Introduction: There have been many advances in reducing the rate of inappropriate ICD therapy through standardised programming and enhanced discrimination features (Friedman P et al., 2014). ICD discriminators have evolved over time and now offer better sensitivity and specificity in SVT versus VT detection. Despite this, there are instances where patients still receive inappropriate therapy for arrhythmias incorrectly classified by the device.
Case: An 84-year-old male with a background of ischaemic cardiomyopathy was implanted with a primary prevention CRT-D in 2011 and underwent a generator change in 2019 with an Abbott Quadra Assura CRT-D device. Post generator change, multiple remote monitoring transmissions were received for arrhythmia between 01:00 am and 02:00 am over a 15-day period. The transmissions showed prolonged periods of nocturnal VT with a cycle length of 516ms. All episodes were terminated successfully with 1–2 cycles of burst ATP however detection was delayed on some occasions due to inappropriate discrimination (Figure 1).
Discussion: The use of discriminators is important in clinic practise, additionally knowledge of the atrial rhythm is vital in understanding where the arrhythmia is originating. Evidence of the effectiveness of dual chamber discriminators versus single chamber discriminators is variable.
The OPTION trial (Kolb et al., 2014) concluded that dual chamber discriminators reduced the risk of inappropriate shocks compared to single chamber discriminators. Equally, Peterson P et al. (2017) found that in those with no pacing indication, dual chamber devices did not offer any significant reduction in inappropriate therapies. There have been no studies which directly compared discriminators between manufacturers. Direct comparison is often difficult because the same term can mean different things across different manufacturers and there is also variation in the decision tree for dual chamber discrimination. In Medtronic devices, onset and stability come before the A and V relationship. In the Abbott, Boston Scientific and Biotronik, the A and V relationship is established first. Brown M L et al., 2002 evaluated the effectiveness of Medtronic’s PR logic with the addition of wavelet in appropriate discrimination of SVT versus VT. It found that the combination of wavelet with PR logic reduced false positive detections by 79%.
As far as single chamber discrimination is concerned morphology discriminators have changed significantly over the years and data about sensitivity and specificity from older studies are not relevant. Sylvain Ploux et al. from CHU Bordeaux (2019) are due to publish a study looking at the performance of morphological discriminators in patients who had a CRT or dual chamber device. Of the three main manufacturers, Abbott has a good sensitivity and specificity ratio, Medtronic is already at its best sensitivity and specificity however Boston is at its worst. In Boston devices, nominal morphology settings lead to a high sensitivity but low specificity. This can be overcome by reducing the match score to 83%.
Conclusion: Dual chamber discrimination offers little benefit in terms of reduction of inappropriate shocks over single chamber discrimination, particularly if morphology discriminators have a high sensitivity and specificity. Knowledge of how decision trees differ between manufacturers is vital in device selection and optimal programming of ICDs in order to prevent inappropriate therapy.
