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This is a clinician-written, evidence-based guide aligned to the MCC Examination Objectives. It is structured by clinical presentation — the way the MCCQE tests and the way patients actually present. Management reflects current Canadian guidelines (CMA, CFPC, CPS). Always cross-reference with institutional protocols and clinical judgment.
Key points
- Two pathways: shockable (VF/pulseless VT) = defibrillate immediately + CPR + epinephrine + amiodarone. Non-shockable (asystole/PEA) = CPR + epinephrine + find and fix reversible cause
- High-quality CPR: rate 100-120/min, depth >=5 cm (adults), full recoil, minimal interruptions (<10 sec for pulse/rhythm checks), 30:2 ratio (or continuous with advanced airway)
- Defibrillation: biphasic 120-200 J (or max if unsure). Resume CPR immediately after shock — do NOT stop to check rhythm
- Reversible causes (Hs and Ts): Hypovolaemia, Hypoxia, Hydrogen ion (acidosis), Hypo/hyperkalaemia, Hypothermia; Tension pneumothorax, Tamponade, Toxins, Thrombosis (coronary + pulmonary)
- Post-ROSC: targeted temperature management (TTM) 32-36C for 24h, coronary angiography if STEMI or suspected ACS, neuroprognostication at >=72h
Approach to the Presentation
Cardiac arrest is the ultimate medical emergency. Survival depends on the chain of survival: early recognition, early CPR, early defibrillation, early advanced care, and post-arrest care. Out-of-hospital cardiac arrest (OHCA) survival to discharge in Canada is approximately 8-10%. The most common initial rhythm in adult OHCA is VF/pVT (~25-35%), which has the best prognosis if defibrillated early. Asystole and PEA have poorer prognosis and require identification of reversible causes. The MCCQE1 expects you to know the ACLS algorithms, the Hs and Ts, and post-ROSC care.
Differential Diagnosis — Reversible Causes (Hs and Ts)
| diagnosis | likelihood | key features | distinguishing test |
|---|---|---|---|
| Hypovolaemia | must-not-miss | Trauma, haemorrhage (GI, ruptured AAA, ectopic), severe dehydration. PEA with narrow QRS, flat IVC on POCUS | Clinical + FAST exam. Treat: aggressive volume resuscitation, blood products, source control |
| Hypoxia | must-not-miss | Airway obstruction, respiratory failure, drowning. Check SpO2, ETCO2 | Ensure adequate ventilation. Check ETT position, lung sounds |
| Hyperkalaemia | must-not-miss | CKD, AKI, rhabdomyolysis, medications (ACEi + spironolactone + NSAID). Tall peaked T waves, widened QRS, sine wave | STAT potassium. Treat: IV calcium gluconate (membrane stabilisation) + insulin/dextrose + bicarbonate |
| Hypothermia | must-not-miss | Environmental exposure, immersion, elderly. Core temp <30C. Osborn (J) waves on ECG. Resistant to defibrillation until rewarmed | Core temperature. "Not dead until warm and dead." Active rewarming |
| Tension Pneumothorax | must-not-miss | Trauma, mechanical ventilation. Absent lung sliding on POCUS, tracheal deviation, absent breath sounds | Clinical + POCUS. Immediate needle decompression then chest tube |
| Cardiac Tamponade | must-not-miss | Trauma (penetrating), post-procedure, malignancy, aortic dissection. Pericardial fluid on POCUS | Bedside POCUS. Emergent pericardiocentesis or thoracotomy |
| Thrombosis — Coronary (MI) | must-not-miss | Most common cause of adult cardiac arrest. STEMI on post-ROSC ECG or shockable rhythm in patient with risk factors | Post-ROSC 12-lead ECG. Emergent coronary angiography if STEMI or high suspicion for ACS |
| Thrombosis — Pulmonary (Massive PE) | must-not-miss | Known VTE risk factors, recent immobility/surgery. RV dilation on POCUS, PEA with wide QRS | Bedside POCUS (RV dilation). Consider empiric systemic tPA (50 mg bolus) during arrest if massive PE suspected |
| Toxins / Drug Overdose | common | Empty bottles, track marks, toxidrome findings. Opioids (miosis, respiratory depression), TCA (wide QRS, seizures), beta-blocker/CCB (bradycardia) | History, toxicology screen, specific antidotes: naloxone (opioids), sodium bicarbonate (TCA), glucagon (beta-blocker), high-dose insulin (CCB) |
| Hydrogen Ion (Acidosis) | common | DKA, lactic acidosis, renal failure, toxins (methanol, ethylene glycol). Severe acidosis impairs myocardial contractility and response to vasopressors | ABG/VBG. Consider sodium bicarbonate if pH <7.1 or hyperkalaemia-related arrest |
Recognition & Initial Assessment
Symptoms
Unresponsive — no response to verbal or physical stimulation
Absent or abnormal breathing (agonal gasps are NOT normal breathing)
No palpable pulse (check carotid for <=10 seconds)
Signs
Check rhythm: VF/pVT (shockable) vs Asystole/PEA (non-shockable)
ETCO2 <10 mmHg during CPR suggests poor prognosis; sudden rise to >40 suggests ROSC
POCUS during rhythm check (<=10 sec): cardiac activity, pericardial fluid, IVC, lung sliding
Investigations During Arrest
First-line
Continuous cardiac rhythm monitoringClassify as shockable (VF/pVT) or non-shockable (asystole/PEA). Reassess rhythm every 2 minutes during CPR
End-tidal CO2 (ETCO2) waveform capnographyConfirms ETT placement, monitors CPR quality (target ETCO2 >20 mmHg), detects ROSC (sudden ETCO2 rise)
Point-of-care blood gaspH, K+, lactate, glucose — identifies hyperkalaemia, acidosis, hypoglycaemia
Bedside POCUSDuring pulse/rhythm checks: cardiac activity (organised vs standstill), RV dilation (PE), pericardial fluid (tamponade), IVC (hypovolaemia), lung sliding (pneumothorax). <10 sec windows
Second-line
Post-ROSC 12-lead ECGSTEMI? New arrhythmia? QTc prolongation? Wide QRS (toxin)?
