August 29, 2025

425. Case Report: The Hidden Culprit – Unraveling the Cause of Malignant Ventricular Arrhythmias in a Young Adult – Trinity Health Livonia Hospital

54 minutes

CardioNerds guest host Dr. Colin Blumenthal joins Dr. Juma Bin Firos and Dr. Aishwarya Verma from the Trinity Health Livonia Hospital to discuss a fascinating case involving malignant ventricular arrhythmias. Expert commentary is provided by Dr. Mohammad-Ali Jazayeri. Audio editing for this episode was performed by CardioNerds Intern,Julia Marques Fernandes.

This case explores the puzzling presentation of exercise-induced ventricular tachycardia in a young, otherwise healthy male who suffered recurrent out-of-hospital cardiac arrests. With no traditional risk factors and an unremarkable ischemic workup, the challenge lay in uncovering the underlying cause of his malignant arrhythmias. Electrophysiology studies and advanced imaging played a pivotal role in systematically narrowing the differentials, revealing an unexpected arrhythmogenic substrate. This episode delves into the diagnostic dilemma, the role of EP testing, and the critical decision-making surrounding ICD placement in a patient with a concealed but life-threatening condition.

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Pearls- Malignant Ventricular Arrhythmias

This case highlights the challenges and importance of diagnosing and managing ventricular arrhythmias in young, seemingly healthy individuals. Here are five key takeaways from the episode:

Electrophysiology (EP) studies play a crucial role in identifying arrhythmogenic substrates in patients with exercise-induced ventricular tachycardia (VT) without obvious structural heart disease. In this case, substrate mapping revealed late abnormal ventricular afterdepolarizations in the basal inferior left ventricle, providing valuable insights into the underlying mechanism.

Cardiac MRI can be a powerful tool for detecting subtle myocardial abnormalities. The subepicardial late gadolinium enhancement (LGE) in the lateral and inferior LV walls suggested an underlying myocardial process, even when other imaging modalities appeared normal.

The VT morphology can provide clues about the underlying mechanism. In this case, the right bundle branch block pattern with a northwest axis and shifting exit sites pointed towards a scar-mediated mechanism rather than a channelopathy or idiopathic VT.

Implantable cardioverter-defibrillator (ICD) placement is crucial for secondary prevention of sudden cardiac death (SCD) in patients with malignant ventricular arrhythmias, even in young individuals. The patient's initial deferral of ICD implantation highlights the importance of shared decision-making and patient education in these complex cases.

"Scar-mediated VT introduces the risk of new arrhythmogenic substrates over time, reinforcing the need for ICD therapy even when catheter ablation is considered." This pearl emphasizes the dynamic nature of the arrhythmogenic substrate and the importance of long-term risk mitigation strategies.

Notes - Malignant Ventricular Arrhythmias

Notes were drafted by Juma Bin Firos.

1. What underlying pathologies cause ventricular arrhythmias in young patients without overt structural heart disease?

Myocardial fibrosis:

Detected via late gadolinium enhancement (LGE) on cardiac MRI

Present in 38% of nonischemic cardiomyopathy cases

Increases sudden cardiac death (SCD) risk 5-fold

Often localized to subepicardial regions, particularly in the inferolateral left ventricle (LV)

May precede overt systolic dysfunction by years

Subclinical cardiomyopathy:

67% of young VT patients show subtle cardiac dysfunction

Suggests VT may be the first manifestation of cardiomyopathy

Can include early-stage genetic cardiomyopathies (e.g., ARVC, LMNA mutations)

Often associated with preserved ejection fraction (EF >50%)

Arrhythmogenic substrate:

EP studies localize re-entry circuits to specific regions:

Basal inferior LV near the mitral annulus (as in this case)

Right ventricular outflow tract (RVOT) in idiopathic VT

Papillary muscles or fascicular regions

Substrate can exist even with normal EF and no visible structural abnormalities on echocardiography

Channelopathies:

Long QT syndrome (LQTS): QTc >460ms in males, >470ms in females

Brugada syndrome: Coved ST elevation in V1-V3

Catecholaminergic polymorphic VT (CPVT): Normal resting ECG, bidirectional VT with exercise

Short QT syndrome: QTc <330ms

Inflammatory conditions:

Myocarditis: Can cause transient or persistent arrhythmogenic substrate

Cardiac sarcoidosis: Patchy inflammation and fibrosis, often affecting the septum

2. How do electrophysiology studies differentiate scar-mediated VT from channelopathies?

Substrate mapping:

