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Arrhythmias (General)

DEFINITION

A cardiac arrhythmia is any abnormal heart rhythm. In healthy adults, the heart beats rhythmically 60 to 100 times per minute. And the pulse (felt at the wrist, neck, or elsewhere) corresponds to the contractions of the heart’s two large chambers, called ventricles. The other two chambers of the heart are called atria.

Under normal conditions, the electrical impulse for each heartbeat originates in the heart’s sinus node. It is the heart’s natural pacemaker, located in the upper part of the right atrium. From the sinoatrial node, the electrical impulse “travels” to the atrioventricular node (AVN), which is located between the atria. It is then transmitted through the bundle of His (a series of modified cardiac muscle fibers located between the ventricles) and from there the impulse enters the muscles of the ventricles. This causes them to contract, producing a heartbeat.

Cardiac arrhythmias are usually classified according to their origin, either as ventricular or supraventricular arrhythmias (occurring in areas above the ventricles, usually in the atria). They can also be classified based on their effect on heart rate, with bradycardia indicating a heart rate of less than 60 beats per minute and tachycardia indicating a heart rate of more than 100 beats per minute.

Some common types of cardiac arrhythmias include :

  1. Sinoatrial node dysfunction – This usually causes a slow heart rate (bradycardia – 50 beats per minute or less). The most common cause is scar tissue that develops and replaces the sinoatrial node. It is not known why this happens. Sinus node dysfunction can also be caused by coronary artery disease, hypothyroidism, severe liver disease, hypothermia, typhoid fever, or other causes. It may also be the result of “parasympathicotonia.”
  1. Supraventricular Arrhythmias – This diverse family of cardiac arrhythmias causes tachycardia that originates in the chambers (cavities) of the heart located above the ventricles. In most cases, the problem is either an abnormality in the AV node or an abnormal pathway (accessory bundle branch) that bypasses the normal route of the electrical impulse.
  1. Atrial fibrillation – This is a supraventricular arrhythmia that causes tachyarrhythmia, during which the atria experience “fibrillation” (trembling) instead of normal contraction. During atrial fibrillation, electrical impulses originate in many different locations within the atria rather than at the sinoatrial node. Although these impulses trigger 300–500 contractions per minute within the atria, their extremely high number overwhelms the atrioventricular node, causing the AVN to allow sporadic and irregular impulses to travel down to the ventricles, causing an arrhythmia and usually tachycardia ranging from 100 to 180 beats per minute. However, the ventricular rate may be slower. In atrial fibrillation, due to this lack of atrial contraction, there is an increased risk of blood clots forming inside the heart, as the blood does not circulate properly and remains, in a sense, stagnant. The most significant risk factors for atrial fibrillation are age, high blood pressure, valvular heart disease, and diabetes , and heart heart.
  2. Atrioventricular block (AV block) – In this type of arrhythmia, there is a problem with the transmission of electrical impulses from the sinoatrial node to the ventricles. There are three degrees of AV block:
  • First-degree atrioventricular block (1st AV block), in which the electrical impulse passes through the ventricles, but may take longer than normal.
  • Second-degree atrioventricular block (2nd-degree AV block), in which some heartbeat signals are lost between the atria and ventricles.
  • Third-degree atrioventricular block (3rd AV block): the electrical impulse from the atria does not pass to the ventricles, so the ventricles contract independently on their own.

Some of the causes of atrioventricular block include cardiomyopathy, coronary artery disease, and medications such as beta-blockers and digoxin.

  1. Ventricular tachycardia (VT) – This is an abnormal heart rhythm that originates in either the right or left ventricle. It can last for a few seconds (non-sustained VT) or for several minutes (sustained VT). Sustained VT is dangerous and, if left untreated, often progresses to ventricular fibrillation.
  1. Ventricular fibrillation – In this arrhythmia, the ventricles do not contract effectively, and no actual heartbeat is produced. The result is loss of consciousness, followed by brain damage and death within a few minutes. Ventricular fibrillation is a cardiac emergency. It can be caused by a heart attack, an electrical accident, a lightning strike, or drowning.

Symptoms

Symptoms of these specific arrhythmias include:

  • Sinoatrial node dysfunction – There may be no symptoms, or it may cause dizziness, fainting, and excessive fatigue.
  • Supraventricular arrhythmias – May cause palpitations (a sensation of a racing heart), low blood pressure, and fainting.
  • Atrial fibrillation – Sometimes there are no symptoms. It can cause palpitations, fainting, dizziness, weakness, difficulty breathing, and angina, which is chest pain caused by reduced blood flow to the heart muscle. Some people with atrial fibrillation alternate between arrhythmia and long periods of completely normal heartbeats.
  • First-degree atrioventricular block does not cause any symptoms. Second-degree atrioventricular block causes an irregular or slow heartbeat. Third-degree atrioventricular block can cause a very slow heart rate, dizziness, and fainting.
  • VT – Non-sustained VT may cause a mild “fluttering” sensation in the chest. Sustained VT usually causes dizziness or loss of consciousness and can be fatal.
  • Ventricular fibrillation causes a lack of a pulse, loss of consciousness, and death.

