Anti-tachycardia pacing (ATP) is a therapy delivered by an implantable cardioverter defibrillator (ICD) or cardiac resynchronisation therapy defibrillator (CRT-D) that attempts to stop a fast ventricular arrhythmia by delivering rapid, precisely timed pacing pulses to the heart. ATP is painless and, when effective, terminates the tachycardia without the patient being aware that any therapy was delivered.
How it works
When the ICD detects a ventricular tachycardia (VT) at a rate within the programmed ATP zone, instead of immediately charging for a shock it delivers a burst of pacing pulses at a rate slightly faster than the tachycardia. This can interrupt the re-entry circuit driving the VT and restore a normal rhythm. If ATP is unsuccessful after one or more attempts, the device escalates to a defibrillation shock.
Why ATP matters
Defibrillation shocks, while life-saving, are painful and distressing. Repeated shocks are associated with anxiety, PTSD, and reduced quality of life. ATP allows many episodes of VT to be treated silently and painlessly, reducing the psychological burden of living with an ICD significantly.
Limitations
ATP is only effective for organised ventricular tachycardia and is not effective for ventricular fibrillation, which has no organised circuit to interrupt. It is also not available in the subcutaneous ICD (S-ICD), which is one reason why the S-ICD is not suitable for patients who require ATP therapy.
Patient experience
Many ICD recipients experience episodes of ATP therapy without knowing it has happened. The first indication is often found at a routine device check, when stored electrograms reveal that the device detected and terminated an episode. If symptoms such as dizziness or palpitations occur around the time ATP is delivered, patients should report them to their device clinic.