This study will evaluate the acute effect of ultrasound-navigated left ganglion stellate block to suppress ventricular arrhythmia in patients with arrhythmic storm.

• The study will include patients with drug-refractory arrhythmic storm indicated for left ganglion stellate block (LGSB) before or after catheter ablation.
• Included participants will be dived based on the need for mechanical ventilation and catheter ablation performed <5 days before the study
• Subsequently, the participants will be randomized to LGSB or to a sham (placebo) procedure.
• The primary endpoint will be a reduction of the burden of clinical arrhythmia >50% 24 hours after LGSB without escalation of antiarrhythmic therapy.
• The study will include 80 patients over 4 years.

Inclusion Criteria:

1. arrhythmic storm <24 hours before inclusion:

   • 3 or more episodes of sustained ventricular tachycardia (VT) or ventricular fibrillation (VF) terminated by external or internal shock,
   • or incessant VT lasting >30 minutes,
   • or very frequent nonsustained or sustained VT leading to hemodynamic instability with the need of escalation of the therapy

2. clinical indication for LBGS based on the judgment of the physician, independent of the study

Exclusion Criteria:

1. known allergy to bupivacaine
2. prior LBGS performed <7 days before the study
3. known reversible provoking trigger of the arrhythmias
4. ventricular arrhythmias triggered by premature ectopic beats during bradycardia
5. hemodynamically tolerated idiopathic VT in patients without structural heart disease

Patients, attending staff, and outcome assessors will not know whether the patient received the actual LGSB or a sham (placebo) procedure. The sham procedure will consist of subcutaneous application of a small amount (1ml) of the local anesthetic drug to the region of expected LGSB procedure.