Role of Cardiac Magnetic Resonance Imaging in Patients with Idiopathic Ventricular Arrhythmias

Evaluation of patients with high burden of premature ventricular contractions by comprehensive transthoracic echocardiography

Background

The prevalence and prognosis of premature ventricular contractions (PVCs) among individuals without structural heart disease are uncertain. Standard transthoracic echocardiography is a common method in evaluation of underlying cardiovascular disease and is recommended as a diagnostic method in PVC patients. However, it is unclear whether comprehensive echocardiographic examination can identify pathological findings in PVC patients with a normal standard echocardiogram.

Method

We included forty consecutive patients with a high PVC burden (>10,000 PVCs/day) and normal findings at a standard echocardiogram and exercise test. All subjects were investigated by a comprehensive echocardiographic examination using parameters usually not included in a routine work-up. We compared the results with 22 age and sex-matched controls.

Results

In six additional parameters–global longitudinal strain, right ventricular strain, septal-lateral delay, ventricular-arterial coupling, integrated backscatter and left atrial activation time–a statistically significant difference was shown between PVC patients and controls. Among these parameters, global longitudinal strain had a high reliability between operators.

Conclusions

Despite normal findings at standard echocardiography, the PVC group showed signs of impaired heart function when more comprehensive echocardiography parameters were used.

Occurrence and morphology of ventricular arrhythmias in apparently normal hearts in relation to late gadolinium enhancement on cardiovascular magnetic resonance

Cardiac magnetic resonance (CMR) is the gold standard for evaluating myocardial fibrosis. Few studies have explored the association between ventricular arrhythmias (VAs) and fibrosis in apparently normal hearts. We aimed to investigate the association between the occurrence and morphology of VAs and left ventricular late gadolinium enhancement (LV-LGE) in patients without known structural heart diseases. This study enrolled 78 patients with apparently normal hearts who underwent 24-h ambulatory Holter electrocardiogram (ECG) and CMR examinations simultaneously. The presence and extent of LGE was determined using CMR imaging and compared based on occurrence and morphology of VAs. The clinical characteristics were also recorded and calculated. LV-LGE was observed in 19 (37.3%) and 4 (14.8%) patients with and without VAs, respectively (P = 0.039). It was more frequently observed in patients with polymorphic VAs (P = 0.024). The polymorphic VAs had a higher tendency of LGE extent than monomorphic VAs, while the difference did not reach statistical significance (P = 0.055). In multivariable analyses, the presence of polymorphic VAs [hazard ratio (HR) 11.19, 95% CI 1.64-76.53, P = 0.014] and hypertension (HR 4.64, 95% CI 1.08-19.99, P = 0.039) were associated with greater prevalence of LV-LGE. In patients without structural heart diseases, besides hypertension, multiple VA morphologies on Holter ambulatory ECG measurements is another important marker of increased incidence of myocardial fibrosis.

Magnetic Resonance Detects Structural Heart Disease in Patients with Frequent Ventricular Ectopy and Normal Echocardiographic Findings

The prognosis of patients with ventricular ectopy and a normal heart, as evaluated by echocardiography, is virtually unknown. Cardiac magnetic resonance (CMR) can detect focal ventricular anomalies that could act as a possible site of origin for premature ventricular contractions (PVCs). The aim of this study was to investigate the presence of cardiac anomalies in patients with normal findings at echocardiogram.

METHODS

Fifty-one consecutive patients (23 women, 28 men, mean age 59 years) with very high PVC burden (>10,000 PVC/day) and normal findings at standard echocardiography and exercise test were examined with CMR. The outcome was pathologic findings, defined as impaired ejection fraction, regional wall motion abnormalities, abnormal ventricular volume, myocardial edema and fibrosis.

RESULTS

Sixteen out of 51 patients (32%) had structural ventricular abnormalities at CMR. In five patients CMR showed impairment of the left ventricular and/or right ventricular systolic function, and six patients had a dilated left and/or right ventricle. Regional wall motion abnormalities were seen in six patients and fibrosis in four. No patient had CMR signs of edema or met CMR criteria for arrhythmogenic right ventricular cardiomyopathy. Five patients had extra-ventricular findings (enlarged atria in three cases, enlarged thoracic aorta in one case and pericardial effusion in one case).

CONCLUSIONS

In this study 16 out of 51 patients with a high PVC burden and normal findings at echocardiography showed signs of pathology in the ventricles with CMR. These findings indicate that CMR should be considered in evaluating patients with a high PVC burden and a normal standard investigation.

