ECG criteria
- The left arm (LA) electrode is removed from its standard location and placed on the patient's back; the exact anatomical point varies across different methodological descriptions and is not universally accepted
- Chest electrodes are recorded on the posterior thorax in positions that the author of the method associated with V4–V6, but shifted posteriorly; reproducible coordinates (intercostal space, anatomical lines) are not standardized, unlike V7–V9
- Three modified leads are obtained as a conditional analogue of posterior V4–V6; there is no established standard numbering or scheme in modern guidelines
- For standard V7–V9 leads (which solve the same clinical task in practice): V7 is the posterior axillary line, V8 is the midscapular line, V9 is the paraspinal line, all three in the horizontal plane of V6 (fifth intercostal space)
- ST-segment elevation in these leads supports the diagnosis of acute posterior injury; for V7–V9, the recommended threshold is ≥ 0.5 mm in two contiguous leads, whereas for the Slopak method, an independent validated threshold has not been established and is usually extrapolated
- Compared with reciprocal ST depression in V1–V3 on a standard ECG; a tall R wave and an R/S ratio > 1, predominantly in V1–V3 (especially in V2), serve as an auxiliary, non-specific sign and do not replace the recording of posterior leads
- In inferior MI or clinical suspicion of right ventricular involvement, additional right chest leads are recorded, especially V4R; the result is interpreted together with the clinical picture and inferior leads, and a normal recording does not rule out right ventricular involvement
What it looks like on ECG
Slopak leads are not a separate device-based system, but rather a historical method of modifying standard 12-lead ECG to examine the posterior wall of the left ventricle. The left arm electrode is removed and placed on the patient's back; the exact point in the original description is anatomically defined, but in available retellings it is reproduced inaccurately, and a detailed scheme suitable for student training (specific intercostal space, anatomical lines) is not provided in modern reference books. Chest electrodes are connected along the posterior chest wall in positions associated with V4, V5, and V6, but shifted posteriorly—thus yielding three modified leads as a conditional analogue of posterior V4–V6; due to the lack of a unified scheme, calling them "Slopak 1–3" as a standardized designation is incorrect.
This is fundamentally different from standard V7–V9 leads, where all three points are strictly defined: the horizontal plane of V6 (fifth intercostal space), and in terms of depth—the posterior axillary line (V7), midscapular line (V8), and paraspinal line (V9). Slopak leads and V7–V9 solve the same clinical task, but they are not technically identical, and the results of one method cannot be unconditionally equated with the other. Therefore, in modern practice, when posterior MI is suspected, standardized V7–V9 leads are recorded rather than reproducing the historical Slopak technique.
In acute posterior myocardial infarction, ST-segment elevation is expected in the posterior leads, whereas a standard ECG shows mirror ST depression in V1–V3 and/or a tall R wave with an R/S ratio > 1, predominantly in V1–V3. Posterior leads are recorded when a standard ECG raises suspicion of posterior MI (ST depression in anterior chest leads in the setting of inferior or lateral MI), but ST elevation needs to be confirmed by direct recording over the posterior wall.
| Parameter | Standard leads | Slopak leads |
|---|---|---|
| LA electrode | left arm | back (point not unified) |
| What is seen in posterior MI | ST depression in V1–V3 | ST elevation (without standardized threshold) |
| Number of leads | 3 chest leads (V4–V6) | 3 modified leads (analogue of posterior V4–V6) |
| Reproducibility | high | limited, the method is not unified |
Mechanism
The posterior wall of the left ventricle (supplied by the circumflex branch of the left coronary artery or the right coronary artery) does not face any standard chest electrode. During its acute injury, the ST elevation vector is directed posteriorly, which is why V1–V3 record reciprocal ST depression and an increasing R wave rather than elevation. Moving the recording point to the back, closer to the posterior wall, allows visualization of direct ST elevation from the injury zone itself—this principle underlies both Slopak leads and standardized V7–V9. The threshold of ≥ 0.5 mm for V7–V9 is an empirical criterion adopted in ECG standardization guidelines, rather than a consequence of the electrode's distance from the heart.
