**2.3 Epidemiology**

DCM ranks third as the cause of SCD among cardiomyopathies, after arrhythmogenic right ventricular cardiomyopathy (ARVC) and hypertrophic cardiomyopathy. SCD accounts for roughly a third of all-cause mortality among hereditary DCM patients. Rates of SCD vary among the patients in regard to their New York Heart Association (NYHA) functional status (**Table 2**). Notably, in patients with NYHA class I and II, 50–60% of deaths are classified as sudden, while in NYHA class IV patients, only 20–30% of deaths are sudden [10]. This is explained by the fact that in NYHA class IV, most patients die from progressive heart failure [12]. In most cases, potentially fatal arrhythmias present in a setting of systolic ventricular dysfunction, although the proportion of SCD is higher among patients with lower NYHA status. However, there is a subset of patients (reported to vary from 2% to one third of the DCM population) who present early in the disease course with


#### **Table 2.**

*Risk of sudden cardiac death as a proportion of overall mortality according to New York Heart Association classification.*

**161**

DCM at any age, is also an established risk factor.

**2.4 Risk stratification**

**Table 3.**

*Sudden Cardiac Death in Hereditary Dilated Cardiomyopathy*

Clinical Low LVEF (<25–30%)

Genetic Desmosomal mutations

*Factors associated with a high risk of life-threatening arrhythmias.*

life-threatening arrhythmias (**Table 3**) or unexplained syncope that are not related to the severity of LV dysfunction [13, 14]. This specific entity is referred to as arrhythmogenic DCM (AR-DCM). Patients who suffer from AR-DCM, compared to other DCM patients, have a higher risk of experiencing major arrhythmic events and SCD. Thus, a family history of SCD in an AR-DCM patient results in a higher burden of life-threatening arrhythmias and a higher risk of SCD [7]. It is important to mention that DCM patients, due to their high incidence of atrial fibrillation, also have a higher risk for ischemic stroke. However, it should be noted that if a cause of death other than arrhythmia is confirmed, the death will not be classified as sudden.

Absence of beta-blockers

NSVT on Holter monitoring

Mechanical dispersion

LMNA mutation SCN5A mutation FLNC mutation RBM20 mutation PLN mutation

Impaired global longitudinal strain

Family history of SCD

AR-DCM

Imaging Midwall late gadolinium enhancement

QT dynamicity T-wave alternans

It is crucial to identify patients at high risk of a fatal arrhythmia. There are clues in the clinical history, electrocardiographic, imaging characteristics, and specific genetic features that need to be taken into account. Factors such as QRS duration, QT-interval dispersion, and T-wave alternans have been suggested as risk markers [15]. A considerable burden of ventricular arrhythmias (runs of VT) is usually present in a setting of advanced ventricular dysfunction with left ventricular ejection fraction (LVEF) <25%, which is a validated risk factor. Survived cardiac arrest and sustained ventricular tachycardia with hemodynamic compromise imply a high risk of recurrent arrhythmia and are classified as secondary prevention for an implantable cardioverter defibrillator (ICD) [16]. Unexplained syncope may be secondary to arrhythmia and constitutes a risk factor [15]. In the Marburg Cardiomyopathy study (MACAS), which excluded patients with a history of sustained VT or VF, unexplained syncope within the previous 12 months, and amiodarone therapy, it was shown that a low LVEF (<30%) was the only independent factor for major arrhythmic events. Patients with NSVT and patients who were not on beta-blockers upon enrollment also run a high risk for ventricular arrhythmias. Thus, the combination of documented NSVT on Holter monitoring with a low LVEF (<30%) increased the arrhythmic risk by eight-fold [17]. Family history of SCD, defined as SCD in a first degree relative <40years of age or SCD in a relative with confirmed

*DOI: http://dx.doi.org/10.5772/intechopen.91702*

**Factors associated with a high risk of arrhythmias**

Ambulatory QRS duration


#### **Table 3.**

*Factors associated with a high risk of life-threatening arrhythmias.*

life-threatening arrhythmias (**Table 3**) or unexplained syncope that are not related to the severity of LV dysfunction [13, 14]. This specific entity is referred to as arrhythmogenic DCM (AR-DCM). Patients who suffer from AR-DCM, compared to other DCM patients, have a higher risk of experiencing major arrhythmic events and SCD. Thus, a family history of SCD in an AR-DCM patient results in a higher burden of life-threatening arrhythmias and a higher risk of SCD [7]. It is important to mention that DCM patients, due to their high incidence of atrial fibrillation, also have a higher risk for ischemic stroke. However, it should be noted that if a cause of death other than arrhythmia is confirmed, the death will not be classified as sudden.

## **2.4 Risk stratification**

It is crucial to identify patients at high risk of a fatal arrhythmia. There are clues in the clinical history, electrocardiographic, imaging characteristics, and specific genetic features that need to be taken into account. Factors such as QRS duration, QT-interval dispersion, and T-wave alternans have been suggested as risk markers [15]. A considerable burden of ventricular arrhythmias (runs of VT) is usually present in a setting of advanced ventricular dysfunction with left ventricular ejection fraction (LVEF) <25%, which is a validated risk factor. Survived cardiac arrest and sustained ventricular tachycardia with hemodynamic compromise imply a high risk of recurrent arrhythmia and are classified as secondary prevention for an implantable cardioverter defibrillator (ICD) [16]. Unexplained syncope may be secondary to arrhythmia and constitutes a risk factor [15]. In the Marburg Cardiomyopathy study (MACAS), which excluded patients with a history of sustained VT or VF, unexplained syncope within the previous 12 months, and amiodarone therapy, it was shown that a low LVEF (<30%) was the only independent factor for major arrhythmic events. Patients with NSVT and patients who were not on beta-blockers upon enrollment also run a high risk for ventricular arrhythmias. Thus, the combination of documented NSVT on Holter monitoring with a low LVEF (<30%) increased the arrhythmic risk by eight-fold [17]. Family history of SCD, defined as SCD in a first degree relative <40years of age or SCD in a relative with confirmed DCM at any age, is also an established risk factor.

#### **2.5 Imaging**

Imaging can be used to predict arrhythmia risk. In cardiac magnetic resonance imaging, midwall late gadolinium enhancement (LGE) can detect fibrosis. Even if magnetic resonance imaging is not able to detect fibrosis, it may still be found by advanced T1 mapping techniques before and after gadolinium infusion. This is a prominent finding due to the fact that it corresponds to macroscopic midmyocardial fibrosis on postmortem examination [18]. In echocardiography, an impaired global longitudinal strain, a marker of myocardial regional contractility, may reflect myocardial fibrosis [19]. It has been demonstrated that an impaired global longitudinal strain is associated with increased arrhythmic events [20]. A predictor of arrhythmias is also mechanical dispersion, which is defined as the standard deviation of the time to peak negative strain among the different myocardial segments [20].
