Characteristics of Patients With Arrhythmogenic Left Ventricular Cardiomyopathy: Combining Genetic and Histopathologic Findings

The enrolled study population was extracted from an ARVC/cardiomyopathy registry from IRCCS Centro Cardiologico Monzino, by a dedicated heart team composed of cardiologists, cardiac radiologists, electrophysiologists, and cardiac pathologists. All enrolled patients were evaluated between August 2014 and January 2019.

All consecutive patients reaching a diagnosis of ALVC were included. Inclusion criteria for a diagnosis of ALVC were as follows:

PLUS one of the following diagnostic features:

Patients without genetic testing were excluded. Additionally, all patients with a clinical suspicion of cardiac sarcoidosis due to initial radiological/clinical findings, or with a history of a recent (<3 months) infection at the time of CMR were excluded, to reduce the risk of including phenocopies. Patients with a positive family history up to 3 generations of any cardiomyopathy other than ARVC were excluded as well. Endurance athletes (defined as per training regime >6 h/wk of practicing sports with a moderate to intense dynamic component and any athlete practicing sports at a professional level) were also excluded from the analysis.

The data that support the findings of this study are available from the corresponding author upon reasonable request.

All patients underwent a routine diagnostic evaluation comprising: a detailed personal and family history, a lifetime sport activity assessment, a 12-lead ECG, 24-hour Holter monitoring; transthoracic echocardiography, gadolinium-enhanced CMR, and genetic testing for cardiomyopathy associated genes, performed with Next Generation Sequencing. In addition, all patients were offered an invasive evaluation that included electrophysiological study (single site programmed stimulation from the LV) and endocardial 3-dimensional electroanatomic voltage mapping (EVM) of the LV to stratify for individual arrhythmic risk. In patients accepting the invasive evaluation, an EVM-guided EMB from the LV was performed to confirm diagnosis.¹⁰

This study was approved by both the scientific and ethical review board at Centro Cardiologico Monzino, IRCCS, and complies with the Declaration of Helsinki. Patients gave informed consent to the study and to all tests and procedures performed. Procedural details regarding CMR protocols, genetic analysis, electrophysiological study, EVM, and EVM-guided EMB are described in Methods in the Data Supplement.

The main goal of the study was to present clinical, ECG, and imaging data from our ALVC population, to better characterize this subset of patients. Compliance to the 2010 ITFC was assessed in every patient, and rates of patients reaching a probable, borderline, and definite diagnosis were reported as well.

All statistical analyses ware performed using SPSS (version 23, IBM SPSS Statistic). Distribution of continuous variables was tested using a Shapiro-Wilk test. Normally distributed continuous variables were reported as mean±SD, while non-normally distributed variables as median (interquartile range). Categorical variables were reported as frequencies (percentages).

A total of 25 patients (19 probands; 6 related family members) were enrolled. Age at disease diagnosis was 53 (48–59) years. Fifteen (60%) patients were male. Nineteen (76%) patients were symptomatic at presentation, palpitations (36%) being the most commonly reported symptom, while the remaining 6 (24%) patients (n=2 probands), were asymptomatic. Baseline demographic characteristics are summarized in Table 1.

An invasive evaluation was performed in 18 (72%) patients. Table 3 summarizes these findings.

EVM was acquired in all 18 patients. In 6 (24%) cases, only endocardial LV mapping was performed, while in 12 (48%) patients a biventricular EVM was acquired. In the RV, areas with low bipolar (1/12) or unipolar (3/12) voltages were uncommon and presented exclusively in the septal area. Particularly, the RV lateral subtricuspid area showed normal voltages, which is uncommon for classical ARVC. In the LV, areas of low bipolar (9/18) or unipolar (12/18) voltages were more common. An agreement analysis between CMR and EVM findings showed an overall inter method agreement of 83% at septal, 73% at anterior, 50% at lateral, and 66% at posterior segment sites (Appendix II and Table I in the Data Supplement). PES from the ventricles was performed in all 18 patients. In 10 (40%) nonsustained ventricular arrhythmias were induced, while a sustained VT was induced in 8 (32%) patients.

Upon ALVC disease diagnosis, an implantable cardioverter defibrillator was implanted in 11 (44%) patients (n=8 for primary prevention; n=3 for secondary prevention). Over a mean follow-up time of 16 (11–28) months, 9 (36%) patients experienced a complex arrhythmic event (n=2 non sustained ventricular tachycardia; n=6 sustained ventricular tachycardia; n=1 ventricular fibrillation), that in 6 cases was treated with an implantable cardioverter defibrillator shock. No cardiac transplantation or cardiac deaths were witnessed.

