8 Integrated ECG Case Practice

Scope and safety

These cases support learning and do not replace supervised training or clinical judgment. In an emergency, activate the appropriate response team and follow current local protocols.

Assess the patient and identify instability

Begin with the patient’s condition, not the ECG label. Assess responsiveness, airway and breathing, pulse, blood pressure, perfusion, mental status, chest discomfort, and signs of heart failure.

If the patient is pulseless, begin CPR and follow the cardiac-arrest algorithm. Do not delay CPR to obtain a 12-lead ECG.

Determine whether the rhythm is causing cardiopulmonary compromise. Relevant signs include hypotension, shock, acute altered mental status, ischemic chest discomfort, or acute heart failure. Unstable tachyarrhythmia with a pulse generally calls for prompt synchronized cardioversion. Pulseless ventricular fibrillation or pulseless ventricular tachycardia calls for CPR and unsynchronized defibrillation.

Read the ECG systematically

After the initial assessment, read the ECG in a consistent order. Confirm the patient, calibration, and lead placement; determine rate and regularity; inspect P waves and their relationship to QRS complexes; assess QRS width, axis, intervals, and ST–T changes; and compare with prior tracings when available.

Classify the rhythm by regularity and QRS width, but do not let a rhythm label distract from ischemia, shock, hypoxia, or other reversible causes. Stabilize immediate instability first, recognize time-critical coronary occlusion, and then investigate causes and refine the diagnosis.

Look for ischemia and additional lead clues

In suspected acute coronary syndrome, obtain and interpret a 12-lead ECG promptly, with a target of within $10$ minutes of first medical contact. Repeat the ECG if symptoms persist or the first tracing is nondiagnostic. A normal or nondiagnostic tracing does not rule out acute coronary syndrome.

Interpret suspected ST elevation in clinical context and in contiguous leads. Guideline thresholds are generally at least $1\,\mathrm{mm}$ in two contiguous leads other than V2–V3; thresholds in V2–V3 vary by age and sex.

ST depression in V1–V3 can be a reciprocal clue to posterior injury. Consider posterior leads V7–V9 when this pattern and the clinical situation raise concern, and repeat ECGs as clinically indicated. Right-sided leads can also add information: ST elevation in V4R supports right-ventricular involvement in an inferior infarction pattern.

Match rhythm patterns to the response

A stable, regular narrow-complex tachycardia with P waves that are not clearly visible is consistent with re-entrant supraventricular tachycardia. Assess for causes and monitor the patient. If appropriate, use vagal maneuvers; adenosine may be considered for a regular rhythm under the applicable protocol. The adult tachyarrhythmia algorithm lists an initial rapid IV push of $6\,\mathrm{mg}$, followed, if needed, by $12\,\mathrm{mg}$. Reassess for instability; if it develops, prioritize synchronized cardioversion rather than delaying for medication.

An irregularly irregular narrow-complex rhythm with no consistent P waves and a rapid ventricular rate is atrial fibrillation with rapid ventricular response. If the tachyarrhythmia is causing instability, urgent synchronized cardioversion is generally indicated. Support airway and breathing, monitor continuously, obtain IV access, and evaluate for ischemia and other causes of shock. ST depression may reflect demand ischemia or concurrent acute coronary syndrome; do not assume its cause from the ECG alone.

Treat regular wide-complex tachycardia as potentially ventricular tachycardia while obtaining expert help and assessing for ischemia or other causes. If the patient is stable, an antiarrhythmic infusion and expert consultation may be considered. Adenosine is considered only for regular, monomorphic wide-complex tachycardia. If instability develops, perform synchronized cardioversion; if the patient becomes pulseless, switch to CPR and defibrillation for shockable ventricular fibrillation or pulseless ventricular tachycardia.

A slow heart rate accompanied by compromise is symptomatic bradycardia, not merely a low number. Atrial activity dissociated from a slow, regular ventricular rhythm with broad QRS complexes is concerning for high-grade or complete AV block. Support airway and breathing, monitor, obtain IV access, address reversible causes, and prepare for pacing and expert consultation. The bradycardia algorithm recommends atropine; if it is ineffective, consider transcutaneous pacing and/or dopamine or epinephrine infusion, with transvenous pacing considered as appropriate. Evaluate and treat suspected myocardial ischemia urgently in parallel.

Recognize time-critical coronary patterns

ST elevation in leads II, III, and aVF with reciprocal ST depression in I and aVL indicates an acute inferior STEMI pattern. ST elevation in V4R supports right-ventricular involvement. This is a time-critical coronary-occlusion pattern: activate the STEMI or reperfusion pathway immediately, and do not wait for troponin results before escalation.

Treat hypotension and monitor closely. Right-ventricular involvement can make patients especially sensitive to reduced preload, so assess hemodynamics before giving therapies that may lower blood pressure. Reperfusion decisions and medications should follow current acute coronary syndrome guidance and local protocols.

Apply the priorities to practice cases

Use the same priorities when applying the approach to new cases: identify the rhythm or ECG concern, determine whether the patient is unstable, and state the first treatment priority.

• Stable regular narrow rhythm: A patient has a regular narrow-complex rate of $182/\mathrm{min}$, normal blood pressure, and no ischemic symptoms. This is stable regular narrow-complex tachycardia. Assess and monitor; consider vagal maneuvers and adenosine if appropriate to the rhythm and protocol. Reassess for instability throughout.

• Possible posterior occlusion: A patient has ongoing chest pain and horizontal ST depression in V1–V3 without diagnostic ST elevation on the standard tracing. Consider posterior leads V7–V9 and repeat ECGs as clinically indicated. The ST depression can be a reciprocal clue to posterior injury that may not be apparent on the standard 12-lead; escalate suspected acute coronary occlusion through the acute coronary syndrome pathway.

• Pulseless wide-complex rhythm: If a patient becomes unresponsive and pulseless and the monitor shows a chaotic, disorganized ventricular rhythm, treat it as cardiac arrest with a shockable rhythm. Start high-quality CPR, attach a defibrillator, and deliver unsynchronized defibrillation according to the arrest algorithm. Resume CPR promptly and continue the algorithm.