A 52-year-old woman with a 10-year history of diabetes and hypertension presents with recurrent episodes of palpitations lasting 30 seconds to 2 minutes, occurring 3–4 times daily. She denies syncope or chest pain. Vital signs are normal. ECG during sinus rhythm shows left ventricular hypertrophy. A 24-hour Holter monitor reveals 47 episodes of wide complex tachycardia with a rate of 160–180 bpm, each lasting <2 minutes and terminating spontaneously. Echocardiography shows an ejection fraction of 52% with concentric LVH. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** This patient has recurrent, monomorphic, hemodynamically tolerated VT in the setting of structural heart disease (LVH from hypertension and diabetes). The key discriminator is the presence of an identifiable substrate (scar/fibrosis) rather than a primary electrical disorder. ## Differential Diagnosis of Monomorphic VT | Feature | Scar-Related Reentry | Fascicular VT | LVOT VT | Polymorphic VT | |---------|---------------------|---------------|---------|----------------| | **Substrate** | Scar/fibrosis from MI or cardiomyopathy | Fascicles of left anterior fascicle | Structurally normal heart | Electrical abnormality (QT↑, Brugada) | | **Structural disease** | Present (EF ↓ or wall motion) | Rare; normal EF | Absent; normal EF | Variable | | **Morphology** | Monomorphic | Monomorphic (RBBB, LAFB) | Monomorphic (RBBB, LPFB) | Polymorphic, changing axis | | **Hemodynamics** | Tolerated or unstable | Usually tolerated | Tolerated | Often unstable | | **Response to adenosine** | No response | Sensitive (terminates) | Sensitive (terminates) | No response | | **Mechanism** | Macro-reentry around scar | Micro-reentry within fascicle | Triggered activity (DAD) | Triggered or reentry | ## Why Scar-Related Reentry? **High-Yield:** The clinical clues are: 1. **Structural substrate present:** LVH from chronic hypertension and diabetes creates areas of fibrosis and scar. 2. **Monomorphic morphology:** All 47 episodes are similar (same re-entrant circuit). 3. **Hemodynamically tolerated:** EF 52% (preserved) allows tolerance of VT without syncope. 4. **Age and comorbidities:** 52 years with DM + HTN = high likelihood of myocardial fibrosis even without prior MI. 5. **Frequency and duration:** Recurrent, short bursts are typical of scar-related macro-reentry. **Clinical Pearl:** Hypertension and diabetes cause diffuse myocardial fibrosis and microvascular ischemia, creating a substrate for re-entrant VT even without overt MI or reduced EF. ## Why Not the Other Options? **Fascicular VT:** - Occurs in young, structurally normal hearts (this patient has LVH). - Highly sensitive to adenosine (would terminate, aiding diagnosis). - Rare in patients >50 years with hypertension. **LVOT VT:** - Requires a structurally normal heart (this patient has LVH). - Sensitive to adenosine and beta-blockers. - Typically presents in younger patients without comorbidities. **Polymorphic VT:** - ECG shows monomorphic complexes, not changing morphology. - Associated with QT prolongation, Brugada, or catecholaminergic triggers—not mentioned here. - Holter would show varying QRS axis; this case describes uniform episodes. ## Management Implications ```mermaid flowchart TD A[Monomorphic VT + Structural Disease]:::outcome --> B[Scar-Related Reentry]:::outcome B --> C{EF Assessment}:::decision C -->|EF ≤35%| D[ICD + Antiarrhythmic]:::action C -->|EF >35%| E[Antiarrhythmic ± Ablation]:::action D --> F[Reduce sudden cardiac death risk]:::outcome E --> G[Symptom control + risk stratification]:::outcome ``` **Next steps:** - Stress test to exclude inducible ischemia. - Consider cardiac MRI to identify scar pattern. - Initiate beta-blocker (first-line for scar-related VT). - If recurrent despite beta-blocker, consider amiodarone or catheter ablation. - Reassess EF; if it declines to ≤35%, ICD is indicated. [cite:Harrison 21e Ch 226]