**3. Primary prevention trials**

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

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

However it is worth noting that, in most centers, the deployment of an ICD for primary pre‐

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

Coronary disease is the main etiology of heart disease in Western countries and the major cause of heart failure and SCD.It is defined by the presence of significant coronary stenosis

Sudden death associated with CHD may occur in the acute context or months to years after MI. At least 50% of all SCDs due to CHD occur as a first clinical event and among subgroups

SCD risk is associated with the conventional risk factors for coronary atherosclerosis [16] in‐ cluding obesity, smoking [17], genetic predisposition [18], [19], ECG pattern of LVH or

The rhythm most often recorded at the time of sudden cardiac arrest is VT or VF [21]. The pathophysiological mechanism underlying the arrhythmias can be variable and mul‐

Transient factors may interact with a fixed substrate that, in ischemic heart disease, is attrib‐

In chronic stage of CHD, the occurrence of SCD has an inverse relation with EF of left ven‐ tricle and, at present, this is the parameter most widely used to categorize "high risk" pa‐

Other factors that have been demonstrated to contribute to the risk for SCD after MI include the presence of non-sustained ventricular tachycardia (nsVT), inducible VT by EP testing

LBBB, certain angiographic parameters or heart rate profile during exercise [20].

vention far exceeds the number of devices placed for secondary prevention.

23% to 36% and a reduction in absolute mortality of 1.5% to 3% per year.

in a main coronary vessel or by the demonstration of previous MI.

of patients thought to be at relatively low risk for SCD [15].

reduction in arrhythmic death [13].

(Level of Evidence A) [14].

46 Cardiac Defibrillation

**2. Clinical parameters**

tifactorial.

tients for SCD.

uted to scar-based re-entry.

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-HeFT)8 and Immediate Risk Stratification Improves Survival (IRIS) [33].

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

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

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‐ rhythmias inducible during electrophysiology study [14].

As a rule, ICD implantation is not indicated in patients recovering from an acute MI (less than 40 days) or CABG surgery (within 90 days) or in patients with NYHA class IV.

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 in SCD-HeFT [34].

There is still a controversy regarding the effect of Cardiac Resynchronization Therapy (CRT) on the risk of ventricular tachyarrhythmias, specially in patients at higher risk of heart fail‐ ure [36].Some studies suggested that epicardial activation in CRT may cause dispersion of depolarization and prolongation of QT interval [37].

A positive MTWA determined an approximately 2.5-fold higher risk of cardiac death and life-threatening arrhythmia and showed a very high negative predictive value both in ische‐ mic [46] and no ischemic patients . According to guidelines, it is a recommendation class IIa the use of TWA to improve the diagnosis and risk stratification of patients with ventricular

Sudden Death in Ischemic Heart Disease http://dx.doi.org/10.5772/52661 49

In a small study in patients post-MI and EF less than or equal to 30%, microvolt TWA was better than QRS duration at identifying a high-risk group and also a low-risk group unlikely

SAECG permits the identification of low-amplitude signals (microvolt level) at the end of the QRS complex referred to as late potentials. These indicate regions of abnormal myocar‐ dium with slow conduction believed to serve as markers of the substrate for reentrant ven‐ tricular tachyarrhythmias [48]. It has a high negative predictive value but its value is lower

The main variables studied included the autonomic heart rate variability (HRV)/turbulence

HRV corresponds to a beat-to-beat variance in cardiac cycle length resulting from the sym‐ patho-vagal influence on the sinus node. HRV is a term that encompasses a large number of

In general, if such measures are extremely low, it is considered that there is autonomic dys‐ function and this has been shown to independently predict the risk of SCD in post-infarct

Methods based on non-linear dynamics and HR turbulence seams to provide better prog‐

Several studies have evaluated the prognostic value of heart rate variability in patients with ischemic heart disease [53]. In the randomized defibrillator in AMI trial (DYNAMIT), which used reduced SDNN combined with reduced left ventricular ejection fraction measured ear‐ ly (within 2weeks) after AMI as an inclusion criterion, there was no mortality benefit from

On the contrary, in the cardiac arrhythmias and risk stratification after myocardial infarction (CARISMA) study, reduced HR variability measured at 6weeks after AMI, particularly the very-low frequency spectral component, was a powerful index in predicting arrhythmic events. The REFINE trial (Risk estimation after infarction, non-invasive evaluation) con‐ firmed that HRV and HR turbulence yield more powerful prognostic information for ar‐

Despite these promising results, further prospective studies are needed to determine the

arrhythmias [14].

to benefit from ICD therapy [47].

after coronary revascularization. [49]

**5. Autonomic variables**

and the baroreceptor sensitivity.

patients [50].

different measures derived from 24-h Holter recordings.

nostic information than the traditional ones [51], [52].

ICD therapy in these presumably high risk patients [32].

usefulness of these parameters in clinical practice.

rhythmic events when measured later (6–10weeks) after AMI [54].

Recently, MADIT-CRT trial showed an inverse association between reverse remodeling and the risk of subsequent ventricular tachyarrhythmias: in high responders to resynchroniza‐ tion therapy (defined as ≥25% reduction in LVESD), there was a 55% lower risk of arrhyth‐ mias at 1-year post-implantation.

It seems that reverse remodeling had a dual effect of both heart failure and arrhythmia risk reduction [38].
