Arrhythmia

 

The heart is a four chambered muscular organ that beats to pump blood to our body. It has two upper chambers called atria and two lower chambers called ventricles. The atria are the chambers that receive blood and ventricles pump the blood to the rest of the body. We have all felt our hearts beat fast at some time. It is more common in elderly. It is usual except when it feels like a flutter in the chest or neck when it can be an arrhythmia. Not all arrhythmias are dangerous but the serious ones can be life threatening.

Knowing about arrhythmia

An arrhythmia is a medical condition characterized by an abnormal rate or rhythm of the heart. Electrical impulses generated in the pacemaker or other small foci in the heart cause it to beat rhythmically and at a controlled rate as they travel across the heart muscles. A change in sequence or timing of these impulses may cause erratic heart beats. As a result, the heart may beat fast or slow. A heart rate more than 100 is called tachycardia and one less than 60 is called bradycardia.

Causes

An arrhythmia is caused by defect in either generation or conduction of electrical impulses in the heart. The pacemaker that generates the signals may fail or the channels that convey signals to the rest of the heart may be blocked. Hence, the heart is not able to beat as a synchronous set of muscles.

There can be various reasons for aberrant electrical impulses. Sometimes, the cause may not be apparent.

  • An arrhythmia may occur if any focus other than the main pacemaker starts generating impulses. In that case, these new impulses add to the impulses from the pacemaker and lead to an abnormal heart rate or rhythm.
  • A heart attack, which is dying of the heart muscles due to lack of blood supply and hence oxygen, is a common cause for arrhythmias. It can damage the heart’s electrical system.
  • Other conditions that affect the heart can influence the electrical system. Some of these are heart failure, a very high blood pressure, and alteration in the activity of the thyroid gland which produces hormones that can affect heart rate.
  • Smoking, alcohol, and certain drugs like cocaine and amphetamines can affect the heart rate.

Arrhythmias can be congenital. The pacemakers or the conduction pathways can be malformed since birth.

Types

Arrhythmias are generally of four types: premature beats, supraventricular arrhythmias, ventricular arrhythmias, and bradyarrhythmias.

Commonest type of arrhythmia, a premature beat is one that comes sooner than normal and is followed by a pause after which there is a more forceful beat that is felt. Premature beats may arise in the atria, premature atrial contractions (PACs) or in the ventricles, premature ventricular contractions (PVCs).

Supraventricular arrhythmias comprise paroxysmal atrial tachycardia (PAT) or paroxysmal supraventricular tachycardia (PSVT). Electrical signals generated at new places in the atria interfere with the firing of the natural pacemaker. This leads to a rapid heart rate that does not enable it to fill in properly before it contracts. Electrical signals in the heart's upper chambers fire abnormally, which interferes with electrical signals coming from the sinoatrial (SA) node --- the heart's natural pacemaker. A series of early beats in the atria speeds up the heart rate. The rapid heartbeat does not allow enough time for the heart to fill before it contracts so blood flow to the rest of the body is compromised.

Ventricular arrhythmias comprise the ventricular tachycardia (VT). Electrical impulses originate in the ventricles and interfere with those coming from the natural pacemaker. The heartbeat hence rises and ventricles do not have enough time to fill before they contract. VT is usually caused in consequence to another condition in the heart like a heart attack, abnormality in the heart muscles or in one of the valves. Besides this, it can occur as a side effect to medicines like digitalis or some other medicines used to actually treat arrhythmias, exercise, emotional excitement, or a sudden change in posture.

A low heart rate may be seen even without an underlying arrhythmia as in sleep, in elderly, or athletes. A bradyarrhythmia is one that causes a heart rate of 60 per minute. It can be caused by a defect in the natural pacemaker, or the conduction path in the heart either due to a heart attack or any other heart disease. It may be caused by some other medical conditions like a low body temperature.

Seriousness of Arrhythmias

Premature beats are not serious in most cases. These are common in teenagers and children and usually have no cause and need no treatment.

SVTs can be seen in children and women, anxious people, or may occur due to excess smoking, alcohol, caffeine, or physical fatigue, in which case these are not serious. These can also occur with a heart attack or with a diseased valve in the heart. In extreme cases these can lead to unconsciousness or arrest in the heart. A life threatening type of SVT is called the Wolff-Parkinson-White syndrome. In this, the electrical signals in the heart travel along an extra pathway from the atria to the ventricles and disrupt the timing of the usual signals.

Arrhythmias that arise in the ventricles are potentially more serious than those that arise in the atria. VTs that last a few seconds do not cause much problems but the ones that last long can result in dizziness, unconsciousness and arrest in the heart. It may eventually turn into a fibrillation, another type of arrhythmia.

Atrial fibrillation is a condition where disorganized abnormal signals originate in a number of foci in the atria and cause a heartbeat of as high as 300 per minute. The atria cannot contract and only quiver. AF can cause the heart to fail and cause potential complications. Similar condition in the ventricles is called ventricular fibrillation. This leads to an arrest in the heart.

Diagnosis

You may have an arrhythmia if you have felt abnormal fast, slow, or irregular beats or you have felt as though the heart did pause for a while. You may feel anxious, dizzy, or weak. You may faint, sweat or develop chest pain or shortness of breath.

You may be required to undergo some tests to confirm your arrhythmia. An electrocardiogram (ECG or EKG) records the heart's electrical activity. It requires a few leads and wires to be placed on the skin. You may be advised to wear a holter monitor which is a small, portable machine that you wear for 24 hours to continuous record your ECG as you engage in your daily activities. You may need to run on a treadmill to enable the doctor to produce and record an electrical activity that may not be seen at rest or in course of normal activity. Other tests like tilt table test, event recorder, or magnetic source imaging may be done.

Treatment

Arrhythmias are treated by medicines, medical procedures, or surgery. Medicines called antiarrhymics, like amiodarone, sotalol, flecainide, propafenone, dofetilide, ibutilide, quinidine, procainamide, and disopyramide, restore the normal heart rate and rhythm. These medicines have side effects and can make an arrhythmia worse or even cause a different kind of arrhythmia.

Blood thinning medicines like aspirin, warfarin, and heparin may be used to prevent clotting. Any other medical conditions like a high blood pressure or a deranged thyroid function may need treatment. Some arrhythmias may need a pacemaker which is a device that electrically stimulates the heart to beat at a normal rate. Others may require a jolt of electricity. This is called cardioversion or defibrillation. These devices are generally implanted under the skin in the chest.

If medicines do not work, a thin flexible tube may be threaded through vessels in the arm or upper thigh till the heart and energy delivered through the tube can help to destroy the abnormal foci that generate the abnormal heart beats. This is called catheter ablation. Surgery may be required to either treat any underlying conditions like a blocked vessel in the heart or a defective valve, or to make small cuts or burns that prevent the spread of disorganized signals in heart. You may be advised vagal maneuvers like gagging, immersing face in cold water, holding breath and bearing down, etc. These affect the vagus nerve that controls heart rate.