Cardiac Magnetic Resonance to Detect the Underlying Substrate in Patients with Frequent Idiopathic Ventricular Arrhythmias

BACKGROUND

A routine diagnostic work-up does not identify structural abnormalities in a substantial proportion of patients with idiopathic ventricular arrhythmias (VAs). We investigated the added value of cardiac magnetic resonance (CMR) imaging in this group of patients.

METHODS

A single-centre prospective study was undertaken of 72 patients (mean age 46 ± 16 years; 53% females) with frequent premature ventricular contractions (PVCs ≥ 500/24 h) and/or non-sustained ventricular tachycardia (NSVT), an otherwise normal electrocardiogram, normal echocardiography and no coronary artery disease.

RESULTS

CMR provided an additional diagnostic yield in 54.2% of patients. The most prevalent diagnosis was previous myocarditis (23.6%) followed by possible PVC-related cardiomyopathy (20.8%), non-ischaemic cardiomyopathy (8.3%) and ischaemic heart disease (1.4%). The predictors of abnormal CMR findings were male gender, age and PVCs/NSVT non-outflow tract-related or with multiple morphologies. Patients with VAs had an impaired peak left ventricular (LV) global radial strain (GRS) compared with the controls (28.88% (IQR: 25.87% to 33.97%) vs. 36.65% (IQR: 33.19% to 40.2%), p < 0.001) and a global circumferential strain (GCS) (-17.66% (IQR: -19.62% to -16.23%) vs. -20.66% (IQR: -21.72% to -19.6%), p < 0.001).

CONCLUSION

CMR reveals abnormalities in a significant proportion of patients with frequent idiopathic VAs. Male gender, age and non-outflow tract PVC origin can be clinical indicators for CMR referral.

Slow uniform electrical activation during sinus rhythm is an indicator of reentrant VT isthmus location and orientation in an experimental model of myocardial infarction

BACKGROUND

To validate the predictability of reentrant circuit isthmus locations without ventricular tachycardia (VT) induction during high-definition mapping, we used computer methods to analyse sinus rhythm activation in experiments where isthmus location was subsequently verified by mapping reentrant VT circuits.

METHOD

In 21 experiments using a canine postinfarction model, bipolar electrograms were obtained from 196-312 recordings with 4mm spacing in the epicardial border zone during sinus rhythm and during VT. From computerized electrical activation maps of the reentrant circuit, areas of conduction block were determined and the isthmus was localized. A linear regression was computed at three different locations about the reentry isthmus using sinus rhythm electrogram activation data. From the regression analysis, the uniformity, a measure of the constancy at which the wavefront propagates, and the activation gradient, a measure that may approximate wavefront speed, were computed. The purpose was to test the hypothesis that the isthmus locates in a region of slow uniform activation bounded by areas of electrical discontinuity.

RESULTS

Based on the regression parameters, sinus rhythm activation along the isthmus near its exit proceeded uniformly (mean r²= 0.95±0.05) and with a low magnitude gradient (mean 0.37±0.10mm/ms). Perpendicular to the isthmus long-axis across its boundaries, the activation wavefront propagated much less uniformly (mean r²= 0.76±0.24) although of similar gradient (mean 0.38±0.23mm/ms). In the opposite direction from the exit, at the isthmus entrance, there was also less uniformity (mean r²= 0.80±0.22) but a larger magnitude gradient (mean 0.50±0.25mm/ms). A theoretical ablation line drawn perpendicular to the last sinus rhythm activation site along the isthmus long-axis was predicted to prevent VT reinduction. Anatomical conduction block occurred in 7/21 experiments, but comprised only small portions of the isthmus lateral boundaries; thus detection of sinus rhythm conduction block alone was insufficient to entirely define the VT isthmus.

CONCLUSIONS

Uniform activation with a low magnitude gradient during sinus rhythm is present at the VT isthmus exit location but there is less uniformity across the isthmus lateral boundaries and at isthmus entrance locations. These factors may be useful to verify any proposed VT isthmus location, reducing the need for VT induction to ablate the isthmus. Measured computerized values similar to those determined herein could therefore be assistive to sharpen specificity when applying sinus rhythm mapping to localize EP catheter ablation sites.

