What is the significance of an adult patient with structurally normal myocardium, valve structure, and function presenting with episodic symptomatic accelerated ventricular rhythm?

Clinical Significance of Episodic Symptomatic Accelerated Ventricular Rhythm in Structurally Normal Hearts

In an adult patient with structurally normal myocardium and episodic symptomatic accelerated ventricular rhythm, this represents a generally benign condition that typically requires only clinical follow-up without treatment, though symptomatic cases warrant evaluation to exclude emerging cardiomyopathy and consideration of beta-blocker therapy or catheter ablation if symptoms are significant. 1

Prognostic Significance and Natural History

Accelerated idioventricular rhythm (AIVR) in structurally normal hearts is fundamentally benign. 1 The 2015 ESC Guidelines explicitly state that accelerated ventricular rhythm in otherwise healthy individuals "is a benign arrhythmia and, similar to PVCs in infants, generally disappears without treatment." 1 This applies across age groups, though the guideline specifically addresses pediatric populations where the rhythm is most commonly documented as an incidental finding. 1

The mechanism involves enhanced automaticity from an ectopic ventricular focus, typically originating from the His-Purkinje system or ventricular myocytes, with rates between 60-120 beats per minute (just above the intrinsic ventricular escape rate but below typical ventricular tachycardia rates). 1, 2

Critical Diagnostic Considerations

The presence of symptoms mandates thorough evaluation to exclude three important scenarios:

1. Emerging Cardiomyopathy from Arrhythmia Burden

• Very frequent ventricular ectopy (>10,000-20,000 beats per day) can cause reversible left ventricular dysfunction, termed "PVC-induced cardiomyopathy." 1
• Even "benign" AIVR can result in impaired left ventricular function when sustained or frequent. 2, 3
• One case series documented that 3 of 8 patients with right bundle branch AIVR/VT had impaired left ventricular function that normalized after treatment. 2
• Cardiac evaluation including CMR and assessment of ventricular function is recommended when ventricular arrhythmias are frequent or symptomatic. 1

2. Misdiagnosis of Underlying Structural Disease

• Distinguish AIVR in truly normal hearts from early arrhythmogenic cardiomyopathy, where RVOT arrhythmias may be the initial presentation. 1
• The European Association of Cardiovascular Imaging emphasizes that "the distinction to RVOT-VT may be challenging" in early arrhythmogenic cardiomyopathy, and "the treatment and prognosis differ substantially." 1
• Any findings of regional RV hypokinesia, dyskinesia, or RVOT dilatation by echocardiography or CMR make arrhythmogenic cardiomyopathy more probable and prognosis more severe. 1
• Family history is typically negative in benign RVOT-VT but may be positive in inherited cardiomyopathies. 1

3. Rare Trigger for Malignant Arrhythmias

• Very rarely, idiopathic PVCs from the outflow tract may trigger malignant ventricular arrhythmias even in patients without structural heart disease. 1
• Two patients in one series with RBB-AIVR experienced syncope, indicating potential for hemodynamic compromise. 2

Management Algorithm

Initial Evaluation

• Comprehensive echocardiography to confirm truly normal ventricular structure and function 1
• 12-lead ECG to characterize arrhythmia morphology and exclude other abnormalities 1
• 24-hour Holter monitoring to quantify arrhythmia burden 1
• Exercise testing to assess for exercise-induced arrhythmias or ischemia 1
• Family history assessment to exclude inheritable channelopathies or cardiomyopathies 1
• Consider cardiac MRI if any suspicion of subtle structural abnormalities, particularly involving the right ventricle 1

Treatment Decisions Based on Symptoms and Burden

For Asymptomatic or Minimally Symptomatic Patients:

• Follow-up without treatment is the recommended approach. 1
• The ESC Guidelines give a Class I, Level B recommendation that "asymptomatic children with frequent isolated PVCs or an accelerated ventricular rhythm and normal ventricular function be followed-up without treatment." 1
• Serial monitoring to identify development of LV dysfunction or progression to sustained VT 1

For Symptomatic Patients:

• Beta-blockers represent first-line pharmacologic therapy. 2
• Metoprolol was "proven to be the most effective drug to decelerate the arrhythmia rate and relieve symptoms" in patients with RBB-AIVR/VT. 2
• Beta-blockers are preferred over other antiarrhythmics due to "important proarrhythmic effects and long-term toxicity of other agents." 1

For Refractory Symptomatic Cases or Arrhythmia-Induced Cardiomyopathy:

• Catheter ablation is highly effective and curative. 2, 3
• Ablation should be performed at experienced centers, particularly in younger patients where there are concerns about lesion growth in developing myocardium. 1
• One case series showed successful ablation with normalization of left ventricular function in patients who had developed cardiomyopathy. 2, 3
• In young children, catheter ablation is only indicated as second-line therapy after failed medical management. 1

Common Pitfalls to Avoid

Do not dismiss symptoms without quantifying arrhythmia burden. Even "benign" rhythms can cause cardiomyopathy if the burden is high enough (>10-20% of total beats). 1

Do not assume structural normality based on echocardiography alone. Cardiac MRI may be necessary to exclude subtle right ventricular abnormalities suggestive of early arrhythmogenic cardiomyopathy. 1

Do not confuse AIVR with ventricular tachycardia requiring urgent intervention. AIVR has gradual onset/termination and rates typically <120-130 bpm, whereas VT is abrupt with rates usually >150 bpm. 1

Do not use verapamil in infants <1 year of age as it may cause acute hemodynamic deterioration. 1

Recognize that high arrhythmia burden (>9000 VPCs per 24 hours) in the absence of severe structural alterations increases probability of benign RVOT-VT rather than arrhythmogenic cardiomyopathy. 1