Heart & Circulatory Health

Disturbances of Heart Rhythm

Written by Dr. Alok Vinod Kulkarni and medically reviewed by iCliniq medical review team.

 

Contents


The normal rhythm of the heart is called sinus rhythm. Any disturbance resulting from multi-factorial 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.

Mechanism of Conduction

  • 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 downward 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.

Arrhythmia Generation

Under basal conditions, the maximum rate of firing of cells occurs in the sinoatrial node. Under duress, the whole of the heart can start to generate an abnormal rhythm. When the SA node malfunctions, back-up 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 blockade in the conduction system or when other parts of the heart serve to act as secondary pacemakers.

Classification of Arrhythmia

Broadly, arrhythmias are classified into,

  1. Tachyarrhythmias, an abnormal heart rhythm where the heart beats in a rapid fashion and results in a rapid heart rate.
  2. An abnormal rhythm where the heart beats in a very slow fashion, bradyarrhythmias.

The other common type of arrhythmias include premature contractions, supraventricular arrhythmias and ventricular arrhythmias.

Premature Contractions:

Premature contractions that occur in the heart's upper chambers 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 flutter in the chest or skipped heart beats. These do not require active intervention unless they are part of a more serious symptom.

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.

1. Atrial Fibrillation (AF):

It is characterized by 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 sequel of atrial fibrillation include stroke and heart failure. Stroke results when blood clots form in the atrial chamber and get embolized to the brain. The inefficient pumping of the atria results in the ventricles not getting adequate blood. As a result other vital organs are not suffused with blood. The body's increasing demand for blood is not met. The inefficient filling of the ventricles results in heart failure.

2. 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.

3. Paroxysmal Supraventricular Tachycardia (PSVT):

This begins and ends abruptly. It is common in young people and in especially those who indulge in vigorous and strenuous physical activity. The electrical impulses traversing 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. This results in an extra heart beat. 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.

4. Wolff-Parkinson-White Syndrome:

This is a special type of PSVT. An aberrant pathway exists for conduction of electrical impulses.

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 intervention in the form of defibrillation or what is more commonly known as DC shock. Torsades de pointes (twisting of points) is a type of ventricular fibrillation with a characteristic pattern on the ECG.

Common Clinical Presentations of Arrhythmias

Any arrhythmia presents with one or more of the following symptoms:

  1. Irregular heart beat - beating too fast (palpitations) or too slow.
  2. Skipped beats.
  3. Extra beats.
  4. Dizziness.
  5. Syncopal attacks.
  6. Lightheadedness.
  7. Chest pain.
  8. Sweating.
  9. Anxiety.
  10. Fatigue.
  11. Shortness of breath.

It is imperative to rule out thyroid dysfunction or anxiety disorders.

Special Investigations

  1. Electrocardiogram (ECG): Records the heart rhythm and shows if it is beating too fast or too slow.
  2. Echocardiogram (Echo): Shows areas of poor contractility, structural changes, blood flow to the heart, etc.
  3. Holter Monitor: Records ECG for 24 to 48 hours period.
  4. Event Monitor: It is similar to a Holter monitor, but records ECG only during specific events.
  5. 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.
  6. Electrophysiological Studies: A flexible guide wire is passed from a major artery in the thigh and it is guided to the chambers of the heart wherein it records the electrical activity.
  7. Other modalities include coronary angiography, stress testing and tilt-table testing.

Treatments available for abnormal heart rhythms

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) may also be used. These are 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 these 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 the heart to beat at a normal pace and rhythm.
  • People at risk for ventricular fibrillation are fitted with a device called implantable cardioverter defibrillator (ICD) which shocks the heart into a normal rhythm upon sensing that the heart is beating in 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.

In summary, arrhythmias represent a common and clinically vexing problem. Specialist cutting edge interventions are available in today's age for the treatment of these problems.

Are you suffering from irregular heart beat? Do not worry. For more detailed explanation consult a cardiologist online --> https://www.icliniq.com/ask-a-doctor-online/cardiologist

Last reviewed at: 07.Sep.2018

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