View source for Puzzle 2008 01 062 Answer

{{NHJ|
|mainauthor= '''A.A.M. Wilde, J. Hrudova, J.G.M. Tans'''
|edition= 2009:01,062
}}
[[Image:Puzzle_2008_01_062_fig1.jpg|Figure 1|thumb]]
[[Image:Puzzle_2008_01_062_fig2.jpg|Figure 2|thumb]]

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.