Antiarrhythmic Agents 191- Increase in the duration of ventricu-
lar systole (QT interval). - Decrease in amplitude of T waves.
- Depression of ST segment.
- Reduction in conduction velocity
(widening of QRS complex).
Extracardiac actions:
a. Quinidine in normal individuals pro-
duce a decrease in blood pressure af-
ter oral and IV administration.
b. Quinidine has got antimalarial, anti-
pyretic, oxytocic and skeletal muscle
relaxant activity also.
It is well absorbed orally, undergoes ex-
tensive hepatic oxidative metabolism. 90%
quinidine is bound to plasma protein. The
drug is distributed to most tissues except
brain. About 20% is excreted unchanged by
the kidney.
Adverse effects include SA block or ar-
rest, high grade AV block, ventricular tachy-
cardia, arrhythmia or ventricular asystole,
polymorphic ventricular tachyarrhythmia,
hypotension (particularly when given IV),
cinchonism, tinnitus, loss of hearing, gas-
trointestinal upset, severe headache, diplo-
pia, photophobia, etc.
It is indicated in prevention of atrial ar-
rhythmia, atrial fibrillation or flutter, par-
oxysmal supraventricular tachycardia, ven-
tricular premature beats and ventricular ta-
chycardia.
PROCAINAMIDE
It has got quinidine like cardiac prop-
erty. It depresses the excitability of both
atria and ventricles. Contractility and con-
ductivity are also depressed. It has got mini-
mal vagolytic action.
It decreases the rate of rise of action po-
tential and prolongs the effective refractory
period.
After oral administration it is absorbed
quickly, about 20% is bound to plasma pro-
tein up to and 70% of a dose is excreted in
urine in unchanged form.
Adverse effects include renal failure,
hypotension (when given IV), anorexia, nau-
sea, vomiting, Q-T prolongation. Rarely there
is diarrhoea, giddiness, psychosis, hallucina-
tion, mental depression, hypersensitivity,
agranulocytosis, myalgia, angioedema, skin
rash, digital vasculitis. Procainamide can
cause syndrome that resembles SLE, which
is reversible on discontinuation of
procainamide; leukopenia and thrombocy-
topenia.
It is indicated in ventricular arrhyth-
mia, ventricular premature depolarization
and paroxysmal ventricular tachycardia,
supra-ventricular tachycardia and atrial ar-
rhythmia.DISOPYRAMIDE
It has got anticholinergic and mem-
brane depressant properties and like qui-
nidine, it is effective against most of the
atrial and ventricular arrhythmias. It has no
effect on sinus rate.
Adverse effects include dry mouth, con-
stipation, blurred vision, urinary urgency
and occasional urinary retention, nausea,
vomiting, diarrhoea, abdominal pain,
hypoglycaemia, jaundice, coronary heart
failure and hypotension.
It is indicated in atrial and ventricular
arrhythmias in digitalised and non-