**6. Discrimination SVT/VT**

Discrimination of SVT and VT may present a challenge not only for devices using artificial intelligence and programmed algorithms but even for experienced physicians. Principally the following wide QRS complex arrhythmias should be considered: VT, SVT with bundle branch block, SVT with accessory pathway or pacing in left (via coronary sinus) or right ventricle. Table 3 shows the discrimination criteria of the 12 channel ECG for SVT/VT. No single criterion is sensitive and specific enough to provide sufficient discrimination value. Therefore, combination of several criteria should be implemented in the device algorithms to correctly diagnose arrhythmias. Table 4 shows the availability of discrimination criteria in single or dual chamber ICDs.

**7. Stability**

tive intervals to calculate mean difference.

tricular tachycardia and atrial fibrillation AF.

**8. Sudden onset**

Stability is the variability of tachycardia CL (figure 9). In general, VTs have a reasonably stable CL while numerous SVTs have beat-to-beat variability in their CL (AF, Sinus tachycardia, etc). However, some SVTs may have stable CL as well: circus movement tachycardia, atrioventricu‐ lar nodal re-entry tachycardia or atrial flutter (Aflut) – so this criterion has his limitations. Even AF may have a quite stable CL in the case of very high frequency. Anyway, several random‐ ized controlled studies {e.g. MADIT II [7]} proved a significant decrease (p=0.030) of inappro‐ priate ICD therapies (table 5). Therefore, programming of stability criterion is recommended in single chamber devices up to 260ms CL and indual chamber devices in the case V <A. The programmed value depends on the manufacturer, and lies in general for single and dual cham‐ ber devices around 40ms (-20 to + 20ms) [8]. Boston and St. Jude Medical use the last 12 consec‐ utive intervals and compare the second longest and the shortest interval to calculate the difference in ms (or percentage ratio). Medtronic and Biotronik use the last 3 and 4 consecu‐

Tachycardia Discrimination Algorithms in ICDs

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

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**Figure 9.** Notice variability of CL in ms (in red numbers) from beat to beat in normal sinus rhythm, monomorphic ven‐

Initiation of the tachycardia may also provide information on the mechanism and origin of the arrhythmia. The heart rate in the case of a sinus tachycardia at physical activity rises


**Table 3.** Sensitivity (in sense of frequency) and specificity of different ECG criteria for differentiation SVT and VT.


**Table 4.** Variation of SVT and VT discrimination criteria in single and dual chamber ICDs (+ achievable; - not achievable).
