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10 free Paramedic practice questions: 12-Lead ECG Interpretation and STEMI Recognition

These are real questions from the same bank the app draws from. Each one is written to the NREMT Paramedic content specifications and kept inside the Paramedic scope of practice. Pick an answer and you get the full rationale, including why the other three options are wrong.

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Question 1 of 10

A 62-year-old patient reports chest tightness that began an hour ago. The 12-lead ECG shows 1 mm of ST elevation in V2 and 1 mm in V3, measured at the J point, with no reciprocal depression. The vital signs are BP 142/86, P 92, R 20, and SpO₂ 96% on room air. How should this tracing be read?

Show the answer and rationale

Correct answer · V2 and V3 carry a higher threshold, so this is under the bar

Contiguity is the first check and this tracing passes it, since V2 and V3 sit side by side on the chest wall. Neighboring precordial leads are contiguous, even where the wall labels change from septal to anterior between them. The second check is the millimeter bar, and that is where this one fails. V2 and V3 carry a higher bar than the rest of the leads, because normal J point elevation is tallest in those two leads even in a healthy heart. One millimeter there is the trap answer. Keep treating this as an acute coronary syndrome and repeat the tracing during transport.

Why the others are wrong

Absent reciprocal depression rules out an acute occlusion here: Reciprocal depression supports an occlusion when it is present, and plenty of real infarctions never show it. Its absence is not a rule out.

These leads are not contiguous, so the thresholds do not apply: V2 and V3 sit next to each other on the chest wall, so they are contiguous. V2 is a septal lead and V3 is an anterior one, and that does not break the pairing. The problem is the height, not the grouping.

This meets criteria, so activate the catheterization team now: Contiguity is only the first of two checks. The tracing clears that one and then fails on the bar for these specific leads, so activating here commits a team on elevation that has not reached threshold.

Question 2 of 10

A 66-year-old patient with 40 minutes of chest pressure has a 12-lead ECG showing 2 mm of horizontal ST depression in V1, V2, and V3 with unusually tall R waves in those leads. The vital signs are BP 136/82, P 88, R 18, and SpO₂ 97% on room air. What is the most appropriate next step with the ECG?

Show the answer and rationale

Correct answer · Add V7 through V9 to look for posterior involvement

The posterior wall has no lead of its own, so it shows up backwards. Depression in V1 through V3 with tall R waves in those leads is the mirror image of elevation and Q waves happening on the back of the heart. Extend the tracing with V7 through V9 to see it directly. A confirmed posterior infarction carries the same urgency as any other ST elevation infarction, and getting there starts with putting leads on the back.

Why the others are wrong

Repeat the same tracing in 10 minutes and compare: Serial tracings are worth doing, and waiting 10 minutes while the mirror image of an infarction sits in front of you costs muscle that does not come back.

Add V4R to look for right ventricular involvement: V4R is the extension that belongs with an inferior group in II, III, and aVF. Nothing in this tracing points at the inferior wall.

Treat the depression as subendocardial ischemia only: Calling it subendocardial ischemia and stopping there is how posterior infarctions get transported as low acuity chest pain. The tall R waves are the clue that this is a wall, not diffuse ischemia.

Question 3 of 10

A 59-year-old patient has 30 minutes of chest pressure and a 12-lead ECG showing 2 mm of ST elevation in II, III, and aVF with reciprocal depression in I and aVL. The lungs are clear and the neck veins are distended. The vital signs are BP 92/58, P 62, R 18, and SpO₂ 96% on room air. Aspirin has been given. What additional tracing should be obtained before any preload reducing medication?

Show the answer and rationale

Correct answer · A right sided tracing that includes V4R

Every inferior ST elevation infarction gets V4R, and this one is telling you why before you even look. Clear lungs with distended neck veins and a soft pressure alongside an inferior infarct is right ventricular involvement until proven otherwise. That ventricle is preload dependent, so nitroglycerin can drop the filling pressure it is living on and take the blood pressure with it. Confirm with V4R first. If the right sided lead is elevated, withhold nitroglycerin and give fluid instead.

Why the others are wrong

A repeat 12-lead recorded after 10 minutes: Serial tracings matter across a long transport, and repeating the same 12 leads tells you nothing about the right ventricle. The pressure will not wait 10 minutes either.

A 30 second rhythm strip recorded in lead II: A rhythm strip answers rate and regularity. The question in front of you is which chamber is infarcted, and lead II cannot see the right ventricle.

