**5. The arguments for and against performing DFT testing**

Since implanting ICD's in the early 1980's, VF induction and testing the device ability to re‐ store sinus rhythm not only helped in determining DFT's, but also allowed testing of the sensing capability of the device, the ability of the programmed algorithm to recognize the arrhythmia, and the ability of the capacitors to deliver the stored energy. This was an impor‐ tant step in testing a new device that is designed to treat a lethal arrhythmia. Patients who were found to have high threshold had intervention performed to attempt to lower the DFT's. If the thresholds could not be lowered then many physicians did not implant the de‐ vice. This was because of the concern that a shock might change a stable VT into VF and then not be able to terminate it. There were several reports of increased mortality in patients with high DFT and case reports of deaths due to failed defibrillation. [23,28,52-54] (table 5). Intuitively, finding DFT will result in reduced mortality as it allows the recognition of pa‐ tients who will not respond to the shock and therefore find a subgroup of patients who need further intervention. However, this matter is not so simple.

Testing involves induction of ventricular fibrillation in patients with significant heart dis‐ ease with a potential for morbidity and mortality. Complications associates with DFT test‐ ing include worsening heart failure, hemodynamic compromise, cerebrovascular accidents and even deaths. In the Canadian Experience study by Bernie et al which looked at 19,067 patients, thirty five patients (0.18%) had serious complications [61]. The recognition of the complications was coupled with improvements in the lead and defibrillator technology. In addition, ICD use expanded considerably after studies showed its benefit not only in secon‐ dary but also in primary prevention of sudden death. This changed the risk benefit ratio of DFT testing. Several studies gradually emerged that questioned the need to find DFT (ta‐ ble 5). This lack of benefit of DFT testing shown in several studies may be explained by several factors:

The proximal coil location should be in the high SVC and brachiocephalic area rather than

The phase duration of defibrillation is critical in achieving sinus rhythm [9-10]. The optimal phase duration is not exactly known and it can be optimized in some devices for individual

Changing a nominal parameter should not be taken lightly, as these are the ones tested and proven with clinical research. Any adjustment made to the settings should be verified by re‐

Several invasive choices that reduce DFT are available. Changing the RV lead location may reduce DFT. The standard RV position is the RV apex. This has the advantage of a stable position and good threshold. Alternative lead positions that have good thresholds are the right ventricular outflow tract (RVOT) and the septum. An active fixation system should be used in these areas. A right free wall position has the highest DFT [47-48]. Changing the shock vector may lower DFT. This can be achieved by incorporating subcutaneous array or an additional lead in the azygous vein or the coronary sinus [49-51]. Upgrading to higher

Since implanting ICD's in the early 1980's, VF induction and testing the device ability to re‐ store sinus rhythm not only helped in determining DFT's, but also allowed testing of the sensing capability of the device, the ability of the programmed algorithm to recognize the arrhythmia, and the ability of the capacitors to deliver the stored energy. This was an impor‐ tant step in testing a new device that is designed to treat a lethal arrhythmia. Patients who were found to have high threshold had intervention performed to attempt to lower the DFT's. If the thresholds could not be lowered then many physicians did not implant the de‐ vice. This was because of the concern that a shock might change a stable VT into VF and then not be able to terminate it. There were several reports of increased mortality in patients with high DFT and case reports of deaths due to failed defibrillation. [23,28,52-54] (table 5). Intuitively, finding DFT will result in reduced mortality as it allows the recognition of pa‐ tients who will not respond to the shock and therefore find a subgroup of patients who need

Testing involves induction of ventricular fibrillation in patients with significant heart dis‐ ease with a potential for morbidity and mortality. Complications associates with DFT test‐ ing include worsening heart failure, hemodynamic compromise, cerebrovascular accidents and even deaths. In the Canadian Experience study by Bernie et al which looked at 19,067 patients, thirty five patients (0.18%) had serious complications [61]. The recognition of the complications was coupled with improvements in the lead and defibrillator technology. In addition, ICD use expanded considerably after studies showed its benefit not only in secon‐ dary but also in primary prevention of sudden death. This changed the risk benefit ratio of

the low SVC and atrial area as the later is associated with higher DFT value [45].

peated induction and the reassurance of a successful defibrillation.

output devices may be useful in patients with borderline elevated thresholds.

**5. The arguments for and against performing DFT testing**

further intervention. However, this matter is not so simple.

patients with high DFT's [46].

