Cardiac Arrest: MCCQE1 Preparation Guide

Introduction

Cardiac arrest is the abrupt loss of heart function in a person who may or may not have diagnosed heart disease. It is a critical topic for the MCCQE1 as it requires immediate recognition and management, testing the Medical Expert, Collaborator, and Communicator CanMEDS roles.

In Canada, there are approximately 35,000 to 45,000 out-of-hospital cardiac arrests (OHCA) each year. Survival rates vary significantly across provinces, emphasizing the importance of standardized care.

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Definition: Cardiac arrest is defined as the cessation of cardiac mechanical activity, confirmed by the absence of signs of circulation (no pulse, unresponsiveness, and apnea or agonal breathing).

This guide covers the etiology, pathophysiology, and management of cardiac arrest based on the Heart and Stroke Foundation of Canada guidelines, optimized for your MCCQE1 preparation.

Etiology: The H’s and T’s

For MCCQE1, you must memorize the reversible causes of cardiac arrest. These are classically grouped into H’s and T’s. Identifying these during a “code blue” is a critical skill tested in Clinical Decision Making (CDM) cases.

The 5 H’s and 5 T’s

The H’s	Clinical Context & Canadian Management Notes
Hypovolemia	History of trauma, GI bleed, or dehydration. Look for flat neck veins. Treatment: Fluid resuscitation/Blood products.
Hypoxia	Airway obstruction or respiratory failure. Ensure patent airway and high-flow oxygen.
Hydrogen Ion (Acidosis)	Pre-existing metabolic acidosis (e.g., DKA, renal failure). Consider Sodium Bicarbonate (specific indications only).
Hyper/Hypokalemia	Hyper: Renal failure, ECG (peaked T waves). Tx: Calcium gluconate, Insulin/Glucose. Hypo: Diuretics use. Tx: Magnesium/Potassium.
Hypothermia	Common in Canadian winters. “Not dead until warm and dead” (core temp < 30°C to 32°C).

The T’s	Clinical Context & Canadian Management Notes
Tension Pneumothorax	Deviated trachea, absent breath sounds. Tx: Needle decompression (2nd ICS mid-clavicular or 4th/5th ICS mid-axillary).
Tamponade (Cardiac)	Beck’s Triad (Hypotension, JVD, Muffled heart sounds). Tx: Pericardiocentesis.
Toxins	Opioids (Naloxone), TCAs (Bicarb), Beta-blockers (Glucagon). Review Canadian toxicology guidelines.
Thrombosis (Pulmonary)	PE. History of DVT/immobilization. Consider thrombolysis if high suspicion during arrest.
Thrombosis (Coronary)	MI. ST-elevation on ECG (if ROSC achieved) or history. Tx: PCI.

Classification of Rhythms

Understanding the difference between Shockable and Non-Shockable rhythms is the cornerstone of the ACLS (Advanced Cardiovascular Life Support) algorithm.

Shockable Rhythms

Ventricular Fibrillation (VF) & Pulseless Ventricular Tachycardia (pVT)

These rhythms respond to defibrillation.

Ventricular Fibrillation (VF): Disorganized electrical activity; no effective contraction. Most common initial rhythm in witnessed sudden cardiac arrest.
Pulseless Ventricular Tachycardia (pVT): Organized ventricular rhythm but no pulse is generated.

Key Management:

Defibrillation: Priority #1. High-energy unsynchronized shock.
CPR: Resume immediately after shock.

Management: Canadian ACLS Guidelines

The following steps align with the Heart and Stroke Foundation of Canada’s 2020 Guidelines (and 2022 updates).

Step 1: BLS Assessment

Check responsiveness.
Activate Emergency Response System (Call 911 or Code Blue).
Get AED/Defibrillator.
Check pulse and breathing simultaneously (< 10 seconds).

Step 2: Start CPR

If no pulse: Start cycles of 30 compressions : 2 breaths.
Quality: Push hard (5-6 cm depth) and fast (100-120 bpm). Allow full recoil. Minimize interruptions.
CO2 Monitoring: Use waveform capnography. PETCO2 < 10 mmHg indicates poor CPR quality.

Step 3: Rhythm Check & Defibrillation

Apply pads. Analyze rhythm.
If Shockable (VF/pVT): Shock immediately (Biphasic: 120-200J; Monophasic: 360J). Resume CPR immediately for 2 minutes.
If Non-Shockable (Asystole/PEA): Resume CPR immediately. Do not shock.

Step 4: Pharmacotherapy

Epinephrine: 1 mg IV/IO every 3-5 minutes.
- Timing: For Non-Shockable, give ASAP. For Shockable, give after 2nd shock.
Amiodarone: For refractory VF/pVT (after 3rd shock).
- First dose: 300 mg bolus.
- Second dose: 150 mg.
Lidocaine: Alternative to Amiodarone. 1-1.5 mg/kg first dose.

