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Cardiac & Cardiovascular Systems
Cardiac magnetic resonance (CMR) imaging has an important emerging role in the evaluation and management of patients with cardiomyopathies, especially in patients with dilated cardiomyopathy (DCM). It allows a non-invasive characterization of myocardial tissue, thus assisting early diagnosis and precise phenotyping of the different cardiomyopathies, which is an essential step for early and individualized treatment of patients.
- cardiac magnetic resonance
- dilated cardiomyopathy
- myocardial fibrosis
1. Introduction
Dilated cardiomyopathy (DCM) is the most common cardiomyopathy originating from multiple causes which can be clinically presented with heart failure, occasionally requiring heart transplantation, and an increased risk of ventricular arrhythmias and/or sudden cardiac death [1]. Idiopathic DCM is characterized by a dilated left ventricle (LV) with impaired systolic function in the absence of abnormal loading conditions (e.g., uncontrolled hypertension, valvular heart disease, congenital heart disease) or significant coronary artery disease [2].
The prevalence of DCM ranges from 1/2500 up to 1/250 people, mainly due to changes in diagnostic criteria and geographical variations [3]. Recent studies using genetic screening have suggested that up to 40% of DCM is inherited, and mutations in over 40 different genes have been implicated in its pathogenesis [4]. For many years now, DCM has been considered to be an irreversible condition, with a late diagnosis and a poor prognosis, but the advances in pharmacological and surgical treatment have significantly improved the prognosis of DCM, with an estimated survival of up to 85% at 10 years free from heart transplantation [5].
However, nowadays, by the time the patients are diagnosed, they often tend to have severe contractile dysfunction and remodeling of both ventricles, reflecting a long period of asymptomatic silent disease progression and the development of myocardial fibrosis. Detailed characterization of these parameters has a pivotal role in the prognostic stratification of DCM patients and in improving clinical management. In this setting, cardiac magnetic resonance (CMR) emerges as a reliable imaging modality providing functional and structural data and fundamental information regarding tissue composition [6]. Using imaging techniques such as late gadolinium enhancement (LGE) and qualitative/quantitative parameters including T1 mapping, T2 mapping, and T2* mapping, tissue characterization is useful for the differential diagnosis of secondary causes of DCM and in the assessment of the probability of ventricular remodeling with a potential role in guiding individualized treatment strategies [7].
2. Evolving Role of CMR in Cardiomyopathy
Non-ischemic DCM is a range of conditions that primarily affect the heart muscle with a heterogeneous clinical presentation and natural history. Determining the etiology of each type of cardiomyopathy is of major clinical importance as it has implications for optimal treatment strategies and prognosis. Cardiovascular imaging plays an integral part in diagnosis, etiology, risk stratification, and prognosis [1,2,3,4,5,6,7,8]. First, through its ability to characterize the myocardial tissue using multiple different imaging parameters, CMR provides insights into the etiology of underlying heart failure and its prognosis. The latest European Society of Cardiology guidelines (ESC 2023) in cardiomyopathy recognize that CMR should be considered (Class IIa, Level C) in DCM, to distinguish between an ischemic or non-ischemic etiology, and in HCM, for the differential diagnosis, and assessment of the diagnostic criteria [9].
An accurate and reproducible cardiac evaluation always includes chamber size quantification, myocardial wall thicknesses, ventricular function and mass measurement using traditional cine sequences, steady-state free precession (SSFP), in short and long axis (2, 3, and 4 chamber) view and tissue characterization sequences. Late gadolinium enhancement (LGE)-identified fibrosis correlates with histological changes, fibrosis biomarkers and can assess myocardial viability [10]. The pattern of LGE allows for the differential diagnosis between ischemic and non-ischemic DCM with good specificity [11]. Μid-wall fibrosis represents an independent predictor of mortality and morbidity beyond left ventricular ejection fraction (LVEF) in DCM. A cohort study of 427 consecutive patients with DCM implicated the prognostic value of midwall LGE in a comparison between DCM patients with and without LGE which showed that the presence and extent of LGE was associated with increased death probability (26.8% vs. 10.6%) and with an increased risk of arrhythmic event (29.6% vs. 7%) [12].
T1 mapping is a novel and robust CMR technique which offers quantitative measures of the myocardial signal. It creates a pixel-wise parametric map, in which each pixel reflects the absolute value of T1, coded in color [13]. Moreover, it directly measures the extracellular volume (ECV) fraction from T1 values before (native T1) and after administration of gadolinium. According to recent studies, in patients with DCM, ECV and native T1 are emerging as prognostic predictors of mortality independent of the presence of both LVEF and LGE [12]. Furthermore, an increased native T1 value seems to be present as an early imaging marker of adverse outcomes before the presence of LGE [13]. The presence of fibrosis visible microscopically in CMR on LGE images also represents a risk factor for patients with hypertrophic cardiomyopathy (HCM). The presence and extent of fibrosis in LGE correlates with the risk of sudden cardiac death (SCD) [14]. The extent of LGE appears to have more discriminatory value than its presence, in particular when LGE is ≥15% of the left ventricular (LV) mass, which demonstrated a significant increase in SCD risk [15]. Increased native myocardial T1 values and an elevated ECV fraction were found in HCM, even in non-hypertrophic segments with preserved contraction function or in patients without LGE, suggesting that myocardial tissue remodeling may precede morphological and functional changes [16]. Also, in patients with arrhythmogenic cardiomyopathy, the CMR became crucial for diagnosis and risk stratification for arrhythmic events. A study showed that CMR was an independent predictor of ventricular arrhythmias, and regional wall strain assessed using cine CMR reliably predicts arrhythmogenic ventricular tachycardia substrate [17].
