Cardiac magnetic resonance with late gadolinium enhancement (LGE) is a well-established method for in vivo detection of myocardial scarring. Several recent studies have investigated the prognostic value of LGE in patients with hypertrophic cardiomyopathy (HC). We discuss the prevalence and patterns of scarring in HC and its pathophysiologic significance, with focus on ventricular arrhythmias and sudden cardiac death. The available evidence that myocardial scar demonstrated by LGE is a good independent predictor of cardiac mortality in HC is summed up. Recommendations of current guidelines for prevention of sudden cardiac death in HC are discussed with regard to recent results, and the significance of LGE as an emerging risk factor is pointed out. In conclusion, it is demonstrated that LGE has incremental value in addition to clinical risk factors for risk stratification and management of patients with HC.
Hypertrophic cardiomyopathy (HC) is a complex genetic cardiac disorder with substantial variability in phenotypic expression and natural progression. Population prevalence is estimated to be 1 in 500. Recent studies have demonstrated the utility of cardiac magnetic resonance (CMR) in addition to classic clinical risk factors with regard to prediction of cardiac death. We describe the available evidence that myocardial scar demonstrated by late gadolinium enhancement (LGE) is a good independent predictor of cardiac mortality (including sudden cardiac death [SCD]) and might therefore provide incremental value in addition to clinical risk factors for management of patients with HC.
Prognosis
HC is a common cause for SCD in young adults including competitive athletes, often occurring in mildly or even completely asymptomatic patients. Apart from SCD, HC may progress to advanced heart failure (“end-stage phase”) with left ventricular remodeling, systolic dysfunction, and an even higher risk of cardiac death. Unfortunately, the average loss of a patient’s lifetime caused by an HC-induced lethal event is much greater than that caused by most other heart diseases because of the early manifestation of HC, often with sudden death without previous warning.
Myocardial Scarring in HC
CMR offers not only high spatial resolution and complete 3-dimensional coverage of the entire heart but also can visualize myocardial scarring in vivo by LGE. Even small scars, which are not detectable with any other technique, can be visualized. LGE has been demonstrated to be a marker of adverse outcomes in ischemic and nonischemic cardiomyopathies. Because scarring is an established substrate for occurrence of ventricular tachyarrhythmias and SCD in patients with coronary artery disease, the same is suspected in HC.
Choudhury et al were the first to demonstrate that myocardial scarring visualized by LGE is a common finding in patients with HC (present in 81%). The pattern of scarring in HC does not correspond to perfusion territories of epicardial coronary arteries but is related to areas of hypertrophy, with typical patchy or multiple foci. These scars are predominantly located within the mid myocardium, whereas in ischemic heart disease a subendocardial pattern is typical. Examples of characteristic scarring in HC are shown in Figures 1 and 2 . Moon et al also described a high prevalence of LGE in patients with HC (79%). During follow-up, extent of scar visualized by CMR was associated with progressive ventricular dilation and clinical markers of SCD. A more recent study by Adabag et al demonstrated that myocardial scarring indicated by LGE not only was associated with a sevenfold increase in risk of nonsustained ventricular tachyarrhythmias but also was the only independent predictor of this arrhythmia. Consequently, LGE might be regarded a predictor of adverse events in the setting of HC. Figure 1 visualizes typical findings of a patient from our institution with extensive areas of LGE and sustained ventricular tachycardia illustrating this concept.
Myocardial Scarring in HC
CMR offers not only high spatial resolution and complete 3-dimensional coverage of the entire heart but also can visualize myocardial scarring in vivo by LGE. Even small scars, which are not detectable with any other technique, can be visualized. LGE has been demonstrated to be a marker of adverse outcomes in ischemic and nonischemic cardiomyopathies. Because scarring is an established substrate for occurrence of ventricular tachyarrhythmias and SCD in patients with coronary artery disease, the same is suspected in HC.
Choudhury et al were the first to demonstrate that myocardial scarring visualized by LGE is a common finding in patients with HC (present in 81%). The pattern of scarring in HC does not correspond to perfusion territories of epicardial coronary arteries but is related to areas of hypertrophy, with typical patchy or multiple foci. These scars are predominantly located within the mid myocardium, whereas in ischemic heart disease a subendocardial pattern is typical. Examples of characteristic scarring in HC are shown in Figures 1 and 2 . Moon et al also described a high prevalence of LGE in patients with HC (79%). During follow-up, extent of scar visualized by CMR was associated with progressive ventricular dilation and clinical markers of SCD. A more recent study by Adabag et al demonstrated that myocardial scarring indicated by LGE not only was associated with a sevenfold increase in risk of nonsustained ventricular tachyarrhythmias but also was the only independent predictor of this arrhythmia. Consequently, LGE might be regarded a predictor of adverse events in the setting of HC. Figure 1 visualizes typical findings of a patient from our institution with extensive areas of LGE and sustained ventricular tachycardia illustrating this concept.
Prevention of SCD
Implantable cardioverter–defibrillators (ICDs) are highly effective devices to abort ventricular tachycardia or ventricular fibrillation and multiple studies reporting on successful prevention of SCD in HC by implantation of ICDs have been published in recent years. It is generally agreed that implantation of an ICD is strongly warranted for secondary prevention in patients with previous cardiac arrest or sustained and spontaneously occurring hemodynamically relevant ventricular tachyarrhythmia, mirrored by a class I indication for this high-risk group in the recently published American College of Cardiology Foundation/American Heart Association guidelines. However, clinical decision making is far more challenging for primary prevention of SCD because precise identification of individual high-risk patients by clinical risk markers remains difficult owing to the heterogeneity of HC, low positive predictive values of clinical risk factors, and some ambiguity about the definitions of these risk factors. For instance, maximum wall thickness may differ between echocardiographic and CMR measurements. One also has to consider that device implantation is an invasive measure and leads to inappropriate shocks in up to 25% of patients with HC and the need for recurring device service and generator changes.
According to current American College of Cardiology Foundation/American Heart Association guidelines, ICD implantation for primary prevention is recommended in the presence of ≥1 of the following 3 major risk factors ( Table 1 ): extreme hypertrophy (interventricular septum ≥30 mm), sudden death presumably caused by HC in ≥1 first-degree relative, and ≥1 recent unexplained syncopal episode (indication class IIa, level of evidence C). However, some investigators have argued that implantation of an ICD in patients with a solitary major risk factor is not based on robust data. For example, “unexplained syncope” is a common event in younger and elderly patients and often may be orthostatic or neurocardiogenic in origin. Thus, it might not be advisable to base the decision toward an ICD solely on this symptom.