Causes
- Acute posterior (true-posterior) myocardial infarction, isolated or as part of an inferoposterior or posterolateral injury
- Suspicion of posterior injury with unexplained ST depression in V1–V3 in the setting of ACS clinical presentation
- Historically—an alternative to V7–V9 leads in laboratories where the Slopak method was used; currently rarely used
Differential diagnosis
- V7–V9 leads: solve the same task, electrodes are placed along the posterior axillary line, midscapular line, and paraspinally in the V6 plane, without relocating the LA electrode—currently a standardized and recommended method (AHA/ACCF/HRS 2009); Slopak leads have practically fallen out of routine use and lack the same degree of standardization
- Nehb leads: a bipolar system, more commonly used in stress monitoring; they do not replace standard ECG and V7–V9 when acute posterior MI is suspected
- Isolated ST depression in V1–V3 without posterior MI: a non-specific sign; may reflect ischemia, repolarization abnormalities in left ventricular hypertrophy, right bundle branch block, and other causes—posterior injury is ruled out by recording posterior leads in the appropriate clinical context
Clinical significance and management
Acute posterior injury with diagnostic ST elevation in posterior leads (V7–V9) is regarded as a STEMI-equivalent and warrants immediate invasive reperfusion strategy within the same timeframes as classic STEMI. Slopak leads were historically used for the same purpose, but as a non-standardized method, they do not replace V7–V9 where the latter are available. For a physician at the interpretation stage, it is important: in case of ST depression in V1–V3 amidst ACS symptoms, especially combined with inferior or lateral MI, not to limit oneself to the standard 12 leads, but to record posterior leads (preferably V7–V9). In inferior MI or clinical suspicion of right ventricular involvement, additional right chest leads are recorded, primarily V4R; a normal recording does not rule out right ventricular involvement, and the result is evaluated together with the clinical picture. The definitive diagnosis of myocardial infarction is established based on clinical presentation, ECG, and troponin dynamics, although in the presence of a compelling picture, the reperfusion decision is not delayed until biomarker results are available.
Common interpretation errors
- Confusing the Slopak technique with V7–V9 and failing to specify which method was used in a particular laboratory, even though they are not interchangeable methods
- Applying the threshold of ≥ 0.5 mm recommended for V7–V9 to Slopak leads as a validated independent criterion
- Failing to record posterior leads in isolated ST depression in V1–V3, thereby missing a true-posterior MI
- Interpreting ST elevation in posterior leads as proof of "transmural injury" instead of evaluating it in the clinical context
- Considering a normal V3R–V4R recording sufficient to rule out right ventricular infarction
1. What is the recommended threshold for ST elevation in two contiguous leads supporting the diagnosis of acute posterior injury in V7–V9?
For standardized posterior V7–V9 leads, a threshold of ≥ 0.5 mm in two contiguous leads is accepted.
2. What fundamentally distinguishes the Slopak method from standard V7–V9?
In the Slopak method, the LA electrode is moved to the back, and chest electrode positions are less standardized compared to the strictly defined V7–V9 lines.
3. What finding on a standard ECG serves as an indication for recording posterior leads?
ST depression in anterior chest leads can be a reciprocal sign of posterior MI, which requires confirmation by direct recording of ST elevation in posterior leads.
Frequently asked questions
How do Slopak leads differ from V7–V9?
Both methods are aimed at detecting ST-segment elevation in posterior infarction. For V7–V9, the electrode positions are strictly defined: the posterior axillary, mid-scapular, and paravertebral lines in the V6 plane, without moving the limb electrode. In Slopak leads, the left arm electrode is moved to the back, and the chest electrodes are recorded posterior to the V4–V6 positions, though precise landmarks vary across different descriptions of the technique. Currently, clinical practice and guidelines favor V7–V9.
What is the correct spelling of the eponym — Slopak or Slapak?
In both Russian and English literature, the established spelling is "Slopak" (Slopak leads). The variant "Slapak" is occasionally found, but it should be considered an inaccurate spelling rather than an alternative correct form.
When should posterior leads be recorded in suspected posterior MI?
In cases presenting with acute coronary syndrome and ST-segment depression in V1–V3, particularly in the setting of inferior or lateral infarction, when it is necessary to confirm true posterior myocardial infarction by direct recording of ST-segment elevation.
What ST-segment elevation criterion is used in posterior leads?
For standardized V7–V9, the recommended threshold is ST-segment elevation ≥ 0.5 mm in two contiguous leads, supporting the diagnosis of acute posterior injury in the appropriate clinical context. For Slopak leads, the same threshold is usually extrapolated, but it has not been separately validated for this non-standardized technique.
Are Slopak leads used today?
In practice, this technique has been largely superseded by standardized V7–V9 leads, which have more precise anatomical definitions, are easier to reproduce, and are described in modern ECG recording guidelines.
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
- Orlov V.N. Guide to Electrocardiography
- Surawicz B., Knilans T. Chou's Electrocardiography in Clinical Practice
- 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.