**14. Decision making for single or dual chamber ICD**

(a)

(b)

**Figure 18.** a: This is an example for measurement AV association during AFl with 2:1 activation. Although stability says stable CL <40ms there is an association between A and V. 160-150ms = 10ms for AVA interval (standard < 40ms for SVT) indicate association with RA. The algorithm vote for SVT and AVA interval outvotes stability. b: This is an example for measurement AV dissociation during AFl and VT. The second longest minus second shortest AV interval

Tachy/Sinus ratio counter is an algorithm from St. Jude Medical to avoid oversensing bige‐ miny during sinus tachycardia, t-wave oversensing or cluster caused by lead fracture. In fig‐ ure 19 calculation of CL ratio of 2.5 (500ms/200ms) over the last 12 sinus beats is illustrated. For every ratio of 2.5 the algorithm counts -1, and for counter <3 over the last 12 beats the algorithm votes for bigeminy and for >3 for VT. Medtronic has developed an algorithm called Lead Integrity Alert™; a short RR counter combined with daily lead impedance mon‐ itoring as early warning system for lead fracture. These algorithms have growing impor‐ tance due to the rising number of lead fracture problems over the last years. Biotronik also developed its t-wave detection protection algorithm. Furthermore, all manufacturers use an

automatic gain control as dynamic sense control to avoid t-wave oversensing.

(190ms-130ms=60ms) is voted by delta >40ms for dissociation and VT.

**13. Tachy/Sinus ratio**

152 Cardiac Defibrillation

In the last decade the issue of implanting single or dual chamber ICD was thoroughly dis‐ cussed. The negative influence of ventricular pacing in DAVID I trial [10] could be avoided in the DAVID II trial [11], which demonstrated similar prognoses in single and dual cham‐ ber patients for freedom of unfavourable ventricular pacing. The 1&1 trail of Bansch et al [9] failed (p=0.08) to demonstrate superiority of dual chamber devices to prevent inappropriate therapy in ICD patients. Also in MADIT II no benefit for dual chamber ICD patients could be confirmed [4]. The Detect SVT study by Friedman et al [12] could show a significant de‐ crease of inappropriate therapy in dual chamber patients (with 30.9% in 1,090 episodes ver‐ sus 39.5% in 1,253 episodes in single chamber ICD patients (p=0,03, see figure 20). Superiority was reported in the diagnose of AF, Aflut and atrial tachycardia (figure 21). No benefit could be demonstrated in sinus tachycardia, lead dysfunction and t-wave oversens‐ ing. Still, even dual chamber ICDs may fail to discriminate appropriately (figure 22a-f). This figure also may help to explain why inappropriate ICD therapy could have a negative effect on mortality in ICD patients. An recently, not jet published abstract of HRS congress 2012 of Friedman et al. of a prospective randomized trail of dual chamber versus single chamber ICD to minimize shocks in optimally programmed devices with optimal 30/40 detection of Medtronic devices no significant superiority of dual chamber devices could measure in at‐ tention to inappropriate therapies. Significant more AF was detected in the dual chamber device group. Generally, the choice of single or dual chamber does not depend on the inten‐ tion of a better SVT discrimination (e.g. patients with paroxysmal AF). Main indication for dual chamber ICD is the necessity of atrial pacing.

(a)

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(b)

(c)

**Figure 20.** Comparison of inappropriate SVT detection in single and dual chamber ICDs. Notice 30.9% inappropriate SVT detection in 1,090 episodes in dual chamber versus 39.5% in 1,253 episodes in single chamber ICD patients (p=0.03) [12].

**Figure 21.** Comparison of inappropriate SVT detection in single and dual chamber ICDs. A trend for superiority was estimated in AF, AFl and atrial tachycardia in the Detect SVT study [12].

**Figure 20.** Comparison of inappropriate SVT detection in single and dual chamber ICDs. Notice 30.9% inappropriate SVT detection in 1,090 episodes in dual chamber versus 39.5% in 1,253 episodes in single chamber ICD patients

**Figure 21.** Comparison of inappropriate SVT detection in single and dual chamber ICDs. A trend for superiority was

estimated in AF, AFl and atrial tachycardia in the Detect SVT study [12].

