ABC of clinical electrocardiography: Acute myocardial infarction—Part I
BMJ 2002; 324 doi: https://doi.org/10.1136/bmj.324.7341.831 (Published 06 April 2002) Cite this as: BMJ 2002;324:831All rapid responses
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Congratulations to the editors and authors of this publication. It is really very clear and useful, including the figures that match exactly the written text.
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The article is of practical usefulness in that it ensures that right ventricular infarction and posterior wall infarction are not be missed if right space leads and leads V7,V8 and V9 are routinely included in the initial evaluation of suspected A.M.I.
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Dear Editor
Morris and Brady (1) describe the typical electrocardiographic changes of acute myocardial infarction. Many limitations of those features are also clarified, however others also merit attention. For example, there is a small minority of patients (4%) with an acute myocardial infarction in whom serial electrocardiograms remain normal, and these patients may be at high risk for morbidity and mortality (2).
Transient electrocardiographic changes are also common. Adams et al (3) compared the electrocardiograms recorded at home with those on admission to hospital from 137 patients with suspected acute myocardial infarction. Hospital tracings were performed within 4 hours in 135 (99%) patients while 127 (93%) of the patients had their hospital recordings within 6 hours from the onset of the symptoms. Ninety-three (68%) patients were confirmed to have definite or probable acute myocardial infarction. The electrocardiograms recorded within 6 hours from onset of symptoms, showed that regional ST elevation was highly specific (95%) in early acute myocardial infarction, with a sensitivity of 53%. However, major electrocardiographic changes between home and hospital tracings was noted in 27/93 (29%) of the patients including some with regression of major ST elevation or bundle branch block to non- specific abnormalities.
ST depression in a patient with suspected infarction imposes diagnostic problems. It could be due to unstable angina, non- Q wave infarction, or true posterior infarction. Hence the diagnosis of unstable angina remains retrospective. However, Lee et al (4) reported that in patients with suspected acute myocardial infarction, ST depression > 3 mm without reciprocal ST elevation except in lead aVR, was 90% specific for acute myocardial infarction with a 41% sensitivity, which is similar to that for ST elevation (3). It is unlikely that the ST depressions in the patients of the latter study were all due to posterior wall infarctions as ST depressions were widespread and found from four to over eight electrocardiographic leads (4). Unfortunately they had a poor prognosis. Furthermore, ST depression in the anteroseptal leads V1-V3 in association with ST segment elevation in the inferolateral leads II, III, aVF, V5 and V6 often reflect contiguous injury in the true posterior wall of the left ventricle (5).
References
1. Morris F, Brady WJ. Acute myocardial infarction- Part- I: ABC of Clinical Electrocardiography. Brit Med J 2002; 324: 831- 834.
2. Turi G, Rutherford JD, Roberts R, Muller JE, Jaffe AS, Rude R, Parker C, Raabe DS, Stone PH, Hartwell TD, Lewis SE, Parkey RW, Gold HK, Robertson TL, Sobel BE, Willerson JT, Braunwald E and Co-operating Investigators from the MILIS Study Group. Electrocardiographic, Enzymatic and scintigraphic criteria of acute myocardial infarction as determined from a study of 726 patients: A Multi- centre Investigation for the Limitation of Infarct Size (A MILIS Study). Am J Cardiol 1985; 55: 1463- 68.
3. Adams J, Trent R, Rawles J, and the GREAT Group. Earliest electrocardiographic evidence of myocardial infarction: implications for thrombolytic therapy. Brit Med J 1993; 307: 409- 13.
4. Lee HS, Cross SDI, Rawles DIM, Jenning KPH. Patients with suspected myocardial infarction who present with ST segment depression. Lancet 1993; 342: 1204- 7.
5. Vincent R. Advances in early diagnosis and management of acute myocardial infarction. J Accid Emerg Med 1996; 13: 74-79.
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Drs Morris and Brady are to be complimented for simplifying the presentation of the ecg changes recorded in established AMI. The Editors of the BMJ deserve the same compliment for publishing the ABC series of ecg and other topics.
As early as 1946, R.H. Bayley (Am. H. J. 31:677)puplished his findings on ischemia and injury following acute ligation of the anterior descending coronary artery in the exposed heart of the dog with continuous ecg electrode recording on the epicardial surface of the left ventricle. The earliest ecg change was a negative T wave change which was labeled ischemia and was followed sequentially by ST elevation (injury) and Q wave(infarct).
