Discriminators sudden onset

So how can the ICD differentiate sinus tachycardia from VT Most ICDs can be programmed in their VT zones with a discriminator commonly referred to as "sudden onset." This can be used to help limit delivery of therapy for sinus tachycardia. Sudden onset tries to take advantage of the fact that sinus tachycardia, as opposed to VT, typically does not initiate in a sudden fashion. Other SVTs, however, can typically initiate in a sudden manner. In any case, an ICD may rarely deliver therapy for sinus tachycardia simply by the fact that a sustained rate criteria has been met should such a function be programmed on (it is actually quite common for both a sudden onset and sustained duration feature to be programmed on simultaneously). 

A sudden onset function will not likely be of much use for the ICD to discriminate AT from VT since both can initiate in this fashion. A ventricular morphology or width discriminator may help, again in the absence of BBA. Not all ATs conduct each beat to the ventricles, so this information ( P waves > R waves) in a dual chamber ICD event recording may allow the interpreter to help rule in the diagnosis of SVT. It should be noted that dual tachycardias, i.e. SVT and VT, can coexist in which the number of registered P waves is still greater then the number of registered R waves. 

For the EGM interpreter the near simultaneous activation of ventricle and then atria with identical VEGM R wave morphology to that of the baseline rhythm should raise the suspicion of AVNRT. As regards the ICD interpretation of this rhythm, a discriminator such as sudden onset will not help. An ICD with ventricular morphology or width discrimination may be useful, so long as BB A does not occur. However, the sustained tachycardia rate alone, as in the previous, and subsequent SVTs, may result in the ICD treating this rhythm as a ventricular tachyarrhythmia should a sustained rate criterion be programmed on. 

Management Solution Consider a discriminator such as sudden onset that may decrease the likelihood of shocking for sinus tachycardia. A ventricular morphology discriminator might also be effective for this purpose (this ICD did not have that function). Also, a physician will sometimes prescribe medication with beta-adrenergic blocking activity in an attempt to prevent the native heart rate from reaching the VT zone. 

Management Solution A sudden onset discriminator would not likely help as both an atrial tachycardia and an VT can initiate suddenly. A morphology discriminator (not available in this device) in the VT treatment zone might be helpful. AAD treatment could be considered for frequent VT. 

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