Post-ROSC labsCBC, BMP, troponin, lactate, coagulation, blood gas, toxicology screen if suspected
Post-ROSC CXRETT position, pneumothorax, pulmonary oedema, rib fractures from CPR
Specialist
Coronary angiographyEmergent if STEMI on post-ROSC ECG. Consider if no obvious non-cardiac cause and shockable rhythm
1
Shockable rhythm (VF / Pulseless VT)
- Defibrillate immediately: biphasic 120-200 J (or max if unsure)
- Resume CPR for 2 minutes immediately after shock (do NOT check pulse)
- After 2nd shock if still VF/pVT: epinephrine 1 mg IV q3-5 min
- After 3rd shock if refractory: amiodarone 300 mg IV bolus, then 150 mg if recurs
- Continue cycle: CPR 2 min → rhythm check → shock if shockable → repeat
- Search for and treat reversible causes (Hs and Ts) throughout
2
Non-shockable rhythm (Asystole / PEA)
- CPR immediately — no shock
- Epinephrine 1 mg IV as soon as possible, then q3-5 min
- Rhythm check every 2 minutes — if shockable rhythm develops, switch to shockable algorithm
- AGGRESSIVELY search for reversible cause — this is the key to surviving PEA/asystole
- Consider termination of resuscitation if no reversible cause found after prolonged effort (discuss with team, consider context)
3
High-quality CPR standards
- Rate: 100-120 compressions/min
- Depth: >=5 cm (at least 2 inches) but not >6 cm
- Full chest recoil between compressions (do not lean on chest)
- Minimise interruptions: <10 seconds for rhythm/pulse checks
- Rotate compressors every 2 minutes to prevent fatigue
- 30:2 compression:ventilation ratio without advanced airway; continuous compressions with advanced airway
- Monitor with ETCO2 — target >20 mmHg (indicates adequate CPR quality)
4
Post-ROSC care
- Targeted temperature management (TTM): 32-36C for >=24h (comatose patients after ROSC)
- 12-lead ECG immediately: emergent PCI if STEMI
- Haemodynamic optimisation: MAP >=65 mmHg, vasopressors/inotropes as needed
- Avoid hyperthermia (<=37.5C), hyperoxia (target SpO2 92-98%), hypoglycaemia, and hypotension
- Neuroprognostication: defer >=72h after ROSC (or >=72h after rewarming from TTM). Use multimodal assessment (clinical exam, EEG, somatosensory evoked potentials, neuroimaging, biomarkers)
- ICU admission for all post-arrest patients
MCCQE1 Exam Tips
- 1Shockable = VF/pVT → defibrillate immediately. Non-shockable = asystole/PEA → CPR + epinephrine + find the cause
- 2Epinephrine 1 mg IV q3-5 min in ALL cardiac arrest. Amiodarone 300 mg IV ONLY for refractory VF/pVT (after 3rd shock)
- 3The Hs and Ts mnemonic is critical: Hypovolaemia, Hypoxia, H+ (acidosis), Hypo/hyperK+, Hypothermia; Tension pneumo, Tamponade, Toxins, Thrombosis (PE + MI)
- 4ETCO2 <10 mmHg after 20 min of CPR is a poor prognostic indicator. Sudden ETCO2 rise >40 = likely ROSC
- 5Post-ROSC: TTM 32-36C for comatose patients. Do NOT prognosticate <72h — too early. Hypothermia delays neurological recovery
- 6If question describes PEA arrest in a dialysis patient: think HYPERKALAEMIA — give IV calcium first
- 7If question describes cardiac arrest in a pregnant patient >20 weeks: manual left uterine displacement during CPR + prepare for perimortem caesarean section at 4-5 minutes if no ROSC
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