A posterior tracing that includes V7 to V9: Posterior leads are the extension for depression with tall R waves in V1 through V3. This tracing has an inferior group, which points right rather than back.

Question 4 of 10

A 49-year-old patient reports an ache across the chest that started while carrying groceries in from the car and has not let up. The 12-lead ECG shows 2 mm of ST elevation in aVL, with no ST change in I, V5, V6, or any other lead. The vital signs are BP 154/92, P 76, R 18, and SpO₂ 98% on room air. Which reading of this tracing is correct?

Show the answer and rationale

Correct answer · Not an injury pattern, because one lead alone never meets the criteria

One elevated lead is never enough, no matter how tall the segment looks. The criteria ask for new ST elevation in two or more contiguous leads, meaning leads that watch the same wall or the wall next door, because one lead disagreeing with all of its neighbors is far more likely to be a misplaced electrode, artifact, or a normal variant than a dying wall. aVL has neighbors, and they are I, V5, and V6. When none of them agree, the tracing has not met the bar, so you repeat it rather than activating on it. Carry the habit of grouping the leads by wall before you ever look at the millimeters, because contiguity is the check that decides most of these tracings.

Why the others are wrong

High lateral injury, because aVL watches the high lateral wall: aVL really does watch the high lateral wall, so naming the territory is the right instinct. Naming a wall is not the same as meeting the criteria, and the high lateral cluster needs I to agree with aVL before this counts.

Inferior injury, because aVL sits electrically opposite the inferior wall: It is true that aVL and the inferior leads look at the heart from opposite sides, which is why reciprocal change shows up between them. That relationship works the other way around here, since there is no inferior elevation for aVL to mirror.

Not an injury pattern, because aVL needs 2.5 mm before it counts: A higher millimeter bar does exist, so reaching for one is a reasonable move. That higher bar belongs to V2 and V3, not to aVL, and even 5 mm in aVL alone would still fail for the reason that matters, which is that nothing next to it agrees.

Question 5 of 10

A 71-year-old patient reports crushing chest pain for 25 minutes. The 12-lead ECG shows 3 mm of ST elevation in II, III, and aVF with reciprocal depression in I and aVL. The lungs are clear in all fields. The vital signs are BP 84/56, P 46, R 20, and SpO₂ 95% on room air. Which management decision does this combination of findings drive?

Show the answer and rationale

Correct answer · Withhold nitroglycerin and treat the pressure with fluid titrated to perfusion

An inferior pattern with hypotension and clear lungs is a right ventricular infarct until a right sided tracing proves otherwise. The right coronary artery feeds the inferior wall and the right ventricle, so one lesion explains both. A right ventricle that has been hit is preload dependent, meaning it needs volume arriving to push anything forward, so any drug that drops preload can crash the pressure in a way you cannot undo in the field. That is why the chest pain protocol you have run a hundred times gets interrupted here. You hold the nitroglycerin and you give fluid titrated to perfusion, reassessing lung sounds between boluses so you hear it the moment the left side stops keeping up.

Why the others are wrong

Start vasoactive support now, since fluid has nowhere to go at this pressure: Vasoactive support is a genuine option in this patient, and the lesson keeps it on the table. It belongs after fluid, not instead of it, because a right ventricle short on volume has nothing for a pressor to squeeze.

Give nitroglycerin for the ischemia and recheck the pressure after each dose: Nitroglycerin is the reflex for ischemic chest pain and the protocol really does run straight through it, which is exactly what makes this the trap. A preload reducer in a preload dependent right ventricle drops the pressure off a cliff, and rechecking after the dose is too late to help.

Treat the rate with atropine and hold every other decision until it rises: A rate of 46 is doing real damage to the output, and the same artery explains it, so the instinct is sound. Volume comes first here, and the lesson treats the rate per protocol only if perfusion fails to improve once fluid is on board.

Question 6 of 10

A 13-year-old patient has had a stabbing pain under the breastbone since waking, a week after a fever and sore throat, and the pain sharpens with every deep breath. The 12-lead ECG shows concave ST elevation in II, III, aVF, I, aVL, V4, V5, and V6, the PR segment is depressed, and nothing on the tracing mirrors the elevation from the opposite side. The vital signs are BP 104/62, P 112, R 24, and SpO₂ 97% on room air. Which condition does this pattern identify?

