MEDICINE IS NOT AN EXACT SCIENCE
RAMON F. ABARQUEZ, JR., MD, EFACC, FASCC, FPCP, FPCC, CSPSH Academician Project, National Academy of Science and Technology Professor Emeritus, College of Medicine, UP Manila
Dr. Ramon F. Abarquez, Jr. has been one of the most prolific consultant writers of H&L and its sister publication, Vital Signs. Highly esteemed in the medical community, he is the founding president of Philippine Society of Hypertension and a past president of the Philippine College of Physicians
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Using SPECT, MRI wall thickening, and ECG-ST changes to identify culprit artery location, it was correctly designated in 91 percent, 82 percent, and 91 percent of cases, respectively. All three modalities have been used for indirect visual designation of the culprit artery in patients with first-time acute coronary occlusion. [Ubachs, J Electrocardiol. 2009 Mar-Apr;42(2):198-203) ECG is as predictive as SPECT imaging.
The most powerful ECG criteria: ST elevation in lead III over lead II and ST depression in lead I over lead aVL and ST changes in lead I suggested the location of the culprit artery in 192 of 194 patients (nearly 99 percent) with a sensitivity and specificity of 100 percent and 89 percent, respectively, for predicting the right coronary artery and for predicting the left circumflex artery, 89 percent and 100 percent, respectively. [Huang, Am J Emerg Med. 2016 Sep;34(9):1772-8)]
The ST elevation (STE) sensitivity for left anterior descending (V1-3), right coronary artery (II<III aVF), left circumflex (aVL) and diagonal branch/double anterior descending/ramus intermediate was 98.8 percent, 93.7 percent, 31.7% percent and 44.4 percent, respectively; the specificity was 94.3 percent, 87.6 percent, 99.0 percent and 99.1 percent, respectively. The proximal/distal location was correctly identified in 62.4 percent of cases with relevant implications for clinical management and selection of appropriate therapeutic strategies [Slavich, G Ital Cardiol (Rome). 2012 Oct;13(10):676-84]
Five studies investigated if STE in aVR is valuable for the diagnosis of left main stem stenosis (LMS) in non-ST-segment AMI (NSTEMI). STE in aVR has a high negative predictive value (NPV) for LMS. STE in aVR is valuable for distinguishing proximal from distal lesions in the left anterior descending artery (LAD) in anterior ST-segment elevation AMI (STEMI) with a sensitivity of 47 percent, a specificity of 96 percent, a positive predicative value (PPV) of 91 percent and a NPV of 69 percent.
ST-segment depression (STD) in lead aVR, distinguishes lesions in the circumflex artery from those in the right coronary artery in inferior STEMI, with a sensitivity of 37 percent, a specificity of 86 percent, a PPV of 42 percent, and an NPV of 83 percent. The absence of aVR STE appears to exclude LMS as the underlying cause in NSTEMI; in the context of anterior STEMI. STE aVR indicates a culprit lesion in the proximal segment of LAD. [Kuhl, Ann Noninvasive Electrocardiol. 2009 Jul;14(3):219-25]
Prevalence of RCA involvement as the infarct-related artery (IRA) was different in three study groups (94.1 percent in ST elevation group, 83.1 percent in isoelectric group and 70.3 percent in ST depression group, P = 0.049). Presence of ST elevation had a sensitivity and specificity of 13.68 percent and 96.97 percent, for detecting RCA lesions, respectively. Presence of STE (II, III, aVF) is highly suggestive of RCA lesions versus LCX lesions, whereas absence of ST elevation cannot rule out RCA lesions. Presence of ST depression has a moderate sensitivity (66 percent) and specificity (55 percent) for LCX lesions. [Pourafkari Ann Noninvasive Electrocardiol. 2016 Jul;21(4):389-96]
QRS in ACS outcome
In patients with STEMI the amount of myocardial area at risk (MaR) indicates the maximal potential loss of myocardium if the coronary artery remains occluded. During the time course of infarct evolution ischemic MaR is replaced by necrosis, which results in a decrease in ST segment elevation and QRS complex distortion. [Carlsen, J Electrocardiol. 2014 Jul-Aug;47(4):540-5]
Several key findings: (1) Both Q wave area and Selvester QRS-score increased with LV infarct size (p<0.001), with greatest difference at 10 percent threshold of LV infarct size. (2) Q wave area increase more (> 2.5 fold) at a 10 percent infarct threshold than did Selvester QRS-score (< 2-fold). (3) When diagnostic thresholds to exclude infarcts = 10 percent myocardium, both ECG methods yielded similar negative predictive value (Selvester QRS-score: 92-94 percent | Q wave area: 89-91 percent), although specificity was lower for Selvester QRS-score (17-25 percent) than for Q wave area (44-45 percent). Q wave area provides better stratification of LV infarct size. [Weinsaft, Coron Artery Dis. 2014 Mar;25(2):138-44]