Historically, ARVC has been considered to constitute a right sided disease, with LV involvement representing a sign of advanced disease. In recent years, however, several phenotypes of ARVC presenting with early (or even isolated) LV involvement have been described and for which specific diagnostic criteria are lacking.^{3–8,12–14} An amendment of the current ITFC focusing on the LV is needed, but evidence to support new criteria are currently scarce. Therefore, our study aimed at presenting clinical characteristics of a selected cohort of patients reaching a clinical diagnosis of ALVC through CMR, genetic testing, EVM and EMB, to increase that body of data needed for new evidence-based diagnostic criteria for ALVC.

All patients included in this study had a clinico-pathological diagnosis of ALVC based on our inclusion criteria. None of those patients fulfilled a major ARVC 2010 ITF criterion except for genetics, indicating that these patients had predominant LV involvement, which has been also referred to as ALVC.⁵ This diagnosis was suspected primarily upon the results of CMR imaging. All patients presented with a subepicardial nonischemic LGE pattern and fatty infiltration in the LV.^6–9,15 To account for possible CMR phenocopies of the disease, additional inclusion criteria were postulated, based on data reported in current consensus documents.^6,8,13 All included patients needed to present at least one additional feature between either a pathogenic/likely pathogenic variant in an ARVC gene associated with LV involvement (in our cohort mainly driven by DSP mutations) or an EMB sample showing substantial fibro-fatty infiltration obtained from the anterolateral and postero-lateral wall of the LV.

Patients in our cohort reached a clinical diagnosis of ALVC at a median age of 53 years, which is higher than what is usually reported in several large cohorts comprising classical ARVC phenotypes.^16,17 This finding may be explained by a mixture of factors: (1) the lack of a clear diagnostic consensus and criteria for ALVC contributed to a delay in referral and diagnosis; (2) competitive athletes were excluded per protocol from our cohort. Although the impact of physical activity on disease progression seems to affect mostly patients with variants associated with a classical ARVC phenotype (eg, PKP-2 driven),^18,19 its influence on the development of ALVC is yet to be determined; (3) ALVC patients in our cohort presented with a low symptomatic arrhythmia burden. Arrhythmias represent one of the most common symptoms for referral of patients with ARVC, and their absence may account for a delay in referral and diagnosis.⁶

No consensus regarding the arrhythmogenicity of an ALVC phenotype has been reached yet, with current risk calculators not accounting for ARVC phenotype differences.²⁰ The overall arrhythmic burden at presentation of our cohort was relatively lower if compared with previously described cohorts of patients with ARVC with LV involvement, with no events of ventricular fibrillation and with 11 (44%) patients (4 family members) presenting without complex arrhythmias and <500 PVCs on 24 hours Holter ECG at disease diagnosis.^14,21 However, 36% of the cohort experienced complex ventricular arrhythmias during a relatively short follow-up time (median follow-up time 16 months), showing a potentially increased arrhythmic risk in this subset of patients. These findings need to be validated in larger cohort but, if confirmed, may bear important implications on the diagnosis and risk stratification protocols of patients with ALVC.

The most common ECG alteration in this cohort, as expected, was TWI. Anterolateral and inferior TWI on peripheral leads were a very common finding, with 17 (68%) of patients presenting with TWI in at least one of the 2 groups of leads. Considering only single leads, TWI were most common in leads aVL, aVF, and I, in agreement with a supposed lateral and postero-inferior extension of the disease.⁶ In precordial leads, TWI was most common in V₅ and V₆, with TWI extending from V₅ to V₆ being the most common multi-lead pattern, again pointing to a disease localization in the lateral mid- and midbasal- LV free wall area, as hypothesized by consensus statements.^5,8 Additional electrodes in V₇ and V₈ were not placed, but given the ECG and CMR agreement on disease localization on available data, they would have been expected to present TWI, as well. An assessment of TWI agreement with EVM in diseased substrate localization has been performed an reported in Table II in the Data Supplement.

