High lateral myocardial infarction on ECG

كيف يظهر في التخطيط

The most pronounced direct changes are in leads I and aVL, which look at the high (basal) segments of the lateral wall of the LV. ST-segment elevation appears in them, sometimes with a peaked, "hyperacute" T wave at the earliest stage. The formal STEMI criterion is ST elevation ≥ 1 mm in two contiguous leads; I and aVL are contiguous, but isolated elevation in only one of them does not meet this criterion. At the same time, isolated elevation in aVL with reciprocal depression in III is a known pattern of occlusive infarction and requires urgent clinical assessment regardless of formal classification.

Reciprocal changes — ST depression in III (and often in aVF, II). This is a typical reciprocal change to elevation in aVL: its presence, especially dynamically and together with the clinical picture of ischemia, increases the specificity of the finding for acute occlusion, but the severity of depression does not provide a reliable quantitative estimate of probability — it depends on coronary anatomy, collaterals, time from symptom onset and cardiac position.

The South African flag sign has been described separately: ST elevation in I and aVL (horizontal band), reciprocal ST depression in III (vertical band) and ST elevation in V2 (corner of the flag), typical of occlusion of the first diagonal branch. ST depression in V1–V3 should not be confused with this sign — if concomitant posterior ischemia is suspected, it is advisable to record V7–V9.

Pathological Q in I and aVL does not always form — the infarction zone may be small, and the Q wave here is low-amplitude and short even in norm, so it is interpreted with caution.

الآلية

The high lateral segments of the LV are supplied by the first diagonal branch of the LAD, the obtuse marginal branch of the circumflex artery, or the ramus intermedius — a separate intermediate branch arising from the bifurcation or trifurcation of the left coronary artery trunk between the LAD and the circumflex artery, and not a branch of the latter. The size of the affected zone depends on the caliber and territory of the specific artery and may range from small to extensive — a large diagonal, marginal branch or ramus intermedius can cause extensive anterolateral or lateral MI. The injury vector is directed toward leads I and aVL, which creates ST elevation in them, while the opposite pole of this vector forms reciprocal depression in III. With a small volume of affected myocardium, the amplitude of changes is often modest, and MI is easily missed, especially if one relies only on the classic criterion of ST elevation in two contiguous precordial leads.

الأسباب

• Occlusion of the first diagonal branch of the LAD
• Occlusion of a branch of the circumflex artery (obtuse marginal branch)
• Occlusion of the ramus intermedius
• Part of a more extensive anterolateral or inferolateral infarction with proximal involvement
• Multivessel disease with involvement of the lateral wall

التشخيص التفريقي

• Benign ST elevation (normal variant, early repolarization syndrome) — no reciprocal depression in III, no dynamics, no clinical picture of ischemia
• LV hypertrophy with ST-T changes — diffuse changes, high QRS voltage, deep S in V1–V2, ST-T direction opposite to the main QRS wave, no acute dynamics
• Pericarditis — diffuse, usually concave ST elevation and PR depression, without reciprocal ST depression in most leads; the exception is aVR and sometimes V1
• Inferior myocardial infarction — ST elevation is determined in at least two of the contiguous leads II, III, aVF, often maximal in III, and reciprocal depression — in I and aVL (reverse picture)
• Wellens syndrome and other NSTE-ACS patterns — no ST elevation, changes involve the T wave in precordial leads

الأهمية السريرية والتكتيكات

The formal STEMI classification requires ST elevation ≥ 1 mm in two contiguous limb leads — usually I and aVL. Isolated elevation in only aVL with reciprocal depression in III does not automatically satisfy this criterion, but is known as a pattern suspicious for occlusive infarction (OMI), and with persistent ischemic symptoms and a convincing dynamic ECG pattern, the ACS algorithm must be activated immediately with suspicion of occlusion and the patient urgently referred for coronary angiography/primary PCI. ST elevation in I/aVL must not be interpreted as insignificant because of its low amplitude — the clinical picture and reciprocal depression in III, which increases the specificity of the finding, are important. Serial ECGs should be recorded, additional leads V7–V9 recorded if posterior ischemia is suspected, troponin assessed dynamically, without delaying the reperfusion strategy in a clear clinical-ECG picture. Thrombolysis is used only if STEMI criteria are met, there are no contraindications and timely PCI is impossible.

الأخطاء الشائعة أثناء قراءة تخطيط القلب

• Ignoring ST elevation in aVL because of its low amplitude (1–1.5 mm) — in combination with depression in III this is often the only early sign of occlusion
• Interpreting ST depression in III as independent ischemia of the inferior wall rather than as a reciprocal change
• Automatically assigning the diagnosis of "STEMI" to isolated elevation in only aVL without assessing the contiguous lead I and the clinical picture
• Missing the South African flag sign because of focusing only on limb leads without assessing V2
• Waiting for a pathological Q in I/aVL as a mandatory criterion — it may be entirely absent
• Rejecting the diagnosis of MI in the absence of changes in precordial leads or, conversely, ignoring involvement of V2–V6 in more extensive damage

الأسئلة الشائعة

المصطلحات ذات الصلة

المزيد في قسم «نقص تروية واحباط عضلة القلب»

القسم بأكمله

المصادر

• Goldberger's Clinical Electrocardiography، الطبعة الحالية
• Hampton. The ECG in Practice
• Surawicz, Knilans. Chou's Electrocardiography in Clinical Practice
• ESC Guidelines for the management of acute coronary syndromes, 2023

مادة تعليمية لطلاب كليات الطب والأطباء. لا تحل محل التوصيات السريرية والفحص الطبي؛ يُفسر تخطيط القلب دائماً جنباً إلى جنبกับการحالة السريرية.