**12. SVT/VT discrimination algorithms in dual chamber devices**

only two criteria are active (standard), stability and morphology are recommended, and 1 out 2 votes is required for the diagnosis of SVT. Anyway, differentiation between SVT and VT in single as well as dual chamber ICD remains difficult and should be carefully checked

(a)

(b)

**Figure 16.** a: This episode of a dual chamber tachycardia detection (Atlas DR St. Jude Medical) with A>V during AF with a CL around 100ms demonstrates the hardly difficult decision-making in spite of all common discrimination algo‐ rithms. The ventricular EGM shows a fast stable tachycardia with a CL of around 300ms and sudden onset as well as nearly same EGM signal like intrinsic activation before. This tachycardia falls in VF zone and the morphology criteria founds a match to intrinsic activation of stored template. Although morphology votes for SVT, stability outvote for VT <40ms (sudden onset not active), but anyway the CL falls in VF zone in this case without active SVT discrimination algorithm the device detected this episode as VF and start charging shock therapy (\*). b: The same episode stopped spontaneously without any therapy and the shock is aborted by the device. The example underlined the importance of long detection intervals (TDI 18-24 not 12 like in this case), the need of competent discrimination algorithm also in short CL under 300ms and the difficult interpretation of an episode not only by the device but also by physicians in

decision making SVT or VT.

by the physician at each follow-up visit (figure 16a-b).

150 Cardiac Defibrillation

Detection and diagnose of arrhythmias in dual chamber devices is more complex, and the mechanism of decision making is harder to demonstrate. Discrimination algorithms are still based on the principles explained above. Significant addition is the comparison of atrial (A) and ventricular (V) frequency (figure 17). In case of V>A VT therapy is initiated directly. For cases with V=A or V<A further discrimination algorithms are used to differentiate between SVT and VT. For V<A programming of morphology and stability criteria is recommended. For V=A programming of morphology criterion may be sufficient. In addition for V<A episodes measurement of the A-V-A intervals may differentiate SVTs with 2:1 activation from VTs with VA dissociation during AF/Aflut. Measurement of A-V-A intervals by St. Jude Medical devi‐ ces (AV Detection Enhance™) is illustrated in figure 18a-b. This algorithm counts the last 12 AV intervals and calculates the difference between the second longest and second shortest AV interval; difference < 40ms suggests association between A and V and decides for SVT. A com‐ parable algorithm based on pattern recognition typical for Aflut or SVT with 1:1 AV-conduc‐ tion is used by Medtronic called PR-Logic™ and by Biotronik called SMART™. Sorin use an algorithm more orientated to CL stability called PARAD(+)™[9].

**Figure 17.** The rate branch differentiates between V<A, V=A and V>A. For VA dissociation a VT will therapies by ICD directly. In case of V=A a sinus tachycardia or other 1:1 SVT should inhibited by ICD and in case of retrograde activa‐ tion of a VT the ICD should delivered therapy. For V<A and AF/AFl therapy should inhibited and V<A with VT and cur‐ rent AF/AFl therapy should delivered.

**Figure 19.** This is an example for measurement Tachy/Sinus ratio. Over the last 12 interval the ratio 500/200 turns out 2.5. For this value the algorithm counts -1 and calculate this over the last 12 beats. For a value <3 SVT and >3 VT is

Tachycardia Discrimination Algorithms in ICDs

http://dx.doi.org/10.5772/52657

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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

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

dual chamber ICD is the necessity of atrial pacing.

assumed.

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

## **13. Tachy/Sinus ratio**

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.

**Figure 19.** This is an example for measurement Tachy/Sinus ratio. Over the last 12 interval the ratio 500/200 turns out 2.5. For this value the algorithm counts -1 and calculate this over the last 12 beats. For a value <3 SVT and >3 VT is assumed.
