An abnormal heart rhythm is called arrhythmia. The causes of arrhythmia are multifactorial. This article discusses the common types, common clinical presentations, and the available treatment modalities to tackle arrhythmia, which is a clinically vexing problem.
The normal rhythm of the heart is called sinus rhythm. Any disturbance resulting from multifactorial causes results in an abnormal heart rhythm. When the sinus rhythm is lost, it results in an arrhythmia. The branch of medicine dealing with abnormal heart rhythms is called electrophysiology.
Normally, an electric impulse is generated in the sinoatrial node (SAN), which is also called the pacemaker of the heart.
From the SAN, the impulse is conducted down to the atrioventricular node (AVN).
The AVN causes a delay in conduction called the AV nodal delay, and from here, the electrical impulse travels downwards into the ventricles through the bundle of His and Purkinje fiber systems.
Any disturbance in this normal mechanism of conduction results in an arrhythmia.
Under basal conditions, the maximum rate of firing of cells occurs in the sinoatrial node. Under duress, the whole heart starts to generate an abnormal rhythm. When the SA node malfunctions, backup rhythms come into force as a result of secondary pacemakers. This also happens when there is impedance to the conduction of normal electrical impulses in the conduction system. In summary, an arrhythmia results if the natural pacemaker of the heart malfunctions or if there is a blockage in the conduction system, or when other parts of the heart serve to act as secondary pacemakers.
Arrhythmia is classified into,
Tachyarrhythmia is an abnormal heart rhythm where the heart is beating in a rapid fashion and results in a rapid heart rate.
An abnormal rhythm where the heart starts to beat in a very slow fashion is known as bradyarrhythmia.
Also, they are broadly classified as,
A. Sinus Rhythms:
1. Atrial Tachyarrhythmias
Atrial ectopic beats (extrasystoles, premature beats).
Atrial flutter (AF).
Atrial fibrillation (AFib).
Supraventricular tachycardia (SVT).
AV nodal reentry tachycardia (AVNRT.)
Atrioventricular reentrant tachycardia (AVRT).
2. Ventricular tachyarrhythmias
Ventricular ectopic beats (extrasystoles, premature beats).
Ventricular tachycardia (VT).
Ventricular fibrillation (VF).
Torsades de pointes.
1. Sick sinus syndrome (SSS).
2. Atrioventricular (AV) block:
Mobitz type I (Wenckebach) block.
Mobitz type II block.
Third-degree (complete) heart block.
3. Bundle branch block:
Right bundle branch block (RBBB).
Left bundle branch block (LBBB).
The other common type of arrhythmias includes premature contractions, supraventricular arrhythmias, and ventricular arrhythmias.
1. Premature Contractions:
Premature contractions that occur in the heart's upper chambers are called premature atrial contractions (PACs), and those occurring in the heart's lower chambers are called premature ventricular contractions (PVCs). Premature beats are quite common and are asymptomatic most of the time. If symptomatic, they present with symptoms like a flutter in the chest or skipped heartbeats. These do not require active intervention unless they are part of a more serious symptom.
2. Supraventricular Arrhythmias:
These are tachycardias that arise in the atrium. These include atrial fibrillation, atrial flutter, paroxysmal supraventricular tachycardia (PSVT), and Wolff-Parkinson-White (WPW) syndrome.
a. Atrial Fibrillation (AF) - It is characterized by the rapid and disorganized quivering of the walls of the atrial chambers. This quivering is called fibrillation. Atrial fibrillation occurs when the pacemaker activity shifts from the SAN to AVN or somewhere near the pulmonary veins. The common causes of atrial fibrillation include hypertension, rheumatic heart disease, alcohol usage, and hyperthyroidism. The two common sequelae of atrial fibrillation include stroke and heart failure. Stroke can result when blood clots form in the atrial chamber. The inefficient pumping of the atria causes inadequate blood to reach the ventricles. As a result, other vital organs are not suffused with blood and the body's increasing demand for blood is not met. Therefore, inefficient filling of the ventricles results in heart failure.
b. Atrial Flutter - It is less common than atrial fibrillation. The heart beats in a fast and regular fashion, and that is how it differs from atrial fibrillation, wherein the rhythm is irregular and disorganized. The symptoms and complications of atrial flutter are similar to that of atrial fibrillation.
