https://ecgvn.com/en/tags/bazett-formula/ Recent content in Bazett Formula on ECG Library – LITFL Basics Hugo en-us Tue, 08 Oct 2024 00:00:00 +0000 https://ecgvn.com/en/posts/qt-interval/ Tue, 08 Oct 2024 00:00:00 +0000 https://ecgvn.com/en/posts/qt-interval/ <h4 id="definition">Definition</h4> <ul> <li>Time from the start of the Q wave to the end of the T wave</li> <li>Represents time taken for ventricular depolarisation and repolarisation, effectively the period of ventricular systole from ventricular isovolumetric contraction to isovolumetric relaxation</li> </ul> <p><a href="https://litfl.com/wp-content/uploads/2018/10/ECG-waves-segments-and-intervals-LITFL-ECG-library-3.jpg"><img alt="ECG basics: waves, segments and intervals LITFL ECG library" loading="lazy" src="https://litfl.com/wp-content/uploads/2018/10/ECG-waves-segments-and-intervals-LITFL-ECG-library-3.jpg"></a></p> <hr> <h5 id="the-qt-interval-is-inversely-proportional-to-heart-rate">The QT interval is inversely proportional to heart rate:</h5> <ul> <li>The QT interval <em>shortens</em> at faster heart rates</li> <li>The QT interval <em>lengthens</em> at slower heart rates</li> <li>An abnormally prolonged QT is associated with an increased risk of ventricular arrhythmias, especially <a href="https://litfl.com/polymorphic-vt-and-torsades-de-pointes-tdp/">Torsades de Pointes</a></li> <li><a href="https://litfl.com/short-qt-syndrome-ecg-library/">Congenital short QT syndrome</a> has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death</li> </ul> <hr> <h5 id="how-to-measure-the-qt-interval">How to measure the QT interval</h5> <ul> <li>The QT interval is usually measured in either lead II or V5-6, however the lead with the longest measurement should be used</li> <li>Several successive beats should be measured, with the maximum interval taken</li> <li>Large U waves (&gt; 1mm) that are fused to the T wave should be included in the measurement</li> <li>Smaller U waves and those that are separate from the T wave should be excluded</li> <li>The <em>maximum slope intercept method</em> is used to define the end of the T wave (see below)</li> </ul> <p><a href="https://litfl.com/wp-content/uploads/2018/08/QT-interval-with-u-waves-maximum-T-wave-slope-intersection.png"><img alt="QT interval with u waves maximum T wave slope intersection" loading="lazy" src="https://litfl.com/wp-content/uploads/2018/08/QT-interval-with-u-waves-maximum-T-wave-slope-intersection-1024x472.png"><img alt="QT interval with u waves maximum T wave slope intersection" loading="lazy" src="https://litfl.com/wp-content/uploads/2018/08/QT-interval-with-u-waves-maximum-T-wave-slope-intersection-1024x472.png"></a></p>