Cardiovascular manifestations in idiopathic inflammatory myopathies

Cardiovascular involvement in idiopathic inflammatory myopathies (IIM) is an understudied area which is gaining increasing recognition in recent times. Recent advances in imaging modalities and biomarkers have allowed the detection of subclinical cardiovascular manifestations in IIM. However, despite the availability of these tools, the diagnostic challenges and underestimated prevalence of cardiovascular involvement in these patients remain significant. Notably, cardiovascular involvement remains one of the leading causes of mortality in patients with IIM. In this narrative literature review, we outline the prevalence and characteristics of cardiovascular involvement in IIM. Additionally, we explore investigational modalities for early detection of cardiovascular involvement, as well as newer approaches in screening to facilitate timely management. Key points • Cardiac involvement in IIM in majority cases is subclinical and a major cause of mortality. • Cardiac magnetic resonance imaging is sensitive for detection of subclinical cardiac involvement. Supplementary Information The online version contains supplementary material available at 10.1007/s10067-023-06599-4.


Introduction
Idiopathic inflammatory myopathies (IIM) are heterogeneous, multisystem diseases with varied phenotype and presentation. Several subtypes are recognized, including dermatomyositis (DM), juvenile DM (JDM), clinically amyopathic DM (CADM), polymyositis (PM), inclusion body myositis (IBM), immune-mediated necrotizing myopathy (IMNM), anti-synthetase syndrome (ASS), and overlap myositis [1]. A diagnosis of IIM is associated with significant morbidity and an increased risk of mortality. Cancer, pulmonary involvement and cardiovascular disease are the most common causes of death worldwide [2][3][4]. Notably, a significant link between inflammation and cardiovascular involvement in rheumatic diseases has been described [5,6]. Thus, patients with IIM are at an increased risk of cardiovascular involvement.
Despite advances in the management of patients with IIM, identification of cardiac involvement in these patients is often delayed. Limitations of clinical examination and traditional cardiac investigations have led to recognition of newer imaging modalities for the early detection of cardiac involvement in IIM.

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This narrative review focuses on recent literature regarding cardiovascular involvement in patients with IIM, including its manifestation as a result of disease activity, cardiac inflammation and damage or comorbid cardiovascular risk factors. The authors discuss various investigational modalities for evaluating cardiac involvement with emphasis on the newer imaging modalities. This review aims to explore the undiscovered impact of cardiac involvement in patients with IIM, newer modalities for accurate identification and assessment, and the unmet need for standardized investigational protocol.

Methods
The two largest medical databases, namely Scopus and PubMed were searched on the same day for relevant articles published between 2000 and 2022. The search terms used were [myositis OR dermatomyositis OR polymyositis OR inclusion body myositis OR idiopathic inflammatory myopathy OR autoimmune myopathy OR idiopathic inflammatory myopathies OR autoimmune myopathies] AND [cardiovascular risk OR heart failure OR cardiomyopathy OR cardiovascular disease OR myocarditis OR heart infarction OR heart disease OR heart arrhythmia OR coronary artery disease OR ischemic heart disease OR thromboembolism] as outlined in previously published methods protocols for narrative reviews [7]. Only data published in English were included. Case reports, case series with less than 10 cases, letter to editor, book chapters, and animal studies were excluded. Since most of the literature on myositis was covered in the above-mentioned databases, and Web of Science is rich in older literature and information in regional languages, these were considered beyond the scope of the authors' current work. The detailed search strategy and results are outlined in Fig. 1. Additional studies were identified from references of the extracted articles and included where relevant.

