Bursts or ramps ? - Visia XT VR

Patient

Male implanted with a single chamber defibrillator (Visia XT VR) for ischaemic cardiomyopathy.

Trace

1-What diagnosis is suggested by the interval plot?
The plot shows a probable arrhythmic episode identical to the previous trace with sudden acceleration into the VT zone; 3 bursts prove ineffective, a ramp interrupts the arrhythmia.

2- What is your final diagnosis?
The tachycardia is identical to the previous tracing; the first 3 bursts (fixed rate) are ineffective; the first ramp (increasing rate) allows termination.

Take home message

In a burst, the cycle length is constant throughout the sequence (no change in rate from one stimulus to the next); this is the type of sequence most commonly used in clinical practice and probably the least aggressive; according to the latest recommendations, a burst should be preferred over other pacing sequences.
In a ramp, the cycle length is reduced from one stimulus to the next by the value of the programmable decrement.
In a ramp+ (specific to this manufacturer), the cycle length decreases for the first 3 intervals and then remains constant thereafter.
The shorter the coupling intervals, the more aggressive the therapy and the greater the risk of accelerating the tachycardia; according to the latest recommendations, for a burst, a coupling interval of 88% of the cycle length of the tachycardia (calculated over the last 4 cycles before diagnosis) should be programmed. Ramps should be programmed at long coupling intervals (88-90%) and a limited number of pulses so as not to stimulate too aggressively. Medtronic devices add an impulse for each ramp sequence (so ramps become increasingly aggressive).
Smart Mode can be programmed to deactivate a therapy when it has proved ineffective; this algorithm deactivates an ATP pacing sequence that has been ineffective for 4 consecutive episodes (variable depending on the platform).
An additional option is the programming of the progressive therapy algorithm, which ensures that each therapy delivered for the same episode is at least as aggressive as the previous therapy.
This patient presented with numerous episodes of VT effectively treated by ATP; rapid and effective treatment by ATP enabled the patient to remain asymptomatic with a good quality of life while preserving battery longevity.

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