**8. Sudden onset**

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 slowly and gradually. Other SVTs or ventricular arrhythmias cause a sudden and marked jump in the heart rate (or fall in CL). Primary role of the Sudden onset criterion is therefore the diagnose of sinus tachycardia (figures 10 and 11). However, in some studies the algo‐ rithm using this criterion resulted in delayed VT detection (figure 12) or could not show sig‐ nificant reduction of inappropriate ICD therapy (table 5). Therefore, programming of sudden onset criterion is recommended above all in younger patients who could reach high HR at physical activity and could tolerate longer the hemodynamic consequences of a po‐ tential VT. This group is generally underrepresented in large ICD studies, which may be the reason why the effect on the incidence of inappropriate ICD therapy could not be proven.

**Programming Inappropriate shock No inappropriate shock P value**

Tachycardia Discrimination Algorithms in ICDs

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

147

Lowest VT zone (beats/min) 169.3 ± 19.9 171.9 ± 14.5 0.540 Lowest VT zone detection time (s) 2.45 ± 1.99 2.42 ± 2.07 0.830 Stability on % (n) 17 (14) 36 (30) 0.030 Sudden onset on % (n) 16 (13 23 (19) 0.160

V>a on% (n) 31 (10) 50 (18) 0.054 Atrial fibrillation discriminator on % (n) 34 (11) 44 (16) 0.210

**Table 5.** Influences of discrimination algorithms to inappropriate ICD-shock according to single and dual chamber

**Figure 12.** Notice prolonged detection of sustained VT caused by graduated onset algorithm of a Medtronic device. There is a VT with obviously change in vector and stable CL of 370 ms. The graduated onset is calculated graduated

Depending from manufacturers a time window can be defined for SVT/VT discrimination in VT zones. In case of an episode identified as SVT the device may suspend the programmed

caused by 10 beats of another tachycardia leads to a negative sudden onset criteria.

Number of patients 83 83

Number of patients 32 36

Single chamber

Dual chamber

**9. Timer**

detection in MADIT II trial [4].

**Figure 10.** Demonstration of sudden onset calculation: The device compares RR1 with mean from RR2 to RR5 (Biotro‐ nik), onset (%) = (RR1\*100]/mean from RR2 to RR5 for Boston, standard 10% or for Medtronic graduated onset (%) mean from RR1 to RR4 / mean RR5 to RR8, standard 81%

**Figure 11.** Demonstration of the St. Jude Medical algorithm for sudden onset (standard ∆150-160]. In this case of ∆ <200ms the algorithm decides for SVT.


**Table 5.** Influences of discrimination algorithms to inappropriate ICD-shock according to single and dual chamber detection in MADIT II trial [4].

**Figure 12.** Notice prolonged detection of sustained VT caused by graduated onset algorithm of a Medtronic device. There is a VT with obviously change in vector and stable CL of 370 ms. The graduated onset is calculated graduated caused by 10 beats of another tachycardia leads to a negative sudden onset criteria.

## **9. Timer**

slowly and gradually. Other SVTs or ventricular arrhythmias cause a sudden and marked jump in the heart rate (or fall in CL). Primary role of the Sudden onset criterion is therefore the diagnose of sinus tachycardia (figures 10 and 11). However, in some studies the algo‐ rithm using this criterion resulted in delayed VT detection (figure 12) or could not show sig‐ nificant reduction of inappropriate ICD therapy (table 5). Therefore, programming of sudden onset criterion is recommended above all in younger patients who could reach high HR at physical activity and could tolerate longer the hemodynamic consequences of a po‐ tential VT. This group is generally underrepresented in large ICD studies, which may be the reason why the effect on the incidence of inappropriate ICD therapy could not be proven.

**Figure 10.** Demonstration of sudden onset calculation: The device compares RR1 with mean from RR2 to RR5 (Biotro‐ nik), onset (%) = (RR1\*100]/mean from RR2 to RR5 for Boston, standard 10% or for Medtronic graduated onset (%)

**Figure 11.** Demonstration of the St. Jude Medical algorithm for sudden onset (standard ∆150-160]. In this case of ∆

mean from RR1 to RR4 / mean RR5 to RR8, standard 81%

146 Cardiac Defibrillation

<200ms the algorithm decides for SVT.

Depending from manufacturers a time window can be defined for SVT/VT discrimination in VT zones. In case of an episode identified as SVT the device may suspend the programmed therapy only within this specified time interval, when the time runs out, the device delivers VT therapy (SVT time out). Also in case of an episode identified as VT the device may switch to the VF therapy after a specified time interval (VT time out). Generally these coun‐ ters are not recommended because SVTs usually continue for longer time periods and such timer could force an ATP or shock delivery inappropriately. However, in individual cases (e.g. in patients with very low ejection fraction who could not tolerate higher HR for a lon‐ ger time) programming a time out intervals may be considered for safety reasons.