Step 5: Reassessment

Check rhythm every 2 minutes.
Pulse check only if organized rhythm is seen.
Switch compressors to avoid fatigue.

Canadian Drug Context

While Vasopressin was historically used, it has been removed from the simplified cardiac arrest algorithm in current Canadian guidelines. Stick to Epinephrine and Amiodarone (or Lidocaine) for MCCQE1 purposes.

Post-Cardiac Arrest Care (ROSC)

Return of Spontaneous Circulation (ROSC) is just the beginning. The MCCQE1 often tests the immediate post-resuscitation phase.

Airway/Breathing: Maintain SpO2 92-98% (avoid hyperoxia) and PaCO2 35-45 mmHg. Start ventilation at 10 breaths/min.
Circulation: Maintain MAP > 65 mmHg. Use IV fluids and vasopressors (Norepinephrine is usually first-line).
Targeted Temperature Management (TTM):
- Indicated for comatose patients with ROSC.
- Goal: Select and maintain a constant temperature between 32°C and 36°C for at least 24 hours.
- Note: Recent trials (TTM-2) suggest strict normothermia (avoiding fever) is as effective as hypothermia, but for exam purposes, recognize TTM as a standard of care for neuroprotection.
Coronary Intervention: Emergent coronary angiography is recommended for all patients with ST-elevation and unstable patients with high suspicion of AMI.

Canadian Guidelines & Ethical Considerations

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Canadian Context: In Canada, decision-making regarding resuscitation involves specific ethical frameworks and provincial forms.

Advance Directives: Be familiar with terms like DNR (Do Not Resuscitate) and provincial equivalents (e.g., MOST in BC, Goals of Care in Alberta).
Termination of Resuscitation (TOR): For OHCA, paramedics may stop resuscitation if:
1. Arrest was not witnessed by EMS.
2. No bystander CPR was performed.
3. No ROSC after full ACLS protocol.
4. No shocks were delivered.

Key Points to Remember for MCCQE1

Chest Compressions: High-quality CPR is the single most important intervention affecting survival.
Defibrillation: Early defibrillation for VF/pVT significantly improves outcomes.
Epinephrine Timing: In non-shockable rhythms, early epinephrine administration correlates with better survival.
Reversible Causes: Always mentally run through the H’s and T’s during the code.
Pregnancy: If a pregnant patient (>20 weeks) arrests, perform Left Lateral Uterine Displacement to relieve aortocaval compression while doing compressions.

Sample Question

Clinical Scenario

A 62-year-old male collapses while shoveling snow in Winnipeg. Bystander CPR is initiated immediately. Paramedics arrive 6 minutes later and find the patient in Ventricular Fibrillation (VF). He receives one defibrillation shock and 2 minutes of CPR. A second rhythm check reveals persistent VF. A second shock is delivered, and CPR is resumed immediately. Vascular access is established.

Which of the following is the most appropriate next pharmacologic intervention?

Options

A. Amiodarone 300 mg IV push
B. Epinephrine 1 mg IV push
C. Lidocaine 1.5 mg/kg IV push
D. Sodium Bicarbonate 50 mEq IV push
E. Atropine 1 mg IV push

Explanation

The correct answer is:

B. Epinephrine 1 mg IV push

Explanation: According to the ACLS algorithm (Heart and Stroke Foundation of Canada / AHA), for a shockable rhythm (VF/pVT) that persists:

Shock 1 -> CPR 2 mins.
Shock 2 -> CPR 2 mins + Epinephrine 1 mg IV.
Shock 3 -> CPR 2 mins + Amiodarone 300 mg IV (or Lidocaine).

Therefore, after the second shock, Epinephrine is the correct medication.

Option A (Amiodarone): Indicated after the third shock for refractory VF/pVT.
Option C (Lidocaine): An alternative to Amiodarone, also indicated after the third shock.
Option D (Sodium Bicarbonate): Only indicated for specific conditions like hyperkalemia or tricyclic antidepressant overdose, not routinely for VF.
Option E (Atropine): No longer recommended for routine use in cardiac arrest (previously used for PEA/Asystole).

References

Heart and Stroke Foundation of Canada. 2020 Guidelines for CPR and Emergency Cardiovascular Care. Available at: https://cpr.heartandstroke.ca
Medical Council of Canada. Objectives for the Qualifying Examination.
Panchal AR, et al. 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care. Circulation. 2020.
Sandroni C, et al. Post-cardiac arrest care: epidemiology, pathophysiology, and current consensus. Intensive Care Med. 2018.