Diagnosis

The doctor will ask you about your family history of coronary artery disease, cardiac arrhythmia, fainting, or sudden death due to heart problems. They will also review your personal medical history, including any risk factors for cardiac arrhythmias (such as coronary artery disease, cardiomyopathy, and thyroid, and medications).

During the physical exam, your doctor will check your heart rate and pulse, listen to your heart for heart valve murmurs, and check for any physical signs of an enlarged heart.

The electrocardiogram (ECG) can often confirm the diagnosis of a cardiac arrhythmia. However, because cardiac arrhythmias can come and go, an ECG taken in a doctor’s office may appear normal. In this case, a HOLTER rhythm.

When a patient has ventricular fibrillation (a medical emergency), the patient is unconscious, not breathing, and has no pulse. If available, electrical defibrillation should be administered as soon as possible. If it is not available, cardiopulmonary resuscitation (CPR) should be started immediately.

Duration

The duration of a cardiac arrhythmia depends on its cause. For example, atrial fibrillation caused by overactivity of the thyroid may not last very long once the thyroid is treated. However, cardiac arrhythmias resulting from progressive or permanent damage to the heart tend to be long-term. When a heart attack causes ventricular fibrillation, death can occur within a few minutes.

Prevention

Cardiac arrhythmias caused by coronary artery disease can be prevented by taking the following steps to modify your risk factors:

  • A healthy diet, including fruits and vegetables, fish, dietary fiber, and protein, and avoiding saturated and trans fats.
  • Managing your cholesterol and high blood pressure.
  • Quitting smoking.
  • Weight management.
  • Daily exercise.

Drug-related cardiac arrhythmias can be minimized by consulting a healthcare professional or pharmacist about any potential interactions with other medications. It may be necessary to switch to a different medication or adjust the dosage of a medication.

Treatment

The treatment of a person’s cardiac arrhythmia depends on its cause:

  • Sinoatrial Node Dysfunction – In individuals with frequent, severe symptoms, the standard treatment is the implantation of a permanent pacemaker.
  • Supraventricular arrhythmias – This depends on the cause of the arrhythmia. In some people, massaging the carotid sinus in the neck will stop the problem. Others need medications such as beta-blockers, calcium channel blockers, digoxin, and amiodarone. Some patients respond only to a procedure called ablation (ablation), which “destroy” an area of abnormal tissue to prevent that electrical impulse from traveling from the atria to the ventricles.
  • Atrial fibrillation – Overactivity of the thyroid can be treated with medication or surgery. Atrial fibrillation can also be caused by mitral or aortic valve disease and can be treated by replacing damaged heart valves. Medications such as beta-blockers (for example, atenolol and metoprolol—Lopresor), amiodarone (Angoron), diltiazem (Tildiem), or verapamil (Isoptin), can be used to slow the heart rate. Medications such as amiodarone can be used to reduce the likelihood that atrial fibrillation will recur. Other treatment options include cardioversion, or electrical cardioversion (an electric shock to the heart to restore a normal heart rhythm).
  • Atrioventricular block – first-degree atrioventricular block usually does not require any treatment. Patients with second-degree atrioventricular block may be monitored with frequent ECG, especially if they have no symptoms and a heart rhythm that is suitable for their daily activities. Some patients with second-degree atrioventricular block may require a permanent pacemaker. Third-degree atrioventricular block is almost always treated with a permanent pacemaker.
  • VT – Non-sustained VT may not require treatment if there is no structural heart damage. Sustained VT always requires treatment, either with intravenous medication or defibrillation (electroshock), which can restore the heart’s normal rhythm.
  • Ventricular fibrillation – It is treated with defibrillation, which delivers an electric shock to the heart to restore its normal rhythm. People who have survived ventricular fibrillation and those at high risk are likely candidates for an implantable cardioverter-defibrillator (ICD). The device is similar to a pacemaker, with leads connected to the heart and a power source placed under the skin.

When to Call a Doctor

Call your doctor if you have any symptoms of a heart arrhythmia, including palpitations, dizziness, fainting, fatigue, shortness of breath, and chest pain. Call for emergency help immediately if someone develops a severe irregular heartbeat. If you cannot feel a pulse and the person is not breathing, begin CPR until emergency responders arrive.

Forecast

The prognosis for cardiac arrhythmias depends on the type of arrhythmia and whether the person has a history of coronary artery disease, congestive heart failure, or some other disorder of the heart muscle. The prognosis for ventricular fibrillation is poor, and death occurs rapidly without emergency treatment. Most supraventricular arrhythmias have an excellent prognosis. The prognosis is good for AV block, even third-degree AV block. The implantation of permanent pacemakers and defibrillators, as well as effective medications, has improved the prognosis for many people with severe cardiac arrhythmias.