Class I Antiarrhythimic agents

Class I agents are (Na+) channel blockers. They are called Membrane Stabilizing agents. The 'stabilizing' is the word used to describe the decrease of excitogenicity of the plasma membrane which is brought about by these agents. They are divided into 3 groups on base of effects on action potential.

Class Ia

• Quinidine is used for Slow VT & Brugada VT.

• disopyramide has a negative Inotropy effect and is used for HOCM.

• Procainamide is used for wide complex tachycardia & WPW.

Class Ib

• Lidocaine is a iv. drug and it is used for Ischemic-VT (after MI) and some experts also use for TDP. It should be adjusted in patients with liver disease & heart failure.

• Mexiletine is a p.o. drug and rarly some experts use it for some VT:s, when Lidocaine has helped in acute phase (in CCU) and in ECG, QT-time has prolonged.

Class Ic

• Flecainide, propafenone

• They reduce maximal rate of change in the velocity of depolarization. They increase RR, PR, and QRS.

• They are used frequently widely for prevent paroxysmal AF.

• They can induce postrepolarization refractoriness, thereby could suppress ectopy and reduce inducible VF.

• The initial results of CAST I was published in 1989 and the CAST II results published in 1992. In both trials, antiarrhythmic drugs effectively suppressed asymptomatic ventricular arrhythmias but increased arrhythmic death. Because the suppression hypothesis was refuted, the common practice of using antiarrhythmic drugs to suppress asymptomatic arrhythmias in patients after acute myocardial infarction has been curtailed.

• They can suppress the sinus node in patients with SSS and impair AV and infra nodal conduction in patients with conduction disease. They have slow kinetics.

Class IC; Flecainide (& Propafenone)

• Contraindicated in structural heart diseasein & in ischemic heart disease. (Echt DS...et al. N Engl J 1991)

• Flecainide is used frequently widely for prevent paroxysmal lone AF. Some experts use that also for control of intractable symptoms caused by PVC.

• It is recommended that always Flecainide (or other drugs from this class) should be used with beta-blocker. Because when Flecainide is slowing the atrial rate in atrial flutter, 1:1 AV conduction could be happen. So beta-blocker is needed for AV nodal blocking, because sometimes the patient rhythm could be flutter.

• Flecainide use-dependently increases in PR and QRS durations of up to 25% compared with baseline. A greater increase in the QRS duration may be a marker for proarrhythmia risk. (Aliot E...et al. Europace.2011)

• Should be used with caution in the presence of significant conduction system disease, including intraventricular conduction delay or BBB. AHA/ACC/HRS Guideline 2014

How to start flecainide in paroxysmal AF? (AF –the Role of Flecainide, Fifth edition, edited by MJ Pekka Raatikainen, MD)

• Echo + (Exercise testing)→ start the treatment → Repeat the exercise test after 3-5 days → If high proarrhythmia risk then finish the drug.

• Routine exersice testing is not mandatory if CAD can be excluded otherwise. So if there is not CAD-risk factor then you can start without exercise test. Anyway if you start Flecainide, after 3-5 days exercise test is necessary to evaluate proarrhythmia risk.

• Abnormal Exercise test; Ischemia, QRS widens > 30-50%, multiple VES or VT

 

 

 

Compilation by Dr. Samad Ali Moradi, According to Finnish cardiology references, ESC guidline & author work experience.