Epidemiology
Although first described in 1899 by Oppenheim, cardiac involvement in myositis was not a well-recognized manifestation until the 1970s [8,9]. The understanding and definition of cardiac involvement in myositis have significantly evolved in recent years owing to the advent of more sensitive diagnostic techniques [10]. The prevalence of cardiac manifestations in IIM varies widely, ranging from 6 to 75% depending on the patient inclusion criteria, definition of cardiac involvement, and the imaging modalities used. Importantly, a substantial proportion of cardiac involvement in myositis is subclinical, with fewer than 10% being clinically manifest unless investigated [9]. The EuroMyositis registry, comprising 3067 cases across 11 countries, reported that cardiac involvement occurring due to the IIM disease process was most frequent in the connective tissue diseasesoverlap myositis group and was least frequent in patients with IBM [11]. (Table 1) Several independent research groups worldwide have reported an increased risk of cardiovascular mortality in patients with IIM. For instance, a Swedish populationbased nationwide cohort study by Dobloug et al. found that cardiac disease was one of the most common causes of mortality among IIM patients [2]. In a retrospective cohort study by Limaye et al., a standardized mortality ratio (SMR) of 1.75 was reported in IIM; the ratio was highest in the DM subtype at 2.40. The study also found that cardiovascular disease accounted for nearly one-third of deaths in the cohort of 364 individuals from South Australasia, followed by infection (22%) and malignancy (11%) [12]. Similarly, a large Korean population-based study of 3014 cases confirmed a high SMR and a high incidence of cardiovascular disease, even in young individuals with IIM (DM: 15.0, PM: 8.1) [14]. Dankó et al. conducted a survival analysis of 162 Hungarian patients and found that lung and cardiac complications were the most frequent causes of death. Death attributable to cardiovascular complications occurred late in the course of the disease (median 59 months). Cardiovascular manifestations were responsible for 8 out of 18 deaths (two cases of arrhythmia, three of heart failure, two of cardiac arrest, and one of myocardial infarction) and were identified as significant adverse prognostic factors [13].

Mortality and cardiovascular involvement
Collectively, these studies suggest cardiac complications are a common cause of mortality among IIM patients.

Risk of cardiovascular disease
Accumulating evidence suggests an increased incidence of cardiovascular diseases such as acute coronary syndrome, heart failure, and arrhythmias in patients with IIM. Two meta-analyses (Xiong et al. and Ungprasert et al.) have examined the association between IIM and cardiovascular events in patients with PM and DM. The study by Xiong et al. included 25,433 patients with PM/DM and found a 2.3-fold increase in the risk of cardiovascular events within the first 5 years of IIM diagnosis. Moreover, PM/ DM was identified as an independent risk factor for the development of cardiovascular events [15]. The study by Ungprasert et al., which comprised 13,201 patients, reported a 2.24-fold increased risk of cardiovascular disease in patients with IIM. Indeed, cardiovascular disease was identified as the leading cause of mortality in this 1 3 cohort [16]. Prieto et al. conducted a study in the UK comprising 603 patients with IIM and reported a significantly greater rate of cardiovascular events in patients with IIM than in healthy controls, even after adjustment for traditional cardiovascular risk factors. This finding suggests that the increased risk could not be entirely attributed to traditional cardiovascular risk factors and was partly accounted for by the systemic inflammation present in these patients. The excess risk was most apparent in the first 5 years post IIM diagnosis and then appeared to decline [17]. These results are consistent with a case-control study which reported an increased risk of cardiovascular disease in patients with IIM, even in the absence of traditional risk factors [18]. Overall, the evidence suggests that patients with IIM have an increased risk of developing cardiovascular disease, particularly within the first 5 years of IIM diagnosis. This risk cannot be entirely attributed to traditional cardiovascular risk factors and may be partly due to systemic inflammation. (Table 2) Diabetes mellitus, hypertension, and dyslipidemia are traditional risk factors for coronary heart disease. Several studies have investigated the prevalence of these risk factors in patients with IIM [12,19,[21][22][23][24][25][26][27]. For instance, Diederichsen et al. observed a higher prevalence of hypertension (71% versus 42%) and diabetes mellitus (13% versus 0%) in patients with DM and PM compared to age-and sexmatched healthy controls. Patients with IIM also had significantly higher levels of serum triglycerides. Multivariate analysis revealed that smoking and age were associated with accelerated atherosclerosis in this cohort [20].

