12-lead ECG and STEMI Recognition Practice Questions

31 multiple-choice questions on 12-lead ECG and STEMI recognition for paramedic and EMT students, from Chapter 18 (Cardiovascular Emergencies). Read each question, pick your answer, then tap Show answer to check it and read the explanation.

31 practice questions

1. Per current AHA/ACC criteria, what is the STEMI threshold for new ST elevation in leads other than V2 and V3?

   1. A. 1 mm in any single lead
   2. B. 1 mm in two contiguous leads
   3. C. 2 mm in two contiguous leads
   4. D. 0.5 mm in three or more leads
   Show answer

   Answer: B. 1 mm in two contiguous leads

   New ST elevation at the J point of at least 1 mm in two or more contiguous leads (other than V2 and V3) meets STEMI criteria. A single lead is not enough.

2. A 52-year-old woman with chest pressure has new ST elevation in V2 and V3. What is the minimum elevation in these leads that meets STEMI criteria?

   1. A. 1 mm
   2. B. 2 mm
   3. C. 1.5 mm
   4. D. 2.5 mm
   Show answer

   Answer: C. 1.5 mm

   For V2 and V3, the threshold is 1.5 mm in women regardless of age, 2 mm in men 40 or older, and 2.5 mm in men under 40. These leads normally show some ST elevation.

3. A 35-year-old man with crushing chest pain has new ST elevation in V2 and V3. What is the minimum elevation in these leads that meets STEMI criteria?

   1. A. 2.5 mm
   2. B. 1 mm
   3. C. 1.5 mm
   4. D. 2 mm
   Show answer

   Answer: A. 2.5 mm

   Men under 40 have a higher normal ST elevation in V2 and V3, so the threshold is 2.5 mm. For men 40 and older it is 2 mm.

4. A 61-year-old has ongoing chest pain despite nitroglycerin, a BP of 84/50, and ST depression without ST elevation on serial 12-leads. What is the best destination?

   1. A. A non-PCI ED for fibrinolytic therapy
   2. B. An ED chest pain unit for observation and stress testing
   3. C. The closest ED, since there is no ST elevation
   4. D. A PCI center for an immediate invasive strategy
   Show answer

   Answer: D. A PCI center for an immediate invasive strategy

   Current ACC/AHA ACS guidance treats NSTE-ACS with hemodynamic instability, cardiogenic shock or refractory pain as very high risk, needing an immediate invasive strategy (angiography within about 2 hours), so a PCI-capable center with early notification is best. The absence of ST elevation does not make this patient low risk. Fibrinolytics are not indicated without ST elevation, and observation with stress testing is for low-risk patients, not one with refractory pain and hypotension.

5. In an inferior STEMI, which finding best suggests that the right coronary artery, rather than the circumflex, is the culprit?

   1. A. ST elevation in lead I and in lead aVL as well
   2. B. ST elevation greater in lead II than in lead III
   3. C. Deep ST depression isolated to lead aVR
   4. D. ST elevation greater in lead III than in lead II
   Show answer

   Answer: D. ST elevation greater in lead III than in lead II

   ST elevation that is greater in III than in II, often with reciprocal ST depression in I, points to the right coronary artery because the injury vector points rightward. ST elevation in I and aVL, or greater in II than in III, favors the circumflex, which supplies the lateral wall. ST changes in aVR alone do not identify the inferior culprit.

6. In an inferior STEMI, reciprocal ST depression is most commonly seen in which leads?

   1. A. I and aVL
   2. B. V5 and V6
   3. C. II and aVF
   4. D. V7 and V9
   Show answer

   Answer: A. I and aVL

   High lateral leads I and aVL face roughly opposite the inferior wall, so they often show reciprocal depression. Reciprocal changes increase confidence that elevation reflects true STEMI.

7. A 50-year-old had the sudden 'worst headache of her life' and is now drowsy. Her 12-lead shows deep, wide, inverted T waves across the precordial leads and a long QT. She has no chest pain. What best explains the ECG?

   1. A. An anterior STEMI that needs fibrinolysis
   2. B. Hypothermia producing Osborn waves
   3. C. A brain bleed causing 'cerebral' T waves
   4. D. Early repolarization in a healthy adult
   Show answer

   Answer: C. A brain bleed causing 'cerebral' T waves

   Subarachnoid hemorrhage and other acute brain injuries can cause a surge of catecholamines that produces deep, wide T-wave inversions, QT prolongation and sometimes ST changes ('cerebral T waves'); the priority is the neurologic emergency, and fibrinolytics would be dangerous. These changes are not a STEMI, Osborn waves are a hump at the end of the QRS in hypothermia, and early repolarization causes ST elevation with upright T waves.

