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Case 014: Routine Surveillance in Duchenne Muscular Dystrophy

Clinical Presentation

Setting: Cardiology clinic

Patient: 12-year-old male with Duchenne muscular dystrophy (DMD), diagnosed at age 4, presenting for annual cardiac surveillance.

History: - DMD confirmed by genetic testing (exon 45-52 deletion) - On deflazacort since age 5 - Uses wheelchair full-time since age 10 - On enalapril 5mg BID since age 8 (started prophylactically) - No cardiac symptoms reported - Mother notes he seems "more tired" recently but attributes to disease progression

Review of Systems: - No chest pain - No palpitations - No syncope - Mild dyspnea with transfers (baseline) - Good appetite, no edema - Sleeps flat, no orthopnea

Physical Exam: - HR 95, BP 105/68, SpO2 97% on RA - BMI 18 (5th percentile - typical for DMD) - Pseudohypertrophy of calves - Proximal muscle weakness, Gower's sign not testable (non-ambulatory) - Cardiac: Regular rhythm, no murmur, no gallop - Lungs: Clear - Abdomen: Soft, no hepatomegaly - Extremities: No edema

Initial Workup

ECG: - Sinus rhythm, HR 92 - Tall R waves in V1-V2 (R/S ratio >1 in V1) - Deep Q waves in I, aVL, V5-V6 - ST-T changes laterally

Echocardiogram: - LV end-diastolic dimension: 48mm (Z-score +1.2) - LV ejection fraction: 48% (previously 55% one year ago) - Mild inferolateral wall motion abnormality - Trivial mitral regurgitation - Normal RV function - No pericardial effusion

Prior Echo (1 year ago): - LVEF 55% - No wall motion abnormalities

BNP: 180 pg/mL (previously <50)

Clinical Reasoning Questions

Question 1

What is the significance of the ECG findings in this patient?

Answer The ECG pattern is **characteristic of DMD cardiomyopathy**: **Typical DMD ECG findings:** - **Tall R waves in V1-V2** with increased R/S ratio (reflects posterior wall fibrosis causing loss of posterior forces) - **Deep narrow Q waves in lateral leads** (I, aVL, V5-V6) - reflect inferolateral fibrosis - **ST-T abnormalities** in lateral leads **Pathophysiology:** - Dystrophin deficiency causes myocyte membrane instability - Posterior and inferolateral walls affected first (watershed regions) - Fibrosis leads to characteristic electrical changes before functional decline **Clinical Relevance:** - ECG changes often precede echocardiographic abnormalities - The pattern is so characteristic it can suggest DMD in undiagnosed patients - Progression of ECG changes correlates with disease severity

Question 2

How do you interpret the change in ejection fraction from 55% to 48%?

Answer This represents **clinically significant decline** requiring intervention escalation: **Key Points:** 1. **7% drop in one year is concerning** - DMD cardiomyopathy can progress rapidly in adolescence 2. **EF 48% = Stage B heart failure** - LV dysfunction without symptoms 3. **Timing is critical** - ages 10-15 are highest risk for rapid cardiac decline 4. **"Normal" EF may be misleading** - non-ambulatory patients have reduced preload demands; EF of 55% in DMD is not truly "normal" **Why Adolescence is High-Risk:** - Pubertal growth spurt increases cardiac demands - Cumulative dystrophin deficiency effects - Respiratory decline compounds cardiac stress - Many patients develop cardiomyopathy by age 18 **Management Implications:** - This decline should prompt medication escalation - Consider adding beta-blocker - Increase ACE inhibitor dose - Closer follow-up (q6 months vs annually) - Cardiac MRI for tissue characterization

Question 3

What is the recommended cardiac surveillance protocol for DMD?

Answer **2022 DMD Care Considerations Recommendations:** | Age | Echo Frequency | ECG | Additional | |-----|----------------|-----|------------| | At diagnosis | Baseline | Yes | Establish care | | < 10 years | Every 1-2 years | Annual | | | ≥ 10 years | **Annual minimum** | Annual | More frequent if abnormal | | Any decline | Every 6 months | | Consider CMR | | Symptomatic | Every 3-6 months | | BNP trending | **Cardiac MRI Indications:** - Poor echo windows (scoliosis, body habitus) - Discrepancy between symptoms and echo - Baseline tissue characterization - Detect early fibrosis (LGE) before EF decline **Additional Monitoring:** - BNP/NT-proBNP trending - Holter if palpitations or arrhythmia concern - Coordination with pulmonary function testing

Question 4

What are the current guideline recommendations for cardioprotective therapy in DMD?