Traditional cardiovascular risk factors
This same study showed that the presence of coronary artery atherosclerosis, as evidenced by calcification on computed tomography scan, was more prevalent in IIM patients. However, this was associated with the presence of traditional cardiovascular risk factors rather than IIMspecific factors [20]. Conversely, Prieto et al. reported an increased risk of cardiovascular diseases in patients with IIM even in the absence of traditional cardiovascular risk factors [17]. A systematic review and meta-analysis by Qin et al. also reported that patients with IIM were 1.44, 1.67, and 1.48 times more likely to have hypertension, diabetes mellitus, and dyslipidemia respectively, when compared with non-IIM individuals [22]. In a case-control study by Wang et al., untreated patients with early PM (n = 60) had dyslipidemia characterized by high triglyceride and low high-density lipoprotein cholesterol levels, suggesting a high risk of atherosclerosis [19]. Similarly, a study by Pakhchanian et al. using the TriNetX database (5578 DM patients) found that 66.82% of patients had hypertension as opposed to 25.05% of the general population. The prevalence of ischemic heart disease (27.18% vs 7.3%) and diabetes mellitus (33.87% vs 12.14%) was also higher in DM patients when compared to the general population [23]. In contrast, a single-centre study (n = 39 patients) conducted by Oreska et al. found no significant differences in the prevalence of traditional risk factors between patients with IIM and healthy controls [24]. While mixed results have been reported, large cohort studies and meta-analyses all suggest an increased risk of cardiovascular risk factors in patients with IIM.
A possible mechanism for accelerated cardiovascular disease in IIM was explored in a study evaluating the antioxidant function of high-density lipoprotein (HDL) particles isolated from patient blood. The protective function of HDL in IIM patients was abnormal compared to healthy controls, with patients with DM and those with higher disease activity having particularly impaired HDL function [21]. Together, these studies underscore the need to determine the relative contribution of conventional risk factors vis-à-vis disease-specific inflammation-induced accelerated atherogenesis in the development of cardiovascular disease.   Table) Various types of conduction system abnormalities have been described in patients with IIM, including supraventricular and ventricular tachycardia, fascicular blocks, bundle branch blocks, and atrioventricular (AV) blocks. In a large retrospective cohort study of 32,085 patients with DM or PM, Naaraayan et al. reported a significantly higher prevalence of atrial fibrillation, atrial flutter, supraventricular tachycardia, and unclassified arrhythmias in patients with IIMs < 70 years old compared with matched controls. The prevalence of arrhythmias was found to be higher in men than in women. Importantly, the diagnosis of arrythmias was associated with significant in-hospital mortality among patients with PM/DM [28]. A cross-sectional study of 112 IIM patients (78 DM and 34 PM) by Deveza et al. reported a higher frequency of arrhythmia in patients with PM when compared with DM. However, there was no significant difference in the occurrence of arrhythmias between IIM patients and the control group [29]. In a retrospective cohort study of 75 patients with IIM by Huang et al., PM and positive serum anti-mitochondrial antibodies (AMA) were strongly associated with ventricular arrhythmia in PM/DM patients with myocardial involvement [30]. Several mechanisms which may predispose to arrhythmias in patients with chronic inflammatory diseases such as IIM have been hypothesized, including infiltration of atria or ventricle by inflammatory cell infiltrate, autonomic dysfunction with resultant reduced heart rate variability and 'acquired channelopathies' due to release of cytokines or autoantibodies [31]. In a clinicopathological study of 16 autopsied patients with PM/DM conducted by Haupt et al., direct involvement of the conduction system by myositis and contraction-band necrosis was described [32]. Table) Inflammation is known to play a role in promoting thrombosis by upregulating procoagulant pathways, downregulating natural anticoagulant factors and suppressing fibrinolysis [33]. An increased incidence of thrombosis in patients with chronic inflammatory diseases and autoimmune diseases is well described [34][35][36][37][38]. Patients with IIM are no exception, with several studies having reported a significantly increased risk of venous thromboembolism in patients with DM/PM [34,[39][40][41][42]. An enhanced in vitro thrombin generation profile in patients with DM/PM has been demonstrated, which may correlate to an increased risk of thromboembolic events [43]. Carruthers et al. reported an eight-and six-fold higher risk of developing venous thromboembolism in patients with DM and PM respectively. Notably, this risk was highest during the first year for patients with PM and during the initial 2 years after diagnosis in patients with DM, potentially attributable to uncontrolled inflammatory activity [44]. Similarly, in a retrospective analysis of 1144 Chinese patients with IIM, over half of IIM patients with thromboembolic events developed this complication in the 6 months before or after diagnosis of IIM. Increased myositis disease activity, malignancy, infection, and duration of steroid use were significant risk factors for thrombosis in this study [45]. A Swedish population-based cohort study (Antovic et al.), found that the risk of thromboembolic events was eight times higher in patients with IIM than in the general population, with the highest observed in patients with DM and a history of cancer. In line with other reports, the incidence rates were maximum in the first year post diagnosis and decreased thereafter [46]. Conversely, another retrospective cohort study found that age at diagnosis was the only independent risk factor for thrombotic events in patients with IIM. For each year of age, there was a 3.5% increased chance of experiencing a thrombotic event in patients with IIM. In their cohort of 253 patients with IIM, only 6% had anti-phospholipid antibodies, with no significant difference between the patients and comparators [47].

