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A 4-months old boy with a rather rare ECG

Below you find the ECG of a 4-months old boy who presented with congenital sinus node dysfunction with low heart rates. Aside from low heart rates the ECG finding you see below prompted us to perform genetic testing. Can you spot what we considered a pathology that warrants further testing?

When taking a closer look at the repolarisation you find the QT interval to measure ...ms. Corrected for heart rate - QTc is 290 ms (Bazett). This is quite short. In fact, it is pathologically short.

Mostly you would look for QT prolongation to rule out long QT syndrome. However, you should also be suspicious of short QT interval. I.e. a QTc <370ms.

Short QT syndrome (SQTS; https://litfl.com/short-qt-syndrome-ecg-library/ ) represents a rare disorder of repolarisation, based on ion-channel mutations. Diagnosis can be made, analogous to long QT syndrome, using the Schwartz score for SQTS (QTc, JTp, clinical and family history; Veltmann, C., Borggrefe, M. A 'Schwartz score' for short QT syndrome. Nat Rev Cardiol8, 251–252 (2011). https://doi.org/10.1038/nrcardio.2011.51).

Patients suffering form SQTS are at risk for ventricular arrhythmias and sudden cardiac death. Treatment consists mainly of risk reduction, implanting an ICD. Quinidine is considered as an adjunct medical therapy.

In our patient, genetic testing revealed KCNQ1 mutation, considered pathological for SQTS. QTc was 290ms (Bazett; QT predicted was 410ms), heart rate 60/min. JTpeak 150ms. Symmetrical T wave. Schwartz / Gollob Score for SQTS = 5 points (QTc <330ms = 3Pts, Genotype + = 2Pts). Suzuki Criteria 2021 (QTcB <315ms, JTp <181ms) postive.

Due to increasingly low heart rates we decided to implant a pacemaker. ICD implantation in this age group is associated with high risk of adverse events, aside from the problem of lack of space for such devices which are designed for adults. Sadly, no devices designed for children exist (yet).

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