7/23/2023 0 Comments Pathological q waves![]() ![]() A rightward mediastinal shift in left pneumothorax may contribute to the apparent loss of left precordial R waves.In dextrocardia, normal R wave progression may be restored by recording right-sided precordial leads, assuming that there are no underlying structural abnormalities.Slow R wave progression in the precordial leads, sometimes with actual QS waves, may be due solely to improper placement of chest electrodes above their usual position or on, rather than under, the left breast in women. Misplacement of chest lead electrodes is an important cause of anterior pseudo-infarction patterns.Prominent Q waves may be associated with a variety of other positional factors that alter the orientation of the heart in relation to the lead axis: A QS complex in which the QRS is entirely negative can also occur in lead V1 as a normal variant and rarely in leads V1 and V2. Depending upon the electrical axis, more prominent Q waves (as part of QS or QR-type complexes) can also appear in the limb leads: in aVL with a vertical axis and in leads III and aVF with a horizontal axis. As a result, small (<0.04 sec in duration) "septal" Q waves typically occur in the lateral precordial leads (which have a left-right spatial orientation) and in one or more of the limb leads (except aVR). These early septal depolarization forces are oriented anteriorly and to the right. PHYSIOLOGIC AND POSITIONAL FACTORS - Physiologic activation of the ventricles begins at the left side of the interventricular septum. (See "Electrocardiogram in the diagnosis of myocardial ischemia and infarction".) Ī broader discussion of the electrocardiogram in MI is provided elsewhere. Furthermore, even pathologic Q waves due to infarction may regress or disappear entirely following the event. Accordingly, Q waves should always be interpreted in the clinical context. To the contrary, Q waves can be related to one or more of the following four factors ( table 1) :Ĭlinicians should be aware of three principles with respect to Q waves: not all Q waves are pathologic, not all pathologic Q waves are due to myocardial infarction caused by fixed coronary artery occlusion, and there is no consensus on the precise criteria for the diagnosis of pathologic Q waves with respect to their width, extent, and location. The presence of a Q wave does not indicate any specific electrophysiological mechanism. (See "Basic principles of electrocardiographic interpretation".) Failure to appreciate the other causes of Q waves can lead to important diagnostic errors. Although prominent Q waves are a characteristic finding in myocardial infarction, they can also be seen in a number of noninfarct settings. Technically, a Q wave indicates that the net direction of early ventricular depolarization (QRS) electrical forces projects toward the negative pole of the lead axis in question. INTRODUCTION - By definition, a Q wave on the electrocardiogram (ECG) is an initially negative deflection of the QRS complex. ![]()
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