![]() ![]() In the present era of thrombolytic therapy and primary angioplasty for STEMI, the reversal of abnormal Q waves occurs more frequently. Most commonly the Q waves develop while the ST-segment is still elevated and persist for a variable number of days, weeks, months, or years and often indefinitely 2. Myocardial Infarction with Abnormal Q Waveĭuring an acute myocardial infarction, the development of new Q waves indicates myocardial necrosis, which starts 6 to 14 hours after the onset of symptoms 2 4. The definition of a wide Q wave does not apply to leads aVR and V1, which may normally lack the initial R wave.Ī Q wave is also considered abnormal, even if it is less than 30 ms in duration, when it is present in leads that normally display an initial R wave (leads V2 and V3) 2. Such a finding, however, has low specificity and should not be used as a reliable marker of myocardial infarction in practice 2. Some authors consider the amplitude of the Q wave a criterion of abnormality, when the amplitude of the Q wave exceeds 25% of the following R wave. On the electrocardiogram, an abnormal Q wave is usually defined in adults as one that has a duration of 0.04 s (a small square) or more 2. In the posterior leads V7–V9, Q wave duration of 0.03 s may be observed in 20% of normal male subjects 2. The amplitude usually is less than 0.2 mV, although it may reach 0.4 mV (4 small squares) 2.Īn amplitude of 0.4 mV or more may be encountered in teenagers. The duration of the Q waves is 0.03 s or less. Q waves in these leads are present more often in young subjects than in subjects older than 40 years. ![]() They are seen most frequently in lead V6, less frequently in leads V5 and V4, and rarely in V3. Small Q waves may be present in left precordial leads in more than 75 percent of normal subjects 2. In lead aVR the Q wave is usually is part of the QS morphology. The QS pattern in lead III is more prevalent in obese and the QS pattern is more prevalent in lead aVL in slender subjects 2. In leads III, aVF, and aVL the initial R wave may be absent, and a QS or QR deflection may represent a normal variant 2 3. ![]() This lead accounts for most of the erroneous diagnoses of myocardial infarction 2. In lead III, Q wave duration is occasionally as long as 0.04 s but rarely is it 0.05 s. The depth of the Q wave is less than 25% of the following R wave or less than 0.4 mV (4 small squares) in all limb leads, but lead III is the exception 2. With the exception of leads III and aVR, the Q waves in the limb leads normally do not exceed 0.03 s in duration (a little more than half a small square) 2. The duration of the Q wave is of considerable importance in the diagnosis of myocardial infarction. In limb leads, the Q wave is present in one or more of the inferior leads (leads II, III, aVF) in more than 50% of normal adults and in leads I and aVL in about 50% 2. Normal Q wave Normal Q Wave in Limb Leads The Q wave is the short initial downward stroke of the QRS complex formed during the beginning of ventricular depolarization 1. ![]()
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