Show the answer and rationale

Correct answer · Acute pericarditis inflaming the whole pericardial sac

A true occlusion is territorial, meaning the elevation groups in leads that share a wall and the opposite wall usually shows the mirror. This tracing does the opposite. The elevation is everywhere at once, it is concave, PR depression rides along with it, and there is no opposite wall to check against, because the whole sac is inflamed rather than one artery being closed. The history seals it, since pleuritic pain that sharpens with every deep breath in the week after a viral illness is the classic pericarditis story, and an inflamed sac moving against the lung is what makes breathing hurt. This matters because the two conditions go to very different places clinically, and reading a diffuse inflammatory pattern as an infarct sends a patient down a reperfusion pathway that was never the problem.

Why the others are wrong

Left main occlusion producing change across every territory: A left main lesion can starve enough muscle to change nearly every lead, so the scale of the change fits. That pattern shows up as depression almost everywhere with elevation in aVR, which is the reverse of what is on this tracing.

Benign early repolarization, which is common at this age: Benign early repolarization does give concave elevation and it really is common at this age, which makes it the closest call here. It does not bring PR depression with it, and it does not follow a viral illness with pain that sharpens on every deep breath.

An inferior infarction that has spread into the lateral and anterior walls: Extension between neighboring walls is real, so watching elevation spread is sound. Extension still respects coronary anatomy, and no single artery covers the inferior, lateral, and anterior walls at the same time.

Question 7 of 10

A 65-year-old patient has had a squeezing pressure across the chest and nausea since finishing dinner about 30 minutes ago. The 12-lead ECG shows 2 mm of ST elevation in II, III, and aVF, and Q waves wider than 0.04 seconds in V3 and V4. The vital signs are BP 138/86, P 94, R 20, and SpO₂ 96% on room air. What do these two findings represent?

Show the answer and rationale

Correct answer · A new inferior occlusion alongside an older anterior infarction

Two findings sit on this tracing, and they are reporting different moments. Start by putting each one on a wall. The elevation is in II, III, and aVF, the inferior wall, supplied by the right coronary artery. The Q waves are in V3 and V4, the anterior wall, supplied by the left anterior descending artery. Two walls fed by two different arteries means these findings cannot both belong to one event. Now read each finding for what it reports. ST elevation is dying muscle you are watching in real time, and it is the finding that activates the catheterization laboratory. A Q wave wider than 0.04 seconds means necrosis, tissue that already died, so it answers how old rather than how urgent. The anterior wall carries damage from a day that has already passed. The inferior wall is infarcting in front of you, and the inferior wall is the one you act on.

Why the others are wrong

A single inferior occlusion whose changes reached the anterior wall: Infarcts do extend, and watching a territory grow is a habit worth keeping. Extension follows one artery, and the lead groups put II, III, and aVF on the right coronary artery while V3 and V4 belong to the left anterior descending. An inferior occlusion reaches other leads as reciprocal ST depression, which lands in I and aVL, and it does not write Q waves across the chest.

An old anterior infarction only, since Q waves date this tracing: The Q waves really are the older finding on this tracing, so letting them set the date feels reasonable. A Q wave means necrosis and old damage rather than an active occlusion, which lets it speak only for the wall it sits in. It cannot date an elevation that is sitting in a different lead group, and that elevation is the finding that decides where this patient goes.

A new inferior occlusion that the Q waves time at several hours: This is the closest call, since the inferior reading in it is correct and a Q wave really does report age. These Q waves sit in the anterior leads rather than the inferior ones, so they are not reporting on the inferior event at all. Nothing on this tracing tells you how long the inferior occlusion has been running.

Question 8 of 10

A paramedic is measuring the amount of ST deviation on the 12-lead ECG of a 58-year-old patient with chest pain. The vital signs are BP 140/86, P 90, R 18, and SpO₂ 97% on room air. Where on the complex is that measurement taken, and against what reference?

Show the answer and rationale

Correct answer · At the J point where the QRS ends, against the TP or PR baseline

The J point is the spot where the QRS ends and the ST segment begins, and that is where you measure how far the segment has lifted or dropped. You measure it against the baseline, meaning the flat stretch during TP or the PR segment, since the deviation only means something relative to where that lead sits when nothing is happening. Measuring anywhere else inflates or hides the number. This matters most in V2 and V3, where the segment sits high off the baseline even in a healthy heart, which is why those two leads carry a higher bar than the rest. Group the leads by wall first, then measure at the J point, and the millimeters will rarely be what decides the call.

Why the others are wrong

At the end of the P wave, against the segment that follows the P wave: The PR segment is genuinely part of this, since it is one of the baselines you compare against. It serves as the reference line, not as the place on the complex where you take the measurement.

