Supraventricular tachycardia (SVT) is a rapid, abnormal heart rhythm that originates in the upper chambers of the heart, or atria, causing sudden episodes of very fast heartbeats. Catheter ablation is a common, minimally invasive procedure used to treat SVT by targeting and interrupting the specific short-circuiting electrical pathways responsible for the arrhythmia. The initial success rate for SVT ablation is high, often exceeding 90%, offering a lasting solution for many patients. Despite this strong success rate, a small percentage of people experience the return of SVT after undergoing a procedure intended to be curative. Understanding why this recurrence happens involves looking at both technical factors from the procedure and biological factors related to the heart’s natural response.
Incomplete Elimination of the Problem Area
One of the most common reasons for SVT recurrence is the incomplete elimination of the electrical short circuit during the initial procedure. Catheter ablation works by creating precise, permanent scar tissue, known as lesions, to electrically isolate the problematic area of the heart. If the energy applied, whether radiofrequency heat or cryoablation cold, is insufficient or not delivered across the entire target area, the lesion may not be fully transmural, meaning it does not go completely through the heart muscle wall.
This technical issue results in “gaps” in the intended line of electrical block, allowing the abnormal signal to eventually re-conduct through the treated site. These gaps can be particularly problematic in complex anatomical locations or where the heart muscle is thicker. A recurrence that happens relatively soon after the procedure, often within the first few months, is attributed to this kind of incomplete initial lesion.
The goal of the procedure is to create a durable, non-conducting scar to permanently interrupt the circuit. If the catheter was not stable, or if the power was reduced to avoid damage to nearby healthy tissue, a thin or shallow lesion may result. This partially damaged tissue can recover its ability to conduct electrical signals over time, effectively allowing the SVT circuit to be reactivated. In cases of atrial flutter ablation, recurrence is often directly tied to the presence of a tiny, surviving electrical connection across the line that was supposed to be fully blocked.
Body’s Response and New Electrical Pathways
Recurrence that happens months or even years after a seemingly successful ablation often involves the body’s natural healing processes and the underlying condition of the heart. The heart tissue, particularly if the initial lesion was superficial, can regain electrical conductivity in a process called “late reconnection.” This biological recovery effectively bridges the gap in the scar tissue that was initially non-conductive, allowing the electrical signal to pass through again.
The heart initially undergoes a “blanking period” of about three months following ablation, during which inflammation and tissue swelling can cause temporary arrythmia episodes. True late recurrence, however, suggests the long-term biological stability of the lesion was compromised, or that new electrical substrates have emerged.
In some individuals, the underlying disease process that caused the first SVT may continue to progress, leading to the development of new accessory pathways or electrical foci that were not present or active during the first procedure. These newly emergent pathways or foci can become the source of a different type of SVT or a recurrence of the original one. Changes in the heart’s structure or electrical properties over time can create new opportunities for short circuits to form, independent of the area treated in the first ablation.
Determining the Cause and Treatment Options
When SVT recurrence is suspected, cardiologists initiate a systematic diagnostic process to confirm the rhythm and pinpoint its source. Extended heart monitoring, such as wearing a Holter monitor for 24 to 48 hours or using a longer-term event recorder, is necessary to capture the sporadic episodes and document the recurring rhythm. A 12-lead electrocardiogram taken during an episode is also analyzed to compare the characteristics of the recurring SVT with the original one.
The most definitive step is a repeat Electrophysiology (EP) study, which allows for precise mapping of the heart’s electrical activity. During this procedure, the cardiologist can determine if the recurrence is due to a gap in the original lesion line, the emergence of a new pathway, or the recovery of the previously ablated tissue. This mapping provides the necessary anatomical guidance to plan management.
Management options include antiarrhythmic medication and a repeat ablation procedure. Antiarrhythmic drugs control the symptoms and frequency of the episodes, but they do not eliminate the underlying electrical problem. A repeat ablation is highly successful because the initial mapping and the subsequent recurrence provide clearer information about the precise anatomical location requiring treatment. The success rates for repeat procedures are favorable as the target is now better defined.