Arrhythmias

What is an arrhythmia?

Normal Conduction:
To understand what an arrhythmia is, it is important to first understand how a normal heart beats. With each heartbeat, the electrical impulse begins at the sinoatrial node (SA node) which is referred to as the "heart’s pacemaker". Normally, these electrical impulses spread down from the SA node, pass through the atrioventricular node (AV node) eventually reaching the left and right ventricles (the muscular portion of the heart). When passing through the AV node, there is a normal, short delay before the electrical impulses reach the ventricles. After completing one cycle, the SA node fires again resulting in the same progression of electrical events.

Arrhythmias:
When the heart beats too fast, too slow, or with a skipping (irregular) rhythm, a person is said to have an arrhythmia. Some people feel a "palpitation", "skipped beat", "fluttering in the chest", "pounding of the heart" or "racing of the heart,”while others feel tired and lightheaded. Arrhythmias are common and frequently harmless. However, some heart arrhythmias can cause more significant symptoms and even cause sudden death.

What are the major types of arrhythmias?

Bradycardias – Slow heart rates below 60 beats per minute that include:

Sick sinus – Slow heart rate generally caused by a sick and malfunctioning pacemaking SA node.

Conduction block – A block of your heart's electrical conduction can occur in or near the AV node preventing the impulse from reaching the ventricle.

Supraventricular arrhythmias/tachycardias (SVTs) – Fast rhythms that begin in the upper chambers above (“supra”) the ventricles that include:

Premature atrial contractions (PACs) – Early, extra beats that originate in the upper chambers of the heart.

Atrial fibrillation – Fast and chaotic beating of the atrial chambers resulting in quivering (or fibrillation) at around 600 beats per minute. Atrial fibrillation can be brief, lasting a couple minutes or to other extreme, become chronic and permanent.

Atrial flutter – Rapid rhythm, though more organized and regular than atrial fibrillation.

Atrial tachycardia – Rapid heart rhythm that comes from the atria (but not the normal SA node).

AV re-entrant tachycardia (AVRT) – Fast rhythm due to a “bypass” electrical pathway between the atria and ventricle. This “bypass” tract allows the heart to beat unusually fast. Wolff-Parkinson-White syndrome is a common type of AV re-entrant tachycardias and in younger patients can cause sudden death.

AV nodal re-entrant tachycardia (AVNRT) – Rapid heart rate due to having more than one pathway through the atrioventricular (AV) node.

Ventricle arrhythmias/tachycardias – Tachycardias originating in the ventricles include:

Premature ventricular contractions (PVCs) – Early, extra beats that originate in the bottom chambers of the heart.

Ventricular tachycardia (VT). This fast and frequently dangerous beating of the heart coming from the bottom of the heart in the ventricles. Most VT occurs in people with preexisting heart damage. Long QT syndrome, an inherited or acquired abnormality, also puts one at risk for VT. An episode of sustained VT can be a medical emergency and without prompt medical treatment, may result in death.

Ventricular fibrillation. Rapid, chaotic electrical impulses from your ventricle causing quivering and inability to pump blood forward. Without CPR or defibrillation (electrical shock), death may result in minutes. Ventricular fibrillation is frequently triggered by a heart attack.

What symptoms might I have?

Arrhythmias may not cause any signs or symptoms or can result in a feeling of fluttering in the chest, chest pain, shortness of breath, racing heartbeat, dizziness and fainting. If symptoms are present, one should seek medical attention.

Common causes of tachycardias:

• SVTs can be associated with increased age, high blood pressure, excessive alcohol use, thyroid disease, valvular heart disease, smoking, caffeine, drug abuse, and stress. Some medications including over-the-counter medications and prescription medications, dietary supplements and herbal remedies also can cause arrhythmias in some people.

• Ventricular tachycardia can result from underlying heart disease such as a cardiomyopathy (reduced heart function) caused by scar from a previous heart attack or possibly heart enlargement caused by valve abnormalities or a viral infection of the heart muscle. Genetic abnormalities such as long QT and hypertrophic cardiomyopathy also increase one’s risk for this rhythm.

What tests may be useful to make the diagnosis?

Your doctor may order a number of tests to help make the diagnosis. These tests may focus on monitoring your rhythm with a Holter monitor or event recorder after a baseline ECG is taken. Additionally an echocardiogram will be ordered to evaluate your heart function as well as consideration for stress testing and more sophisticated electrophysiologic (EP) testing and mapping.

What major complications can result from these rhythm problems?

Stroke. When your heart’s rhythm is in atrial fibrillation or atrial flutter your atrial chambers are unable to pump blood effectively. Stagnant blood in the atria can form blood clots that travel up to the brain causing a stroke and possibly death.

Congestive heart failure. This can result if your heart is pumping ineffectively for a prolonged period due to a bradycardia or tachycardia.

Death. If your heart goes into ventricular tachycardia, which can become ventricular fibrillation, you are likely to quickly lose consciousness. If the rhythm is not corrected within minutes (by medication or being shocked by a defibrillator) or CPR is not initiated, death may result.

How are these arrhythmias treated?

Treating bradycardias
If the slow heart rhythm is causing symptoms or determined to be dangerous, you may be treated with a pacemaker.

Treating tachycardias

• SVTs – Some medications can slow down your heart rate down, while others can be used to attempt to keep your heart in normal rhythm (referred to as anti-arrhythmics). For patients with SVTs, especially atrial fibrillation and atrial flutter, “converting” that rhythm back to normal by cardioversion may be recommended. If medication and cardioversion are unsuccessful or the SVT is deemed to be potentially curable, you may be considered for a procedure called a cardiac ablation.

• VTs – Quite frequently placement of an automated implantable cardioverter-defibrillator (AICD) may be recommended for ventricular tachycardia (VT). A number of treatment approaches may be attempted for patients with tachycardias originating from the ventricle. The AICD continuously monitors your heart rhythm and if this device detects VT or ventricular fibrillation (VF), it sends out low- or high-energy shocks to reset the heart to a normal rhythm thereby, reducing one’s chance of dying from a fatal arrhythmia. Medication therapy may also be considered.