Antiarrhythmic Agents 193riness in Purkinje and ventricular muscle
fibers.
Amiodarone is slowly and poorly absorbed
after oral administration. It is metabolised
slowly in liver to active metabolite.
Adverse effects include hypotension
due to vasodilatation and depression of
myocardial performance is frequent with the
IV route. Heart block, bradycardia, corneal
microdeposits, photosensitivity, hepatitis,
gastrointestinal upset may occur.
It is indicated in tachyarrhythmias asso-
ciated with WPW syndrome, atrial flutter and
fibrillation, paroxysmal tachyarrhythmias
not responding to other agents. Ventricular
tachycardia and ventricular arrhythmia re-
fractory to other treatment.
BRETYLIUM
It has direct action on myocardium and
interferes with the neuronal release of cat-
echolamines and has direct antiarrhythmic
property. Bretylium may reverse the short-
ening of action potential duration caused by
ischemia. It acts due to K+ channel blockade.
It is used in the treatment of ventricular
tachycardia and ventricular fibrillation.CALCIUM CHANNEL BLOCKERSThe detailed pharmacology is discussed in
chapter ‘Antihypertensive agents’.
These drugs inhibit Ca2+ mediated slow
channel inward current, thus inhibiting Ca2+
mediated depolarization. Phase 4 depolar-
ization in SA node and Purkinje fibres is re-
duced. They also prolong AV nodal effec-
tive refractory period thus AV conduction
is slowed. There is also negative inotropic
action.
It is indicated in PSVT, to control ventricu-
lar rate in atrial flutter or atrial fibrillation.