Arrhythmias: Drug Principles And Indications

The medications used to treat arrhythmias, a heart disorder that affects people in their pediatric years, will be covered in this blog. We will also examine the use of specific medications, their dosage, and indications, as well as the contraindications that apply to them in situations of arrhythmias.

Principles of Therapy in Children

The principles of therapy dictate that we must use the medications in accordance with certain recommendations and restrictions for treating arrhythmias in children. There may be differences in drug pharmacokinetics between the various pediatric age groups. 

The absorption, stomach emptying, and volume of distribution of infants are typically slower. There are differences in hepatic metabolism and renal exertion between children and the paediatric age group.  It's critical to use and dose medications appropriately for the specified indications.
A lot of medications are utilized for pediatric arrhythmias "off-label".

Vaughan-Williams Classification

Generally, this classification is used to divide and most importantly classify the anti-arrhythmic drugs used widely.

A. Class 1 Drugs: also known as sodium channel blockers. They are further divided into 3 sub-classes.

Class 1A Drugs

These medications typically block rapid sodium channels. It is also recognized that they prolong repolarization. In patients with arrhythmias, they lengthen the duration of the action potential. It is especially recognized that certain medication types are employed in atrial arrhythmia patients. Procainamide, disopyramide, and quinidine are a few examples.

Class 1B Drugs

These medications are the less potent sodium channel blockers. They have been shown to shorten patients' action potentials. Ventricular tachycardia is a known condition for which they are specifically used.
Examples include phenytoin, mexiletine, and lidocaine.

Class 1C drugs

They have no effect on the length of the action potential in patients, and they are known to very strongly block sodium channels. Propafenone and flecainide are two examples.

2. Class 2 drugs: also known as beta-blockers.

Examples: propranolol, atenolol, and nadolol.

 C Class 3 drugs: By obstructing the potassium channel, these medications are known to prolong the repolarization.

. Examples: amiodarone.

4. Class 4 drugs: these are calcium channel blockers. Examples: verapamil.

Miscellaneous drugs: these are considered not a part of the original class of drugs. Examples: digoxin, and adenosine.

Also Read: Epidemiology And Syndromes In Congenital Heart Diseases

Key Points Of Regarding Commonly Used Drugs

Class 1A Drugs

Indications: supraventricular tachycardia, atrial fibrillation, atrial flutter, and occasionally ventricular tachycardia are the principal conditions for which they are prescribed. Negative effects: QRS and QTc interval prolongation are among the most common negative effects of these medications.  Haemolytic anemia: disopyramide has anticholinergic effects, while quinidine and procainamide both exacerbate periodic paralysis and drug-induced SLE.

Class 1B drugs

Indications: phenytoin, ventricular tachycardia, and occasionally digoxin toxicity are the conditions for which they are prescribed.  It is well known that using Cimetidine with other medications can make them more toxic together.

Class 1C Drugs

• Indications: for atrial tachycardia patients.
• Adverse effects: these medications have a history of lowering cardiac contractility and causing hypotension and pro-arrhythmia.

Also Read: Rapid Acquisition Of Key Concepts Cardiovascular

Class 2 Drugs

Indications: Propranolol, nadolol, supraventricular tachycardia, and prolonged QTc interval are among the conditions for which it is utilized.
Adverse effects: Typically, these medications cause bradycardia, unconsciousness, and poor academic performance.  In addition, propranolol exacerbates congestive heart failure and causes bronchospasm, hypoglycemia, heart block, and hypotension.

Co-administration of any Beta blocker with CCBs, disopyramide and Flecainide causes decreased ventricular function. 

Class 3 Drugs-amiodarone

Indications: JET, ventricular tachycardia, and supraventricular tachycardia are among the conditions for which these medication classes are appropriate.  Adverse effects: the medications should not be used in situations of iodine toxicity, hypotension, vasodilatory effects, negative inotropic effects, especially when loading an IV dose. Other adverse effects include hypo- or hyperthyroidism, hypertriglyceridemia, liver toxicity, and pulmonary fibrosis.  Recommendation from IAP Pediatric Intensive Care, Third Edition: Steer clear of Amiodarone in newborns as it contains benzyl alcohol preservative, which can kill them.

Class 4 Drugs

 Indications: for supraventricular tachycardia patients.  Adverse effects: comprise bradycardia, a high degree of atrioventricular block, hypotension, extended PR interval, and congestive heart failure.
IAP Ped Intensive Care 3rd Ed, AIIMS PICU Protocol States: Avoid Verapamil in age less than 1 year due to the danger of CVS collapse and death. • Steer clear of simultaneous treatment with Beta-Blockers and Disopyramide.

Also Read: Chest X-ray In Pediatric Cardiology

MCQ 

Why do we avoid amiodarone in neonates?

Ans: Generally, amiodarone is avoided in neonates due to the presence of Bengal alcohol preservative which can cause fatal gasping syndrome in neonates.

Adenosine 

Indications: It can differentiate between tachycardias caused by increased automaticity and re-entrant tachycardia, making it the medication of choice in situations of PSVT (paroxysmal supraventricular tachycardia).  Dosage: 0.1 mg/kg (maximum 6 mg) is the initial dose; 0.2 mg/kg (maximum 12 mg) is the second dose if the condition continues.
Because each brief t1/2 of 10 minutes, a quick IV push and a 5 ml NS flush are administered. 

Adverse effects: these include asystole, bradycardia, atrial fibrillation, flushing, dyspnea, and bronchospasm.  Refrain from using disopyramide, beta blockers, and aminophylline at the same time as they can induce reversible antagonistic effects on adenosine.
In instances of second and third degree heart block, it is also contraindicated.

Hope you found this blog helpful for your NEET SS Pediatrics Cardiology preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.