I would take this further and say, in the presence of tachycardia, if you see two large squares between consecutive qrs complexes anywhere on the ECG, consider flutter! Two large squares between qrs complexes equates to a rate of 150 bpm. ![]() Whenever we see a tachycardia with a heart rate in the region of 150 beats per minute, we must consider the possibility of atrial flutter with 2 to 1 conduction. We can maximise our chances of picking up the diagnosis of atrial flutter with 1 in 2 conduction by following a few simple rules. In cases of flutter with 2 to 1 conduction, all direct evidence of atrial depolarization may be obscured in the frontal leads necessitating inference of the rate of atrial depolarization from other features on the ECG. More usually, prominent T waves in the inferior leads will fuse with and obscure the conducted flutter waves (marked above by an X). Half of the flutter waves have fused with the qrs complexes and are indiscernible (blue arrows in image below indicate 'hidden' flutter wave locations).įurthermore, note that the T waves are of low amplitude in the frontal leads on this particular ECG. If we take the 'close up' of lead II from the ECG above and use computer graphics to adjust the conduction ratio of 2 to 1, you will appreciate the problem. In this situation, evidence of rapid atrial depolarization may be obscured. The blue arrows indicate the position of flutter waves obscured by the qrs complexes.Īs illustrated by our index case, diagnostic problems arise when atrial flutter occurs with a conduction ratio of 2 to 1. With 1 in every 4 flutter waves conducted through the AV node, the ventricular rate is approximately 70 bpm. Conducted flutter waves are marked with an X. The atria are depolarizing 272 times per minute (1500/5.5). There are, in fact, 5.5 small squares (ss) between flutter waves. They are negative in the inferior leads (II, III and aVF consistent with a superiorly directed axis). Note that, at this conduction ratio, we can easily make out 'flutter waves' (red arrows) occurring approximately once every large square. The ECG above shows atrial flutter with 4 to 1 conduction. This is a life-preserving phenomenon limiting the rate of ventricular contraction to a fraction of the rate of atrial depolarization.ĭecrement origin: early 17th century (as a noun): from Latin decrementum ‘diminution’, from the stem of decrescere ‘to decrease’. In situations of very rapid atrial depolarization, the node will only conduct some fraction of the atrial depolarization events to the ventricles. However, the AV node is uniquely capable of mediating ‘decremental conduction’. If 300 atrial depolarization events per minute were conducted to the ventricles, the resulting heart rate would result in failure of the ventricles to fill with blood between beats with a potentially lethal fall in cardiac output. Usually in the region of 300 times per minute. ![]() The diagnosis of atrial flutter is confirmed by identification of atrial depolarization occurring at a rate between 200 and 400 times per minute. To make the diagnosis of atrial flutter we need to identify evidence on the ECG of atrial depolarization occurring at or near this rate (while remembering that there is a range of possible rates). In the majority of cases, the rate of atrial depolarization is in the region of 300 discharges per minute. The rate of atrial depolarization mediated by the re-entrant loop in this condition varies between cases from about 200 to 400 discharges per minute. ![]() Each cycle discharges a depolarization wave superiorly into the left atrium depolarizing the atria (blue arrow). In atrial flutter, a re-entrant loop of depolarization (blue circle) circulates (black arrows) in the wall of the right atrium. The views expressed are not endorsed by any clinical body. ![]() Some of the terms in this article: ss: small squares, bpm: beats per minute, HR: heart rate, index ECG: the ECG featured in the case 'a challenging ECG diagnosis'.ĭisclaimer: this article is an opinion piece. Understanding the mechanism generating tachycardia in atrial flutter and a knowledge of a few 'tricks of the trade' can help increase our chances of making the diagnosis of this arrhythmia.
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