What types of cardiac arrhythmias are there?
Supraventricular Tachycardia. Supraventricular tachycardia (SVT) is a series of very rapid heartbeats that begin in the heart's upper chambers. Generally supraventricular tachycardia is not a life-threatening problem although it can be quite bothersome and frightening. SVT may occur when an extra pathway exists in the atria (top chamber), the AV node or between the atria and ventricles (bottom chamber). An electrophysiology study can be used to identify the origination site of the SVT.
SVT is commonly treated/controlled with medications called anti-arrhythmics. A procedure called a catheter radiofrequency ablation can cure or eliminate SVT. Your doctor will know if this might be an option for you. Two specific categories of SVT are Wolff-Parkinson-White syndrome (WPW) and Atrial Fibrillation.
Wolff-Parkinson-White (WPW) Syndrome. An abnormal bridge of tissue connects the atria (top chamber) and ventricles (lower chamber). This extra pathway, called an accessory pathway, makes it possible for electrical impulses to travel from the atria to the ventricles without going through the AV node. Patients with Wolff-Parkinson-White Syndrome (WPW) experience arrhythmias when an impulse travels down the AV node to the ventricles, and then up through the necessary pathway to the atria. If the impulse continues to travel in a circular pattern, it may cause the heart to contract with each cycle. This could result in a very rapid heartbeat, which could allow extremely rapid and potentially serious rhythms to occur.
Atrial Fibrillation. In patients with atrial fibrillation, multiple sites in the atria (top chamber) send electrical impulses in an uncoordinated fashion. As a result, the atria beat very quickly and ineffectively. The AV node, which acts as a relay station, allows only some of these impulses to travel down the electrical system and stimulate the ventricles. As a result, the heart rhythm is irregular, erratic, and usually (but not always) rapid. Atrial fibrillation may occur once in a while or it may be chronic.
Ventricular Tachycardia (VT). Rapid heart beating, which arises in the ventricles (bottom chambers of the heart), is known as ventricular tachycardia, and can be life threatening. Ventricular fibrillation (VF) exists when the ventricles are quivering and cannot pump blood, collapse and sudden death can follow unless medical help is provided immediately. This is referred to as a 'cardiac arrest'. If treated in time, ventricular tachycardia and ventricular fibrillation can be interrupted with an electrical shock, restoring the heart to a normal rhythm. The most common treatment today for people who have experienced VT or VF is the implantation of an internal cardioverter defibrillator machine also known as an ICD.Medication (anti-arrhythmic drugs) may also be used to treat VT, alone or in conjunction with an ICD.
Bradycardia. Bradycardia is defined as a slow heart rhythm. It is generally divided into 2 categories, sick sinus syndrome or heart block. These slow heart rhythms are usually treated by the implantation of a permanent pacemaker, which takes over the work of the hearts normal pacemaker.
Sick Sinus Syndrome. With sick sinus syndrome, the sinus node (the natural pacemaker of the heart) is damaged. It may not send electrical signals to the chambers often enough, it may skip some signals or it may send too many signals at once. The result may be a heart that beats too slowly (sinus bradycardia), experiences long pauses (sinus pauses) that may cause symptoms of dizziness or fainting spells, or alternates between beating too quickly and then too slowly (tach-brady syndrome).
A-V block or heart block. In this family of arrhythmias, there is some problem in conducting the heartbeat signal from the sinus node to the ventricles. There are three degrees of A-V block: first-degree A-V block, where the signal gets through, but may take longer than normal to travel from the sinus node to the ventricles; second-degree A-V block, in which some heartbeat signals are lost between the atria and ventricles; and third-degree A-V block, in which no signals reach the ventricles, so the ventricles beat slowly on their own with no direction from above. Some common causes of A-V block include coronary artery disease, myocardial infarction (heart attack), or an overdose of the heart medication digitalis.
Sinus node dysfunction. This usually produces a bradycardia (slow heart rate), with a heat rate of 50 beats per minute or less. The most common cause is replacement of the sinus node by scar tissue. Why this happens is not known. Sinus node dysfunction also can be caused by coronary artery disease, hypothyroidism, severe liver disease, hypothermia, typhoid fever, or other conditions. It also can be the result of vasovagal hypertonia, an unusually active vagus nerve.