c. Paroxysmal Supraventricular Tachycardia (PSVT) - This begins and ends abruptly. It is common in young people and especially in those who indulge in vigorous and strenuous physical activity. The electrical impulses traveling from the atria to the ventricles have a 're-entry' pathway through which they re-enter the atria. Hence it is also called AV node re-entry tachycardia (AVNRT). Dual AV node pathways exist for the re-entry to occur, which results in an extra heartbeat. Since it occurs in an episodic fashion, the term paroxysmal is used. The complications of PSVT include syncope, congestive heart failure, cardiomyopathy, and myocardial infarction.
d. Wolff-Parkinson-White Syndrome - This is a special type of PSVT in which an aberrant pathway exists for the conduction of electrical impulses.
3. Ventricular Arrhythmias:
Ventricular arrhythmias include ventricular tachycardia (VT) and the more dangerous ventricular fibrillation (V-fib). Ventricular arrhythmia usually lasts for a few seconds. If it lasts for a longer time, it gets converted to ventricular fibrillation and can pose serious risks. Ventricular fibrillation is life-threatening and needs immediate medical intervention. Torsades de pointes (twisting of points) is a type of ventricular fibrillation with a characteristic pattern on the ECG.
Any arrhythmia presents with one or more of the following symptoms:
Irregular heartbeat - Beating too fast (palpitations) or too slow.
Shortness of breath.
It is imperative to rule out thyroid dysfunction or anxiety disorders.
Electrocardiogram (ECG): Records the heart rhythm and shows if it is beating too fast or too slow.
Echocardiogram (Echo): Shows areas of poor contractility, structural changes, blood flow to the heart, etc.
Holter Monitor: Records ECG for 24 to 48 hours period.
Event Monitor: It is similar to a Holter monitor but records ECG only during specific events.
Implantable Loop Recorder: A device is implanted underneath the chest, and this records the electrical activity of the heart. This is used when arrhythmias are infrequent and to determine their pattern of occurrence.
Electrophysiological Studies: A flexible guidewire is passed from a major artery in the thigh, and it is guided to the chambers of the heart, wherein it records electrical activity.
Other modalities include coronary angiography, stress testing, and tilt-table testing.
1. Drug Therapy:
Beta-blockers are used in the treatment of tachyarrhythmias. These include Metoprolol and Atenolol.
Calcium channel blockers like Diltiazem and Verapamil are also used.
Digoxin (digitalis) is most often used in treating atrial fibrillation.
Since AF patients also run the risk of developing blood clots, blood thinners like Warfarin, Aspirin, Dabigatran, and low molecular weight Heparin (LMWH) are used.
Some drugs are used to revert the heart rhythm to its original state. These are called rhythm reverters, and include Amiodarone, Sotalol, Procainamide, Ibutilide, Dofetilide, Quinidine, Disopyramide, and Flecainide.
Recent studies like HOT-CAFE (how to treat chronic atrial fibrillation) have concluded that rate control is as effective as rhythm control in the treatment of atrial fibrillation.
2. Interventional Procedures:
Bradyarrhythmia mandates the implantation of a pacemaker. This device is implanted underneath the chest and fires electrical impulses to make the heart beat at a normal pace and rhythm.
People at risk for ventricular fibrillation are fitted with a device called implantable cardioverter-defibrillator (ICD), which sends electrical shocks to the heart to beat in a normal rhythm upon sensing an abnormal rhythm.
Catheter Ablation: This is done as a part of electrophysiological studies in arrhythmias unresponsive to drug therapy or to other modalities of treatment. Here, a thin guide wire is passed from the thigh to the heart, and the heart tissue generating abnormal rhythms is selectively burned (ablated).
Cox-Maze Technique: This is done for atrial fibrillation, where atrial tissue is cut and burnt to prevent the transmission of disorganized electrical impulses.
If the cause of the arrhythmia is coronary heart disease, then coronary artery bypass grafting (CABG) is done.
To summarize, arrhythmias represent a common and clinically vexing problem. Specialist cutting edge interventions are available in today's age for the treatment of these problems.
Last reviewed at:
03 Sep 2021 - 6 min read
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