What is the difference between supraventricular arrhythmias (SVT) like atrial flutter and atrial fibrillation?
It is normal for your heart rate to change during the day, depending on your activity level. For example, you can expect your heart rate to increase when you're exercising, but not when you are sitting still.
Any kind of abnormal rhythm or heart rate is called an arrhythmia. Fast, abnormal heart rhythms, with rates over 100 bpm, are called tachyarrhythmias. Supraventricular tachycardia (SVT) is a general term for any fast heart rhythm coming from above the ventricles.
Anyone can develop an arrhythmia, even a young person without a previous heart condition. However, arrhythmias are most common in people over 65 who have heart damage caused by a heart attack, cardiac surgery, or other conditions. Common SVTs include:
- Atrial fibrillation
- Atrial flutter
- Atrioventricular nodal re-entrant tachycardia (AVNRT)
- Wolff-Parkinson-White syndrome (WPW)
(AF or AFib) is the most common SVT, affecting more than 328,000 Australians1. It is one of the causes of stroke, especially among elderly people2. During AF, the heartbeat produced by the atria is irregular and rapid—typically more than 300 bpm—where muscle fibres in the heart twitch or contract. With such a fast heart rate, the heart does not pump efficiently. This may cause blood to pool and can lead to the formation of clumps of blood called blood clots. A stroke can occur if a blood clot travels from the heart and blocks a smaller artery in the brain (a cerebral artery). About 15% of strokes happen in people with atrial fibrillation.
1. Ball J et al (2015), “Estimating the current and future prevalence of atrial fibrillation in the Australian adult population”, Med J Aust 2015; 202 (1): 32-35
2. Wann SL, Curtis AB, January CT, et al. 2011 ACCF/AHA/HRS Focused Update on the Management of Patients With Atrial Fibrillation (Updating the 2006 Guideline). Circulation. 2011;123:104-123
Atrial flutter is similar to atrial fibrillation, with heart rates up to 4 times faster than normal in the atria. It differs from atrial fibrillation (AF) in that the heartbeat is regular, not irregular. With atrial flutter, the electrical signal becomes “trapped” in the right atrium. It repeatedly travels in a circular pattern inside the right atrium, only occasionally “escaping” through the AV node to the ventricles. This causes your atria to beat faster than the ventricles of your heart, at rates between 150 and 450 beats each minute. Most who experience atrial flutter are 60 years and older and have some heart disorder, such as heart valve problems or a thickening of the heart muscle. Atrial flutter also carries the risk of developing blood clots, though not as great as with AF.
AV Nodal Re-entrant Tachycardia (AVNRT)
AVNRT is the second most common SVT. In a normal heart, there is a single electrical pathway, or “gate,” called an atrioventricular node (AV node). The AV node controls the timing and direction of the electrical signal as it travels from the upper chambers (atria) to the lower chambers (ventricles) of the heart. With AVNRT, an extra electrical pathway forms which allows the electrical signal to travel backward through the “gate” (AV Node) at the same time, starting another heartbeat. During AVNRT the electrical signals continuously go around the 2 pathways in a circular pattern called re-entry. This can lead to a very fast heart rate of 160 to 220 beats per minute. AVNRT is most common in people in their 20's and 30's but can occur at any age. It is more common in women than in men.
Wolff-Parkinson-White (WPW) syndrome is a group of fast, irregular heart beats caused by extra muscle pathways between the atria and the ventricles. In WPW, the pathways cause the electrical signals to arrive at the ventricles too soon, and the signals are sent back to the atria in a loop or short circuit. The result is a very fast heart rate. People with this syndrome may feel dizzy, have chest palpitations, or have episodes of fainting. People with WPW may be more likely to develop atrial fibrillation or a more dangerous rhythm called ventricular tachycardia.
These pathways are present at birth. People of all ages, including infants, can experience the symptoms related to Wolff-Parkinson-White syndrome. Episodes of a fast heartbeat often first occur when people are in their teens or early 20s.