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14 Anti-arrhythmics
Non-cardiac – cerebral artery vasodilatation occurs after the administration of
verapamil.Kinetics
Verapamil is used orally and intravenously. Although almost 90% is absorbed from
the gut a high first-pass metabolism reduces its oral bioavailability to about 25%.
Approximately 90% is bound to plasma proteins. It is metabolized in the liver to at
least 12 inactive metabolites that are excreted in the urine. Its volume of distribution
is 3–5 l.kg−^1 .The elimination half-life of 3–7 hours is prolonged with higher doses as
hepatic enzymes become saturated.β-Blockers
The effects of catecholamines are antagonized byβ-blockers. Therefore, they induce
abradycardia (by prolonging ‘diastolic’ depolarization – phase 4), depress myocar-
dial contractility and prolong AV conduction. In addition, someβ-blockers exhibit
adegree of membrane stabilizing activity (class I) although this probably has lit-
tle clinical significance. Sotalol also demonstrates class III activity by blocking K+
channels and prolonging repolarization.
β-Blockers are used in the treatment of hypertension, angina, myocardial infarc-
tion, tachyarrhythmias, thyrotoxicosis, anxiety states, the prophylaxis of migraine
and topically in glaucoma. Their use as an anti-arrhythmic is limited to treatment of
paroxysmal SVT and sinus tachycardia due to increased levels of catecholamines.
They have a role following acute myocardial infarction where they may reduce
arrhythmias and prevent further infarction. Owing to their negative inotropic effects
they should be avoided in those with poor ventricular function for fear of precipitat-
ing cardiac failure.Esmolol
Esmolol is a relatively cardioselectiveβ-blocker with a rapid onset and offset.Presentation
Itis presented as a clear liquid with either 2.5 g or 100 mg in 10 ml. The former should
be diluted before administration as an infusion (dose range 50–200μg.kg−^1 .min−^1 ),
while the latter is titrated in 10 mg boluses to effect.Uses
Esmolol is used in the short-term management of tachycardia and hypertension in
the peri-operative period, and for acute SVT. It has no intrinsic sympathomimetic
activity or membrane-stabilizing properties.