Identifies late abnormal potentials (LAPs) with 92% specificity for re-entry circuits

Utilizes multi-electrode catheters (e.g., Penta Ray) for high-density mapping

LAPs indicate slow conduction through fibrotic tissue, key for re-entry

Absent in purely electrical disorders like channelopathies

Inducibility:

Programmed electrical stimulation (PES) protocols:

Up to triple extra stimuli at multiple sites (RV apex, RVOT, LV)

Burst pacing at cycle lengths down to 200-250ms

Scar-mediated VT is often inducible with aggressive stimulation

Polymorphic VT/VF induction suggests a structural substrate

Channelopathies like Catecholaminergic polymorphic ventricular tachycardia CPVT) typically requires isoproterenol or exercise for induction

VT morphology analysis:

Right bundle branch block (RBBB) + northwest axis localizes to LV basal inferior wall

Left bundle branch block (LBBB) + inferior axis suggests RVOT origin

Fascicular VT: RBBB + left anterior or posterior fascicular block pattern

Papillary muscle VT: RBBB or LBBB with variable axis

Entrainment mapping:

Performed during sustained monomorphic VT

Post-pacing interval minus tachycardia cycle length (PPI-TCL) <30ms indicates critical isthmus

Not applicable to polymorphic VT or channelopathies

Electroanatomic voltage mapping:

Low voltage areas (<1.5mV bipolar) indicate scar tissue

Normal voltage throughout suggests functional (non-scar) VT mechanism

3. What are key management considerations for recurrent VT/VF in young patients?

ICD for secondary prevention:

Class I indication after cardiac arrest or sustained VT without a reversible cause

Reduces mortality from 13% (8-year untreated) to <5%, especially with LGE present

Device selection:

Single-chamber ICD if no pacing indication

Subcutaneous ICD (S-ICD) in young patients to avoid transvenous lead complications

Consider cardiac resynchronization therapy defibrillator (CRT-D) if LBBB or wide QRS

LifeVest limitations:

Bridges ≤3 months; not a long-term solution

Recurrent arrests double mortality vs. prompt ICD implantation

Compliance issues: must be worn consistently to be effective

Oral antiarrhythmic medications:

Amiodarone:

Effective for acute VT suppression

Long-term use limited by side effects (thyroid, liver, pulmonary toxicity)

Beta-blockers: First line for most VT/VF, especially exercise-induced

Sotalol: Alternative for those with preserved LV function

Mexiletine: Adjunct for frequent ICD shocks, especially with LQT3

Catheter ablation:

Consider early in the course for recurrent ICD shocks

Success rates 60-80% for scar-related VT

May reduce ICD shocks and improve quality of life

Limitations: deep intramural or epicardial substrates may require specialized approaches

Lifestyle modifications:

Exercise restrictions: Avoid high-intensity activities that trigger arrhythmias

Stress management: Consider cognitive behavioral therapy or mindfulness training

Avoidance of QT-prolonging medications in LQTS patients

Genetic testing and family screening:

Recommended for suspected inherited arrhythmia syndromes

Can guide management and risk stratification for family members

4. Why does exercise exacerbate arrhythmia risk in these patients?

Sympathetic surge:

Increases myocardial oxygen demand

Enhances automaticity and triggered activity

Can unmask concealed conduction abnormalities

Hemodynamic changes:

Increased preload and afterload stress fibrotic regions

Volume shifts may alter electrolyte concentrations locally

Metabolic factors:

Lactic acid accumulation can promote ectopic beats

Catecholamine release exacerbates ion channel dysfunction in channelopathies

Exercise-induced VT/VF correlates with 8× higher SCD risk vs. rest-onset arrhythmias:

Warrants activity restrictions tailored to individual risk profile

May indicate more malignant substrate or advanced disease process

Treadmill testing:

Should guide therapy in asymptomatic patients with exercise-related VT

Protocols:

Bruce protocol for general assessment

Modified protocols (e.g., longer stages) for specific arrhythmia provocation

Endpoints:

Induction of sustained VT/VF

Achieving target heart rate (85% of age-predicted maximum)

Development of concerning symptoms (pre-syncope, chest pain)

Cardiac rehabilitation:

Supervised exercise programs can improve outcomes

Gradual increase in intensity with continuous monitoring

Helps define safe exercise thresholds for patients

5. How does LGE on cardiac MRI refine risk stratification?

Late gadolinium enhancement (LGE) on cardiac MRI acts like a "scar map" of the heart, revealing areas of damaged or fibrotic tissue. These scars create electrical instability,

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