General principles of treating rhythm disorders
Pharmacotherapy of arrhythmias is not limited to simply prescribing pills, but follows a strict hierarchy of therapeutic goals.
First and foremost, the physician must focus on etiotropic therapy—treating the underlying disease that led to the rhythm disorder. Concurrently, all triggering factors must be eliminated. Only at the third stage is the prescription of specific anti-arrhythmic drugs justified. If the conservative approach proves ineffective, surgical intervention on the cardiac conduction pathways is resorted to in certain cases.
Classification of anti-arrhythmic drugs
Anti-arrhythmics are divided into four main classes. This classification is based on the mechanism of their effect on the conductivity and action potential parameters of cardiomyocytes.
Class I: Sodium channel blockers
These drugs slow down impulse conduction, which leads to the disruption of the pathological excitation circulation circuit (the so-called re-entry mechanism). They also have a variable effect on the duration of the action potential.
- For supraventricular disorders: quinidine, procainamide (novocainamide), disopyramide, ajmaline. They are predominantly used for atrial fibrillation and frequent extrasystoles.
- For ventricular disorders: lidocaine, moracizine (ethmozine). These are the drugs of choice for ventricular tachycardias. The special specificity of lidocaine lies in its high efficacy in patients with myocardial infarction.
Class II: $\beta$-blockers
A typical representative of this group is propranolol. Drugs of this class demonstrate the greatest efficacy in the treatment of atrial (supraventricular) arrhythmias.
Class III: Action potential prolongers
Agents in this group increase the duration of the action potential and the effective refractory period. The main representative is amiodarone. This is a universal drug that is effective in all types of arrhythmias, although in practice the focus is often specifically on atrial disorders.
Class IV: Slow calcium channel blockers
Include verapamil and diltiazem. Like Class III drugs, they have a very wide range of efficacy, but are mostly used for atrial pathologies.
Non-pharmacological treatment methods
In situations where pharmacotherapy is insufficient or emergency intervention is required, device-based techniques are used.
- Relief of acute attacks (emergency therapy). Electrical cardioversion or defibrillation is used to eliminate atrial and ventricular fibrillation, as well as paroxysmal tachycardia.
- Treatment of bradyarrhythmias and conduction disorders. With significant rhythm slowing and complete AV block, implantation of a permanent pacemaker (PM) is indicated. Modern pacemakers are complex programmable systems capable of dual-chamber pacing and adapting the heart rate to physical exertion. Their service life is 7–10 years, and they are widely used in developed countries.
- Prevention of sudden death. Patients at high risk of arrhythmic death undergo implantable cardioverter-defibrillator (ICD) placement. The main feature and limiting factor of this method is its high cost.
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What specific side effects are characteristic of long-term amiodarone intake?
The following side effects are noted for amiodarone, the risk of which increases with long-term use: pneumonitis, pulmonary fibrosis, keratopathy, and photosensitization. In addition, long-term amiodarone intake is listed as a drug-induced cause of hypothyroidism.
What is the classification of anti-arrhythmic drugs that divides them into 4 classes called?
The classification of anti-arrhythmic drugs dividing them into four classes by mechanism of action is called the Vaughan-Williams classification. In sources, it is designated as the Vaughan-Williams classification, 1970, with additions, as well as the E. Vaughan Williams classification modified by D. Harrison. It is based on clinical use and mechanisms of drug action.
For Class I drugs: "Quinidine and company" work on the atria, while "Lidocaine and ethmozine" rescue the ventricles (especially in infarction).
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What is the mechanism of action of Class I drugs?
They block sodium channels, slowing conduction. This breaks the circuit of pathological impulse circulation (re-entry).
Which anti-arrhythmic is considered the most universal?
Amiodarone (a Class III drug). It is effective in all types of rhythm disorders.
In which cases is pacemaker implantation required?
Pacemakers are implanted for bradyarrhythmias, pronounced heart rate slowing, and complete atrioventricular block.
Topik lain untuk dipelajari
- Mechanism of excitation wave circulation (re-entry)
- Pharmacodynamics of lidocaine in myocardial infarction
- Differences between electrical cardioversion and defibrillation
- Operating principles of dual-chamber pacemakers
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