Challenge 20

1. In which clinical scenarios can a short QT be found, that does not necessarily suggest occurrence of this disorder?
2. What are the ECG characteristics suggestive of short QT?
3. What are the clinical implications of this disorder?
4. What are the 6 suggestive indicators of short QT syndrome?
5. What is the prevalence of this disorder and how can a definitive diagnosis be made?

1) Short QTs can be seen in clinical scenarios where there is high serum calcium or potassium levels, hypothermia or acidosis and both acetylcholine and catecholamine can shorten the QT interval. Importantly a shortened QT is a normal physiologic response to a quickened heart rate.

2) There are no strict criteria for the duration of the QT interval in patients with short QT syndrome. The QT interval should be measured without correction as the shortening of the QT is independant of the heart rate. During tachycardia the QT will often be normal but does not show any, or very minimal lengthening, with slower rates. It is mandatory that the QT is therefore measured at a rate as close to 60bpm as possible without correction. Another characteristic found in the ECGs of patients with SQTS is a short ST segment followed by narrow and tall T waves, particularly in the precordial leads. In all published cases of short QT syndro
me the QT was less than 345ms, and it is a fair to state that at a rate of 60bpm a QT interval less than 350ms is not a normal finding.

3) EP testing for short QT syndrome has not been well established but short effective atrial and ventricular refractory periods and induction of atrial or ventricular fibrillation would favour a diagnosis of short QT syndrome and a possible increased probability of sudden cardiac death.

4) Lone AF – especially at a young age. Family member with short QT interval Family member with sudden cardiac death QT interval at 60bpm <350ms ECG with tall and peaked T waves Lack of QT interval prolongation with slowing of heart rate

5) Little importance had previously been given to the short QT ECG characteristic, in fact when the 1st article on SCTS was submitted to a large journal for publication, it was rejected as one of the reviewers had suspected that the short QT was due to a sweep speed error! As the short QT was previously not considered to be of clinical significance one questions how many ECGs of this sort have been previously considered as ‘within normal limits’ and dismissed without further consideration. So far, Short QT Syndrome (SQTS) has been diagnosed in 7 families worldwide (2 in USA, 2 in Germany, 1 in Spain, 1 in the Netherlands, and 1 in Italy.) One of the families in the US has just recently been diagnosed with the disease and all the details about this family are not known yet. In the six other families where more information exists, 15 people have an ECG with a short QT-interval and two of these have died suddenly. In addition seven people from these families, who had no ECG prior to death, have died suddenly and therefore presumed SQTS patients. Out of this total of 22 patients classified as having SQTS, 10 are women and their ages ranging from 3 months to 84 years. The ages at the time of sudden cardiac death varied from 3 months to 62 years. As of June 2005, three different genetic mutations had been identified in families with SQTS, so where the patients’ clinical history and ECG are suggestive of this disorder it could be possible that genetic testing could provide the definitive diagnosis although other individuals with SQTS have none of the known genetic abnormalities.

Information on the genetic mutations of this disorder can be found on the short QT syndrome website cited in the references.