**4. Inappropriate ICD therapy**

ent discrimination algorithms and therapies (table 1). Moreover, data on the programming of zones up to 260ms CL with a long detection time are also available {ADVANCE III study [2]}. Until now, no consensus is accepted concerning the number of detection zones (not at least in primary prevention indication), nor clear definition of detection windows is given. Until 2010 most ICDs had no SVT/VT discrimination algorithm available in the VF zone. In primary prevention a VT zone from 360ms CL with long detection time, SVT/VT discrimina‐ tion up to 260ms CL and anti-tachycardia-pacing (ATP) prior or during charging, along with a VF zone from 260ms CL without SVT/VT discrimination and maximal energy shock deliv‐ ery was widely recommended. Depending from device a FVT zone was needed to program an ATP prior or during charging shock up to 280-250ms CL. Newer devices have now inde‐ pendent discrimination algorithm for every detection zone (Medtronic), and provide SVT/VT discrimination algorithms also in VF zone. Furthermore, ATPprior or during charg‐ ing is available in all zones. In secondary prevention patients with documented VTs, the first zone should be programmed 10-20ms above (or 10 bpm below) its cycle length. In younger patients with channel rhythm disorders like long QT syndrome a single zone (<280ms) can be considered. Patients with secondary prevention, very low ejection fraction or repetitive syncope need an individualized, more conservative programming with shorter detection in‐ tervals and less ATPs. Different programming examples for tachycardia detection and thera‐ pies in recent studies with primary prevention patients with ICDs of different

**Figure 1.** Notice critical area of VT and VF discrimination in yellow and orange up to 460ms cycle length

Practically, devices in primary prevention patients can be programmed using either single or two zones with long detection intervals. The programming should be adjusted during the

manufacturers are listed in table 1.

138 Cardiac Defibrillation

follow-up in case of arrhythmic events.

Inappropriate ICD therapy is a delivered ATP and/or shock in absence of VT/VF episode. Inappropriate ICD therapy has serious consequences: proarrhythmic effect, reduced quality of life, psychological stress with depression, unnecessary hospitalisation, early battery de‐ pletion duration and even elevated mortality [3]. Up to 80% of inappropriate ICD therapies are registered in the first year following device implantation [4, 5] figure 2. Atrial fibrillation

(AF) is the most common cause of inappropriate ICD therapy {MADIT II [6], figure 3}. How‐ ever, concerning the rising number of lead dysfunction resulting in oversensing this can be changed in the future. In the SCD-HeFT[3] study with single zone of detection and therapy (18 of 24 beats at a rate ≥188 bpm or ≤320 ms CL) the effect of inappropriate versus appropri‐ ate ICD therapy to the hazard ratio for death (CI 95%) was 1.98 (p=0.002) for inappropriate therapy only (figure 4).It is unclear whether the inappropriate therapy is a cause or only a marker of higher mortality. By all means, consensus exists about the importance of avoiding inappropriate ICD therapies. The incidence of inappropriate ICD therapy depends on the programming of the device – both detection and therapy, and considerable changes were observed over the last years (table 2).

**Figure 4.** Relation of appropriate and inappropriate ICD therapy in SCD-HeFT to mortality [3].

1996 Weber et al[19] 462 55 18

2002 Daubert et al[4] 63 719 66 11,5

2003 Nanthakumar et al[5] 60 261 54 44 2004 Rinald et al[20] 60 155 14 2007 Anselmeet al[21] 64 802 28 15

discrimination algorithm until CL of 260ms and longer detection intervals.

primary prophylactic indication (figure 8 and table 1).

**(n)**

2008 Wilkoff et al[16] 67 700 5,4 (shock, not ATP) 3,6 (shock, not ATP)

**5. Detection Time (DT) or Number of Interval Detection (NID)**

**Table 2.** Incidences of appropriate and inappropriate ICD therapies over the last years. Notice the influence of SVT/VT

Detection of tachycardia occurs after the registration of a certain amount of heartbeats with‐ in or above the programmed HR zone. Signals with CL according to VF zone have priority to signals in VT zone(s). Various algorithms are currently used for validation of a tachycar‐ dia: registering of a specified and programmed number of beats - x out of y (Medtronic and Biotronik, figure 5), a programmed number of beats (x) with resetting after 5 consecutive be‐ low-zonebeats (St. Jude Medical, figure 6) or after a programmed time interval (Boston, fig‐ ure 7). During the last years programming of a long detection time has been established in

**% appropriate ICD**

**% inappropriate ICD**

**therapy**

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**therapy**

**Year Author Mean age Patients**

**Figure 2.** Frequency (y line in %) of inappropriate ICD therapies after ICD implantation (x line in month, y line in %) Nanthakumar K et al[5].