Cardiac magnetic resonance in arrhythmogenic cardiomyopathies

Over the past few years, the approach to the 'arrhythmic patient' has profoundly changed. An early clinical presentation of arrhythmia is often accompanied by non-specific symptoms and followed by inconclusive electrocardiographic findings. In this scenario, cardiac magnetic resonance (CMR) has been established as a clinical tool of fundamental importance for a correct prognostic stratification of the arrhythmic patient. This technique provides a high-spatial-resolution tomographic evaluation of the heart, which allows studying accurately the ventricular volumes, identifying even segmental kinetic anomalies and properly detecting diffuse or focal tissue alterations through an excellent tissue characterization, while depicting different patterns of fibrosis distribution, myocardial edema or fatty substitution. Through these capabilities, CMR has a pivotal role for the adequate management of the arrhythmic patient, allowing the identification of those phenotypic manifestations characteristic of structural heart diseases. Therefore, CMR provides valuable information to reclassify the patient within the wide spectrum of potentially arrhythmogenic heart diseases, the definition of which remains the major determinants for both an adequate treatment and a poor prognosis. The purpose of this review study was to focus on the role of CMR in the evaluation of the main cardiac clinical entities associated with arrhythmogenic phenomena and to present a brief debate on the main pathophysiological mechanisms involved in the arrhythmogenesis process.

Cardiovascular magnetic resonance clarifies arrhythmogenicity in asymptomatic young athletes with ventricular arrhythmias undergoing pre-participation evaluation

Pre-participation sports examination (PPE) is a frequent reason for consultation. However, the exact role of cardiovascular magnetic resonance (CMR) in PPE remains undefined. The additive value of CMR in adolescent athletes with ventricular rhythm disturbances (VRDs) was investigated. We prospectively recruited and evaluated with CMR 50 consecutive, asymptomatic young athletes referred to our tertiary center after identification of VRDs on electrocardiogram (ECG) with otherwise normal standard PPE and echocardiography, and 20 age- and sex-matched healthy volunteer athletes who underwent the same evaluations. The primary outcome was case-control status and the secondary outcome was the discrimination between athletes with VRDs with and without non-sustained ventricular tachycardia (VT). CMR identified arrhythmogenic substrates in all athletes with VRDs. The predominant condition was myocarditis and arrhythmogenic right ventricular cardiomyopathy in patients with and without VT, respectively. Based on penalized regression analysis, late gadolinium enhancement (LGE), early gadolinium enhancement (EGE), extracellular volume fraction (ECV), and T2-mapping, best distinguished between case-control status. The aforementioned indices predicted case-control status independent of age and sex: EGE [Odds ratio (95% confidence interval): 6.89 (2.19-21.62) per 0.5-unit, P<0.001], LGE (perfect prediction), ECV [1.66 (1.25-2.22), P<0.001] and T2 mapping [1.40 (1.13-1.72), P=0.002], among other independent CMR-derived predictors. Only indexed ventricular volumes independently discriminated between VRD patients with and without VT. In this study, asymptomatic young athletes with VRDs and normal PPE/echocardiography were optimally discriminated from healthy control athletes by CMR-derived indices, and CMR allowed for the identification of arrhythmogenic substrates in all cases.

Ventricular arrhythmias and risk stratification of cardiac sudden death in athletes

Sudden cardiac death (SCD) of young athletes is an unexpected and tragic event that could occur during sport activities and is frequently related to ventricular arrhythmias. Identifying athletes at risk of SCD remains a major challenge. While specific characteristics of premature ventricular contractions are considered common and benign, other "uncommon" features should require more accurate investigations, in order to determine eligibility for competitive sports. The most common type of idiopathic premature ventricular contractions originates from ventricular outflow tract and is characterized by an ECG pattern with left bundle branch block and inferior QRS axis (infundibular pattern). Another pattern associated with a good prognosis is the "fascicular" morphology, characterized by a typical right bundle branch block, superior QRS axis morphology and QRS duration <130 ms. Conversely, other morphological features (such as left bundle branch block /intermediate or superior axis or right bundle branch block/intermediate or superior axis and wide QRS) correlate to an underlying substrate. In risk stratification setting, cardiac magnetic resonance plays a key role allowing an accurate identification of myocardial tissue abnormalities, which could affect athletes' prognosis. This review focuses on characteristics of premature ventricular contractions characteristics in terms of morphology, distribution, complexity and response to exercise and describes the possible underlying myocardial substrates. This review also critically analyzes the evaluation process of athletes with premature ventricular contractions necessary for an accurate risk stratification.