8. ST elevation in V4R in a patient with an inferior STEMI indicates:

   1. A. Posterior wall infarction
   2. B. Right ventricular infarction
   3. C. Left main occlusion
   4. D. Lateral wall extension
   Show answer

   Answer: B. Right ventricular infarction

   ST elevation in V4R suggests RV involvement. These patients are preload dependent, so nitrates should be avoided and hypotension is treated with fluid per protocol.

9. A patient with an anterior STEMI develops a new right bundle branch block on the monitor. What should you prepare for?

   1. A. Spontaneous recovery of the infarct
   2. B. A falling risk of cardiogenic shock
   3. C. Rapid improvement after one dose of atropine
   4. D. Sudden high-grade AV block needing pacing
   Show answer

   Answer: D. Sudden high-grade AV block needing pacing

   New bundle branch block in an anterior MI suggests a large, proximal LAD infarct that has damaged the conduction system below the AV node, so it can progress suddenly to complete block with a wide, slow escape; place pacing pads. It does not signal recovery, the risk of shock rises, and atropine works poorly on blocks below the AV node.

10. A 70-year-old with long-standing hypertension has deep S waves and 2 mm of ST elevation in V1 to V3, with very tall R waves in V5 and V6. He has no chest pain. What is the likely explanation?

    1. A. Acute anterior STEMI from LAD occlusion
    2. B. Left ventricular hypertrophy pattern
    3. C. Acute pericarditis
    4. D. Right ventricular infarction
    Show answer

    Answer: B. Left ventricular hypertrophy pattern

    Left ventricular hypertrophy produces large voltages and often ST elevation in V1 to V3 that is proportional to the deep S waves, a common STEMI mimic; comparing with an old ECG helps. In a painless patient with this pattern, an acute anterior STEMI is unlikely, pericarditis causes diffuse ST elevation with PR depression, and RV infarction is seen with inferior STEMI.

11. A 60-year-old with chest pain has horizontal ST depression in V1 to V3 with tall R waves in V1 and V2. What is the best next step?

    1. A. Obtain right-sided lead V4R only
    2. B. Obtain posterior leads V7 to V9
    3. C. Treat as stable angina and monitor
    4. D. Give nitroglycerin and reassess later
    Show answer

    Answer: B. Obtain posterior leads V7 to V9

    ST depression with tall R waves in V1 to V3 can be the mirror image of a posterior STEMI. Posterior leads V7 to V9 can confirm it by showing ST elevation.

12. When posterior leads V7 to V9 are obtained, what ST elevation threshold is generally used to identify a posterior STEMI?

    1. A. 2 mm
    2. B. 1.5 mm
    3. C. 3 mm
    4. D. 0.5 mm
    Show answer

    Answer: D. 0.5 mm

    Posterior leads are farther from the heart, so smaller voltages are seen; ST elevation of 0.5 mm or more in V7 to V9 is considered significant (1 mm in men under 40).

13. Which pair of leads is anatomically contiguous?

    1. A. II and V1
    2. B. I and aVL
    3. C. aVR and V6
    4. D. III and V2
    Show answer

    Answer: B. I and aVL

    Contiguous leads look at adjacent areas of the heart, such as I and aVL (high lateral) or II, III, and aVF (inferior). STEMI criteria require changes in at least two contiguous leads.

14. A 26-year-old with sharp chest pain that improves when leaning forward has diffuse concave ST elevation in most leads and PR depression. This most likely indicates:

    1. A. Anterior STEMI
    2. B. Left main occlusion
    3. C. Posterior STEMI
    4. D. Pericarditis
    Show answer

    Answer: D. Pericarditis

    Diffuse concave ST elevation not limited to one coronary territory, PR depression, and positional pleuritic pain point to pericarditis. A STEMI usually follows a coronary distribution with reciprocal changes.

15. A healthy 22-year-old male has 1 to 2 mm concave ST elevation in V2 to V5 with a notched J point and no symptoms. This most likely represents:

    1. A. Acute anterior STEMI
    2. B. Benign early repolarization
    3. C. Wellens syndrome
    4. D. Right ventricular infarct
    Show answer

    Answer: B. Benign early repolarization

    Benign early repolarization is common in young men and causes concave ST elevation with J-point notching, without reciprocal changes or symptoms. It is a frequent STEMI mimic.

