Sjm Alternating Match Mismatch Morphology Discrimination

cases.

Although this is rarely used today, some ICDs may still be programmed to "committed" mode in which therapy will be delivered after initial tachycardia detection criteria are met even if the arrhythmia spontaneously terminates. This mode of operation may result in frequent or multiple shocks for nonsustained ventricular arrhythmias. Some devices are capable of defibrillation therapy for atrial tachyarrhythmias. Multiple low-energy shocks are one strategy to terminate atrial fibrillation with these devices as an alternative or prelude to high energy therapy.

Multiple Inappropriate Discharges: In the case of repeated inappropriate discharges, the ICD should be promptly inactivated and the patient placed on telemetry with external defibrillation capabilities readily available. Most devices will have therapies inhibited as long as a magnet is in place over the generator. In some devices, prolonged magnet application will inactivate the device until the ICD is reactivated by the programmer or the magnet is applied again. Inappropriate ICD therapies may have many causes, but the most common cause is atrial fibrillation, as shown in Figure 10.9. Other atrial tachyarrhythmias including atrial flutter and sinus tachycardia may also trigger inappropriate ICD therapy. Once the device is inactivated, the atrial arrhythmia can be managed in a conventional manner. If the device cannot be immediately reprogrammed, chemical or electrical conversion of the atrial arrhythmia may be needed if ventricular rate control cannot be achieved. After initial control of the supraven-tricular tachyarrhythmia has been achieved, ICD tachyarrhythmia detection features for discrimination of supraventricular tachyarrhythmia from ventricular tachycardia may be useful in preventing further inappropriate therapies. Presently, it is unclear whether dual-chamber ICDs will decrease the number of inappropriate ICD therapies for supraventricular tachycardias (Fig. 10.10). Additionally, it is unclear whether the use of ventricular electrogram morphology algorithms will decrease inappropriate ICD therapies due to SVTs (see Fig. 10.10C).Ventricular electrogram morphology discrimination when used in conjunction with other SVT discriminators has a suboptimal sensitivity for atrial tachycardia.26 SVTs with subtle rate-related changes in the QRS complex can also trigger inappropriate detection of ventricular tachyarrhythmias. Reprogramming of the percent template match to less rigorous criteria may improve

Figure 10.9. Atrial fibrillation and inappropriate therapy, as recorded by a Guidant Ventak Mini single-chamber ICD. Note the marked irregularity of the intracardiac ventricular electrogram (top tracing) and the ventricular cycle length, which varies between 290 and 500 milliseconds (bottom tracing, marker channel). The ventricular rate eventually falls into the VT zone (denoted by "TS" marker channel), and then ATP therapy is delivered (denoted by "TP" marker channel).

Figure 10.9. Atrial fibrillation and inappropriate therapy, as recorded by a Guidant Ventak Mini single-chamber ICD. Note the marked irregularity of the intracardiac ventricular electrogram (top tracing) and the ventricular cycle length, which varies between 290 and 500 milliseconds (bottom tracing, marker channel). The ventricular rate eventually falls into the VT zone (denoted by "TS" marker channel), and then ATP therapy is delivered (denoted by "TP" marker channel).

Figure 10.10. A: Atrial fibrillation with a rapid ventricular response leading to inappropriate therapy, as recorded by a Medtronic Gem DR dual-chamber ICD. Atrial electrogram (AEGM), ventricular electrogram (VEGM) and marker channel (MARKER) are shown. The patient is in atrial fibrillation with ventricular response from 370 to 500 milliseconds. The occasional long cycle lengths and irregularity prevent ventricular tachycardia detection. Panel B: With faster ventricular rate, the rhythm regularizes and no longer meets "unstable" rate criteria for diagnosis of atrial fibrillation in the VT zone. Antitachycardia pacing therapy is given as a result (arrow). Panel C: Failure of ventricular electrogram morphology discrimination in a St. Jude Photon dual-chamber ICD. The atrial and right ventricular (RV) channels show 1:1 conduction indicative of sinus tachycardia. Checks alternating with "X"s in the markers channel demonstrate an alternating match and mismatch with the stored ventricular electrogram template recorded in sinus rhythm. The poor match with the stored template probably results from misalignment of the electrogram with the template. The patient experienced inappropriate VT detection and ATP therapy.

Figure 10.10. A: Atrial fibrillation with a rapid ventricular response leading to inappropriate therapy, as recorded by a Medtronic Gem DR dual-chamber ICD. Atrial electrogram (AEGM), ventricular electrogram (VEGM) and marker channel (MARKER) are shown. The patient is in atrial fibrillation with ventricular response from 370 to 500 milliseconds. The occasional long cycle lengths and irregularity prevent ventricular tachycardia detection. Panel B: With faster ventricular rate, the rhythm regularizes and no longer meets "unstable" rate criteria for diagnosis of atrial fibrillation in the VT zone. Antitachycardia pacing therapy is given as a result (arrow). Panel C: Failure of ventricular electrogram morphology discrimination in a St. Jude Photon dual-chamber ICD. The atrial and right ventricular (RV) channels show 1:1 conduction indicative of sinus tachycardia. Checks alternating with "X"s in the markers channel demonstrate an alternating match and mismatch with the stored ventricular electrogram template recorded in sinus rhythm. The poor match with the stored template probably results from misalignment of the electrogram with the template. The patient experienced inappropriate VT detection and ATP therapy.

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