Abstract
Background: Electrocardiographic (ECG) diagnosis of acute myocardial ischemia is hampered in the presence of left bundle branch block (LBBB).Objectives: We analyzed the influence of location and duration of myocardial ischemia on the ECG changes in pigs with LBBB.Methods: LBBB was acutely induced in 14 closed chest anesthetized pigs by local electrical ablation. Thereafter, episodes of 5 min catheter balloon occlusion followed by 10 min reperfusion of the left anterior descending (LAD), left circumflex (LCX), and right (RCA) coronary arteries were done sequentially in 5 pigs. Additionally, a 3-h occlusion of these arteries was performed separately in the other 9 pigs. A 15-lead ECG including leads V7 to V9 was continuously recorded.Results: Ablation induced LBBB showed QRS widening, loss of r wave in V1, and predominant R waves in V2 to V9. After 5 min of ischemia the occluded artery could be identified in all cases: the LAD by R waves and ST elevation in V1–V3; the LCX by both ST segment elevation in II, III, aVF, V7 to V9 and ST segment depression in V1 to V4; and the RCA by ST depression and new S-waves in all precordial leads. Three hours after coronary occlusion, ST segment changes declined progressively and only the LAD occlusion could be reliably recognized.Conclusion: LBBB did not mask the ECG recognition of the occluded coronary artery during the first 60 min of ischemia, but 3 h later only the LAD occlusion could be reliably identified. ST elevation in leads V7 to V9 is specific of LCX occlusion and it could be useful in the diagnosis of acute myocardial ischemia in the presence of LBBB.
Highlights
The diagnosis of acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) is a clinical challenge because this condition may entail a high mortality (Col and Weinberg, 1972; Hindman et al, 1978) and, a reliable electrocardiographic (ECG) diagnosis is not often possible (Shlipak et al, 1999; Jain et al, 2011)
We introduced a 6F guiding catheter (Cordis) into a femoral artery and it was advanced to the ostium of the left or the right coronary arteries under fluoroscopic guidance a 3 mm diameter over-the-wire catheter balloon (Cordis) was placed at the mid segment of one of the three main coronary arteries
The 22 pigs with LBBB were submitted to the two study protocols and 8 of them (4 in each protocol) died because of ventricular arrhythmias or AV block induced during the coronary occlusion sequences
Summary
The diagnosis of acute myocardial infarction (AMI) in patients with left bundle branch block (LBBB) is a clinical challenge because this condition may entail a high mortality (Col and Weinberg, 1972; Hindman et al, 1978) and, a reliable electrocardiographic (ECG) diagnosis is not often possible (Shlipak et al, 1999; Jain et al, 2011). The ECG algorithms commonly used to recognize an AMI in patients with LBBB are mainly based on the relationship between ST segment/QRS polarity (Sgarbossa et al, 1996) and on the proportionality between the ST segment/QRS amplitude (Smith et al, 2012). These algorithms afforded a good diagnostic specificity but a reduced sensitivity (Tabas et al, 2008). Electrocardiographic (ECG) diagnosis of acute myocardial ischemia is hampered in the presence of left bundle branch block (LBBB)
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