Puzzle 2008 01 062 Answer

Author(s)	A.A.M. Wilde, J. Hrudova, J.G.M. Tans
NHJ edition:	2009:01,062
These Rhythm Puzzles have been published in the Netherlands Heart Journal and are reproduced here under the prevailing creative commons license with permission from the publisher, Bohn Stafleu Van Loghum.
The ECG can be enlarged twice by clicking on the image and it's first enlargement

Figure 1

Figure 2

A 44-year-old male presented with palpitations. His medical history was otherwise uneventful and the family history revealed pacemaker implants in two of his father’s brothers in their fifties and in one of his brothers (mid-forties). His father was 74 years of age and without cardiac complaints. Physical examination revealed no abnormalities. The ECG presented in figure 1 was obtained. After an adequate period of anticoagulation therapy electrical cardioversion (ECV) was planned. Figure 2 is the ECG shortly after ECV. The patient was not on any therapy other than anticoagulants.

What would your diagnosis be and would you dare to speculate on the cause?

Answer

Figure 1 clearly shows an atrial flutter. However, it is not an ordinary atrial flutter. First of all, the ventricular frequency is 58 beats/min, indicating 4:1 atrial-ventricular block, which is unusual for a relatively young man. Secondly, the frequency of the atrial flutter itself (PP interval) is 260 msec. A regular flutter almost always has a PP interval of 200 msec (300/min) and AV conduction is typically 2:1 leading to a ventricular rate of 150 beats/min. In this case, atrial flutter cycle length is markedly lower and as indicated AV conduction is hampered, ending up in a ventricular rate of 58 beats/min. The ECG after electrical cardioversion is even more abnormal. The rhythm has been converted to sinus rhythm (60 beats/min), the electrical axis is horizontal and the conduction intervals are abnormal; PQ interval is 240 msec, QRS width is 120 msec. QT interval is normal. The two pauses that are present are both the result of SA block. The length of the pause (2000 msec) is twice the PP interval (1000 msec). Hence, conduction is hampered at all cardiac levels: from sinoatrial node to atrium, through the AV junction and in the ventricular muscle itself. Based on the slower than normal flutter rate, conduction within atrial tissue should be considered abnormal as well. The most likely explanation for a generalised conduction disorder at a relatively young age is aberrant sodium channel function. The family history with pacemaker implants at relatively young age fits with that idea. Indeed, molecular genetic screening revealed a mutation in the cardiac sodium channel gene SCN5a (mutation: p.4118 deletion T leading to a premature stop codon at position 1373, i.e. Leu1373X). It is likely that the atrial flutter is the result of abnormal conduction in the atrium. Pacemaker treatment is probably the best treatment at this moment and the patient and other affected family members should avoid using sodium channel blockers, including antiarrhythmic drugs.