Evolution of tracings during an anterior infarction

ECG: Sinus rhythm, normal PR interval; Q-waves from V2 to V6 with high amplitude elevation from V2 to V5 and tall and peaked T-wave (upward slope less steep than the downward slope); depression in lead III with negative T-waves in leads III and aVF;

ECG 1B: Emergency coronary angiography was performed with evidence of an occlusion of the mid-LAD. This ECG was recorded after angioplasty with stent placement; the Q-waves are enlarged with fragmentation and QS pattern in V3; regression of the elevation and sharp decrease in the amplitude of the T-waves;

ECG 1C: Tracing recorded at day 3; appearance of a negative, symmetrical and deep T-wave in the leads initially presenting the elevation;

Comments: The tracings of this patient show the evolution of the electrical changes observed during an acute coronary syndrome with, in chronological order, the onset, apogee and regression of abnormalities of the QRS-complex, the ST-segment and the T-wave. Numerous variants can be observed depending on the duration of the coronary occlusion, the presence of a spontaneous or therapeutic reperfusion and presence of a collateral network.

• First 3 hours after the onset of chest pain: from the first 30 minutes, before any abnormality of the QRS-complex or ST-segment, it is possible to record (in about 50%  of cases), isolated changes of the T-wave of the subendocardial ischemia type, the subendocardial zone being the first to suffer from the lack of oxygen; tall, peaked, sometimes symmetrical T-waves or with a less steep upward slope than the downward slope; this pattern of “giant” T-waves without elevation is transient and never exceeds the fourth hour;
•  From the third hour: the giant T-wave transforms into a ST-segment reflecting the presence of a subepicardial lesion; the ischemia induced by the coronary occlusion generates electrophysiological effects evolving over time with a reduction in membrane resting potential and the duration of the action potential in the ischemic zone and a reduction in the velocity and amplitude of phase 0; these changes lead to a voltage gradient between the normal and ischemic areas responsible for the appearance of the lesion current; the elevation may have a Pardee wave-shaped pathognomonic pattern: convex upward elevation, cove-shaped, sometimes very tall (exceeding 10 to 15 mm), encompassing the T-wave and achieving a large monophasic wave pattern; the elevation generally reaches its maximal amplitude within a few hours; international recommendations have defined a minimum amplitude for confirming the pathological nature: recent onset of elevation in 2 contiguous leads and greater than 0.1 mV in all leads except in V2 and V3; in these two leads, an elevation greater than 0.2 mV in men over 40 years, greater than 0.25 mV in men under 40 years and greater than 0.15 mm in women is required; A ST-segment depression in the leads opposite those directly exploring the ischemic area is common but inconsistent depending on the location of the occlusion. This indirect reciprocal sign has a strong diagnostic value even if of limited amplitude. The delays in the appearance of changes of the ST-segment are not always respected; the interindividual variability is even more pronounced for the onset of the necrosis Q-wave; at the third hour, Q-waves are generally absent or shallow and appear on average from the sixth hour and reach their maximum amplitude prior to the twelfth hour; a reduction in the size of the R waves with the appearance of an initially narrow wave, followed by broad and deep, can be observed in some patients from the second hour; a progressive fragmentation of the QRS-complexes can also be highlighted;
• From D1 to D7: the return of the ST-segment to the isoelectric line depends on the presence of a spontaneous or therapeutic revascularization; in the absence of revascularization, the elevation usually disappears within 7 to 24 hours but can persist longer; the T-wave gradually develops indicating a subepicardial ischemia; the T-wave becomes negative, peaked and symmetrical in the territory initially presenting the elevation; the subepicardial ischemia increases gradually with initially a biphasic pattern after which the T-wave becomes increasingly deeply inverted;
• From 1 to 5 weeks: the subepicardial ischemia becomes maximal with deep inversion of the T-wave towards the end of the third week; this evolution is generally slower in the anterior regions than in the posteroinferior regions; if the ST-segment elevation persists for more than three weeks, an evolution toward a ventricular aneurysm should be evoked;
• Evolution over time: a slow and gradual regression of ischemia is sometimes observed, the T-wave recovering its normal pattern; the regression may be incomplete with the persistence of a more or less symmetrical and more or less deep inversion of the T-wave or of a biphasic, flat or small amplitude T-wave; the necrosis pattern is generally definitive despite the fact that the duration and amplitude of the Q-waves may decrease;

Take-home message: It is common to describe a “stereotyped” sequence of electrical modifications during an acute coronary syndrome. Certain phases may be missing, fleeting or delayed. The initial modifications of the T-wave are often unrecorded for example, the first tracing being too late.