Thus, normal conduction of an electrical impulse through the atrioventricular, or AV, node, then to the ventricles via the His-Purkinje system, is fast and results in a normal QRS duration. When electrical activity does not conduct through the His-Purkinje system, but instead travels from myocyte to myocyte, a longer time is necessary, and the QRS duration is widened.
A widened QRS duration occurs in the setting of a right bundle branch block, left bundle branch block, non-specific intraventricular conduction delay and during ventricular arrhythmias such as ventricular tachycardia — all of which are discussed in detail inside their respective sections in ECG Reviews and Criteria.
Back to Healio. ECG Basics Save. DOI: Prevention of torsade de pointes in hospital settings: a scientific statement from the American Heart Association and the American College of Cardiology Foundation. J Am Coll Cardiol. Bazett and Fridericia QT correction formulas interfere with measurement of drug-induced changes in QT interval.
Heart Rhythm. Comparison of the four formulas of adjusting QT interval for the heart rate in the middle-aged healthy Turkish men. Ann Noninvasive Electrocardiol. Inaccurate electrocardiographic interpretation of long QT: the majority of physicians cannot recognize a long QT when they see one.
The measurement of the Q-T interval of the electrocardiogram. Facilitating assessment of QT interval duration during ventricular pacing. An analysis of the time-relations of electrocardiograms. Heart ; Category : ECG Course. Navigation menu Personal tools Log in. Namespaces Page Discussion. Views Read View source View history. Step 4: Learn how to determine the heart's conduction axis».
Use lead II. Use lead V5 alternatively if lead II cannot be read. ST segment elevation with concave upward appearance may also be seen in other leads; this is often called early repolarization , although it's a term with little physiologic meaning see example of "early repolarization" in leads V :. Convex or straight upward ST segment elevation e. ST segment depression is always an abnormal finding, although often nonspecific see ECG below. Waveform Description Normal ECG is shown below - Compare its waveforms to the descriptions below P Wave It is important to remember that the P wave represents the sequential activation of the right and left atria, and it is common to see notched or biphasic P waves of right and left atrial activation.
Two determinates of QRS voltages are: Size of the ventricular chambers i. Septal q waves should not be confused with the pathologic Q waves of myocardial infarction. The R-V6 is usually smaller than R-V5. In reverse, the s-waves begin in V6 or V5 and progress in size to V2. S-V1 is usually smaller than S-V2.
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