Thromboembolism (Supplementary
Pregnant women with autoimmune disease, including IIM, are also at an increased risk of thromboembolism. Indeed, Bleau et al. studied 43,523 pregnant women with autoimmune disease and observed that the risk of thromboembolism was particularly high for patients with DM comparted to other autoimmune diseases [48]. Atherosclerotic cardiovascular diseases and acute coronary syndrome (Table 3) Numerous studies have investigated the relationship between IIM and cardiovascular events. In a case-control analysis of 10,156 patients with DM conducted in the USA, researchers found that 20% of all DM hospitalizations were associated with an atherosclerotic cardiovascular diagnosis. Patients with DM and atherosclerotic heart disease were twice as likely to die during their hospital stay compared to DM patients who did not suffer from atherosclerotic heart disease (odds ratio (OR) 2.0, 95% confidence interval (CI) 1.7-2.5, p < 0.0001). Furthermore, among patients with both DM and cardiovascular disease, the odds ratio for death was 1.98 when compared to controls with only cardiovascular disease [49]. This suggests an additive effect of DM and cardiovascular disease on risk of death. Similarly, other studies have reported an increased risk of coronary heart disease in IIM patients when compared to controls [50,56].
Patients with IIM are at a significantly increased risk of experiencing an acute coronary syndrome (ACS) when compared to the general population as evidenced by several studies [51][52][53][54]. A study by Lin et al. reported a greater incidence of ACS in men than in women, and in those with hypertension and end stage renal disease. However, the  [54]. Finally, a nested case-control analysis by Tisseverasinghe et al. reported an association between the incidence of myocardial infarction and stroke, hypertension and lipid abnormalities. On the other hand immunomodulators such as methotrexate, azathioprine, antimalarial agents, cyclophosphamide were negatively associated with these arterial events [55]. Thus, factors besides traditional cardiovascular risk factors might contribute to the increased risk of cardiovascular disorders in patients with IIM; a finding which needs to be explored further.

Heart failure (Supplementary Table)
Heart failure is the most frequently reported clinically apparent cardiovascular manifestation in patients with IIM [9,57]. In a retrospective cohort study in Taiwan, patients with PM/ DM showed a significantly increased risk of heart failure as compared to those without PM/DM (HR 2.06, 95%CI 1.36-3.12). The risk of heart failure was found to be highest within first 10 years following diagnosis of PM/DM [58]. In a cross-sectional multicenter study of 108 patients with IIM and with myocardial involvement, 62% of patients presented with heart failure, 56.5% with clinically significant arrhythmia, and 18.5% of patients presented with both. Antimitochondrial antibodies and pulmonary hypertension were significant associated factors [59]. In a single center retrospective study of 32 Chinese patients with IIM and heart failure, 13 of the 17 recorded deaths were attributed to cardiogenic shock [60].

