What is the most likely cause of cardiac arrest in a patient on Day 3 of chemotherapy?

Cardiac Arrest on Day 3 of Chemotherapy: Most Likely Cause

The most likely cause of sudden cardiac arrest on Day 3 of chemotherapy is arrhythmia (Option B), driven by direct cardiotoxic effects of chemotherapeutic agents on cardiac ion channels and myocardial function. 1

Primary Mechanism: Chemotherapy-Induced Arrhythmias

Arrhythmias are well-documented acute complications of chemotherapy occurring within the first days of treatment, with multiple mechanisms:

• Direct cardiac ion channel effects cause QT prolongation, ventricular tachyarrhythmias, bradycardia, and conduction blocks during or immediately after chemotherapy infusion 1
• Acute cardiotoxicity manifests as transient decline in myocardial contractility with incidence <1% immediately after infusion, creating an arrhythmogenic substrate 1, 2
• Specific high-risk agents include anthracyclines (doxorubicin), paclitaxel, 5-fluorouracil, arsenic trioxide, and alkylating agents, all of which can trigger life-threatening arrhythmias within days 1

Why Arrhythmia Over Other Options

Arrhythmia (Most Likely)

• Timing is characteristic: Cardiac arrhythmias from chemotherapy typically occur within 5 days of first administration 1
• High incidence: Arrhythmias are present at baseline in 16-36% of treated cancer patients, with acute events common during infusion 1
• Multiple drug classes implicated: Anthracyclines, taxanes, alkylating agents, fluorouracil, and targeted therapies all cause acute arrhythmias 1, 3
• Mechanism is direct: Ion channel interaction causes immediate electrophysiological instability, not requiring time for infection or thrombosis to develop 1, 3

Sepsis (Less Likely on Day 3)

• Timing doesn't fit: Neutropenia from chemotherapy typically develops 7-14 days post-treatment, not Day 3 1
• Septic cardiac arrest would require established infection with systemic inflammatory response, unlikely this early in chemotherapy course
• While sepsis causes cardiac arrest, the acute timeframe makes chemotherapy-induced arrhythmia more probable

Pulmonary Embolism (Possible but Less Common)

• Cisplatin increases thrombotic risk (deep vein thrombosis, pulmonary embolism), but this is not the most common acute cardiotoxic effect 1
• PE causing cardiac arrest typically presents with pulseless electrical activity (63% of PE arrests), but would be unusual on Day 3 without other risk factors 4, 5
• Incidence is lower: Only 4.8% of cardiac arrests are due to PE in general populations, whereas arrhythmias are far more common with chemotherapy 4

Clinical Approach to This Patient

Immediate diagnostic steps during resuscitation:

• Obtain 12-lead ECG as soon as possible to detect QT prolongation, conduction blocks, or ischemic changes 1
• Check electrolytes immediately (potassium, magnesium, calcium) as chemotherapy-induced imbalances potentiate arrhythmias 1, 6
• Review specific chemotherapy agents administered to identify known arrhythmogenic drugs 1, 2
• Consider bedside echocardiography during resuscitation to assess for acute right ventricular dysfunction (PE) versus global dysfunction (cardiomyopathy) 1, 4

Post-resuscitation management priorities:

• Continuous cardiac monitoring for recurrent arrhythmias is essential 1
• Correct metabolic derangements aggressively, particularly electrolyte abnormalities that lower arrhythmia threshold 1, 6
• Avoid QT-prolonging medications and reassess chemotherapy regimen with oncology 1
• Targeted temperature management 32-34°C for 24 hours if patient remains comatose post-ROSC 1

Critical Pitfalls to Avoid

• Don't assume sepsis without fever, leukocytosis, or source: Day 3 is too early for neutropenic sepsis 1
• Don't overlook drug-specific risks: Anthracyclines, paclitaxel, and 5-FU have particularly high acute arrhythmia rates requiring heightened vigilance 1, 2
• Don't delay thrombolysis if PE is confirmed: If echocardiography shows massive PE with right ventricular dysfunction, thrombolysis improves return of spontaneous circulation (81% vs 43%) 4
• Don't prognosticate neurological outcome before 72 hours post-ROSC, especially with therapeutic hypothermia 1

The constellation of acute presentation on Day 3 of chemotherapy, known cardiotoxic mechanisms of common agents, and high baseline arrhythmia incidence in cancer patients makes arrhythmia the most probable cause of this cardiac arrest. 1, 2