Coronary Territories and Infarct Localization

Every page in this new section rests on one foundational skill: translating a regional wall motion abnormality into a specific coronary territory, and from there into a specific vessel and even a specific lesion location. This is the skill that makes echocardiography genuinely useful for localizing ischemic disease — not just detecting that “something is abnormal.”

Building on What You Already Know

The scoring scale itself — normal, hypokinetic, akinetic, dyskinetic — and the basic concept of the 16-/17-segment model are covered on the LV Systolic Function page, which this page builds directly on rather than repeating. Ejection fraction itself remains the global, volumetric complement to this segment-by-segment approach — the two are read together, not as substitutes for each other. What LV Systolic Function doesn’t cover, and what this page is specifically for, is the precise segment-to-territory mapping, how coronary dominance changes that mapping, how to read lesion position along a vessel from the wall motion pattern itself, and how to go from “these segments are abnormal” to “this points to a specific culprit vessel.”

Coronary Anatomy: The Three-Vessel Framework

This section covers normal anatomy specifically for territory mapping — see Coronary Arteries for anomalous origins, fistulas, and the Kawasaki-specific imaging approach, which this page doesn’t duplicate.

The left main coronary artery arises from the left coronary sinus of Valsalva and divides into the left anterior descending (LAD) artery, running in the anterior interventricular groove toward the apex, and the circumflex (Cx) artery, continuing laterally in the atrioventricular groove. The right coronary artery (RCA) arises from the right coronary sinus and runs inferomedially along the atrioventricular groove.

Coronary dominance determines which vessel supplies the inferior wall — a genuinely important distinction for localization, not just anatomic trivia:

• About 80% of patients are right-dominant: the RCA gives rise to the posterior descending artery (PDA), which lies in the inferior interventricular groove.
• About 20% are left-dominant: the circumflex artery gives rise to the PDA instead.

This means inferior wall akinesis points to the RCA in most patients, but to the circumflex in a meaningful minority — worth keeping in mind before assuming RCA disease from inferior findings alone.

The 17-Segment Model and Its Territory Map

The LV is divided into three levels from base to apex — basal, mid-cavity, and apical — corresponding to proximal, middle, and apical lesion locations along each coronary artery. At the basal and mid-cavity levels, the ventricle is divided clockwise into six segments starting at the interventricular groove: anterior, anterolateral, inferolateral (posterior), inferior, inferior septal, and anterior septal. The apical region, because of the ventricle’s natural tapering, is divided into only four segments — anterior, lateral, inferior, and septal — plus a single additional segment for the apical cap itself, giving 17 segments in total.

In routine clinical practice, a 16-segment model is used instead, excluding the apical cap specifically because it’s difficult to visualize on standard imaging without contrast.

The Territory Map

Territory	Segments supplied
LAD	Anterior septum (base and mid); anterior free wall (base and mid); apical septum; apical anterior wall; apical cap
Circumflex	Anterolateral wall; inferolateral (posterior) wall
PDA (RCA if right-dominant, Cx if left-dominant)	Inferior septum; inferior free wall

A few genuine nuances worth holding onto rather than treating this table as absolute:

• The anterolateral wall’s supply is variable — depending on how much the diagonal branches of the LAD contribute versus the circumflex’s obtuse marginal branches, isolated diagonal branch disease can produce a discrete anterolateral wall motion abnormality that looks like it belongs to the Cx territory.
• Apical supply is genuinely the most individually variable territory in the entire model. In some patients the LAD wraps around the apex to supply the apical segment of the inferior wall; in others, the PDA extends around the apex to supply the apical segment of the anterior wall. Most commonly, the apex receives dual supply from both the LAD and the PDA. This variability is exactly why an LAD that extends around the apex can produce inferior apical akinesis that might otherwise be mistaken for PDA disease — the apex is where territory assignment is least reliable as a rule and most dependent on the individual patient’s anatomy. It’s also the site where LV aneurysm most often forms, given the LAD’s predominant apical supply.
• The inferolateral (posterior) wall can be supplied by either vessel — extension branches from the RCA, or obtuse marginal branches of the circumflex — another genuine source of territory overlap at the margins.
• Proximal RCA disease can cause RV free wall ischemia or infarction — worth actively considering RV involvement whenever inferior wall findings are present. See Evaluation of the Right Ventricle for the standard RV assessment this fits into.

Lesion Position Along the Vessel Changes the Pattern

This is the key insight that turns territory mapping into genuine localization: where a lesion sits along a vessel, not just which vessel is diseased, determines which segments are affected.

• A lesion in the distal third of a vessel affects only the apical segments it supplies.
• A lesion in the mid-segment affects the mid-cavity and apical segments together, sparing the base.
• A proximal lesion affects the entire territory, including the basal segments.