Myocarditis (Supplementary Table)
Diagnosing myocarditis in patients with inflammatory myopathies poses a challenge due to its subclinical nature in the majority of cases [9]. The prevalence of myocarditis in IIM has been reported to be 38% on cardiac pathology [61]. Conversely, Dieval et al. reported that the prevalence of clinically apparent was 3.4% in patients with ASSD. Myocarditis was the initial presenting feature in 42% of the ASSD patients with myocarditis in this study. Myocarditis was reported to be associated with active disease but not with any particular antibody specificity [62]. Liu et al. reported a shorter disease duration, more manifestations of heart failure

Autoantibodies
Emerging data indicate an association between cardiovascular disease and certain myositis-specific antibodies, myositis-associated antibodies and anti-mitochondrial antibodies [64][65][66]. In a longitudinal cohort study comprising 619 adult and 371 juvenile patients with IIM, 31 adult patients were diagnosed with cardiomyopathy. While only 5% of adult patients in this cohort were AMA-positive, the presence of this antibody was associated with the development of cardiomyopathy and persistent muscle weakness. Notably, this association was not seen in the pediatric population [67]. Additionally, a retrospective case review reported cardiac involvement in five of seven patients with positive anti-mitochondrial antibodies. The authors noted that cardiac function in patients with cardiomyopathy or myocarditis could improve with immunosuppression [68]. In another study of 63 patients with IIM (DM, PM, CADM), those who were anti-MDA5 (melanoma differentiation-associated protein 5) positive (N = 21) showed significantly lower T waves amplitude on the electrocardiogram (ECG) than anti-MDA-5 negative patients. Nonetheless, there were no differences in the contractile function of the heart between the two groups. These low amplitudes were restored during the remission phase, suggesting a possible role for aberrant immune responses associated with active anti-MDA5+ DM [69].
Juvenile dermatomyositis (Table 4) JDM, although rare, is the most common childhood inflammatory myopathy. There are several similarities between the clinical features of JDM and those of adult DM [78]. Cardiovascular risk factors and metabolic syndrome appear prevalent among patients with JDM. For instance, several studies have observed a high frequency of hypertension [70,71], dyslipidemia [70][71][72][73] and elevated body fat percentage [70,74] in JDM patients versus controls. In several studies, metabolic abnormalities were found to be correlated with JDM disease activity [70,72]. Importantly, increased rates of cardiovascular involvement have been observed even in the absence of traditional cardiovascular risk factors, suggesting that such risk factors may not completely account for the increased rates of cardiovascular disease in JDM [71].
Potential cardiac manifestations in JDM include pericarditis, systolic or diastolic dysfunction and electrocardiographic abnormalities [75,76,79]. In a cross-sectional study of 57 patients with JDM, 18% of the patients had cardiac involvement-defined as left ventricular systolic or diastolic dysfunction on echocardiography, which was mostly subclinical. Patients with cardiac involvement showed higher disease activity 1 year after diagnosis and an unfavorable lipid profile [73]. In a cross-sectional study of 59 patients with JDM examined at a median of 16.8 years after disease onset, both systolic and diastolic dysfunction were reported to be linked to longer disease duration and high disease activity score of skin but not muscle at 1 year. The cumulative prednisolone dose was also a predictor of diastolic dysfunction. Thus, sustained early skin activity could predict cardiac dysfunction in the long term [76].
A low heart rate variability (HRV) is a strong predictor of cardiac arrest [80]. Barth et al. demonstrated a lower HRV in patients with active JDM than in those with inactive JDM, indicating the presence of autonomic nervous system dysregulation in JDM. This reduced HRV was found to be associated with elevated inflammatory markers, reduced myocardial function, and active disease [77].
Abnormal nailfold capillary density (NCD) is an indicator of systemic vasculopathy and thus may have utility in the evaluation of JDM. Barth et al. did not find any significant differences in the electrocardiography, heart rate variability, and systolic or diastolic function between patients with low and normal NCD. However, these authors reported an association between lung involvement and low NCD. A plausible explanation for the lack of association between NCD and cardiac dysfunction could be the small sample size of the study, making the study underpowered to demonstrate this association [75].

