Slow Heart Rhythms
Slow heart rhythms, bradycardias, occur because:
- The SA node fails to produce an electrical signal.
- The electrical signal does not conduct normally down the pathway.
- If the signal does not pass through the AV node (gatekeeper), this is called a heart block.
Fast Heart Rhythms
Fast heart rhythms, tachycardias, are related to fast and irregular electrical signals through the pathway. When the heart is very fast and irregular, it may quiver. This is called fibrillation.
Some tachycardia rhythms occur due to an extra pathway in the heart.
Supraventricular Tachycardia (SVT)
SVT is a fast heartbeat that occurs in the upper chambers (atria) of the heart. The most common SVT is AV nodal re-entrant tachycardia (AVNRT). This common arrhythmia can be treated with radiofrequency ablation or medication.
Another SVT is Wolf-Parkinson-White (WPW) syndrome. WPW has an extra or accessory pathway. The extra electrical signal speeds up the heart rate. Patients with WPW may be asymptomatic; however, others may experience occasional palpitations, transient loss of consciousness and in rare cases, sudden cardiac death. WPW is usually diagnosed by an EKG and may be managed with routine medications, depending on one's cardiac history, symptoms and other risk factors. Further evaluation may be undertaken including performing an electrophysiology study, and if indicated, a radiofrequency ablation.
Atrial fibrillation is the most common SVT in older adults.
Atrial fibrillation (AF) is an arrhythmia that starts in multiple sites in the upper chambers of the heart. It is an irregular rhythm that causes the atria to quiver instead of contracting regularly. The atrial rate can be very rapid, but the atrioventricular node (a structure in the middle of the heart) helps to limit the number of electrical impulses that can pass to the heart's lower chambers. Atrial fibrillation makes your pulse irregular and unusually fast.
Atrial flutter is an SVT more common in people who have lung or heart disease. In atrial flutter, the upper chambers of the heart (atria) are electrically over-stimulated as many as 300 times per minute, compared to the normal rate of 60 to 100 times. Atrial flutter usually results in tachycardia (rapid heart rate); occasionally, the heart rate will be too slow. Treatment for atrial fibrillation or atrial flutter may be medication, electrical cardioversion or radiofrequency ablation.
Ventricular Tachycardia (VT)
Ventricular arrhythmias originate in the lower chambers (ventricles) of the heart. This can be due to muscle damage to the heart. VT can develop into a more serious arrhythmia, VF (ventricular fibrillation). If the heart muscle can't pump effectively, cardiac arrest may occur. In this life-threatening condition, the ventricles quiver, pumping a small amount of blood out of the heart.
Severe ventricular tachycardia and ventricular fibrillation can be converted into normal rhythm with a controlled electrical shock from a defibrillator.
Symptoms of an irregular heart rhythm you may feel:
- Fainting or blackout problems
- Shortness of breath
- Palpitations (fast heart rate, fluttering, "skipping a beat")
- Lightheadedness or dizziness
- Chest discomfort or pain