126 Cardiac Defibrillation


It is therefore important to have to prospective randomized study to give us a clear an‐ swer. One prospective, but not randomized study (SAFE-ICD) showed no benefit of DFT testing [60]. The result of an ongoing study (SIMPLE trial) may give a more clear direc‐ tion once finished [70].

The approach to DFT testing has changed over time. A recent study in 111 Italian centers over the period 2007 to 2010 involving 2,082 patients documented the trend change [71]. It reported DFT testing to be performed in 38% of patients with the incidence declining annu‐ ally from 36% in 2007 to 28% in 2010. In 13% of centers, the test was performed routinely, and in 38% it was not performed at all. The reasons for not performing DFT testing in this survey were the policy of the center in 44%, a primary indication for the implant in 31% and doing a device replacement in 15%. Not doing DFT testing can certainly make the ICD im‐ plant simpler. The simplification is not just related to the procedure itself, but starts with the initial step of taking the consent from the patient. It is not a simple task to explain the risk to the patient in a lay term without confusing him. A physician has to explain that after the surgery has finished successfully, there will be a need to stop the heart; and that there is a chance, even though very small, that he may have a problem like stroke or that we may not be able to restore his heart to beat back again.


**Author details**

Address all correspondence to: munirzaqqa@yahoo.com

systole. *Am J Physiol*, 128, 500-505.

[1] Wiggers, C. J., & Wegria, R. (1940). Ventricular fibrillation due to single, localized in‐ duction and condenser shocks applied during the vulnerable phase of ventricular

Defibrillator Threshold Testing http://dx.doi.org/10.5772/52594 129

[2] Zima, E., Gergely, M., Soós, P., et al. (2006). The effect of induction method on defib‐ rillation threshold and ventricular fibrillation cycle length. *J Cardiovasc Electrophysiol.*,

[3] Yashima, M., Kim, Y. H., Armin, S., et al. (2003). On the mechanism of the probabilis‐ tic nature of ventricular defibrillation threshold. *Am J Physiol Heart Circ Physiol.*, Jan,

[4] Day, J. D., Doshi, R. N., Belott, P., Birgersdotter, , et al. (2007). Inductionless or limit‐ ed shock testing is possible in most patients with implantable cardioverter- defibrilla‐ tors/cardiac resynchronization therapy defibrillators: results of the multicenter ASSURE Study (Arrhythmia Single Shock Defibrillation Threshold Testing Versus Upper Limit of Vulnerability: Risk Reduction Evaluation With Implantable Cardi‐

[5] Swerdlow, C. D., Davie, S., Ahern, T., et al. (1996). Comparative reproducibility of defibrillation threshold and upper limit of vulnerability. *Pacing Clin Electrophysiol.*,

[6] Hwang, C., Swerdlow, C. D., Kass, R. M., et al. (1994). Upper limit of vulnerability reliably predicts the defibrillation threshold in humans. *Circulation.*, Nov, 90(5),

[7] Swerdlow, C. D., Ahern, T., Kass, R. M., et al. (1996). Upper limit of vulnerability is a good estimator of shock strength associated with 90% probability of successful defib‐ rillation in humans with transvenous implantable cardioverter-defibrillators. *J Am*

[8] Mirowski, M., Mower, M. M., Reid, P. R., et al. (1982). The automatic implantable de‐ fibrillator. New Modality for treatment of life-threatening ventricular arrhythmias.

overter-Defibrillator Implantations). *Circulation.*, May 8;, 115(18), 2382-9.

Jordan University Hospital, Jordan

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284(1), H249-55.

Dec, 19(12 Pt 1), 2103-11.

*Coll Cardiol.*, Apr, 27(5), 1112-8.

*Pacing Clin Electrophysiol.*, May, 5(3), 384-401.

2308-14.

Munir Zaqqa\*

**References**

**Table 5.** Studies favoring and against DFT testing.

## **6. Conclusion**

The approach to DFT testing has changed since ICD's were first introduced. It has changed from being an essential part performed in all the patients to being done in less than one third of the patients at current time. The need for DFT testing is a balance between benefit and risk with studies showing conflicting results. Most recent studies show equal benefit risk ratio for DFT testing. A prospective randomized study is needed to resolve the issue and there is currently one being performed. When this study is finished it should give a more clear answer regarding this issue.