Investigations (Table 5)
Given that cardiovascular involvement is one of the most common causes of increased morbidity and mortality in patients with IIM, screening of patients for cardiac involvement is of paramount importance. As most patients have subclinical cardiac involvement, the need for highly sensitive and noninvasive testing methods is gaining importance.

Electrocardiogram (ECG)
Electrocardiographic changes are common in patients with IIM [94], with abnormalities detected in approximately 32.5-72% of patients [9]. In a study by Deveza et al., onethird of patients with DM and PM had electrocardiographic abnormalities including conduction disorders, chamber enlargement, and rhythm disturbances. The various rhythm disturbances observed were ventricular extrasystoles, atrial fibrillation, first-degree AV block, supraventricular tachycardia, and supraventricular extrasystoles. These abnormalities were more frequent in PM than in DM (50% versus 24.4%, p = 0.008]. However, the study did not find any significant difference in electrocardiographic abnormalities between patients and control groups, except for a higher prevalence The authors did not find any significant differences in the ECG, heart rate variability, and systolic or diastolic function between patients with low and normal NCD. However, they reported an association between lung involvement and low NCD. A plausible explanation for the lack of association between NCD and cardiac dysfunction could be the small sample size of the study, making the study underpowered to demonstrate this association Norway of left ventricular hypertrophy in the former [29]. In a study of IMNM, 55 out of 86 patients had an abnormal electrocardiography. Of the various abnormalities, prolongation of the corrected QT interval (QTc) was the most frequent [81]. Conversely, patients with sporadic inclusion body myositis do not appear to have increased risk of cardiac involvement compared to the general population, as evidenced by the similar frequencies of ECG abnormalities between the two groups [82].

Echocardiography
Echocardiographic abnormalities are reported in 14-65% of patients with IIM [3]. Left ventricular diastolic dysfunction (LVDD) is the most common echocardiographic abnormality [61,81,84,95,96]. Several studies have demonstrated that IIM patients have a greater prevalence of LVDD compared to the general population [83,84,95]. A study by Wang et al. reported a statistically significant association between LVDD and disease duration, pointing towards increased subclinical cardiac involvement with disease advancement [83]. Diederichsen et al. reported that age, disease duration, presence of myositis-specific or myositis-associated autoantibodies, and high cardiac 99m Tc-PYP uptake are associated with LVDD. This association between LVDD and increased cardiac 99m Tc-PYP uptake indicated myocardial inflammation as a primary cause of cardiac involvement in patients with IIM [84].
In a study of patients with generalized autoimmune disease (comprising 60 patients with scleroderma, 60 patients with systemic lupus erythematosus, and 15 patients with DM/PM) pathologic valvular leaflet thickening and/or pericardial thickening on echocardiography was found in 46.7% of patients with DM/PM. Pericardial effusion was also reported in 66.7% of the patients with DM/PM. All 15 patients with DM/PM had dilated right ventricle with elevated right ventricular systolic pressure [85].
Left ventricular systolic function has long been assessed using left ventricular ejection fraction (LVEF). However, LVEF has limited sensitivity in detecting early subclinical cardiac involvement, as it typically does not worsen until cardiac function is severely compromised. Speckle tracking echocardiography is an emerging modality for detection of subclinical cardiac involvement by directly assessing myocardial wall deformation [97]. Echocardiographic assessment using the long axis strain and not LVEF for evaluating systolic involvement in patients with IIM has been recommended [94].
In a study of 60 patients with PM/DM with preserved LVEF, speckle-tracking echocardiography demonstrated subtle systolic dysfunction. The severity of cardiac involvement was related to the systemic disease burden [86]. Guerra et al. reported a 4.9-fold higher risk of subclinical ventricular systolic dysfunction in patients with IIM than to healthy controls using speckle tracking echocardiography. The basal and mid-segments of the anterior, anteroseptal, and lateral walls of the left ventricle were the most frequently involved. However, in their study, the cardiac involvement was not associated with disease duration or disease activity [87]. In a study by Liu et al. using speckle tracking echocardiography, it was noted that in patients with PM and DM, the myocardium at the base was more severely affected than at the apex. This pattern of basal weakness was successful in accurately differentiating myocardial involvement of DM and PM from acute viral myocarditis [88].  [91]. Cardiac magnetic resonance (CMR) imaging has shown promise in the early detection of cardiac involvement in patients with IIM. A case series of 53 patients with PM, DM or non-specific myositis reported myocardial LGE patterns that were consistent with inflammation. Despite a normal LVEF, 54.5% of the patients had positive LGE. There was no significant correlation between the clinical symptoms and CMR results [92]. Several studies have demonstrated the superiority of multiparametric CMR approaches to conventional methods (ECG and echocardiography) in early detection of cardiac involvement, even in patients with negative LGE [100][101][102]. Based on their study evaluating CMR in patients of IIM at first diagnosis and after a year of receiving standard treatment, Xu et al. suggested that multiparametric CMR could help monitor response to effective treatment [103]. In a case series of 20 patients with sporadic IBM, CMR demonstrated decreased left and right ventricular stroke volumes and increased early myocardial enhancement compared to controls. However, these changes were attributed to hypertensive heart disease in these patients. Of note, there was no statistical difference in the LGE between patients and controls [104].