(p=0.03) [12].

154 Cardiac Defibrillation

(c)

is detected (NID 12] and the first shock is delivered. d: Same episode 43 seconds later. After the first shock ventricular fibrillation with syncope of patient is following, second shock (ineffective) at second 52 of episode is delivered. e: Same episode 65 seconds later. The third shock, now effective, is delivered during ventricular fibrillation and episode ends with sinus rhythm.f: This picture of the same episode turns out reasons for detection of AF in the VT zone. A temporary AF undersensing in RA rolls this episode in V=A branch. Generally based from 1:1 tachycardia in this branch stability is not sensible and programmed in this branch. In this case there are morphology and sudden onset discrimi‐ nation active. For understandable reasons morphology votes for SVT and sudden onset for VT and resulting VT thera‐ py starts. As previously described sudden onset criteria is not recommended in this branch and an always problematic

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Avoiding of inappropriate therapy delivery is one of the major issues in ICD therapy. In the last decade several new algorithms were developed to improve sensitivity and specificity of tachycardia detection. Current recommendation for primary prevention patients is the pro‐ gramming of a fast VT zone from 187 to 250 bpm with long NID or DT [30/40] for Medtron‐ ic, 12 seconds for Boston, 18/24 for St. Jude Medical and Biotronik), is ATP prior or during charging followed by shock therapy. For devices that not allow SVT discrimination in this zone a separate VF zone above 250 bpm should be programmed to make SVT discrimination possible in a VT zone of 187 to 250 bpm. If a second VT zone around 150-187 bpm is pro‐ grammed, a long NID (minimum 25 beats or 60 seconds) with stability and morphology dis‐ crimination algorithm without time out rule is recommended. Algorithms for early detection of lead fracture, sinus/tachy ratio and impedance monitoring are recommended when available. In patients with long QT syndrome or other risk for primary VF a single zone over 220 bpm is recommended. In dual chamber ICDs stability, morphology and A-V-A (or equivalent) SVT discrimination algorithms are recommended in the analysis of V=A and V<A tachycardias. Implantation of dual chamber ICD for better SVT/VT discrimination

No algorithm is sensitive or specific enough to substitute the individual adaptation of ICD detection and therapy for every patient. Detailed knowledge of ICD algorithms may provide the necessary basis for the cardiologist to program devices individualized for each patient. Stored episodes should be carefully evaluated at every follow-up visit to further improve

Heartcenter Brandenburg and Immanuel Klinikum Bernau, Department of Cardiology, Ber‐

discrimination algorithm.

**15. Summary/Conclusion**

only is not indicated by currently available studies.

Address all correspondence to: m.seifert@immanuel.de

discrimination of SVTs and VTs.

**Author details**

nau bei Berlin, Germany

Martin Seifert\*

**Figure 22.** a: Demonstration of an AF episode in a CRT-D device with dual chamber detection (Promote St. Jude Medi‐ cal) A>V with CL around 344 to 270ms. Depending of CL the device counts VT (T) and VF (F) beats for detection. In this device no SVT discrimination algorithms are allowed in VF zone. b: Same episode 12 seconds later. After detection VT episode (NID 12] first VT therapy (ATP) is given. c: Same episode 27 seconds later. After acceleration of AF a VF episode

is detected (NID 12] and the first shock is delivered. d: Same episode 43 seconds later. After the first shock ventricular fibrillation with syncope of patient is following, second shock (ineffective) at second 52 of episode is delivered. e: Same episode 65 seconds later. The third shock, now effective, is delivered during ventricular fibrillation and episode ends with sinus rhythm.f: This picture of the same episode turns out reasons for detection of AF in the VT zone. A temporary AF undersensing in RA rolls this episode in V=A branch. Generally based from 1:1 tachycardia in this branch stability is not sensible and programmed in this branch. In this case there are morphology and sudden onset discrimi‐ nation active. For understandable reasons morphology votes for SVT and sudden onset for VT and resulting VT thera‐ py starts. As previously described sudden onset criteria is not recommended in this branch and an always problematic discrimination algorithm.
