<p>Disopyramide&rsquo;s Class 1a activity is similar to that of quinidine in that it targets sodium channels to inhibit conduction. Disopyramide depresses the increase in sodium permeability of the cardiac Myocyte during Phase 0 of the cardiac action potential, in turn decreasing the inward sodium current. This results in an increased threshold for excitation and a decreased upstroke velocity.<br />
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Disopyramide prolongs the PR interval by lengthening both the QRS and P wave duration. This effect is particularly well suited in the treatment of ventricular tachycardia as it slows the action potential propagation through the atria to the ventricles.<br />
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Disopyramide does not act as a blocking agent for beta or alpha adrenergic receptors, but does have a significant negative inotropic effect on the ventricular myocardium. As a result, the use of disopyramide may reduce contractile force up to 42% at low doses and up to 100% in higher doses leading to heart failure.<br />
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This provides a possible treatment for atrial and ventricular fibrillation, as it restores pacemaker control of the tissue to the SA and AV nodes</p>