Introduction
One speaks of atrial flutter when the atria of the heart contract for a limited time or permanently much faster than the ventricles. Normally, the atria and the ventricles form a coordinated unit. Blood flows from the body’s circulation and from the lungs into the atria of the heart.
After electrical excitation, the atrial cells contract through the sinus node and pump the blood into the ventricles. The electrical excitation is conducted from the sinus node through the atria to the AV node. The AV node transmits the excitation to the heart cells of the ventricles via a system of pathways.
The electrical activation causes the blood-filled chambers to contract and pump it into the body’s circulation. At the same time, the atria fill with new blood and the electrical excitation wave has activated the last heart cell. The heart is now ready for a new cycle, which begins again with a new excitation and the filled atria.
The electrical activation of the heart cells is controlled by both the sinus node and the AV node, whereby the AV node transmits the rhythm of the sinus node in first priority. Should the sinus node fail, the AV node can set its own rhythm. This system is intended to create and guarantee a regular rhythm that can be adapted to external requirements.
The normal rhythm of this process generates a pulse rate of 60 – 80 beats/minute at rest. In the case of atrial flutter, the atrial cells are activated by their own and are no longer caused by the sinus node. This process can be triggered by a so-called re-entry mechanism.
In this case, the excitation does not occur centrally at the sinus node, but in a different area of the atria. This activation is also transmitted to all cells of the atria. This can lead to an acceleration of the rhythm so that the pulse rate increases to 200 – 350 beats/minute.
In this case one speaks of a “fluttering” of the atria. Due to the nature of the AV node, in most cases this fast frequency is not transmitted 1:1 to the ventricles, but only every 2nd or 3rd beat. This also increases the heart’s beat frequency, but not as massively as in the atria.
Atrial flutter is often triggered by organic diseases of the heart. Both atrial flutter and atrial fibrillation cause a disturbed propagation of excitation within the atria. Circular excitation within the atria causes an increased contraction of the atria and usually also of the ventricles.
In contrast to atrial fibrillation, the transmission of excitation from the atria to the ventricles is usually regular. For example, every second or third excitation is transmitted to the ventricles. In atrial fibrillation, this excitation transfer is irregular.
In addition, atrial flutter results in a clearly defined spread of the excitation, whereby the atria are excited in an orderly fashion. In addition, atrial flutter is usually associated with a typical ECG finding. A characteristic “sawtooth pattern” is shown instead of a straight isoelectric line. While catheter ablation has a higher probability of success in typical atrial flutter, atrial fibrillation often shows a better response to medication. A transition between atrial flutter and atrial fibrillation is possible.
All articles in this series:
