ECG criteria
- V7 — along the posterior axillary line at the level of V4–V6 (5th left intercostal space)
- V8 — along the scapular line on the left at the same horizontal level
- V9 — along the paraspinal line on the left at the same level
- ST-segment elevation in two contiguous leads V7–V9 ≥0.5 mm is the primary criterion for acute posterior MI; elevation ≥1 mm increases specificity. There is no separate threshold for men under 40 years in V7–V9.
- Isolated ST elevation in a single lead does not confirm posterior MI — electrode placement must be checked, ECG dynamics and clinical presentation assessed
- Correlation with ST depression in V1–V3 and R/S ratio >1 in V1–V2 on a standard ECG
- Q wave in V7–V9 and/or inverted T wave may appear in the subacute stage
What it looks like on ECG
Leads V7–V9 are a continuation of the precordial electrode line posterior to V6, at the same horizontal level (5th left intercostal space, unless the heart is displaced):
| Lead | Location |
|---|---|
| V7 | posterior axillary line |
| V8 | scapular line (at the tip of the scapula) |
| V9 | paraspinal line to the left of the spine |
Normally, wave amplitudes in V7–V9 are lower than in standard precordial leads due to the greater distance of the electrode from the myocardium and the tissue volume between it and the heart — this is normal and does not indicate low voltage. In acute posterior myocardial infarction, ST-segment elevation ≥0.5 mm appears in two contiguous leads V7–V9 (elevation ≥1 mm is a more specific threshold) with possible reciprocal mirror changes in V1–V3: ST depression, sometimes a tall and broad R wave. ST elevation in only a single lead without dynamic changes and clinical correlation is not considered diagnostic — such a result requires checking electrode placement and a repeat recording. In the subacute and scar stages, a pathological Q wave and inverted T wave may form in V7–V9, reflecting completed necrosis of the posterior left ventricle.
Mechanism
The posterior wall of the left ventricle (supplied by the circumflex artery, less commonly the right coronary artery) does not project directly onto any standard precordial lead — V1–V3 "view" it from the opposite, anterior side of the chest. Therefore, transmural injury of the posterior wall is recorded in V1–V3 as a mirror image: as ST depression instead of elevation. Leads V7–V9 are oriented toward the posterior and posterolateral surface of the heart and allow registration of ST elevation in direct posterior leads, with the same polarity as direct leads in anterior or inferior MI.
Indications for recording
- ST-segment depression in V1–V3 without obvious ST elevation in other leads in a patient with ACS presentation
- Tall R wave and R/S ratio >1 in V1–V2 in the presence of ischemic symptoms
- Suspected isolated posterior MI (often combined with inferior or lateral MI)
- Inferior MI with uncertainty regarding posterior wall involvement (to assess the extent of the lesion)
Differential diagnosis
- Right ventricular hypertrophy: tall R in V1 is present, but there is no ST elevation in V7–V9 and no ACS clinical presentation
- Right bundle branch block: wide QRS with typical morphology in V1, waves in V7–V9 without ischemic ST shifts
- WPW with a delta wave mimicking a tall R in right precordial leads: short PR interval and delta wave are present
- Normal variant with low amplitude in V7–V9 without ST dynamics — a repeat serial recording resolves the question
Clinical significance and management
In the presence of acute ischemia symptoms, ST elevation in two contiguous leads V7–V9 ≥0.5 mm accompanied by ST depression in V1–V3 is regarded as a sign of probable acute coronary occlusion and a STEMI equivalent, requiring immediate reperfusion therapy within the same timeframe as classic STEMI, regardless of the absence of formal ST elevation criteria in the 12 standard leads. The diagnosis of myocardial infarction is confirmed based on the clinical presentation and troponin dynamics, rather than an isolated ECG finding. V7–V9 should be recorded promptly when posterior ischemia is suspected: with ischemic ST depression in V1–V3, especially with a tall R and positive T wave, in inferior MI, or with ongoing ACS symptoms. A negative result in the setting of high clinical probability does not definitively rule out posterior MI — the decision is made based on the combination of ECG, troponin, and clinical findings.
Common interpretation errors
- Failing to record V7–V9 in isolated ST depression in V1–V3, mistaking it for non-ST-segment elevation ACS without signs of occlusion
- Confusing low wave amplitude in V7–V9 (normal due to tissue thickness) with pathological low voltage
- Failing to align the level of electrodes V7–V9 horizontally with V4–V6
- Interpreting ST elevation in a single V7–V9 lead as sufficient confirmation of posterior MI without checking contiguity, dynamics, and electrode position
- Failing to account for the fact that the ST elevation criterion in V7–V9 is lower (0.5 mm) than in anterior precordial leads, and applying the same thresholds as for V2–V3
1. Where is the V8 electrode placed?
V7 — posterior axillary line, V8 — scapular line, V9 — paraspinal line, all at the level of V4–V6.
2. Which finding on a standard ECG should raise suspicion for posterior MI and prompt the recording of V7–V9?
ST depression in right precordial leads is a reciprocal mirror image of ST elevation in the posterior wall; a tall, often broad R wave may reflect the mirror image of a posterior pathological Q wave and is not mandatory in the early phase.
3. What ST elevation threshold in V7–V9 is most commonly used as a criterion for acute posterior MI?
For posterior leads, the threshold is lower than for anterior precordial leads: usually ≥0.5 mm in two contiguous leads, with ≥1 mm being a more specific criterion.
Frequently asked questions
When should V7–V9 be recorded?
In the presence of ST-segment depression in V1–V3 in a patient with acute ischemic symptoms, especially when combined with inferior myocardial infarction — to avoid missing posterior MI as a sign of acute coronary artery occlusion.
What ST-elevation threshold is considered pathological in V7–V9?
A threshold of ≥0.5 mm is used in two contiguous leads V7–V9; elevation ≥1 mm is considered a more specific sign. There is no separate age- and sex-specific threshold for men under 40 years in V7–V9 — such criteria apply to V2–V3.
Why is the wave amplitude in V7–V9 lower than in V5–V6?
Electrodes are located farther from the heart, with more chest tissue between them and the myocardium, so the amplitude naturally decreases — this is not a sign of pathology.
Is posterior MI in V7–V9 the same as STEMI?
ST elevation in two contiguous leads V7–V9 in the presence of ACS presentation is considered a STEMI equivalent and leads to the same emergency reperfusion management as classic STEMI, even though formal STEMI criteria may be absent in the standard 12 leads.
Is it necessary to record V7–V9 in any ACS?
No, routine recording is not required — the indication arises in the presence of ST depression in V1–V3 or a tall R in V1–V2 in the setting of ischemic symptoms.
ECG Course
Interpretation from basics to myocardial infarction — learn to read any ECG using a systematic algorithm.
- Video lessons and theory for every topic
- Simulator case studies under every lesson
- Unlimited ECG simulator practice
- Study guide: "All ECGs in 25 minutes"
ECG Strip Simulator
ECG, radiology, histology, pathomorphology, pharmacology — thousands of flashcards with detailed explanations.
- Real ECG strips, not textbook drawings
- Instant answers and explanations
- Streaks and progress tracking in your dashboard
Related terms
More in the «Phenomena and Eponyms» section
Sources
- AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram, 2009
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- Orlov V.N. Guide to Electrocardiography
- ESC Guidelines for the management of acute coronary syndromes, 2023
Educational material for medical students and physicians. Does not replace clinical guidelines and physical examination; the ECG must always be interpreted in conjunction with the clinical picture.