**5. Autonomic variables**

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

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‐

It seems that reverse remodeling had a dual effect of both heart failure and arrhythmia risk

Classically, the presence of Left Bundle Branch Block (LBBB) was considered of major prog‐ nostic importance, associated with the occurrence of sudden death in patients with ischemic heart disease. This was based on earlier studies, most of them performed before the era of

In more recent investigations, especially those resulting from secondary analyses of MUSTT and MADIT-II trials, it has become clear that QRS prolongation is related with mortality af‐ ter MI, although the magnitude of the relationship between abnormal intraventricular con‐

In an analysis of MUSTT trial, the authors noted that patients with LBBB had lower ejection fractions and higher incidence of symptomatic heart failure, suggesting that the increase in

In the MADIT-II cohort with prolonged QRS its duration (QRSd) was found to be an inde‐ pendent predictor of SCD in medically managed patients (HR 2.12) but not in ICD-treated patients (HR 0.77).This was attributed to the fact that ICD-treated MADIT II patients died

In the cardiac resynchronization therapy trial (MADIT-CRT), CRT dramatically reduces the progression of HF in patients with a low ejection fraction and a wide QRS complex. QRS du‐ ration and morphology was considered an important prognostic factor indicating more ad‐

Other electrocardiographic parameters in which the prognostic value was evaluated were T-wave alternant (MTWA), the signal-averaged ECG (SAECG) and QT parameters and

One of the parameters with more consistent results was MTWA. TWA consist of a fluctua‐ tion of the amplitude or morphology of the T wave every other beat assessed during exer‐

predominantly of non-sudden HF, and QRSd would not predict HF mortality [42]

depolarization and prolongation of QT interval [37].

mias at 1-year post-implantation.

**4. ECG measurements**

vanced cardiac pathology [43].

cise testing or atria pacing [45].

dynamics [44].

percutaneous coronary revascularization [39].

duction and SCD in CHD remains unclear [40].

overall mortality was probably due to a sicker population [41].

reduction [38].

48 Cardiac Defibrillation

The main variables studied included the autonomic heart rate variability (HRV)/turbulence and the baroreceptor sensitivity.

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 different measures derived from 24-h Holter recordings.

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 patients [50].

Methods based on non-linear dynamics and HR turbulence seams to provide better prog‐ nostic information than the traditional ones [51], [52].

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

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

Despite these promising results, further prospective studies are needed to determine the usefulness of these parameters in clinical practice.

Reduced baroreflex sensivity, a quantitative index of primarily vagal reflexes, evaluated by the phenylephrine method or by a non-invasive measurement [55], is also useful in assess‐ ing the risk of SCD [56, 57].

sociated with a high risk for VT/FV and the characteristics of NSVT could not predict the

Sudden Death in Ischemic Heart Disease http://dx.doi.org/10.5772/52661 51

The echocardiogram is a fundamental exam for the identification of candidates for ICD im‐ plantation. Although an LVEF of <40% is commonly used for stratification of patients at risk for ventricular arrhythmias, it does not allow accurate discrimination of patients with or without sudden arrhythmic death. Moreover, sudden arrhythmic death also occurs in pa‐

The technical advances in echocardiography will probably allow exploring the appraisal val‐ ue of new variables beyond the ejection fraction of the left ventricle in the risk stratification.

In a unicenter study a greater involvement of peri-infarct zone longitudinal strain was inde‐ pendently associated with an increased risk of having an appropriate ICD therapy on followup. In such study the odds of dying in a patient with a peri-infarct zone strain value of -6% was approximately 11.5 times that of a patient with a peri-infarct zone strain value of -17% [65].

Cardiac MRI allows characterization of cardiac morphology in patients with poor echo car‐ diographic window and provides an estimate of the location and amount of intramyocardial

The presence of myocardial scar or fibrosis as measured by delayed enhancement after ad‐ ministration of gadolinium has been recently associated with post-infarct arrhythmic death [66], [67] suggesting that contrast-enhanced MRI may enable better risk stratification for ICD implantation among patients with prior MI compared with traditional variables such as

Roes S et al identified infarct tissue heterogeneity on contrast-enhanced MRI as a strong pre‐ dictor of spontaneous ventricular arrhythmia in ICD therapy recipients [68]. In a more re‐ cent study from a tertiary center which included the monitoring of 52 patients, it was identified a relationship between the transmurality of infarction and the occurrence of spon‐

Ischemic heart disease is the heart disease in which most often there is indication for an ICD implantation. However, after placed, these devices are used in a minority of patients in the

taneous ventricular arrhythmias in patients with chronic ischemic cardiopathy [69].

inducibility [63].

**8. Echocardiographic parameters**

tients with an LVEF of ≥40% [64].

**9. Cardiac magnetic resonance**

fibrosis.

LVEF and NYHA class.

**10. Conclusion**

context of primary prevention.