Answer **Prophylactic Therapy (before LV dysfunction):** | Medication | Evidence | Timing | |------------|----------|--------| | **ACE inhibitor** | Class IIa | Start by age 10 (or at diagnosis if older) | | **ARB** | Alternative | If ACE-I intolerant | | **Beta-blocker** | Variable | Some centers add prophylactically | **This Patient's Current Therapy:** - Enalapril started at age 8 = appropriate prophylaxis - However, now has LV dysfunction requiring escalation **Treatment of Established Cardiomyopathy:** | Stage | Medications | |-------|-------------| | EF 45-55% (declining) | ACE-I/ARB + Beta-blocker | | EF <45% | ACE-I/ARB + Beta-blocker + consider aldosterone antagonist | | EF <35% or symptoms | Full heart failure therapy, advanced HF evaluation | **Evidence Base:** - ACE inhibitors shown to delay cardiomyopathy onset - Combination therapy may slow progression - Early treatment preserves function longer than waiting for symptoms

Question 5

What medication changes would you recommend for this patient?

Answer **Recommended Changes:** 1. **Add Beta-Blocker:** - Carvedilol 3.125mg BID, titrate up - OR Metoprolol succinate 12.5mg daily, titrate - Benefits: Reduce heart rate, improve remodeling, antiarrhythmic 2. **Increase ACE Inhibitor:** - Increase enalapril from 5mg BID to 10mg BID (if tolerated) - Monitor creatinine and potassium - Consider ARB switch if cough develops 3. **Consider Aldosterone Antagonist:** - Spironolactone 12.5-25mg daily - Evidence for cardiac fibrosis reduction - Monitor potassium closely 4. **Follow-up Plan:** - Recheck echo in 3-6 months - BNP trending - Consider cardiac MRI for tissue characterization **Goals:** - Stabilize or improve EF - Prevent symptomatic heart failure - Preserve quality of life **What to Avoid:** - Don't wait for symptoms - DMD patients often don't report dyspnea due to inactivity - Aggressive diuresis rarely needed early - NSAIDs (worsen renal/cardiac function)

Question 6

The family asks about his long-term cardiac prognosis. How do you counsel them?

Answer **Prognostic Counseling:** **General DMD Cardiac Timeline:** - Cardiomyopathy develops in nearly all patients by age 18 - Mean age of symptomatic HF: 15-20 years - Cardiac cause of death in ~40% (respiratory in ~40%) - With modern care, survival into 30s increasingly common **Positive Prognostic Factors for This Patient:** - Early prophylactic therapy initiated - Declining EF detected on surveillance (not by symptoms) - Opportunity to escalate before symptomatic HF **Honest Discussion Points:** - "We've caught a change in heart function early - this allows us to intensify treatment" - "With aggressive medical therapy, we can often stabilize or slow progression" - "Close monitoring allows us to adjust treatment as needed" - "The goal is to maintain quality of life and function as long as possible" **Advanced Care Planning:** - Discuss goals of care proactively - Palliative care involvement for symptom management - Transition planning for adult cardiology - Information about mechanical support and transplant (though challenging in DMD) **Hope with Realism:** - Gene therapy trials ongoing - Exon-skipping therapies may provide some cardiac benefit - Improved survival with comprehensive care

Key Teaching Points

  1. DMD ECG pattern is characteristic: tall R in V1, deep Q laterally, ST-T changes
  2. Start ACE inhibitors by age 10 regardless of cardiac function
  3. Annual surveillance mandatory after age 10 (more frequent if abnormal)
  4. Adolescence is high-risk period for rapid cardiac decline
  5. Don't wait for symptoms to escalate therapy - DMD patients underreport dyspnea
  6. Cardiac MRI valuable for detecting fibrosis before EF decline
  7. EF "normal" values may be misleading in non-ambulatory patients
  8. Multidisciplinary care (cardiology + pulmonology + neurology) essential

References

  • DMD Care Considerations Working Group. Lancet Neurol. 2022
  • Feingold B, et al. Circulation. 2017;136:e535-e578