61-year-old man implanted with a Lumax 340 HF-T triple-chamber ICD for dilated cardiomyopathy with left bundle branch block; event report (yellow color) in the setting of a classified SVT.
4 channels are available: the markers with the time intervals, the atrial sensing channel (A), the right ventricular sensing channel (RV) and the left ventricular sensing channel (LV).
When the atrial rate is faster than the ventricular rate, two groups of arrhythmias must be discriminated: dual tachycardias (VT + SVT) and conducted SVT (atrial flutter, AF, atrial tachycardia).
As explained previously, the first discrimination step upon programming of the SMART algorithm is a comparison between ventricular and atrial rates. When the atrial rate is faster than the ventricular rate (RR>PP), the device analyzes the stability of the RR intervals.
When the ventricular rhythm is deemed unstable, the device concludes to SVT (conducted AF). An interval classified AFib decrements the VT counter by 4.
When the ventricular rhythm is deemed stable, the differentiation between dual tachycardia (VT + flutter) and conducted atrial flutter is difficult for an algorithm which does not include the morphology criterion. In both instances, the RR intervals > PP intervals and the RR intervals are generally stable. To discriminate the latter, the device uses the relationship between atrial and ventricular signals. If there is an N:1 relationship (2:1, 3:1 or 4:1), the ventricular interval is classified as atrial flutter with an AFlut marker and decrements the VT counter by 1. If this relationship N:1 does not exist, a dual tachycardia is identified with a VT marker.