Only a single patient presented with an Epsilon-like wave in V₅ through V₆, an ECG sign that in recent times has lost some of its clinical importance in ARVC diagnosis due to a low inter-operator reproducibility, and that does not appear essential in characterizing patients with ALVC either.²² Low QRS voltages on surface 12-lead ECG²³ were present in 4 patients. Low QRS voltages have been described in advanced stages of the classical ARVC phenotype with extensive LV involvement, when the FFR has greatly reduced the amount of myocardial tissue of the LV.²³ The relatively low rate of low QRS voltages in the study cohort is probably due to a less advanced LV disease stage of the included patients with ALVC, compared with reported data from patients with ARVC with late LV involvement. QRS fragmentation in the right ECG leads has been reported capable of localizing the area of diseased substrate in classical ARVC forms²⁴; in our cohort, QRS fragmentation was unfortunately not observed and a similar assessment could not be replicated. Further studies focusing on this aspect are needed. CMR data in our population showed normal LV dimensions in contrast to dilated cardiomyopathy, but focal LV dyskinesia and bulging in up to 40% of the population. LGE distribution in these patients preferentially involved the postero-lateral basal area of the LV, in which additional fatty infiltration at CMR was visualized.

The strength and novelty of this study is given by the availability of pathological findings of FFR found in EVM-guided EMB from the LV, and further by the high percentage of patients harboring a pathogenic or likely pathogenic DSP variant (Figure 2). This makes the presence of phenocopies such as cardiac sarcoidosis highly unlikely. The observed disease distribution confirms the hypothesized disease distribution from several consensus documents and reviews,^5,6 with disease originating in the lateral and posterior mid-to-basal segments of the LV, with a relative sparing of the apex, and probably involvement of the septum at later stages. Low voltages in these regions were retrieved at EVM in a large part of the population. Of note, agreement between EVM and LGE data was fairly good (Appendix II in the Data Supplement), but not perfect, indicating a complementary role of the two methods in detecting the areas affected by FFR.

All included patients presented a clear ALVC phenotype, with several further testing pointing towards that diagnosis. However, by the 2010 ITFC, <50% of the cohort reached a definitive or even a borderline ARVC diagnosis. The only major criterion fulfilled across the cohort was genetic testing positive for ARVC-related variants, while depolarization criteria (TWI in V₄ and beyond) and arrhythmic criteria (24-hour PVC count >500) represented the vast majority of the fulfilled minor criteria. Sustained and nonsustained VTs encountered in our cohort presented with morphologies non included in the ITFC (mostly RBBB like morphologies), while EMB were not performed in the ITFC contemplated areas (LV). CMR LV involvement is currently not included by the 2010 ITFC, and this test does not help in reaching a final ITFC diagnosis, unless the RV is involved, as well.

Although presenting some areas of overlapping with athletes subpopulations,²⁵ the 2010 ITFC were drafted to be very specific for a RV-dominant or biventricular ARVC phenotype. The precocious left-sided involvement of the disease, due also to the paucity of available data at the time, was not extensively assessed, and a clear diagnosis of ALVC is not contemplated by the current ITFC. A clinical diagnosis nowadays is highly dependent on CMR and requires a genetic and EMB confirmation, although several characteristics (TWI or arrhythmia morphology) may be used as complementary diagnostic data. Reporting data from patients with ALVC may help generating the body of evidence needed to back up new diagnostic criteria to amend and complement the currently RV-effective ITFC.

The specificity and rigorosity of the inclusion criteria reduced the number of enrolled patients. Therefore, this study should be interpreted as a spearhead presentation of data, requiring further validation on a large scale. Yet, our study represents a first attempt to define specific characteristics of a highly characterized ALVC population undergoing extensive evaluation. ALVC clinical diagnosis was defined upon a clinically accepted CMR pattern and validated with genetic or EMB findings, trying to increase the specificity and reliability of disease diagnosis. The LGE pattern used for diagnosis was derived from available literature on the topic; however, further studies are needed to specifically address the specificity of this single findings alone in patients with ALVC. Endurance athletes were excluded from the analysis to reduce the number of phenocopies involved: further studies assessing the impact of physical exercise on both phenotype presentation and outcomes of patients with ALVC are, therefore, needed.

The ALVC phenotype in this cohort was characterized by a preferential disease involvement of the lateral and posterior basal area of the LV, as shown from ECG and CMR data, where endocardial low voltages and EMB samples showing FFR were retrieved. A strong genetic component, driven from variants harbored in DSP and DSG2 genes, characterizes patients with ALVC. Strictly adhering to the current ITFC consensus, less than half of this ALVC cohort reached a definite or even borderline ARVC diagnosis. An amendment to the current ITFC is needed to better diagnose patients with ALVC.