At the midpoint of the ST segment, against the top of the R wave: The middle of the segment is where the elevation often looks biggest, so the eye is drawn there. The measurement is standardized at the J point, and the R wave is a voltage rather than a baseline to measure from.

At the peak of the T wave, against the flat line that follows the T wave: The T wave is part of repolarization, so watching it is not wasted effort. Deviation is measured where the ST segment starts rather than at the peak of the wave that ends it.

Question 9 of 10

A 72-year-old patient is hypotensive and anxious with distended neck veins and heart sounds that are hard to hear. Breath sounds are present and equal in all fields. The monitor shows the height of the complexes alternating from beat to beat, and the 12-lead ECG shows no ST elevation in any lead. The vital signs are BP 82/60, P 128, R 26, and SpO₂ 94% on room air. Which condition fits this picture?

Show the answer and rationale

Correct answer · Pericardial tamponade compressing the heart from outside

Fluid filling the pericardial sac faster than the sac can stretch squeezes the heart from the outside, so it cannot fill. The bedside picture is hypotension, distended neck veins, and heart sounds that are muffled by the fluid between the heart and your stethoscope. On the monitor you may see the complexes alternate in height beat to beat, which happens because the heart is swinging in the fluid. Breath sounds stay clear and equal, and that is what separates it from a tension pneumothorax, which also distends the neck veins and drops the pressure but takes the breath sounds on one side with it. Field care is supportive with access, oxygen, and rapid transport, because drainage is a hospital procedure.

Why the others are wrong

Tension pneumothorax, since venous return is being obstructed: Obstructed venous return is exactly the right mechanism family, and tension pneumothorax belongs in it. That diagnosis takes the breath sounds away on the affected side, and these are present and equal.

Right ventricular infarction, since the neck veins are distended: Distended neck veins with a soft pressure genuinely does describe a right ventricular infarct, which makes this the closest call on the list. A right ventricular infarct rides with an inferior elevation pattern, and this 12-lead has no elevation anywhere.

Cardiogenic shock, since the pressure has fallen with a fast rate: Hypotension with a fast rate is the headline of cardiogenic shock, so the vital signs fit. Cardiogenic shock comes from the muscle failing and usually brings crackles with it, while this heart is being squeezed from outside with clear lungs.

Question 10 of 10

A paramedic obtains a 12-lead ECG on a patient with chest discomfort and notes new ST elevation in lead III only, with no changes in any other lead, including II and aVF. What is the most appropriate interpretation of this finding?

Show the answer and rationale

Correct answer · This is a nondiagnostic finding; reassess and continue monitoring

STEMI criteria are built on contiguity, not on lead count: the elevation has to show up in two or more leads looking at the same wall. Lead III's neighbors are II and aVF, the inferior group, and this question tells you explicitly that II and aVF are unchanged. One lead standing alone with its own territory silent is the classic profile of artifact, a misplaced electrode, or a non-ischemic baseline shift, so the finding does not meet criteria. Nondiagnostic is not the same as benign. This patient still has chest discomfort, so the move is serial monitoring and a repeat 12-lead, because a genuinely evolving infarct will recruit its neighboring leads on the next tracing.

Why the others are wrong

Activate the cath lab as a STEMI alert: A STEMI alert is exactly right the moment contiguous elevation appears: II, III, and aVF together, or V2 through V4 together, because the clock on reperfusion starts with your radio call. Here only lead III is elevated and both of its inferior partners are explicitly normal, so the activation criterion has not been met. The key beats it because a false activation spends a cath team on an artifact and, worse, trains you to trust a lone lead; the discipline is to repeat the tracing rather than call it early.

This is a diagnostic lateral wall STEMI: The lateral wall is leads I, aVL, V5, and V6: anchor it to where those electrodes sit, out on the left side looking in from the side. Lead III is not one of them; it belongs to the inferior group with II and aVF. The key beats it because this option misassigns the territory on top of misapplying the criteria: even if a lone elevated lead counted, it would point inferior, and it would still need a partner.

Apply posterior leads immediately for a suspected posterior MI: Posterior leads are the right next step when V1 through V3 show ST depression with tall R waves, since anterior depression is the mirror image of elevation on the back wall and posterior leads confirm it. This tracing shows elevation in lead III and no anterior depression at all. The key beats it because there is no posterior pattern to chase; the actionable finding is that a single lead is nondiagnostic, which calls for reassessment rather than a hunt for a different infarct.

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