
1.
Cause:
a.
Angina pectoris is a symptoms of ischaemic heart disease caused by a
relative insufficiency of coronary blood flow.
b.
Develops when the blood supply is inadequate to meet myocardial demand.
2.
Stable angina:
a.
Characterized by predictable precipitating factors (e.g. exercise,
emotion or heavy meal) causing retrosternal chest pain and usually lasting no
more than a few minutes following rest.
b.
Cause is usually due to atherosclerotic obstruction to coronary blood
flow.
3.
Unstable angina:
a. New
or sudden worsening of previous angina occurring at rest or minimal effort.
b.
Symptoms frequently herald the onset of myocardial infarction.
4.
Variant angina: symptoms are due to coronary vasopasm and can
occur at rest, often during the night.
Principles of drug therapy
1.
Treatment objective is to unload the heart or to prevent / relax spasm of
the coronary arteries so that oxygen need is adequately met.
2.
Determinants of oxygen consumption:
a.
Preload: the venous filling and stretching of the heart and its muscle
fibers, which evokes the contractility.
b.
Afterload: the peripheral arteriolar resistance against which the heart
must eject blood.
c.
Heart rate: determines the duration of diastole during which
intramyocardial pressure is low enough to allow myocardial perfusion to occur
via the coronary arteries.
3. The
heart can be unloaded by:
a.
halting the provocative exercise (physical or emotional).
b.
reducing the preload (venous return).
c.
reducing the afterload (arteriolar resistance).
d.
reducing the rate.
e.
dilating the coronary arteries.
4.
Summary of treatment:
a. Any
contributory cause is treated when possible, e.g. anaemia, dysrhythmia.
b. Life
style is changed so as to reduce the number of attacks, e.g. weight reduction,
quit smoking.
c. For
immediate pre-exertional prophylaxis: glyceryl trinitrate sublingually or
nifedipine.
d. For
an acute attack: glyceryl trinitrate (sublingual) or nifedipine (bite capsule).
e. For
long-term prophylaxis: propranolol, nifedipine or diltiazeim, isosorbide
dinitrate or mononitrate and antiplatelet therapy with aspirin.
5.
Individualization of drug therapy:
a.
Variant angina: calcium channel blockers, avoid beta-blockers.
b.
Beta-blockers should not be used in patients with history of asthma,
incipient heart failure, diabetes or bradyarrhythmias.
c.
Nitrates and calcium channel blockers are preferred in chronic
obstructive pulmonary disease.
d.
Hypertension with tendency to tachyarrhythmias: beta-blockers or calcium
channel blockers.
Individual drugs
1.
Organic nitrates reduce preload and afterload and dilate the main
coronary arteries.
2.
Beta-adrenoceptor blocking drugs reduce myocardial contractility and slow
the heart rate.
3.
Calcium channel blockers reduce cardiac contractility, dilate the
coronary arteries and reduce afterload.