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Friday, 24 November 2017

Arrhythmias (Rhythm disturbances)

In an adult the heart beats between 60-100 bpm. Each heart beat is initiated by an electric impulse arising spontaneously from the normal pacemaker of the heart called the sinoatrial node (SA node) . The SA node is located at the upper part of the right atrium where the superior vena cava enters it.


For a normal heart beat to occur the electric impulse starts at the SA node , travels through specialized conduction tissue to the atrioventricular node (AV node). On the way it activates the right and left atrium. The AV node is situated at the junction of the atria and the ventricles. The AV node regulates the conduction of electrical impulses in to the ventricles. From the AV node the electrical impulse traverses the bundle of His, then the left and right bundle and through the purkinje fibers stimulates the myocardium (heart muscle).


On an average the heart beats 100.000 times a day, pumping almost 7500 liters of blood through its chambers to the rest of the body and then back to the heart. Over 70 years that adds up to more than 2.5 billion heart beats.


Abnormalities in the heart could result in a slow heart rate (bradycardia) or in a fast heart rate (tachycardia). They are collectively called cardiac arrhythmias. Today most arrhythmias are treatable. This was not the case 50 years ago. Over the last 50 years we have been able to understand arrhythmias better and newer technologies have given us life saving treatments for many of these life threatening conditions.


Resuscitation a patient from cardiac arrest due to an abnormally fast heart rhythm simply and effectively with an electrical shock using an external defibrillator was one of the most significant advances.


 Types of Arrhythmias


The SA node and AV node can malfunction and result in an abnormally slow heart rate. At other times any part of the heart can take over as the heart’s pacemaker giving rise to an abnormal heart rate.

Common types of arrhythmias:


  Premature beats
  A common arrhythmia, affects a large number of people. As an isolated abnormality they are generally benign and asymptomatic. Occasionally patients may complain that they feel the heart has stopped beating momentarily. Caffeine and stress increase the occurrence of premature beats.
  Atrial fibrillation
  Atrial fibrillation - incidence increases with age. Develops when a disturbance in the electrical signals causes the individual muscle fibers in the two atria to contract haphazardly and not in unison. As a result not all blood is forced out of these chambers and the blood that remains there could form clots. At times these clots could get dislodged travel through the body and block blood vessels in the brain and result in a stroke.
  Bradycardia – a slow heart beat or bradycardia causes a person to feel fatigued, dizzy and lightheaded and may result in fainting spells.
  Tachycardia – a fast heart rate (tachycardia) can cause reduced blood circulation. During this fast heart rate a person could feel his heart beating rapidly (palpitations), experience giddiness and could faint.
  Ventricular Arrhythmias

Tachycardia – a fast heart rate (tachycardia) can cause reduced blood circulation. During this fast heart rate a person could feel his heart beating rapidly (palpitations), experience giddiness and could faint.


 Treatment of Arrhythmias


The different modalities we have at our disposal are medications, devices and catheter ablation techniques.

Medications include antiarrhythmic agents which normalize the heart rhythm, drugs to slow down the heart and drugs to prevent blood from clotting in the heart and thus prevent strokes. Devices basically are pacemakers to treat bradycardias and defibrillators to treat the life threatening ventricular arrhythmias. Pacemakers are small devices which contain a battery and the circuit which helps it to detect the normal heart beat and stimulate the heart when it does not detect the patient’s normal heart beat. The pacemaker is placed under the skin on the chest and the wires are guided through the neck veins in to either the right atrium or right ventricle in single chamber pacemakers and into both right atrium and right ventricle in dual chamber pacemakers. Depending on the type of bradycardia the will decide as to what type of pacemaker would be appropriate. The pacemakers available today generally have batteries that last about 8 to 12 years. For ventricular tachycardia’s and ventricular fibrillation there are devices called implantable cardiac defibrillators (ICD). These devices are inserted similar to a pacemaker and when the device detects an abnormal rhythm they either normal it either by rapid pacing or by delivering an electrical shock to the heart. Another method adopted to treat tachyarrhythmia’s is radiofrequency ablation where the abnormal electrical focus is identified and destroyed.



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