16. Which ECG finding is a common STEMI mimic that can make ST elevation difficult to interpret?

    1. A. Left bundle branch block
    2. B. First-degree AV block
    3. C. Sinus arrhythmia
    4. D. Premature atrial complexes
    Show answer

    Answer: A. Left bundle branch block

    LBBB changes ventricular depolarization and repolarization, producing ST elevation in V1 to V3 that may not reflect infarction. LVH, pericarditis, and ventricular pacing are other mimics.

17. In a patient with a known left bundle branch block and chest pain, which finding most strongly suggests acute MI?

    1. A. Discordant ST depression in V5 and V6
    2. B. QRS width of 0.14 seconds in V1
    3. C. Deep S waves in leads V1 and V2
    4. D. Concordant ST elevation of 1 mm or more
    Show answer

    Answer: D. Concordant ST elevation of 1 mm or more

    Under the Sgarbossa criteria, ST elevation of 1 mm or more in the same direction as the QRS (concordant) strongly suggests acute MI. Discordant changes and deep S waves in V1 are expected with LBBB.

18. A pain-free patient who had chest pain yesterday has deeply inverted or biphasic T waves in V2 and V3. This pattern suggests:

    1. A. Critical proximal LAD stenosis
    2. B. Acute pericardial inflammation
    3. C. Benign early repolarization
    4. D. Right ventricular infarction
    Show answer

    Answer: A. Critical proximal LAD stenosis

    This is Wellens syndrome, which indicates critical proximal LAD stenosis with a high risk of anterior MI. The patient needs prompt cardiology evaluation even if pain-free.

19. A 12-lead in a patient with chest pain shows upsloping ST depression at the J point in V1 to V6 with tall, symmetric T waves and no ST elevation. This pattern suggests:

    1. A. Benign early repolarization
    2. B. Acute LAD occlusion
    3. C. Hyperkalemia only
    4. D. Digoxin effect
    Show answer

    Answer: B. Acute LAD occlusion

    This is the de Winter pattern, a STEMI equivalent indicating acute proximal LAD occlusion. Many systems treat it as a STEMI activation.

20. A 12-lead shows ST elevation in aVR with widespread ST depression in most other leads in a patient with severe chest pain. This suggests:

    1. A. Isolated inferior wall STEMI
    2. B. Benign early repolarization
    3. C. Acute pericarditis in stage 1
    4. D. Left main or multivessel ischemia
    Show answer

    Answer: D. Left main or multivessel ischemia

    ST elevation in aVR with diffuse ST depression suggests severe diffuse subendocardial ischemia, as from left main or multivessel disease. These patients are high risk and need urgent cardiology involvement.

21. Within minutes of a coronary occlusion, before ST elevation develops, the 12-lead may show:

    1. A. Hyperacute T waves
    2. B. Pathologic Q waves
    3. C. Delta waves
    4. D. Prominent U waves
    Show answer

    Answer: A. Hyperacute T waves

    Broad, tall hyperacute T waves can be the earliest sign of STEMI. Pathologic Q waves develop later, indicating necrosis.

22. Pathologic Q waves on a 12-lead most often indicate:

    1. A. Myocardial necrosis
    2. B. Early ischemia
    3. C. Acute pericarditis
    4. D. Hypokalemia
    Show answer

    Answer: A. Myocardial necrosis

    Pathologic Q waves (wide or deep) reflect dead myocardium, usually from an established or old infarction. Ischemia typically causes ST depression or T wave inversion.

23. A STEMI patient's ST elevation largely resolves and his pain stops after aspirin and nitroglycerin, before reaching the hospital. What does this most likely mean?

    1. A. The MI is now ruled out, so no PCI or cath is needed
    2. B. Coronary spasm is now proven as the cause
    3. C. The artery may have reopened, but still go to PCI
    4. D. Fibrinolytics are now needed instead
    Show answer

    Answer: C. The artery may have reopened, but still go to PCI

    Pain and ST elevation that resolve together often mean the clot has partly dissolved (spontaneous reperfusion), but the unstable plaque remains and can reocclude at any time, so the patient still needs urgent catheterization; keep the destination and repeat 12-leads. An MI has not been ruled out, relief after nitroglycerin does not prove spasm, and fibrinolytics are not needed when a PCI center is reachable and the ST elevation has resolved.

24. Why is prehospital transmission of a STEMI 12-lead to the receiving hospital important?

    1. A. It replaces the need for troponin
    2. B. It lets EMS give fibrinolytics
    3. C. It shortens time to reperfusion
    4. D. It confirms the computer reading
    Show answer

    Answer: C. It shortens time to reperfusion

    Early notification lets the hospital activate the cath lab before arrival, reducing first-medical-contact-to-device time. Time to reperfusion directly affects how much myocardium is saved.