Now we know that if the electrode faces the lesion elevation of the ST is noted and the ST is downward in the remote or opposite the other electrode.
Futhermore, it maybe emphasized in established AMI(100%) the ecg is diagnostic in 50% of the cases, suggestive in 40% and normal in 10%(2) so that the primary care physician is quite unsure of the dx when only minor T wave or ST changes are noted on the initial ecg tracing, and certainly unreliable in the normal tracing (nonQ wave MI). Here of course one has to rely on ancillary diagnostic modalities such as abnormal cardiac enzymes, Echocardiography with abnormal wall motion of the left ventricle, baring the history and physical findings of the patient which are of utmost importance.
In conclusion, the physician is urged not to make a diagnosis of acute myocardial infarction on the basis of the ecg tracing without fully examining the patient and whatever else is deemed necessary.
References:
1-BMJ 2002:324, 831-834 The ABC of Clinical Electrocardiography Morris F and Brady, W.
2-Impact of the Electrocardiogram on the Delivery of Thrombolytic Therapy in Acute Myocardial Infarction. Sharkey et al. Am.J.Card.73:550,1994
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this article about ecg diagnosis of m.i. is very useful. early repolarization may mimick acute m.i.& in such cases putting patient on continous ecg monitoring & looking for increasing convexity of st segment may be of help, an increase in convexity of st segment suggests acute m.i.
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During a period of 10 years in a CCU, 15 patients with acute myocardial infarction ( AMI ), among a total of 2480, presented with a new -onset right bundle branch block ( RBBB ), complete or incomplete, without Q waves, as a single ECG finding. Right precordial and posterior leads, were not diagnostic. All these patients were treated as a non Q wave AMI, and did not receive thrombolysis.
Eight patients underwent coronariography, and 6 of them were found to have a proximal occlusion of obtuse marginal branch of their circumflex artery, with a near normal remaining coronary net. Two patients had proximal occlusions of their right coronary artery.
Why an AMI of the obtuse margin and adjacent posterior wall of left venticle is accompanied by an RBBB, is not completely clear. However, the therapeutic implications ( thrombolysis or not ), for this entity, remain a challenge.
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WPW syndrome
Early repolarisation syndrome
Acute pericarditis
Variant Angina
Widening of the QRS complex (as a result of hyperkalaemia or as a result of pre-treatment with anti-arrythmic agents such as propafenone or flecainide) which may be minterpreted as new LBBB.
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It was quite interesting to go through the simplyfied basic ECG interpretation.
I expect more in the future on conduction disturbances.
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Right Ventricular Infarction
Dear Sirs
The only thing we would like to stress is that the first recognition of Right Ventricular Infarction was made, electrocardiographically, in 1958, by Professor Quintiliano H. De Mesquita. His paper about the subject was published in 1960 at the official magazine of the Brazilian Society of Cardiology.
Please see the following webpages of Infarct Combat Project were you can find the memories and bibliography of Professor Mesquita about RVI as well a copy of letter by Doctor Myron Prinzmetal, from July 22, 1959, confirming this.
QHM memories about RVI: http://www.infarctcombat.org/memorias/evd.htm
Letter by Myron Prinzmetal: http://www.infarctcombat.org/letter08.html
QHM Memorial: http://www.infarctcombat.org/qhm/homepage.html Apart the first diagnosis of RVI by ECG, there are other important contributions to electrocardiography by Professor Quintiliano H. de Mesquita, as for example:
1948 – Produced a new classification of “Incomplete Bundle Branch Block and presented the type 1a” (Contribuição para o estudo dos bloqueios de ramo. Nova classificação, Arq. Bras Cardiol, 1948;1:75 e Rev Hospital N.S Aparecida, 1949. Republished by the Brazilian Cardiology Society in 2002 at http://www.cardiol.br/tunel/ago/new/015.pdf ) .
1999 - Presented in the I Virtual Congress of Cardiology the paper “Exceptional Patterns of the Wolff-Parkinson-White Syndrome in Rhythm and AV Nodal Tachycardia that Confirm the Prinzmetal's Theory of Accelerated Conduction” published at http://pcvc.sminter.com.ar/cvirtual/tlibres/tnn2346i/tnn2346i.htm (and republished in May 2000 at Ars Cvrandi a brazilian medical magazine)
Kind Regards
Carlos Monteiro
Secretary
Infarct Combat Project
Competing interests: None declared
Competing interests: No competing interests