What is the appropriate initial evaluation and management for a 39-year-old female with a history of breast cancer treated with chemotherapy, presenting with intermittent tachycardia (heart rate 49-140 bpm) and chest wall pressure, without symptoms of nausea, shortness of breath (SOB), or heart palpitations?

Initial Evaluation and Management of Intermittent Tachycardia in a Post-Chemotherapy Breast Cancer Patient

This 39-year-old woman with prior anthracycline chemotherapy presenting with intermittent tachycardia (HR 49-140 bpm) and chest wall pressure requires immediate 12-lead ECG, continuous cardiac monitoring, echocardiogram with LVEF assessment, troponin, BNP, complete metabolic panel with electrolytes, and thyroid function tests to evaluate for chemotherapy-induced cardiotoxicity, arrhythmias, and structural heart disease. 1

Critical Context: Chemotherapy-Related Cardiac Risk

This patient's history of breast cancer chemotherapy 5 years ago places her at significantly elevated risk for cardiac complications:

• Anthracycline-induced cardiotoxicity can manifest years after treatment completion, with median time to LVEF decline of 4.5 months during active treatment, but late effects can occur much later 1
• Cancer itself increases arrhythmia risk, with a 2.4% baseline prevalence of atrial fibrillation and an additional 1.8% incidence after cancer diagnosis 1, 2
• Doxorubicin specifically is associated with both atrial fibrillation and ventricular arrhythmias 1

Immediate Diagnostic Workup

Essential First-Line Testing

12-Lead ECG - Obtain immediately to:

• Identify specific arrhythmia type (atrial fibrillation, atrial flutter, supraventricular tachycardia, ventricular tachycardia) 1
• Assess for evidence of prior myocardial infarction (Q-waves, left bundle branch block) 1
• Evaluate for left ventricular hypertrophy 1
• Measure QT interval for prolongation risk 1

Continuous cardiac monitoring - Essential given the intermittent nature of symptoms to capture arrhythmic episodes 1, 3

Echocardiogram with LVEF measurement - This is the cornerstone assessment:

• Baseline cardiac assessment is recommended for all patients with history of chemotherapy, even years after treatment 1
• Evaluates for anthracycline-induced cardiomyopathy (LVEF decline) 1
• Assesses valvular function and structural abnormalities 1
• Left atrial function may be impaired after chemotherapy, contributing to arrhythmias 4

Laboratory Evaluation

Cardiac biomarkers:

• Troponin to exclude acute coronary syndrome or myocardial injury 1
• BNP/NT-proBNP to assess for heart failure 1

Metabolic panel with specific attention to:

• Electrolytes (potassium, magnesium, calcium) - abnormalities can precipitate arrhythmias 1, 3
• Renal function - affects medication dosing and can contribute to electrolyte disturbances 1

Thyroid function tests (TSH, free T4):

• Hyperthyroidism can cause tachycardia and must be excluded 3
• Beta-blockers may mask hyperthyroid symptoms 5

Risk Stratification Based on Findings

High-Risk Features Requiring Urgent Intervention

Hemodynamically unstable tachycardia:

• Syncope, presyncope, altered mental status, chest pain, acute heart failure, hypotension, or shock require immediate cardioversion 1, 3

Sustained ventricular tachycardia:

• Life-threatening arrhythmia requiring immediate treatment 1
• Cancer patients with stage IV disease have 10-fold increased ventricular arrhythmia burden 1

Severe LVEF decline (<40%):

• Indicates significant anthracycline cardiotoxicity requiring heart failure management 1

Moderate-Risk Features

Symptomatic atrial fibrillation/flutter:

• Common in post-chemotherapy patients (prevalence 2.4% baseline, additional 1.8% post-diagnosis) 1, 2
• Doxorubicin specifically associated with AF 1

LVEF 40-50%:

• Borderline dysfunction requiring close monitoring and potential cardioprotective therapy 1

Initial Management Strategy

For Documented Tachyarrhythmia

If atrial fibrillation/flutter is identified:

• Rate control with beta-blocker is first-line for hemodynamically stable patients 1
• Metoprolol, atenolol, or pindolol are preferred as they have fewer drug-drug interactions compared to carvedilol, propranolol, or nadolol 1
• Start metoprolol tartrate 25-50 mg twice daily, titrating to heart rate control 5, 6

Anticoagulation decision:

• Must be individualized in consultation with oncology 1
• CHA₂DS₂-VASc and HAS-BLED scores not validated in cancer patients 1
• Cancer creates prothrombotic state, but chemotherapy increases bleeding risk 1

If ventricular tachycardia:

• Immediate cardiology consultation required 1
• Assess for structural heart disease and ischemia 1
• Consider electrophysiology referral 1

For Suspected Tachy-Brady Syndrome

Given the wide heart rate variability (49-140 bpm), consider tachy-brady syndrome:

• Identify and correct reversible causes first: discontinue any beta-blockers, calcium channel blockers, or other rate-controlling medications; correct electrolyte abnormalities; treat hypothyroidism if present 3
• If symptomatic bradycardia occurs: atropine 0.5 mg IV every 3-5 minutes (maximum 3 mg total) for acute episodes 3
• Definitive management: permanent pacemaker implantation may be required if symptomatic bradycardia persists, allowing safe use of antiarrhythmic drugs for tachycardia control 3

Addressing the Chest Wall Pressure

Distinguish cardiac from musculoskeletal pain:

• Reproducible chest wall tenderness suggests musculoskeletal etiology 1
• However, troponin and ECG are still mandatory given cardiac risk factors 1
• Radiation-induced coronary disease typically presents 5-10 years post-treatment (less likely at 5 years but possible) 1

If cardiac ischemia suspected:

• Stress testing or coronary CTA recommended 10 years after radiation therapy per guidelines, but consider earlier if symptomatic 1
• Left-sided breast radiation increases coronary event risk 1

Critical Pitfalls to Avoid

Do not dismiss symptoms as anxiety despite flat affect - cancer patients have legitimate increased cardiac risk requiring thorough evaluation 1, 2

Do not delay echocardiogram - LVEF assessment is essential in all post-chemotherapy patients with cardiac symptoms 1

Do not use class IA, IC, or III antiarrhythmics without careful consideration - these have significant drug-drug interactions and QT prolongation risk in cancer patients 1

Do not start beta-blockers without baseline ECG and heart rate documentation - risk of exacerbating bradycardia in tachy-brady syndrome 3, 5

Do not use atropine doses <0.5 mg - paradoxical slowing may occur 3

Do not assume wearable device accuracy - confirm all arrhythmias with medical-grade monitoring 1

Disposition and Follow-Up

Admit if:

• Hemodynamically unstable tachycardia 1, 3
• Sustained ventricular arrhythmias 1
• LVEF <40% with new diagnosis 1
• Symptomatic bradycardia requiring intervention 3
• Troponin elevation or acute coronary syndrome 1

Outpatient management acceptable if:

• Hemodynamically stable 1
• No high-risk features on ECG or echo 1
• Reliable follow-up within 1-2 weeks with cardiology 1
• Continuous ambulatory monitoring (Holter or event monitor) arranged 1