25. A STEMI patient arrives at a hospital without a cath lab and must be transferred for PCI. What is the system goal for his door-in-door-out time at that hospital?

    1. A. 90 minutes or less
    2. B. 60 minutes or less
    3. C. 120 minutes or less
    4. D. 30 minutes or less
    Show answer

    Answer: D. 30 minutes or less

    ACC/AHA STEMI system goals call for a door-in-door-out time of 30 minutes or less at a non-PCI hospital, so EMS crews should be ready to transfer quickly. Ninety minutes is the goal for first contact to device when going directly to a PCI center, and 120 minutes is the time beyond which fibrinolysis is preferred if PCI cannot be done. Sixty minutes is not a recognized goal.

26. Your patient's initial 12-lead is nondiagnostic, but he continues to have ischemic chest pain. What should you do?

    1. A. Wait to repeat it until his pain gets worse
    2. B. Repeat the 12-lead at short intervals
    3. C. Wait until arrival to repeat it
    4. D. Treat it as STEMI from symptoms
    Show answer

    Answer: B. Repeat the 12-lead at short intervals

    Ischemic changes can evolve over minutes. Serial 12-leads (for example, every 15 to 30 minutes or with any change in symptoms) can catch a developing STEMI. Waiting for the pain to worsen or for hospital arrival misses evolving changes, and a nondiagnostic ECG does not justify STEMI treatment.

27. A 12-lead shows a QRS of 0.14 seconds with an rSR' pattern in V1 and a wide S wave in I and V6. This pattern is:

    1. A. Left bundle branch block
    2. B. Wolff-Parkinson-White
    3. C. Left ventricular hypertrophy
    4. D. Right bundle branch block
    Show answer

    Answer: D. Right bundle branch block

    A wide QRS with an rSR' (rabbit ears) in V1 and broad S waves in the lateral leads is RBBB. LBBB shows a broad, mostly negative QRS in V1 and a wide upright R in V6.

28. A patient taking digoxin for heart failure has a sagging, scooped ST depression in several leads, a normal rate and no symptoms. What does this most likely represent?

    1. A. Acute posterior wall STEMI
    2. B. Severe hyperkalemia
    3. C. Expected digoxin effect
    4. D. Brugada pattern
    Show answer

    Answer: C. Expected digoxin effect

    Therapeutic digoxin often causes a downsloping, scooped ST depression that is not by itself a sign of toxicity or ischemia; toxicity is suggested by symptoms and dysrhythmias such as AV block or bidirectional VT. A posterior STEMI causes ST depression in V1 to V3 with tall R waves, hyperkalemia causes peaked T waves, and Brugada causes coved ST elevation in V1 and V2.

29. What is the significance of reciprocal ST depression accompanying ST elevation on a 12-lead?

    1. A. It confirms acute pericarditis
    2. B. It means the ECG is artifact
    3. C. It supports true acute STEMI
    4. D. It rules out coronary occlusion
    Show answer

    Answer: C. It supports true acute STEMI

    Reciprocal depression in leads opposite the injured area increases the specificity of ST elevation for STEMI. Pericarditis and early repolarization usually lack reciprocal changes (except in aVR and V1).

30. A patient with an old anterior MI has Q waves and 2 mm of ST elevation in V1 to V4, but no new symptoms. What is the most useful next step?

    1. A. Give a fibrinolytic right away to open the LAD
    2. B. Compare with a prior ECG if one is available
    3. C. Treat it as pericarditis
    4. D. Discard it as artifact
    Show answer

    Answer: B. Compare with a prior ECG if one is available

    Persistent ST elevation with Q waves weeks after an anterior MI often reflects a ventricular aneurysm. Comparing with an older tracing shows whether the changes are new; if no prior ECG exists and symptoms suggest ischemia, treat it as possible STEMI. Fibrinolysis without clear evidence of a new infarct can cause harm, and pericarditis and artifact do not explain fixed Q waves.

31. ST depression or T wave inversion without ST elevation on a 12-lead most often reflects:

    1. A. Myocardial necrosis
    2. B. Acute pericarditis
    3. C. Myocardial ischemia
    4. D. Normal variant
    Show answer

    Answer: C. Myocardial ischemia

    ST depression and T wave inversion are classic signs of ischemia, as in unstable angina or NSTEMI. Necrosis is reflected by pathologic Q waves.