Cardiac enzymes
Cardiac troponins are highly sensitive markers of cardiac involvement, particularly infarction. A retrospective study by Aggarwal et al. reported elevated cardiac troponin T (cTnT), but not cardiac troponin I (cTnI), in patients with IIM. cTnT levels correlated with total creatine kinase (CK) levels in this study [105]. Of note, cTnT can arise from the skeletal muscles of patients with IIM, which may explain why this enzyme correlates with muscle disease activity [93,106]. Conversely, in a study by Lilleker et al., cTnI levels were higher in patients with cardiac involvement, irrespective of IIM disease activity. cTnI had the highest specificity (95%) and positive predictive value (62%) for the detection of cardiac involvement, although this test lacked sensitivity. cTnT correlated more strongly with the patient and evaluator global assessment and the quality of life as assessed by the Health Assessment Questionnaire (HAQ) than cTnI and CK [93].
In a study of 51 patients with IIM (19 patients with DM, 20 patients with PM, 12 patients with IMNM) patients with IMNM had significantly higher cTnT and CK, but lower N-terminal prohormone of brain natriuretic peptide (NT-proBNP) levels and no positive LGE on CMR when compared to patients with PM and DM, again suggesting that serum CK-MB and cTnT do not accurately reflect myocardial involvement in IIM. NT-pro BNP correlated positively with CMR finding of LGE [90].
Although several diagnostic methods are available for investigating cardiac involvement in patients with IIM, traditional methods such as ECG and echocardiography are not sensitive to detect subclinical and early changes. CMR has proven to be sensitive for the detection of subclinical cardiac involvement, the most frequently encountered cardiac abnormality. Data on nuclear cardiac imaging for detection of myocarditis in patients with IIM is very limited, and needs to be studied further.

Conclusion
Cardiovascular risk factors are prevalent in individuals diagnosed with IIM. Although clinically apparent cardiac involvement is uncommon in patients with IIM, cardiovascular involvement is a major contributor to morbidity and mortality. It remains unclear whether the excess cardiovascular morbidity and mortality seen in IIM is a result of increased prevalence of cardiovascular risk factors, chronic systemic inflammation or subclinical cardiac inflammation. Further research may help understand the relative contribution of these mechanisms.
Of concern, subclinical cardiac involvement may not be identified using conventional investigations such as electrocardiography or echocardiography. Advances in highly sensitive imaging platforms such as CMR, coupled with the increasing availability of these modalities has made it easier to detect subclinical cardiac involvement; however, larger studies are needed to assess the feasibility of employing such imaging modalities in the routine screening of patients with IIM. This scoping review identifies a pressing need to develop guidelines for screening cardiac involvement and cardiovascular risk factors in patients with IIM.

Compliance with ethical standards
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