Introduction:
Ventricular tachycardia (VT) carries a high risk of death and disease. The two mainstays of VT treatment, catheter ablation, and antiarrhythmic medication therapy, are still effective but have drawbacks. In oncology, stereotactic body radiation treatment (SBRT) is frequently utilized to accurately and effectively treat solid tumors that do not require surgery. The use of this method has recently been assessed for the management of VT.
What Is Arrhythmia?
Any irregularity in a person's heartbeat's rhythm or pace is referred to as an arrhythmia. An irregular heartbeat can be caused by electrical impulses that are too fast, too slow, or chaotic during an arrhythmia. The heart cannot pump blood efficiently when it is not beating correctly. This results in impaired function of the brain, lungs, and all other organs, which may cause harm or even death.
Ventricular tachycardia is a type of arrhythmia. When at rest, a healthy heart beats between 60 and 100 times per minute. The heart beats more quickly during ventricular tachycardia, typically at 100 beats per minute or higher.
What Is SBRT or Stereotactic Body Radiation Therapy?
A form of radiation therapy called stereotactic body radiotherapy (SBRT) uses specialized equipment to precisely administer a radiation dose to a tumor. Using the maximum radiation dose possible to eradicate cancer while causing the least amount of harm to the neighboring tissues and organs is the goal of SBRT. This method of radiation therapy is emerging as a new treatment for ventricular arrhythmias and for those who are at risk of refractory ventricular tachycardia. If catheter ablation fails to treat recurrent VT, SBRT may offer an alternative treatment option.
What Are the Steps Involved in Stereotactic Body Radiation Therapy for Arrhythmias?
SBRT minimizes the number of treatments needed for a successful course of treatment by delivering maximum radiation per fraction to a precisely specified target. Accurate imaging and sophisticated treatment planning procedures are required to create a precise dose pattern surrounding the intended area with rapid dose decline in neighboring healthy tissue since SBRT typically has a greater dosage per fraction. Multiple beam angles are selected to minimize exposure at entry sites and nearby structures and maximize interaction at the PTV (planned target volume). This minimizes off-target exposures while enabling a highly targeted and customized radiation dose to reach the target spot.
Methods for Managing Motion:
One of the biggest obstacles to precise radiation administration is physiological mobility. Motion compensation can be achieved in three ways: gating, target tracking, and immobilization. There are two types of immobilization: passive and active. One form of passive immobilization is retaining one's breath; a different kind of active immobilization is compressing one's abdomen to prevent diaphragmatic mobility. Gating employs a marker to track target mobility during respiration and cardiac cycles.
Because cardiac structures exhibit physiologic motions related to respiratory inspiration, expiration, contraction, and relaxation, motion tracking, and immobilization are essential for SBRT targeting myocardial tissue. Moreover, nearby structures that could be exposed to radiation are also moving.
In clinical SBRT operations, two primary categories of stabilization devices have been employed. A foam cushion combined with abdominal compression or a cushion shaped to the patient's body with the help of a vacuum.
Mapping and Imaging the Substrate of Arrhythmias:
For VT radiation to be safe and effective, the arrhythmic substrate must be localized first. Ventricular arrhythmias can be localized using a variety of techniques, and they can be correlated with existing cardiac imaging studies. To create and map the arrhythmia, some centers use non-invasive electrocardiogram (ECG) imaging (ECGi) with a harness that the individual puts on undergoing planned activation through a preexisting implanted cardiac implantable electronic device (CIED).
To assess respiratory motion, the patient receives a four-dimensional computed tomography (CT) scan and a CT simulation scan. The reference data is then integrated with these images, and radiation doctors analyze the results to determine the gross target volume on the simulation images. After that, the planning target volume (PTV) is produced. To account for motion and other uncertainties, the PTV is usually expanded somewhat beyond the target zone. The radiation therapy strategy is designed to minimize the exposure of organs at risk while providing PTV with the recommended radiation dose.
Radiation technicians assist in fitting patients with body stabilization units and securing them. Next, the SBRT process is carried out. The current SBRT protocols allow for a maximum of one session with an average beam-on time of under 20 minutes. It is currently unknown what the ideal radiation dosage is for VT substrate ablation. Administering 25 to 35 Gy (gray) as a single portion reduced arrhythmia. This dosage has consistently been linked to late-stage cardiac fibrosis without electrical activity.
What Are the Adverse Effects of SBRT?
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Some individuals experience weariness one to three days after therapy.
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In some individuals, a CT scan revealed inflammatory lung alterations that were in line with pneumonitis (lung inflammation) brought on by radiation.
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Some may experience pericarditis and deteriorating heart failure after SBRT.
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A few may experience nausea associated with acute radiation poisoning.
Why Is SBRT Used to Treat High-Risk Arrhythmias?
When high-risk cardiac patients receive a single high dosage of radiation therapy, their episodes of rapid, irregular heartbeats can be significantly reduced for almost two years, providing hope to individuals who are already out of other treatments.
An implanted cardioverter defibrillator (ICD) is typically placed on individuals who have survived VT or who are in danger of experiencing it. ICD shocks can save lives, but when they happen frequently over an extended period, they hurt and have a negative impact on quality of life. Catheter ablation is a common treatment for patients with recurrent VT. This procedure is not so effective in VT since there are chances of recurrence of VT and death after the procedure.
Experts developed a technique called electrophysiology-guided noninvasive cardiac radio ablation. This innovative treatment combines imaging and electrical (electrocardiogram) data to identify the specific scar tissue in the patient's heart that is causing the arrhythmias. A single administration of stereotactic body radiation therapy (SBRT), a kind of high-dose radiation, is then administered to target the intended scar tissue.
Conclusion:
An innovative treatment for ventricular arrhythmias with a lot of promise is SBRT. It seems like a non-invasive, efficient solution. More investigation and clinical experience are necessary in randomized clinical trials, considering the novelty of this technology and the absence of prospective clinical data with scant long-term follow-up.
