**1. Introduction**

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 in United States [3].

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‐ mias (ventricular fibrillation/ tachycardia) [5].

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) [7], [8].

Implantable cardioverter defibrillators (ICD) are devices currently available capable of abort life-threatening ventricular tachyarrhythmias and therefore prevent SCD.

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 implantation.

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‐

dia causing severe symptoms [10]. The Canadian Implantable Defibrillator Study (CIDS) trial showed a 20% relative risk reduction in mortality with ICD therapy compared to amio‐ darone [11], although not statistically significant*.* The Cardiac Arrest Study Hamburg (CASH) trial confirm, though not with a statistical level of significance, the beneficial role of ICD therapy in the treatment of cardiac arrest survivors during long-term follow-up [12].A meta-analysis of these trials showed a 28% reduction in mortality due predominantly to a reduction in arrhythmic death [13].

[22] or symptomatic heart failure (HF). Premature ventricular complexes (PVC) predict an increased risk of SCD during long-term follow-up, especially if ≥ 10 PVC per hour. The pres‐ ence of frequent PVCs during or after exercise has been associated with greater risk for seri‐

Sudden Death in Ischemic Heart Disease http://dx.doi.org/10.5772/52661 47

Several other parameters are considered predictors of sudden death, but all with low or moderate predictive values, whose sensitivity and specificity have not yet been studied in

Different noninvasive exams that allow quantification of ischemia (cardiac SPECT) [23], characterization of longitudinal strain abnormalities (echocardiography) [24] or MI scar (Cardiac Magnetic Resonance ) [25], T wave alternant (ECG) or the presence and extent of sympathetic denervation(cardiac 123I-MIBG imaging) were used in order to improve risk

To date, seven multicenter studies were essential for defining the criteria and timing for ICD implantation in ischemic heart disease: Multicenter Automatic Defibrillator Implantation Trial (MADIT [28]), Coronary Artery Bypass Graft Patch (CABG-Patch) [29], Multicenter Unsustained Tachycardia Trial (MUSTT) [30], MADIT II [31], Defibrillators In Acute Myo‐ cardial Infarction Trial (DINAMIT) [32], Sudden Cardiac Death in Heart Failure (SCD-

Low LV ejection fraction (up to 30 to 40%) was the inclusion criterion similar in all of these

Specific criteria in each of the studies were the presence of non sustained ventricular tachy‐ cardia and electrophysiological study showing inducible VT (MADIT and MUSTT), recent coronary revascularization and abnormal signal-averaged ECG (CABG-Patch), recent MI

Based on these trials, the American College of Cardiology, American Heart Association and the European Society of Cardiology guidelines recommend the implementation of ICDs in all patients with an ejection fraction inferior or equal to 30%, as well as patients with EF less than 35% with heart failure New York Heart Association (NYHA) class II or III. ICD can be considered in postinfarction patients with EF to 40% who have sustained ventricular ar‐

As a rule, ICD implantation is not indicated in patients recovering from an acute MI (less

The Number needed to treat (NNT) of ICD implantation in quite different between the trials depending on the severity of the patients evaluated and varied between 4 in MUSTT and 14

than 40 days) or CABG surgery (within 90 days) or in patients with NYHA class IV.

and Immediate Risk Stratification Improves Survival (IRIS) [33].

ous cardiovascular events but not specifically SCD.

stratification of sudden death in ischemic cardiomyopathy [26], [27].

detail in large patient populations.

**3. Primary prevention trials**

(DINAMIT, IRIS) and heart failure (SCD-HeFT).

rhythmias inducible during electrophysiology study [14].

HeFT)8

studies.

in SCD-HeFT [34].

Thus, patients with ventricular tachyarrhythmias (VT or VF), not secondary to a transi‐ ent or reversible cause, meet a Class I indication for ICD therapy. In addition, patients with syncope and significant documented VT/VF also meet indications for ICD therapy (Level of Evidence A) [14].

However it is worth noting that, in most centers, the deployment of an ICD for primary pre‐ vention far exceeds the number of devices placed for secondary prevention.

Compared to optimal medical therapy, the use of ICDs in recent trials for primary prophy‐ laxis in CHD population was associated with a reduction in 5-year all-cause mortality of 23% to 36% and a reduction in absolute mortality of 1.5% to 3% per year.