This logic applies identically across all three territories — a proximal LAD lesion produces a genuinely different wall motion pattern than a distal LAD lesion, even though both are “LAD disease.”

Standard Imaging Views for Wall Motion Assessment

Regional systolic function is assessed by combining data from multiple image planes — no single view shows every segment, and relying on one view risks missing disease outside that plane entirely:

• Parasternal short-axis, at the base, mid-LV, and apical levels — circumferential views showing all segments at each level in a single frame, and the view most directly tied to the clockwise six-segment division described above.
• Parasternal long-axis — shows the basal and mid-ventricular segments of the anterior septum and the posterior (inferolateral) wall.
• Apical four-chamber, apical two-chamber, and apical long-axis — together visualize the apical segments and provide the longitudinal views needed to confirm what the short-axis views show circumferentially.

A practical note on short-axis acquisition: angulating the transducer toward the apex from a fixed parasternal position progressively images more apical levels — but this also introduces oblique, foreshortened cuts if not corrected for, which can create a false impression of a wall motion abnormality where none exists. Confirming any suspected finding in a true, non-oblique short-axis plane is worth the extra step.

From Pattern to Culprit Vessel: A Practical Sequence

1. Score each segment using the standard 1–4 scale (normal, hypokinetic, akinetic, dyskinetic), working through the full 16-segment set systematically rather than scanning for the most obviously abnormal region first.
2. Group the abnormal segments by territory using the table above, holding the genuine overlap zones (anterolateral wall, apex, inferolateral wall) in mind rather than forcing every segment into a single vessel.
3. Use the base-mid-apex distribution to infer lesion position — basal involvement implies a proximal lesion; sparing of the base with mid and apical involvement implies a mid-vessel lesion; isolated apical involvement implies a distal lesion.
4. Check for RV involvement whenever inferior segments are abnormal, given proximal RCA disease’s direct RV consequences.
5. Consider dominance before finalizing a culprit vessel from inferior wall findings — the same pattern implicates the RCA in 80% of patients and the circumflex in the remaining 20%.
6. Don’t expect a perfect match to the table in every patient — individual coronary anatomy varies, and collateral vessels or prior revascularization (stenting or bypass) can further alter the expected pattern. A myocardial segment with a balanced oxygen demand-to-supply ratio shows normal wall motion regardless of whether that supply comes from the native vessel, a collateral, or a graft — genuinely explaining why significant angiographic stenosis and normal echocardiographic wall motion can coexist in the same patient.

Distinguishing Acute from Chronic Infarction at the Segment Level

Beyond localizing which territory is involved, a segment’s diastolic wall thickness offers a genuine clue to timing: a recently infarcted segment typically preserves normal diastolic thickness despite reduced systolic thickening, while a chronic, scarred segment is thinned even in diastole. This distinction matters beyond academic interest — it informs both the clinical timeline being inferred from imaging alone and, genuinely, the segment’s potential for functional recovery after revascularization, a question this section’s dedicated viability assessment page takes up fully.

Why Circumflex Disease Deserves Specific Attention

Circumflex territory disease is worth calling out deliberately, since it’s genuinely easy to miss by means other than echocardiography: it’s often electrocardiographically silent, and the anterolateral and inferolateral walls are poorly visualized on a single-plane right anterior oblique coronary angiogram — the standard projection used during diagnostic catheterization. This makes echocardiographic wall motion assessment a uniquely valuable, non-redundant tool specifically for this territory, rather than simply confirming what another test already showed.

A Note on Direct Coronary Flow Imaging

Beyond wall-motion-based territory assessment, direct Doppler recording of coronary flow velocity (CFV) is possible in the distal LAD, the PDA, and occasionally the circumflex, using dedicated high-frequency imaging and specific Doppler settings. This is a genuinely specialized technique, not part of routine wall motion assessment, but worth knowing about: the presence of retrograde diastolic flow is a specific marker of total or near-total occlusion of the recording vessel, reflecting collateral flow from the contralateral or ipsilateral coronary circulation rather than true antegrade perfusion. Antegrade flow, by contrast, does not exclude total occlusion, since collateral input proximal to the recording site still produces antegrade-directed flow — a genuine limitation worth knowing if this technique is encountered in a report or research context.

Clinical Importance

Everything else in this section — acute MI assessment, mechanical complications, ischemic mitral regurgitation, viability — depends on being able to read a wall motion pattern and say, with real confidence, which vessel and which part of that vessel is responsible. The territory map is only the starting point; the genuine skill is holding the map’s real uncertainties (the apex, the anterolateral wall, dominance, collateralization) alongside its reliable core, rather than treating segment-to-vessel assignment as a fixed lookup table.