The cardiomyopathy in Friedreich's ataxia

Frank Weidemann, et al . The cardiomyopathy in Friedreich's ataxia — New biomarker for staging cardiac involvement

International Journal of Cardiology 194 (2015) 50–57    

Presented by: Dr. Antonis Pantazis (UK)

BACKGROUND

In the paper by Weidemann, et al , patients with autosomal-recessively inherited Friedreich's ataxia often develop first symptoms relate to the spinocerebellar ataxia during adolescence, but sometimes even earlier. They may develop a cardiomyopathy (CM) phenotype, which is similar to hypertrophic cardiomyopathy and potentially progresses towards a life-limiting problem.

OBJECTIVE

To describe the phenotype of Friedreich's ataxia cardiomyopathy and distinguish stages of disease progression.

METHODS

32 consecutive patients with genetically confirmed Friedreich's ataxia were included. All patients received resting electrocardiogram (ECG), 24-hour Holter-ECG, echocardiography with speckle tracking imaging, cardiac magnetic resonance imaging (cMRI) with late enhancement imaging (for replacement fibrosis), and measurement of high-sensitive troponin-T (hsTNT). In addition, morphological parameters were retrospectively compared to data obtained five years before.

RESULTS

Based on criteria comprising ejection fraction (<55%), left ventricular end-diastolic posterior wall thickness (LVPWT ≥ 11 mm), fibrosis on cMRI, hsTNT ≥ 14 ng/ml, or T-wave-inversion, in all but two patients a CM could be detected (94%). Using these criteria the authors proposed the following staging: a) mild CM (n = 5, 16%; T-wave- inversion only); b) intermediate CM (n = 4, 13%; T-wave-inversion with hypertrophy but no fibrosis); c) severe CM (n = 13, 41%; fibrosis with raised hsTNT); and d) end-stage CM (n = 8; 25%; ejection-fraction b 55%). All patients with end-stage CM also showed fibrosis on cMRI, T-wave-inversion, marked elevation in hsTNT, and a de- crease in LVPWT during the last five years (from 10.7 ± 1.2 mm to 9.5 ± 1.3 mm, p = 0.025). In addition, 38% suffered from supraventricular tachycardia on Holter-ECG.

CONCLUSION

A comprehensive cardiac assessment will unravel established cardiomyopathy in almost all patients with Friedreich's ataxia, with electrocardiographic abnormalities as earliest signs. Advanced stages can be characterized by elevated hsTNT and replacement fibrosis leading to recession of hypertrophy, reduction of global myocardial function, and electrical instability.

COMMENTS

Friedreich's ataxia is associated with a type of Cardiomyopathy, which although has resemblance to HCM, is characterized by a number of unique features. It is therefore not unreasonable to name it “Friedreich's ataxia cardiomyopathy”. For example, T- wave inversion is found in the great majority of these patients, even in the absence of any other cardiac manifestation and the CMR late enhancement pattern in patients with Friedreich's ataxia seems different compared with other well-known patterns in hypertrophic cardiomyopathies.

However, not much evidence is available to describe the Friedreich's ataxia phenotype and more particularly, the progression of the phenotype.

This study has access to a reasonably large dataset for cross sectional analysis. However, the definitions of abnormality used in the staging system are without evidence of prognostic usefulness and this fact is acknowledged by the authors.

Certain parameters could improve the analysis, for example the use of calculated relative wall thickness (RWT), especially since the retrospective and longitudinal part of the study is based on echocardiography. It has been previously suggested that adjusting wall thickness for left ventricular size, using the calculated variable of relative wall thickness (RWT), is likely to be a more sensitive means of determining the presence of a LV structural abnormality in Friedreich's ataxia.

The paper is probably the best published cross sectional data collection with detailed diagnostic tests and with the benefit of comparison against a retrospective dataset, which is limited to echocardiography though. It provides good insight into the phenotype of Friedreich's ataxia cardiomyopathy but has limited longitudinal and outcome data to stage the different subtypes of the phenotype. This staging system needs to be used with caution, if at all, in clinical practice and is certainly not associated with risks and decision-making. Further research can take advantage of these detailed observations and endeavor to associate them with outcomes in larger numbers of Friedreich's ataxia patients.