**Author details**

Jolley et al.[47] used image-based finite element models (FEM) to predict the myocardial electric field generated during defibrillation shocks (pseudo-DFT) in a wide variety of subcutaneous electrode positions to determine factors affecting optimal lead positions for subcutaneous implantable cardioverter-defibrillators (S-ICD). An image-based FEM of an adult man was used to predict pseudo-DFTs across a wide range of technically feasible S-ICD electrode placements. Generator location, lead location, length, geometry and orientation, and spatial relation of electrodes to ventricular mass were systematically varied. Best electrode configurations were determined, and spatial factors contributing to low pseudo-DFTs were identified using regression and general linear models.[47] One previously published and validated S-ICD configuration[48] was selected as the base case for normalization of the predicted DFTs of all tested configurations. This is the system proposed by Lieberman et al[48], which uses a low, medial pectoral position of an active generator and a 25-cm posterolateral electrode extending around the back of the left thorax between the 6th and 10th intercostal

The study by Jolley and colleagues revealed that a wide variety of conceivable electrode orientations, some of them quite unusual and not previously reported, were predicted to be as effective or more effective than the base case (pseudo-DFT ratio <=1).[47] Univariate modeling results suggested that a variety of anatomical factors affecting the geometry of system configuration influenced pseudo-DFT. Placement of the generator in the parasternal position was more efficient than more lateral and remote positions (mid-clavicular, anterioraxillary, abdominal). Anterolateral and posterior electrode positions were better than para‐ sternal, and anterolateral better than anterior. Right-sided generators were more efficient than left-sided generators, whereas the converse was true for electrode laterality. Although some of these alternatives represent simple modifications of the previously proposed system, many involve changes in lead design and implant technique that are substantial; in particular, the

Multivariate modeling using linear regression models showed that favorable alignment of shock vector with ventricular myocardium, increased lead length, can horizontal position, contralateral lead-generator position, and distance of can from the heart independently predicted pseudo-DFTs. The relative positions of the generator, the lead(s), and the ventricular myocardium accounted for nearly half of the predicted variability in the pseudo-DFT. This reflects the intuitive observation that electrodes should be positioned to place the heart as nearly between them as possible. This multivariate analysis revealed important principles that may guide the design of subcutaneous ICDs. Placement of the electrodes to align the interelectrode shock vector as closely as possible to the center of mass of the ventricular myocar‐ dium, and use of longer electrode coil lengths are associated with lower DFTs and account for the majority of variability of this parameter. Manipulation of electrode length contributed almost 25% of the variability in pseudo-DFTs, with decreases in pseudo-DFTs predicted with extension of coil length from 5 to 10 cm and longer. Neither of these factors has previously been quantified for subcutaneous electrode placement and may prove useful in determining optimal orientations. Notably, although electrode arrays were often identified as useful in many efficient configurations, the use of an array was generally not necessarily more efficient than a single electrode of equal length similarly positioned. This finding implies both for S-

space, extending the tip as close to the spine as possible.

38 Cardiac Defibrillation

contralateral placement of generator and lead.

Dan Blendea1 , Razvan Dadu2 and Craig A. McPherson2


## **References**


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**Section 3**

**Worth Knowing About Indication, Long-Term**

**Benefit, Challenges, and Monitoring of ICD**

**Therapy**


**Worth Knowing About Indication, Long-Term Benefit, Challenges, and Monitoring of ICD Therapy**

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**Chapter 3**

**Sudden Death in Ischemic Heart Disease**

Sudden cardiac death (SCD) is defined by the death from unexpected circulatory arrest, usu‐ ally due to a cardiac arrhythmia occurring within one hour of the onset of symptoms [1].

It is a major health problem worldwide, with a prevalence estimated in the range of 300 000 to 350 000 cases per year in the United States [2]. Event rates in Europe are similar to those

Coronary heart disease (CHD) is the leading cause of SCD explaining approximately 80% of cases [4]; cardiomyopathies and primary electrical abnormalities account for most of the re‐ mainder. Approximately 50% to 70% of these deaths are related to ventricular tachyarrhyth‐

Available medical therapies, such as beta-blockers [6] or anthiarrhytmic drugs including amiodarone, failed to abolish the occurrence of SCD after a myocardial infarction (MI)

Implantable cardioverter defibrillators (ICD) are devices currently available capable of abort

Although it is not possible to prevent all cases of SCD in the general population, the main issue is the identification of individuals at increased risk that may benefit from ICD

The highest risk of SCD in various heart diseases, either genetic or acquired, is related with the previous occurrence of ventricular arrhythmias [9].In secondary prevention, predomi‐ nantly three randomized clinical trials have established the criteria for ICD implantation.

The antiarrhythmics versus Implantable Defibrillators (AVID) trial showed mortality reduc‐ tion with ICD among survivors of ventricular fibrillation or sustained ventricular tachycar‐

and reproduction in any medium, provided the original work is properly cited.

© 2013 Martins; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

© 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

life-threatening ventricular tachyarrhythmias and therefore prevent SCD.

Additional information is available at the end of the chapter

mias (ventricular fibrillation/ tachycardia) [5].

Elisabete Martins

**1. Introduction**

in United States [3].

[7], [8].

implantation.

http://dx.doi.org/10.5772/52661