**Figure 3.** Reasons of inappropriate ICD therapy in MADIT II [4].

**Figure 4.** Relation of appropriate and inappropriate ICD therapy in SCD-HeFT to mortality [3].

(AF) is the most common cause of inappropriate ICD therapy {MADIT II [6], figure 3}. How‐ ever, concerning the rising number of lead dysfunction resulting in oversensing this can be changed in the future. In the SCD-HeFT[3] study with single zone of detection and therapy (18 of 24 beats at a rate ≥188 bpm or ≤320 ms CL) the effect of inappropriate versus appropri‐ ate ICD therapy to the hazard ratio for death (CI 95%) was 1.98 (p=0.002) for inappropriate therapy only (figure 4).It is unclear whether the inappropriate therapy is a cause or only a marker of higher mortality. By all means, consensus exists about the importance of avoiding inappropriate ICD therapies. The incidence of inappropriate ICD therapy depends on the programming of the device – both detection and therapy, and considerable changes were

**Figure 2.** Frequency (y line in %) of inappropriate ICD therapies after ICD implantation (x line in month, y line in %)

observed over the last years (table 2).

140 Cardiac Defibrillation

Nanthakumar K et al[5].

**Figure 3.** Reasons of inappropriate ICD therapy in MADIT II [4].


**Table 2.** Incidences of appropriate and inappropriate ICD therapies over the last years. Notice the influence of SVT/VT discrimination algorithm until CL of 260ms and longer detection intervals.

## **5. Detection Time (DT) or Number of Interval Detection (NID)**

Detection of tachycardia occurs after the registration of a certain amount of heartbeats with‐ in or above the programmed HR zone. Signals with CL according to VF zone have priority to signals in VT zone(s). Various algorithms are currently used for validation of a tachycar‐ dia: registering of a specified and programmed number of beats - x out of y (Medtronic and Biotronik, figure 5), a programmed number of beats (x) with resetting after 5 consecutive be‐ low-zonebeats (St. Jude Medical, figure 6) or after a programmed time interval (Boston, fig‐ ure 7). During the last years programming of a long detection time has been established in primary prophylactic indication (figure 8 and table 1).

**Figure 5.** Tachycardia detection of a Medtronic device: TS tachycardia sense in VT1 zone; VS ventricular sense; TF fibril‐ lation sense via VT2 zone; FS fibrillation sense. In this case x=12 (<300ms orange points) out of y=16 signals counted for detection of a VF episode with spontaneous conversion to sinus rhythm after 22 beats.

**Figure 7.** Tachcardia detection of a dual chamber device Boston: VS ventricle sense; AS atrial sense (AS) refracted; PVP atrial refracted after ventricle sense; VT ventricular tachycardia sense; VF ventricular fibrillation in VF zone sense; V-Epsd ventricular episode ready for duration; V-Dur duration time complete; Stb stability criteria is right; V-Detect ven‐

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**Figure 8.** Gunderson at al [23] demonstrate ICD shock therapy which is delivered or aborted in the same VT episode

tricular episodes is detected and therapy ATP begins.

according to detection interval NID 12 or 18.

**Figure 6.** Tachycardia detection of a CRT device from St. Jude Medical (dual chamber detection): VS ventricle sense; AS atrial sense; T tachycardia sense in VT zone; ST tachycardia episode sense; X no correspondence with stored QRS templet; little minced meat correspondence with stored templet, NID x=12 (orange points) counted to VT episode with successful ATP. The episode shows a short VA interval with accelerated CL and corresponding templet to intrinsic activation. That means episode could diagnose as VT with VA conduction and wrong stored templet or as SVT (atrio‐ ventricular node reentry tachycardia) with atypical start.

**Figure 7.** Tachcardia detection of a dual chamber device Boston: VS ventricle sense; AS atrial sense (AS) refracted; PVP atrial refracted after ventricle sense; VT ventricular tachycardia sense; VF ventricular fibrillation in VF zone sense; V-Epsd ventricular episode ready for duration; V-Dur duration time complete; Stb stability criteria is right; V-Detect ven‐ tricular episodes is detected and therapy ATP begins.

**Figure 5.** Tachycardia detection of a Medtronic device: TS tachycardia sense in VT1 zone; VS ventricular sense; TF fibril‐ lation sense via VT2 zone; FS fibrillation sense. In this case x=12 (<300ms orange points) out of y=16 signals counted

**Figure 6.** Tachycardia detection of a CRT device from St. Jude Medical (dual chamber detection): VS ventricle sense; AS atrial sense; T tachycardia sense in VT zone; ST tachycardia episode sense; X no correspondence with stored QRS templet; little minced meat correspondence with stored templet, NID x=12 (orange points) counted to VT episode with successful ATP. The episode shows a short VA interval with accelerated CL and corresponding templet to intrinsic activation. That means episode could diagnose as VT with VA conduction and wrong stored templet or as SVT (atrio‐

ventricular node reentry tachycardia) with atypical start.

for detection of a VF episode with spontaneous conversion to sinus rhythm after 22 beats.

142 Cardiac Defibrillation

**Figure 8.** Gunderson at al [23] demonstrate ICD shock therapy which is delivered or aborted in the same VT episode according to detection interval NID 12 or 18.
