History

The concept of treating heart problems with sympathetic blockade has been around for over a century. This was first demonstrated in 1916 with surgical treatment of angina through left cardiac sympathetic denervation (LCSD), a surgical technique that permanently severs sympathetic innervation to the heart.¹ Decades later, LCSD was discovered to reduce the incidence of ventricular fibrillation (VF) during controlled coronary artery occlusion experiments in dogs.² Left stellate ganglion block (LSGB), a percutaneous injection of local anesthetic that temporarily interrupts sympathetic stimulation to the heart, evolved from LCSD and was first reported in 1971 in a patient with long QT syndrome suffering from recurrent VF.³ In 1976, ventricular arrhythmias following brief coronary artery occlusions in dogs were revealed to be substantially decreased with LSGB, and increased with right stellate ganglion block.⁴ This asymmetric response to unilateral stellate ganglion blockade was replicated with experiments on the human heart in 1985.⁵ The clinical effectiveness of LSGB was then demonstrated in a patient with recurrent ventricular fibrillation following myocardial infarction (MI).⁶ LSGB was later recognized as an important adjunctive therapy for the treatment of electrical storm.⁷

Background

Electrical storm is defined as the occurrence of at least three ventricular arrhythmias leading to defibrillation or antitachycardia pacing within 24 hours.⁸ Scar-mediated reentry due to a previous MI is the most common cause, although reversible triggers include ischemia, decompensated heart failure, and electrolyte disturbances. Electrical storm can occur in as many as 10% to 20% in patients with implantable cardioverter-defibrillators (ICDs) placed for secondary prevention, and is associated with significant morbidity and mortality. The development of ventricular arrhythmias marks a progression of underlying structural heart disease, with electrical storm being an independent predictor of mortality that is highest during the first three months after onset.⁹ Unfortunately, electrical storm is usually accompanied by a sympathetic surge often resistant to antiarrhythmic drug therapy, necessitating sympathetic blockade.¹⁰

Sympathetic blockade can be achieved centrally through propofol infusion or via thoracic epidural anesthesia.^11,12 In contrast, targeted injection of local anesthetic near the left stellate ganglion provides sympathetic blockade at the periphery. A similar result can be achieved through an infusion of ropivacaine through a continuous nerve block catheter.^13,14 Short-acting anesthetics such as lidocaine or xylocaine may suppress ventricular arrhythmias for several hours, although longer-acting anesthetics such as mepivacaine or bupivacaine can effectively suppress ventricular arrhythmias for days to weeks.^6,7,15,16 The lasting effect of longer-acting anesthetics may be linked to hemodynamic and metabolic recovery, increasing the threshold for developing ventricular arrhythmias. Termination of electrical storm by LSGB can also stabilize a patient long enough to perform a catheter ablation of a ventricular arrhythmic focus. Alternatively, LSGB can serve as a therapeutic test for suitability for LCSD in patients with refractory ventricular arrhythmias.¹⁰ Unfortunately, sympathetic blockade remains underutilized due to a lack of awareness and understanding of the efficacy and duration of effect.¹⁷

Supporting Evidence

The left and right stellate ganglia provide the majority of the sympathetic innervation to the heart via post-ganglionic fibers, although the left stellate ganglion is quantitatively dominant at the ventricular level.¹⁸ MI may lead to partial denervation of these fibers at the level of the myocardium and paradoxically induce a supersensitivity to catecholamines, making the heart more vulnerable to the electrical induction of ventricular arrhythmias.¹⁹ Sympathetic denervation counteracts this pathologic process by reducing the amount of norepinephrine released at the ventricular level and increasing the ventricular fibrillatory threshold.¹⁸ Coronary vasodilation and vagal stimulation to the heart are also increased. In addition, the QT interval is regulated by cardiac sympathetic innervation; shortening of the QT interval occurs with LSGB whereas lengthening of the QT interval occurs with right stellate ganglion block.²⁰

The benefits of sympathetic blockade in reducing the burden of ventricular arrhythmias have been clearly demonstrated with LCSD in patients following MI and also in patients with long QT syndrome.^21,22 LCSD has also been shown to be effective in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT).²³ In contrast, limited evidence is available concerning the clinical benefits of LSGB in the management of electrical storm aside from case reports. In a prospective study of 49 patients with electrical storm, sympathetic blockade via beta blocker or LSGB followed by oral amiodarone was compared to class I antiarrhythmic therapy.⁷ Out of the 27 patients who were treated with sympathetic blockade, 6 patients underwent LSGB. The one-week survival for the sympathetic blockade group was 77.8%. In a recent series of 8 patients with refractory electrical storm who received adjunctive LSGB through ropivacaine infusion (2 of which also received thoracic epidural anesthesia), 6 patients experienced significant reductions in the number of sustained ventricular arrhythmias.¹⁴ Electrical storm recurred within 24 hours in 3 patients, 2 of which responded to repeated LSGB. Only 1 patient died secondary to arrhythmia.