3. Traditional Risk Stratification Approach in DCM
SCD, secondary to arrhythmia, remains a fatal risk in approximately 30% of those with DCM [18], and an implantable cardiac defibrillator (ICD) is an effective strategy to prevent SCD. Current guidelines recommend selection for ICD based on an ejection fraction (EF) less than 35% [19]; however, most SCD occurs in those with preserved systolic function (EF > 35%) with no prior indication of primary prevention ICD [20]. The DANISH trial suggests that younger patients may have a survival benefit in association with ICD implantation. Subgroup analysis shows that ICDs provided a significant survival benefit in patients under 70 years old, due to a lower risk of non-sudden death; therefore, their measured sudden versus non-sudden death ratio is higher [21].
LVEF value may vary between different imaging modalities, and CMR has emerged as the gold standard technique for LV volume and function assessment, with the added benefit of providing tissue characterization [22]. Independent predictors of all causes of mortality are an indexed left ventricular end-diastolic volume (LVEDVi) on CMR > 120.5 mL/m2 and the presence of more than three segments with midwall fibrosis [23]. Juillière et al. identified in right ventricular ejection fraction (RVEF) an independent predictor of all-cause mortality and a modest predictor of hospitalization due to heart failure (HF) in patients with DCM [24] because of direct right ventricular involvement [24,25,26]. Another parameter that could be evaluated by CMR is the left atrial volume index (LAVi), as a sensitive barometer of LV filling pressure and an important predictor of transplant-free survival and HF risk [27].
Considering the aforementioned patient profiles, it is easy to assume that those patients in the most need of a CMR are patients that are currently living with an implantable cardiac device in order to prevent major cardiac events [28]. As many studies have shown [29], scanning the myocardial contractility pace with the device on maintenance generates images mirroring the actual heart function but might be catastrophic for the device or may lead to major arrhythmic events during examination, which puts the patient at enormous risk. On the other hand, switching off the device produces unrealistic images during CMR, mispresenting the myocardial condition, which actually is the case in each patient currently receiving the most appropriate therapy (CRT) [30]. To overcome that obstacle, the advent of devices including the setting ‘’MR safe mode’’ lead us to be capable of scanning while the device is working with no risk to the health of our patient or the device [31]. This is a chance to overcome the justified uncertainty by physicians worldwide while they provide the most appropriate care to patients which is meticulous and realistic imaging.
4. LGE as an Emerging Risk Stratification Method in DCM
Risk stratification in patients with DCM defines the risk of ventricular arrhythmias and sudden cardiac death. During the risk assessment, the presence of LGE modifies the prognosis, defining a worse outcome [32]. Becker et al. [33] found an increased risk of adverse cardiovascular events in patients with LGE compared to those without microscopically observed fibrosis. In subjects with DCM, LGE predicted the endpoint of cardiovascular mortality with a pooled OR of 3.40 and ventricular arrhythmic events of 4.52. Alba et al. [34] identified LGE as an adverse prognostic value in a population of 1672 individuals with DCM. The presence of LGE (39%) was associated with an annual risk of SCD or appropriate ICD shock of 4.0%. Instead, Di Marco et al. [35] highlighted the strong adverse predictor of LGE across the entire LVEF. Patients with an LVEF between 21% and 35% and the absence of LGE were at low risk compared to individuals with LGE present and an LVEF > 35%.
LGE is present in one out of three patients with DCM, and the non-ischemic pattern is the most common, with a midwall or subepicardial distribution usually identified. Different types of patterns and locations may be identified as additive prognostic markers. Subepicardial distribution, a ring-like pattern, and a septal or multiple-site location are associated with increased adverse arrhythmic risk. In addition, in patients with midwall fibrosis, Assomull et al. [36] found a high incidence of sudden cardiac death and ventricular arrhythmias. Gulati et al. [12] also documented an increased risk of sudden cardiac death in these subjects, independent of the LVEF. Furthermore, several studies documented an increased risk with the coexistence of multiple patterns [34,35]. On the other hand, the site of distribution also modifies the prognosis. Claver et al. [37] described a high incidence of sudden cardiac death in patients with LGE in the septum and free wall compared with those in the septum only. Instead, LGE observed in the right ventricular insertion is considered an unspecific pattern. In a large cohort study of patients with idiopathic DCM, a significant lower incidence of arrhythmic events in subjects with the right ventricular insertion points pattern (IP-LGE pattern) compared with the IP and LV–LGE pattern (LGE present in both right ventricular insertion points and the left ventricle) was documented. In addition, a similar incidence was found with LGE-negative patients. Finally, the ischemic pattern has been also detected in a low number (~5%) in DCM patients [37]. De Angelis et al. [38] identified this LGE pattern with worse long-term outcomes with an adjusted hazard ratio of 2.1. Of note, a recent prospective observational cohort study of 254 patients with early non-ischaemic DCM assessed by CMR by our group (median follow-up 7.9 years) looking into the natural history of fibrosis showed that early DCM is not a benign condition; fibrosis develops early in the phenotypic course and in-depth characterization enhances risk stratification and might aid clinical management [39].
This entry is adapted from the peer-reviewed paper 10.3390/jcm13041017
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