Patient implanted with a dual-chamber defibrillator (Evera XT DR) for ischaemic cardiomyopathy presenting with multiple episodes of paroxysmal atrial fibrillation; 2 detection zones were programmed with a VT zone between 350 and 270 ms.
1, 2, 3. What diagnosis do you suggest on this graph?
The episode analysed was diagnosed as SVT/FA by the device (1); the graph initially shows a very rapid and irregular atrial rhythm associated with a rapid and irregular ventricular rate (alternating cycles detected in the VT zone or outside) compatible with an episode of conducted AF (2); the ventricular rate stabilises in a second phase in the VT zone; the VT counter is filled but no therapy is delivered (3).
- What is your diagnosis?
On the EGM, there is very rapid and irregular atrial activity in favour of atrial fibrillation, as well as irregular ventricular cycles classified as alternating VT or SV; the VT counter is repeatedly reset to 0 following the detection of ventricular cycles classified as SV.
- How does tachycardia develop?
The ventricular rate accelerates and stabilises in the VT zone.
- How do you explain the fact that no therapy is provided?
The VT counter is filled after 16 TS cycles and 2 FS cycles (counter programmed at 16, FS cycles do not modify the VT counter); no therapy is delivered, the PR Logic discrimination algorithm leading to a diagnosis of AF.
Messages to remember
- This tracing demonstrates the usefulness of the Medtronic TV counterTM in preventing inappropriate therapies during an episode of conducted AF; this patient had multiple episodes of relatively rapid conducted AF which were not recorded in the memories, the iterative presence of long cycles allowing the TV counter to return to 0, preventing the counter from being implemented and the episodes from being stored in the memories; in rare cases, as in this trace, the ventricular rhythm stabilised in the VT zone, with the PR Logic providing effective discrimination and preventing inappropriate therapies.
- This specificity is a major advantage of this type of meter; the risk of inappropriate therapies for atrial fibrillation is significantly reduced, especially as the recommendations suggest a trend towards an increase in the number of cycles required to diagnose VT; for an AF episode occurring at a frequency corresponding to the VT zone to result in inappropriate therapies, a combination of the following is required: 1) a number of consecutive cycles in the VT zone (30 in the new recommendations) without any long cycle classified as SV, which is relatively rare when the lower limit of the VT zone is programmed between 150 and 160 beats/minute; in fact, the slightest cycle classified as SV resets the VT counter to 0; 2) a discrimination error by the PR Logic and the Morpholog which operates in a second phase and can correct a diagnostic error; this explains why the risk of inappropriate therapies for AF conducted in the VT zone is relatively low.