A Q wave is the first negative deflection of the QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also... that is not preceded by a R waveFollowing the depolarization of the interventricular septum, ventricular depolarization then progresses from the endocardium through to the epicardium across both ventricles producing an R wave and an S wave. An R wave is the first positive deflection of the QRS.... A normal Q wave is narrow and small in amplitudeThe height or depth of waves and complexes of an ECG in millimetres; represents millivolts where 10 mm is 1 millivolt with a properly calibrated monitor. 1. Six Second ECG Guidebook (2012), T Barill, p. 190. Note that a wide and/or deep Q wave may signify a previous myocardial infarctionThe necrosis or death of myocardial tissue due to insufficient supply of oxygen to the infarcted region. The ability to identify cardiac ischemia, injury and infarction is vital in the management of the majority of cardiac emergencies. Most sudden cardiac... (MI).
A normal Q wave represents a depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... of the ventricular septum, which usually travels from left to right, towards the right ventricleThe right ventricle ejects blood through the main branches of the left and right pulmonary arteries to the lungs. The chambers of the heart are the main drivers within an intricate pathway, delivering blood to the lungs for gas exchange.... When present, a Q wave is the first downward deflection of the QRS complexA collection of waveforms (i.e. QRS complex and the ECG complex). 1. Six Second ECG Guidebook (2012), T Barill, p. 194. While ST segmentSegment (line) between the end of the QRS complex and the beginning of the T wave; the end of the QRS is marked by the J point. Between the QRS complex and the T wave, lies the ST segment. The... deviation is a sign of present events, a prominent Q wave points to an MI that has already occurred, recently to some time ago. A prominent Q wave is like a tattoo – once you have one, it’s pretty much yours for good.
A normal Q wave is usually no deeper than 2 mm and less than 1 small square in width (<0.04 seconds). An abnormal QQ waves are a normal phenomenon when they are narrow (less than 1 mm in width) and shallow (less than 25% the height of the R wave). Q waves that exceed any of these criteria are evidence of prior ST... wave tends to get the most attention. A Q wave that is wider than 1 small square or at least 1/4 the height of the R wave is a significant marker of a myocardial infarctionThe necrosis of tissue; acute myocardial infarction involves the acute death of myocardial cells. 1. Six Second ECG Guidebook (2012), T Barill, p. 198. In Figure 4.16, the Q wave is about 31% the height of the R wave (4/13 = 31%), making the Q wave prominent. The width of the Q wave is also significant with a width of 0.06 seconds. This Q wave is typical of an MI.
The Q waves of Figure 4.16 are abnormal in both depth and width, findings that point to a previous myocardial infarction.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 79-86