Abnormal Myocardial Activation as a Cause of ST elevation: A Study Using Precordial Bipolar Leads (PBL)

The purpose of the study was to describe the ischemic changes occurring during percutaneous transluminal coronary angioplasty (PTCA) using a new method based on Precordial Bipolar Leads (PBL) and Precordial Unipolar Leads (PUL).

Ischemic ECG changes have been attributed to both systolic and diastolic injury currents. The relation between ST-segment shift and QRS changes is unclear and there is a discussion about its significance.

Twelve-lead electrocardiograms (ECGs) were performed in 16 patients before PTCA balloon inflation and immediately after balloon deflation in the proximal left anterior descending coronary artery (LAD). Also, ECG data was used to generate V2-V1 PBL, average V1+V2 lead, and the correspondent loop to explore ECG and spatial vector changes.

(1) The V2-V1 Vs Average V1+V2 loop rotation changed from counterclockwise (CCW) to clockwise (CW) in 14 of 15 patients (93%). (2) In 12 of 16 patients (75%), there was an abrupt change of QRS vector direction, producing a "folding" of the loop. In 10 of these cases, the change occurred between 32 and 49 milliseconds after the QRS initiation. (3) In 3/16 patients the final part of the loop was "transported", without folding, to the turning point. (4) The "folding" of the loop changed the direction of the final QRS forces and the J point and ST-segment were displaced to the left and forward. (5) For this reason, repolarization began from an abnormal anterior location.

(1) Ischemic changes in the QRS loop have a cornerstone point in which the whole loop changes. (2) Once the loop has changed its direction, there are no major modifications in the loop development, but the forces do not aim anymore to the isoelectric point. (3) Alterations of myocardial activation appear to be responsible for ST elevation in hyperacute ischemia.