Frequent Ventricular Premature Beats in Children and Adolescents: Natural History and Relationship with Sport Activity in a Long-Term Follow-Up

Premature ventricular complexes (PVCs) are frequently documented in children. To date, few studies report long-term follow-up in pediatric cohorts presenting with frequent PVCs. The aim of this study is to assess the clinical relevance and long-term outcomes of frequent PVCs (≥ 500/24 h) in a large pediatric cohort. From 1996 to 2016, we enrolled all consecutive patients evaluated at Anna Meyer Children Hospital for frequent PVCs. Symptomatic children were excluded together with those patients with known underlying heart diseases; thus, our final cohort of study included 103 patients (male 66%; mean age 11 ± 3.4 years), with a mean follow-up of 9.5 ± 5.5 years. All patients were submitted to complete non-invasive cardiologic evaluation. The mean number of PVCs at Holter Monitoring (HM) was 11,479 ± 13,147/24 h; couplets and/or triplets were observed in 5/103 (4.8%) cases; 3 patients (2.9%) presented runs of non-sustained ventricular tachycardia (NSVT). High-burden PVCs (> 30,000/24 h) was confirmed in 11/103 (10.6%) patients. During the follow-up, only five patients (4.8%) developed clinical symptoms (3 for palpitations, 1 myocardial dysfunction due to frequent PVCs and NTSV; 1 arrhythmogenic cardiomyopathy); no deaths occurred. Basal PVCs were still present in 45/103 (43.7%) patients. Our data suggest that frequent PVCs may be addressed as a benign condition and should not preclude sport participation if not associated with cardiac malformations, heart dysfunction, or cardiomyopathy. This seems to be true also in presence of very frequent/high-burden PVCs. Otherwise, a careful follow-up is mandatory since sport eligibility should be reconsidered in case of onset of symptoms and/or ECG/echocardiographic changes.

Therapies to limit myocardial injury in animal models of myocarditis: a systematic review and meta-analysis

Current myocarditis guidelines do not advocate treatment to prevent myocardial injury and scar deposition in patients with myocarditis and normal left ventricular ejection fraction. We aimed to ascertain the utility of beta blockers, calcium channel blockers and antagonists of the renin–angiotensin system in ameliorating myocardial injury, scar formation and calcification in animal in vivo models of myocarditis. The project was prospectively registered with the PROSPERO database of systematic reviews (CRD42018089336). Primary outcomes (necrosis, fibrosis and calcification) were meta-analysed with random-effects modelling. 52 studies were systematically reviewed. Meta-analysis was performed compared with untreated controls. In each study, we identified all independent comparisons of treatment versus control groups. The pooled weighted mean difference (WMD) indicated treatment reduced necrosis by 16.9% (71 controlled analyses, 95% CI 13.2–20.7%; P < 0.001), however there was less evidence of an effect after accounting for publication bias. Treatment led to a 12.8% reduction in fibrosis (73 controlled analyses, 95% CI 7.6–18.0%; P < 0.001). After accounting for publication bias this was attenuated to 7.8% but remained significant. Treatment reduced calcification by 4.1% (28 controlled analyses, 95% CI 0.2–8.0%; P < 0.0395). We observed significant heterogeneity in effect size in all primary endpoints, which was predominantly driven by differences between drug categories. Beta blockers and angiotensin-converting enzyme (ACE) inhibitors were the only agents that were effective for both necrosis and fibrosis, while only ACE inhibitors had a significant effect on calcification. This study provides evidence for a role for ACE inhibitors and beta blockers to prevent myocardial injury and scar deposition in in vivo models of myocarditis. There is a need for further well-designed studies to assess the translational application of these treatments.

Cardiolipotoxicity, Inflammation, and Arrhythmias: Role for Interleukin-6 Molecular Mechanisms

Fatty acid infiltration of the myocardium, acquired in metabolic disorders (obesity, type-2 diabetes, insulin resistance, and hyperglycemia) is critically associated with the development of lipotoxic cardiomyopathy. According to a recent Presidential Advisory from the American Heart Association published in 2017, the current average dietary intake of saturated free-fatty acid (SFFA) in the US is 11–12%, which is significantly above the recommended <10%. Increased levels of circulating SFFAs (or lipotoxicity) may represent an unappreciated link that underlies increased vulnerability to cardiac dysfunction. Thus, an important objective is to identify novel targets that will inform pharmacological and genetic interventions for cardiomyopathies acquired through excessive consumption of diets rich in SFFAs. However, the molecular mechanisms involved are poorly understood. The increasing epidemic of metabolic disorders strongly implies an undeniable and critical need to further investigate SFFA mechanisms. A rapidly emerging and promising target for modulation by lipotoxicity is cytokine secretion and activation of pro-inflammatory signaling pathways. This objective can be advanced through fundamental mechanisms of cardiac electrical remodeling. In this review, we discuss cardiac ion channel modulation by SFFAs. We further highlight the contribution of downstream signaling pathways involving toll-like receptors and pathological increases in pro-inflammatory cytokines. Our expectation is that if we understand pathological remodeling of major cardiac ion channels from a perspective of lipotoxicity and inflammation, we may be able to develop safer and more effective therapies that will be beneficial to patients.