54-year-old female with implanted with dual-chamber defibrillator for dilated cardiomyopathy
Summary
episode detected in VT-1 zone at 159 beats/minute
Rhythm ID discrimination
criterion V>A : False
Rhythm ID correlated: True
EGM layout
probable sinus tachycardia with spontaneous conduction; cycles classified as VS
acceleration of heart rate with cycles classified as VT-1
correlated ventricular complexes (percentage exceeding the programmed threshold value of 94%)
V-Epsd marker after 8 cycles in VT-1 zone
end of duration, all previous complexes correlated
cycle-by-cycle analysis of morphology continues; heart rate slows down and cycles are classified as VS
Take home message
this trace corresponds to a sinus tachycardia that is well discriminated by the device; the presence of correlated vectors, a 1/1 A/V relationship and a stable rhythm are suggestive of possible sinus tachycardia or an atrial tachycardia/atrial flutter; progressive acceleration then deceleration favor sinus tachycardia; even if discrimination is correct and the device has correctly diagnosed supra-ventricular tachycardia, in this active patient implanted for primary prevention with no previous episodes of ventricular arrhythmia, it is probably acceptable to raise the VT detection zone to avoid overlap between physiological sinus rates and therapy detection zones.
in this patient, the Rhythm ID and «Discrimination atrial tachyarrhythmia» discriminants are programmed “On»; the device proceeds in several stages
step 1: V>A criterion; if the ventricular rate is considered higher than the atrial rate a diagnosis of VT is made without reference to other discriminants (morphology, stability, AF, etc.); this criterion enables correct discrimination of the majority of VTs presenting with atrioventricular dissociation.
step 2: if the ventricular rate is not considered higher than the atrial rate, the analysis continues with the morphology criterion; if at least 3 out of 10 ventricular cycles are correlated (identical operation to that described for single-chamber), the tachycardia is considered supraventricular and therapies are inhibited ; when this criterion functions correctly (threshold adapted to the patient, satisfactory signal quality), it enables the majority of supraventricular tachycardias (sinus tachycardia, AF, flutter, intra-nodal reentries, orthodromic tachycardias) to be correctly discriminated; the morphology criterion will be misled (diagnosis of VT when it’s a SVT) in the presence of an SVT with aberrant conduction, or in the presence of an antidromic tachycardia conducted over an accessory pathway (anecdotal diagnoses in patients implanted with a defibrillator).
