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Show Diagnosing The Heart Disease Long QT Syndrome with Sinus Arrhythmia Department of Internal Medicine at LDS Hospital Long QT Syndrome (LQTS) is a genetic disorder of the heart where the time the heart takes to chemically repolarize is abnormally long. There are two symptoms of LQTS. First, syncope or passing out. Second, is sudden death. To diagnose LQTS a simple calculation is made from an Electrocardiogram (ECG). It is known as the Bazette formula and is QTc=QT/CL^(.5). A QTc value above .47ms for boys and .48ms for girls is diagnostic for LQTS. Many children show sinus arrhythmia on their ECG. Sinus arrhythmia is a marked difference of 25% or more between shortest cycle length and longest cycle length. In other words it is an irregular heartbeat, and it is caused by respiration patterns. The problem with sinus arrhythmia is that it makes it very difficult to calculate the QTc. This is because while the cycle length is changing from beat to beat, the QT interval changes over time. So the issue is which cycle length to use, the longest, shortest or neither. The common method in the world of cardiology is to use the shortest cycle length and the QT interval that follows. The problem with this is that you will misdiagnose many "normal" children as having LQTS. Our study evaluated five different ways to calculate the QTc with those that show sinus arrhythmia so as to correctly diagnose the Long QT Syndrome. Our results show that an averaging of all cycle lengths and all QT intervals on a ten second ECG, and then using the Bazette formula with those averaged values, will produce the most accurate results. This will enable us to correctly diagnose the largest percentage of those who have sinus arrhythmia. Jason Richards Dr. G. Michael Vincent |
