![]() In the following short review, focused on QT prolongation, it will be attempted to summarise the underlying (patho)physiology of this entity and the extent to which it constitutes a problem with regard to both prevention and management of malignant, potentially lethal arrhythmic events in various substrates. More specifically, disorders may involve abnormal initial repolarization rate (phase 1 of the action potential – Brugada syndrome) or abnormally shortened/prolonged late repolarization (phase 3 – short and long QT syndromes, respectively). Given that different segments and layers of the myocardium have divergent baseline properties and consequently respond differently to stimuli, it is not surprising that several arrhythmic disorders of the myocardium, both congenital and acquired, are related to derangements in precisely this repolarization process. Origin of the U wave is thought to be related to after depolarizations which interrupt or follow repolarization.Ventricular repolarization, as opposed to depolarization, is not a triggered phenomenon following an orderly sequence, hence the dissimilarity between their inscribed electrocardiographic waves rather, ventricular myocytes repolarize at a time and rate determined by their intrinsic electrophysiological properties (relative concentration of ion channel types and isoforms), as well as by the preceding electrical and mechanical events that affect the former.U waves are more prominent at slow heart rates and usually best seen in the right precordial leads.U wave direction is the same as T wave direction in that lead.U wave amplitude is usually The normal U Wave: (the most neglected of the ECG waveforms) ST segment depression is often characterized as "upsloping", "horizontal", or "downsloping". ST segment depression is always an abnormal finding, although often nonspecific (see ECG below) It's a term with little physiologic meaning (see example of "early repolarization" in leads V4-6):Ĭonvex or straight upward ST segment elevation (e.g., leads II, III, aVF) is abnormal and suggests transmural injury or infarction: ST segment elevation with concave upward appearance may also be seen in other leads this is often called early repolarization, although Normal ST segment elevation: this occurs in leads with large S waves (e.g., V1-3), and the normal configuration is concave upward. In the normal ECG the T wave isĪlways upright in leads I, II, V3-6, and always inverted in lead aVR. The normal T wave is usually in the same direction as the QRS except in the right precordial leads. In some normal individuals, particularly women, the T wave is symmetrical and a distinct, horizontal ST segment is present. This gives rise to an asymmetrical T wave. T and followed by a rapid descent to the isoelectric baseline or the onset of the U wave. Often the ST-T wave is a smooth, continuous waveform beginning with the J-point (end of QRS), slowly rising to the peak of the In a sense, the term "ST segment" is a misnomer, because a discrete ST segment distinct from the T wave is usually absent. Small "septal" q-waves may be seen in leads V5 and V6.P duration R in the right precordial leads to R>S in the left precordial leads is V3 or V4.It is important to remember that the P wave represents the sequential activation of the right and left atria,Īnd it is common to see notched or biphasic P waves of right and left atrial activation. (Normal ECG is shown below - Compare its waveforms to the descriptions below) Normal Sino-atrial (SA), Atrio-ventricular (AV), and Intraventricular (IV) conductionīoth the PR interval and QRS duration should be within the limits specified above. The P waves in leads I and II must be upright (positive) if the rhythm is coming from the sinus node. ![]() ![]() Frontal Plane QRS Axis: +90° to -30° (in the adult).Poor Man's Guide to upper limits of QT: For HR = 70 bpm, QT ≤ 0.40 sec for every 10 bpm increase above 70 subtract 0.02 sec, and for every 10 bpm decrease below 70 add 0.02 sec.Bazett's Formula: QT c = (QT)/SqRoot RR (in seconds).With the particular patient's clinical status will the ECG become a valuable clinical tool. Only by following a structured "Method of ECG Interpretation" (Lesson II) and correlating the various ECG findings It takes considerable ECG reading experience to discover all the normal The following "normal"ĮCG characteristics, therefore, are not absolute. It is important to remember that there is a wide range of normal variability in the 12 lead ECG. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |