Ecg Interval

Definition Time from the start of the Q wave to the end of the T wave Represents time taken for ventricular depolarisation and repolarisation, effectively the period of ventricular systole from ventricular isovolumetric contraction to isovolumetric relaxation The QT interval is inversely proportional to heart rate: The QT interval shortens at faster heart rates The QT interval lengthens at slower heart rates An abnormally prolonged QT is associated with an increased risk of ventricular arrhythmias, especially Torsades de Pointes Congenital short QT syndrome has been found to be associated with an increased risk of paroxysmal atrial and ventricular fibrillation and sudden cardiac death How to measure the QT interval The QT interval is usually measured in either lead II or V5-6, however the lead with the longest measurement should be used Several successive beats should be measured, with the maximum interval taken Large U waves (> 1mm) that are fused to the T wave should be included in the measurement Smaller U waves and those that are separate from the T wave should be excluded The maximum slope intercept method is used to define the end of the T wave (see below) ...

S-T Segment The ST segment is the flat, isoelectric section of the ECG between the end of the S wave (the J point) and the beginning of the T wave. The ST Segment represents the interval between ventricular depolarization and repolarization. The most important cause of ST segment abnormality (elevation or depression) is myocardial ischaemia or infarction. Causes of ST Segment Elevation ...

QRS Complex Morphology Main features to consider: Width of the complexes: Narrow versus broad. Voltage (height) of the complexes. Spot diagnoses: Specific morphology patterns that are important to recognise. QRS Complex Naming Convention Courtesy of ECGwaves.com QRS Width Normal QRS width is 70-100 ms (a duration of 110 ms is sometimes observed in healthy subjects). The QRS width is useful in determining the origin of each QRS complex (e.g. sinus, atrial, junctional or ventricular). ...

The J point The J point is the the junction between the termination of the QRS complex and the beginning of the ST segment. The J (junction) point in the ECG is the point where the QRS complex joins the ST segment. It represents the approximate end of depolarization and the beginning of repolarization as determined by the surface ECG. There is an overlap of around 10ms. The J point marks the end of the QRS complex, and is often situated above the baseline, particularly in healthy young males. The J point may deviate from the baseline in early repolarization, epicardial or endocardial ischaemia or injury, pericarditis, RBBB, LBBB, RVH, LVH or digitalis effect. ...

↪ ECG Basics Homepage The PR segment is the flat, usually isoelectric segment between the end of the P wave and the start of the QRS complex. PR segment abnormalities These occur in two main conditions: Pericarditis Atrial ischaemia Pericarditis The characteristic changes of acute pericarditis are: PR segment depression. Widespread concave (‘saddle-shaped’) ST elevation. Reciprocal ST depression and PR elevation in aVR and V1 Absence of reciprocal ST depression elsewhere. NB. PR segment changes are relative to the baseline formed by the T-P segment. ...