Depolarization changes early in the course of myocardial infarction: Significance of changes in the terminal portion of the QRS complex

Abstract

Studies of patients during variant angina have revealed that there are specific changes in the terminal part of the QRS complex that provide information regarding the location of the ischemia. Extending these studies to acute myocardial infarction, the electrocardiogram (ECG) obtained from 32 patients within 5 h of the onset of chest pain was analyzed to determine if similar inferences could be made. A preinfarction ECG was available from each patient for comparison and 30 patients underwent coronary arteriography within 3 weeks of the infarction. The 10 patients with anterior infarction had a decrease (p less than 0.05) in the S wave in leads V2 (0.80 +/- 0.50 mV) and V3 (0.65 +/- 0.43 mV). In 23 patients with inferior infarction an increase (p less than 0.05) in the R wave of lead III (0.47 +/- 0.35 mV), S wave of lead aVL (0.31 +/- 0.23 mV) and R wave of lead aVF (0.37 +/- 0.30 mV) occurred. A strong positive correlation between the R wave changes in leads III and aVF and the S wave in lead aVL (r = 0.94 and 0.91, respectively) suggests that the R and S wave changes in these leads are expressions of the same phenomenon and indicates that the terminal QRS complex is chiefly affected. Eight of 23 patients with inferior infarction and ST depression in the anterior precordial leads had a normal left anterior descending coronary artery. All had an increase in S wave amplitude in leads V2 and V3. Eight patients had inferior infarction, ST depression in anterior leads and severe lesions in the left anterior descending artery or anterior wall motion abnormalities.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical Implication of ST Segment Depression in aVR & aVL in Patients with Acute Inferior Wall Myocardial Infarction

“…The LCX supplies blood to the posterior, posterolateral, posteroinferior, or posteroinferolateral myocardium [25]. During LCX occlusion, posterolateral wall involvement is associated with proximal occlusion because this region is supplied, at least in part, by the obtuse marginal branch of the LC artery [15] [25]. When occlusion of the LCX artery more distally, the posterolateral wall will not be involved, and the ST-segment vector will be oriented more inferiorly [25].…”

“…The ECG changes during LCX artery occlusion is highly variable because of its anatomical distribution. The LCX supplies blood to the posterior, posterolateral, posteroinferior, or posteroinferolateral myocardium [25]. During LCX occlusion, posterolateral wall involvement is associated with proximal occlusion because this region is supplied, at least in part, by the obtuse marginal branch of the LC artery [15] [25].…”

“…During LCX occlusion, posterolateral wall involvement is associated with proximal occlusion because this region is supplied, at least in part, by the obtuse marginal branch of the LC artery [15] [25]. When occlusion of the LCX artery more distally, the posterolateral wall will not be involved, and the ST-segment vector will be oriented more inferiorly [25]. Cardiologists should pay more attention to the tracing of lead aVR when interpreting the 12-lead ECG in clinical practice [26].…”

Site of Transmural Late Gadolinium Enhancement on the Cardiac MRI Coincides With the ECG Leads Exhibiting Terminal QRS Distortion in Patients With ST-Elevation Myocardial Infarctions

“…10,11) The delayed conduction decreases the degree of cancellation, resulting in an increase in R wave and decrease in the S-wave amplitude in leads with terminal S waves on the surface ECG. [12][13][14] The Purkinje fibers are less sensitive to ischemia than the contracting myocytes. 12,13) Hence, for an alteration in the terminal portion of the QRS to occur, there should probably be severe and prolonged ischemia that would affect the Purkinje fibers.…”

Evaluation of depolarization changes during acute myocardial ischemia by analysis of QRS slopes

“…Some of these changes are considered to represent already necrotic areas (Q waves), but other, potentially reversible changes in the QRS complex also appear, although they are less well understood and are usually not considered for clinical decision making. Earlier studies on depolarization changes during ischemia due to acute coronary occlusion have considered QRS prolongation (1)(2)(3)(4)(5), amplitude changes of the R-and S-waves (4,6,7), "distortion" of the terminal part of the QRS complex (8)(9)(10)(11)(12) as well as changes in the high-frequency components of the QRS complex (13)(14)(15).…”