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23. Antiarrhythmic drugs: Difference between revisions
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(Created page with "== Cardiac electrophysiology == We can divide the normal action potential into 5 phases: # Upstroke phase # Early-fast repolarization # Plateau # Repolarization # Diastole thumb|This shows the action potential of the ventricle. The phases are marked with numbers. These phases can be seen on the figure below. Note that this shows the depolarization of the ventricle. The cardiac pacemaker cells don’t have “normal” act...") |
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* Class Ia – Intermediate Na+ channel blockers | * Class Ia – Intermediate Na+ channel blockers | ||
** Quinidine | ** Quinidine | ||
** Ajmaline (oral form: prajmaline) | |||
** (Disopyramide) | ** (Disopyramide) | ||
** (Procainamide) | ** (Procainamide) | ||
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* Class Ic – Strong Na+ channel blockers | * Class Ic – Strong Na+ channel blockers | ||
** Propafenone | ** Propafenone | ||
** | ** Flecainide | ||
Class Ia drugs | Class Ia drugs and mexilitine are rarely, if ever, used. Lidocaine is a local anaesthetic as well, and it's much more often used as that than as an antiarrhythmic. Ajmaline is used to diagnose a rare condition called Brugada syndrome, as it causes characteristic ECG changes in this disease. | ||
=== Mechanism of action === | === Mechanism of action === | ||
These drugs are Na+ channel blockers. These channels are responsible for the phase 0 of the ventricular action potential and phase 4 of the pacemaker action potential. Blocking these channels causes the rate of depolarization during phase 0 to decrease. | These drugs are Na+ channel blockers. These channels are responsible for the phase 0 of the ventricular action potential and phase 4 of the pacemaker action potential. Blocking these channels causes the rate of depolarization during phase 0 to decrease. | ||
Class Ib drugs have a stronger effect on ischaemic myocardium than healthy myocardium, theoretically making them a good choice for arrhythmias that occur after AMI. | Class Ib drugs have a stronger effect on ischaemic myocardium than healthy myocardium, theoretically making them a good choice for arrhythmias that occur after AMI, but only theoretically. | ||
=== Side effects === | === Side effects === | ||
Class Ia drugs prolong the QT-interval, which increases the risk for ''torsade de pointes''. Class Ic drugs are especially proarrhythmic in case of ischaemia and so is contraindicated in ischaemic heart disease. | Class Ia drugs prolong the QT-interval, which increases the risk for ''torsade de pointes''. Class Ic drugs are especially proarrhythmic in case of ischaemia and so is contraindicated in ischaemic heart disease. | ||
Quinidine causes cinchonism, a condition characterised by symptoms like headache, hearing/vision loss, tinnitus, and psychosis. | Quinidine causes cinchonism, a condition characterised by symptoms like headache, hearing/vision loss, tinnitus, and psychosis. Ajmaline may cause headaches, visual disturbances, and intrahepatic cholestasis. | ||
== Class II drugs – beta blockers == | == Class II drugs – beta blockers == | ||