Arrhythmic storm is a real emergency and its treatment could be challenging. Antiarrhythmic drugs are few and often ineffective. Neuromodulation has been grown in evidences but no large multicentric studies are present in literature about safety and effectiveness of Percutaneous Stellate Ganglion Block (PSGB). Patients with an electrical storm refractory to at least one antiarrhythmic drug will receive PSGB and will be enrolled in the present study.

The number of defibrillations before and after the treatment will be compared, complications will be annotated.

This is an international multicenter observational retrospective and prospective short term (24 hours) longitudinal study, promoted and coordinated by the Fondazione IRCCS Policlinico San Matteo of Pavia (Italy).

Materials and methods:

All the patients who will meet the inclusion criteria will be enrolled in the study. Conscious patients with a sufficient free interval between arrhythmic relapses will sign the informed consent for the procedure and for data collection (attached at the study protocol) before the procedure. In case of unconscious patients the medical doctor will perform the procedure being in an emergency situation and the inform consent for data collection will be signed afterward once possible.

Inclusion criteria:

All the patients presenting with an arrhythmic storm defined as more than three sustained ventricular arrhythmias in 24 hours refractory to the standard medical treatment.

Exclusion criteria:

• A previous history of cardiac sympathicectomy
• Having a neck judged by the doctor as non-suitable for the procedure (previous neck surgery, previous burns, presence of large scars, thyroid goiter)

PSGB technique:

Both the two approaches present in literature and commonly used for this technique are allowed for the study:

• The "anatomical" approach which consist in the identification of the Chassaignac's tubercle that represents the point of needle insertion
• The "echo-guided" approach Regardless to the approach (anatomical or echo-guided) the doctor will be able to choose, according to the clinical characteristics of the patients, whether to perform a single shot injection of anesthetic or a continuous infusion of anesthetic. In the second case a catheter will be left in place and connected to an infusion pump.

Study Objectives:

The primary objective is the effectiveness of the PSGB expressed by the reduction of arrhythmic relapses [number of Direct Current (DC) shocks or Anti-Tachycardia Pacing ATP] in the 12 hours immediately after the PSGB as compared to the 6 hours immediately preceding the PSGB of at least 50%.

The secondary objectives are:

1. The comparison of the number of shocks 12h before and 12h after the procedure

2. The feasibility of the procedure expressed as the number of complications within 12 hours from the procedure. The following complications will be considered:

   • Simple hematoma
   • Symptoms due to anesthetic absorbance
   • Hematoma requiring intervention
   • Intravascular injection without complication
   • Intravascular injection with complication
   • Brachial plexus damage
   • Simple vascular damage
   • Vascular damage requiring intervention

3. The comparison of the effectiveness endpoint in patients with and without the appearance of anisocoria

4. The comparison of effectiveness between patients who will receive "anatomical" PSGB and those who will receive echo-guided PSGB

5. The comparison of effectiveness between patients who will receive anaesthetic infusion in the site of PSGB as compared to those who will not.

Statistics:

Sample size: The investigators plan to enroll patients satisfying the inclusion/exclusion criteria over a time horizon of 5 years. Based on our previous experience over the previous 18 months (enrollment of 8 patients) about 5 patients per year are though to be enrolled, thus reaching a sample size 33 patients in the Pavia Center. The success is effectiveness to be not less then 90%, based on our historical cohort. This will yield a confidence interval of 76% to 98%, corresponding to a precision of 11%. Also, with this sample size it will be able to exclude an effectiveness of 70% (considered as the lower bound of acceptability) with a power of 94% (alpha 2-sided 5%).

With the inclusion of further centers, the increased sample size will allow an increased precision of the estimates; for instance for 100 patients precision would be 6.5% (first step already achieved) and for 500 patients would be 2.6%.

Statistical analysis: Data will be described with the mean and standard deviation or the median and 25th-75th percentile if continuous and counts and percent if categorical.

For the analysis of the primary endpoint the rate of effectiveness together with its 95% exact binomial confidence interval will be computed.

Data management:

Data will be collected using the REDCap platform (e-CRF). A personal and password protected account will be created for each investigator who will be able to access only to the data from his/her Center.

Inclusion Criteria:

• age ≥ 18 years,
• presence of arrhythmic storm defined as more than three sustained ventricular arrhythmias in 24 hours refractory to the standard medical treatment.

Exclusion Criteria:

• A previous history of cardiac sympathicectomy
• Having a neck judged unsuitable for the procedure (previous neck surgery, previous burns, presence of large scars, thyroid goiter)

Both the two approaches present in literature and commonly used for this technique are allowed for the study:

• The "anatomical" approach which consist in the identification of the Chassaignac's tubercle that represents the point of needle insertion
• The "echo-guided" approach Regardless to the approach (anatomical or echo-guided) the doctor will be able to choose, according to the clinical characteristics of the patients, whether to perform a single shot injection of anesthetic or a continuous infusion of anesthetic. In the second case a catheter will be left in place and connected to an infusion pump.

All the patients who will meet the inclusion criteria will be enrolled in the study. Conscious patients with a sufficient free interval between arrhythmic relapses will sign the informed consent for the procedure and for data collection (attached at the study protocol) before the procedure. In case of unconscious patients the medical doctor will perform the procedure being in an emergency situation and the inform consent for data collection will be signed afterward once possible.

every study site will be able to have data regarding their patients