Anatomic Considerations

The stellate ganglion, also known as the cervicothoracic ganglion¬, comprises a fusion of the inferior cervical and first thoracic ganglia within the sympathetic chain, present in 80% of the population.²⁴ It is located anterior to the neck of the first rib extending to the body of the C7 vertebra. It lies anterior to the longus colli muscle, which covers the transverse process. Nearby structures at risk for injury include the esophagus medially, the common carotid artery, jugular vein, and vagus nerve laterally, and the thyroid, inferior thyroid vessels, and recurrent laryngeal nerve anteriorly. The vertebral artery is also anterior to the stellate ganglion at the C7 level, making it prone to injury before entering the transverse foramen of C6 (or, less commonly, C5) as it ascends through the neck, posterior to the sympathetic chain. The risk of pneumothorax is also higher at the C7 level.

Current Procedural Approach

LSGB is indicated in patients with electrical storm in the setting of structural heart disease or ongoing myocardial ischemia, though it may also be considered in patients with CPVT or idiopathic ventricular tachycardia. Anesthesiologists with experience in performing nerve blocks are best-suited to perform this procedure, although it may also be performed by clinicians who have a working knowledge of cervical anatomy. LSGB can be performed using a blind paratracheal approach or under fluoroscopic or ultrasound guidance. Although fluoroscopy is helpful for identifying bony structures, ultrasound is preferred because visualization of the needle path helps to avoid injury to nearby structures.²⁴ Ultrasound-guided LSGB can also be readily performed at the bedside using a linear array transducer. The patient should be placed supine with the neck slightly extended. The thyroid cartilage should be palpated, followed by the cricoid cartilage inferiorly, which is at the C6 vertebral level. In the groove lateral to the trachea on the left side is a bony prominence which is Chassaignac's tubercle (or carotid tubercle). This constitutes the anterior surface of the C6 transverse process, which is the target for injection of local anesthetic.

After sterilizing the skin and applying ultrasound gel, an ultrasound probe should be placed on the cricoid cartilage in the transverse position, perpendicular to the trachea and moved laterally as needed for adequate visualization of structures. Color Doppler should be enabled to identify arteries and veins. On the ultrasound image, Chassaignac's tubercle can be identified as a ridge at the level of C6, which flattens out at the level of C7 if the ultrasound probe is moved caudally. After anesthetizing the overlying skin, a 2.5 cm 25 gauge needle should then introduced at the C6 level under ultrasound guidance. The needle should be directed toward the longus colli muscle overlying Chassaignac's tubercle, following an oblique path medial to the common carotid artery and jugular vein. Local anesthetic should be injected just anterior to the longus colli muscle. Only 5 to 7 mL of either 0.25% or 0.5% bupivacaine is required to achieve adequate block of the left stellate ganglion through local spread of anesthetic with this targeted approach.^10,16,24-26

Ipsilateral Horner syndrome may develop following stellate ganglion block, presenting with ipsilateral ptosis and miosis. This suggests that the fibers traversing the upper part of the stellate ganglion are blocked; however, this does not necessarily indicate effective sympathetic blockade to the heart.¹⁸ Recurrent laryngeal nerve block may also occur due to anterior spread of local anesthetic and present as transient hoarseness, although this has been associated with larger volumes of bupivacaine (10-20 mL).²⁷

Conclusion

LSGB is an effective method for terminating electrical storm. When patients do not respond to the traditional approaches of beta blocker and amiodarone therapy, LSGB should be considered as an adjunctive therapy to stabilize the patient and to prevent repeated ICD shocks. Given the increased mortality associated with electrical storm, patients with advanced structural heart disease who develop recurrent ventricular arrhythmias should be referred for advanced heart failure therapies, such as left ventricular assist device implantation and heart transplantation. Ultrasound guidance is helpful for safely performing LSGB at the bedside and should be used whenever possible. Increasing awareness and experience among cardiologists will allow more patients suffering from acute electrical storm to benefit from this procedure.

References

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Keywords: Arrhythmias, Cardiac

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