How is supraventricular tachycardia (SVT) ablation performed?

How SVT Ablation is Performed

SVT ablation is performed by inserting steerable electrode catheters through venous (and sometimes arterial) access into the heart, using electrophysiological mapping to precisely localize the arrhythmia substrate, then delivering radiofrequency energy or cryotherapy to create targeted lesions that eliminate the abnormal electrical pathway. 1

Pre-Procedural Preparation and Access

• Vascular access is obtained through femoral, subclavian, or internal jugular veins using standard percutaneous techniques, with arterial access added for left-sided accessory pathways via retrograde aortic or transseptal approach 1
• Multiple multielectrode catheters are positioned at strategic cardiac locations including the right atrium, His bundle region, coronary sinus, and right ventricle 1
• For left-sided accessory pathways, operators may use either transseptal puncture or retrograde transaortic approach, though transseptal access appears more promising for acute success 2

Diagnostic Electrophysiology Study

The ablation procedure begins with a comprehensive diagnostic EP study that serves three critical functions 1:

• Confirms the presence of the arrhythmia substrate (accessory pathway, dual AV nodal physiology, or ectopic focus)
• Determines conduction characteristics through programmed electrical stimulation with or without pharmacological provocation (isoproterenol, procainamide, adenosine) 3
• Defines the mechanism and precise location of the clinical arrhythmia using diagnostic maneuvers 1

Mapping Techniques

Sequential Activation Mapping

• A roving ablation catheter is systematically moved to different cardiac regions while recording local activation times relative to a reference electrogram 3
• The earliest activation site identifies where the arrhythmia originates, with activation spreading centrifugally from this point 3
• For accessory pathways, mapping identifies the ventricular insertion site where atrial and ventricular electrograms are fused during pre-excitation 1

Advanced Mapping Technologies

• Three-dimensional electroanatomic mapping systems create spatial displays of cardiac anatomy and electrical activation, allowing more precise localization while reducing fluoroscopy exposure 1
• High-density multipoint mapping systems enable simultaneous recording from multiple sites, improving speed and resolution particularly for complex arrhythmias 2
• These technologies have enabled SVT ablation with minimal or zero fluoroscopy, achieving success and complication rates similar to fluoroscopy-guided procedures 1

Energy Delivery

Radiofrequency Ablation (Primary Modality)

• Radiofrequency current (typically 50-70 watts) is the most commonly used energy source, delivered through the tip of the ablation catheter 1
• Energy applications typically last 30-60 seconds per lesion, with the mean number of pulses being approximately 10 applications 4
• Accelerated junctional rhythm during energy delivery serves as a real-time marker of successful slow pathway modification in AVNRT 1

Cryoablation (Alternative Modality)

• Cryotherapy (freezing to -70°C to -80°C) is used as an alternative to minimize AV node injury risk during ablation of AVNRT, para-Hisian atrial tachycardia, and para-Hisian accessory pathways 1
• Cryoablation is particularly favored in children and young adults due to its reversibility during the initial "ice mapping" phase before creating permanent lesions 1
• However, radiofrequency ablation has prevailed for AVNRT due to higher recurrence rates with cryoablation 2

Specific Ablation Approaches by Arrhythmia Type

AVNRT (Most Common SVT)

• Slow pathway ablation is the preferred initial approach, targeting the posteroseptal right atrium near the coronary sinus os and tricuspid annulus 1
• This approach has a lower AV block risk (1%) compared to fast pathway ablation (8%) and avoids hemodynamic consequences of PR prolongation 1
• Fast pathway ablation is reserved only for cases where slow pathway ablation fails 1
• Success rate is approximately 96%, with recurrence rates of 3-7% 1

Accessory Pathways (WPW/AVRT)

• Left free-wall pathways have slightly higher success rates than other locations, with overall initial efficacy approximately 95% 1
• The ablation catheter targets the ventricular insertion site where the accessory pathway crosses the AV groove 1
• Approximately 5% of initially successful cases experience recurrence due to resolution of inflammation/edema, but these can usually be successfully re-ablated 1

Focal Atrial Tachycardia

• Mapping identifies the earliest atrial activation site where the arrhythmia originates 3
• High-density mapping systems are particularly helpful for these challenging cases 2
• Ablation creates lesions at the focal origin to eliminate the ectopic source 2

Success Rates and Outcomes

• Overall success rates for SVT ablation range from 90-98.5%, varying by arrhythmia type and location 1, 4, 5
• Success rates in elderly patients (≥70 years) are comparable to younger populations at 98.5% 5
• The procedure has a learning curve, with success rates improving from 63% to 93% as operator experience increases 4

Complications and Safety Profile

Major Complications (Rare)

• Procedure-related mortality ranges from 0% to 0.2% across large registries 1
• Complete AV block requiring permanent pacemaker occurs in approximately 1% of slow pathway ablations 1
• Cardiac perforation, tamponade, stroke, and coronary artery injury occur in 0.8-1.82% of cases 1, 6

Access-Related Complications

• Hematomas, deep venous thrombosis, arterial perforation, arteriovenous fistula, and pneumothorax from vascular access 1
• These general complications occur in 3-5% of procedures 6

Risk Factors for Complications

• Elderly and multimorbid patients have elevated complication risk 6
• Operator and team experience plays an essential role in minimizing complications 6

Post-Procedure Monitoring

• Uncomplicated SVT ablation patients may be discharged after approximately 4 hours of monitoring in a post-procedure area 1
• Monitoring focuses on detecting transient AV block, vascular complications, and arrhythmia recurrence 1
• Patients with complex ablations or serious comorbidities require extended monitoring, as most major complications occur on the procedure day (54.7%), though some occur up to 5-6 days post-procedure 1

Common Pitfalls to Avoid

• Anterior catheter displacement during slow pathway ablation can cause inadvertent AV node injury; maintain stable posterior positioning 1
• Inadequate mapping before energy delivery increases failure rates; ensure earliest activation is clearly identified 3
• Excessive energy delivery near the AV node or His bundle risks complete heart block; use lower power settings in these regions 1
• Premature hospital discharge after complex ablations may miss delayed complications like pericardial effusion 1