VT diagnosed in the VF zone
Tracing
Manufacturer Abbott
Device ICD
Field Therapy
N° 34
Patient
This 34-year-old man suffering from hypertrophic cardiomyopathy underwent implantation of an Atlas dual chamber ICD for VT complicated by syncope. He was seen after he suffered a syncopal event followed by a shock while exercising.
Main programmed parameters
- VF zone at 222 bpm, VT-2 zone at 200 bpm and VT-1 zone at 171 bpm
- 12 cycles in the VF zone, 12 cycles in the VT-2 zone and 12 cycles in the VT-1 zone were needed for the diagnosis
- Maximum programmed sensitivity at 0.3 mV
- VF zone: one 25-J shock and five 36-J shocks (maximum amplitude); VT-2 zone: 3 bursts followed by one 25-J shock, followed by 3 shocks of maximum energy; VT-1 zone: monitor
- Effective discrimination in the VT-1 and VT-2 zones
- AAI pacing mode at 60 bpm; post-shock DDI pacing at 60 bpm
Graph and trace
The device diagnosed a VF episode prompting a 25-J shock with a 46-Ohm impedance. The diagnosis of VF by the ICD was strictly based on the heart rate criterion instead of the irregular and polymorphic characteristics of the arrhythmia; a VT entering the VF zone is diagnosed as VF; similarly, the diagnosis of restoration of sinus rhythm indicates a slowing of the heart rate instead of a differentiation between sinus rhythm and AF.
Tracing
- Exercise-induced sinus tachycardia with 1:1 conduction (AS-VS);
- Regular monomorphous tachycardia with cycles in the VF zone; after 3 F classified cycles, the episode pacing mode is AAI;
- VF detected after 12 F classified cycles and onset of the capacitors charge (*);
- End of charge;
- Confirmation before delivery of the shock on the second cycle; the instantaneous and average length of the cycles are in the VF zone;
- Delivery of 25-J shock in the atrial vulnerable period. i.e. 150 ms after atrial sensing (not synchronized with the atrial activity);
- 1 sec post-shock blanking;
- Termination of the ventricular arrhythmia and induction of AF with a relatively rapid AV conduction, due to a preserved baseline AV conduction and to the release of catecholamines during exercise; after 6 F classified cycles, VF is redetected and the capacitors are recharged;
- Slowing of AV conduction and diagnosis of return to sinus rhythm after 5 consecutive VS cycles; interruption of the capacitors charge;
- persistent AF.
Other articles that may be of interest to you
Several episodes diagnosed as VF by the ICD, based on a heart rate >200 bpm, are fast monomorphous VT. As discussed earlier, a priority of ICD programming is to lower to a maximum the number of shocks delivered without jeopardizing the safety of the patient. ATP is painless and, by lowering the energy consumption, spares the battery. Consequently, it must be given priority in the treatment of organized ventricular tachyarrhythmias, event when very rapid. In this patient, the VT was rapid, monomorphic, detected in the VF zone and treated by an outright maximum energy electrical shock. However, the programming of a burst of ATP for that arrhythmia might have been appropriate, though it cannot be offered beyond certain heart rate limits. This is another example of the divergent effects of electrical shocks delivered by ICD. On the one hand it terminated a ventricular arrhythmia (its expected function), and on the other, it induced an atrial arrhythmia. The tracing shows that the shock was synchronized with the R wave, though probably fell in the vulnerable period of the sensed atrial activity.