Short PR intervals and tachyarrhythmias in Fabry's disease

Clinical staging of Anderson-Fabry cardiomyopathy: An operative proposal

As a slowly progressive form of hypertrophic cardiomyopathy (HCM), Anderson-Fabry disease (FD) resembles the phenotype of the most common sarcomeric forms, although significant differences in presentation and long-term progression may help determine the correct diagnosis. A variety of electrocardiographic and imaging features of FD cardiomyopathy have been described at different times in the course of the disease, and considerable discrepancies remain regarding the assessment of disease severity by individual physicians. Therefore, we here propose a practical staging of FD cardiomyopathy, in hopes it may represent the standard for cardiac evaluation and facilitate communication between specialized FD centres and primary care physicians. We identified 4 main stages of FD cardiomyopathy of increasing severity, based on available evidence from clinical and imaging studies: non-hypertrophic, hypertrophic - pre-fibrotic, hypertrophic - fibrotic, and overt dysfunction. Each stage is described and discussed in detail, following the principle that speaking a common language is critical when managing such complex patients in a multi-disciplinary and sometimes multi-centre setting.

Arrhythmias in Fabry cardiomyopathy

Fabry disease is an X-linked multisystem disorder caused by deficiency of the α-galactosidase A enzyme. Cardiovascular manifestations include hypertension, coronary disease, arrhythmias, valvular abnormalities, heart failure, and sudden death. Bradycardia and conduction system abnormalities are related initially to abnormal accumulation of glycolipids in the lysosomes of conduction tissues. Hypertrophy and eventual fibrosis provides a substrate for persistent conduction abnormalities and ventricular arrhythmias. Sudden cardiac death can be related to bradyarrhythmias or tachycardias. Enzyme replacement therapy can improve cardiac function and clinical outcomes. Pacemakers or defibrillators are important in the treatment of patients with Fabry disease who are at risk for arrhythmias.

Cardiac-specific over-expression of epidermal growth factor receptor 2 (ErbB2) induces pro-survival pathways and hypertrophic cardiomyopathy in mice

BACKGROUND

Emerging evidence shows that ErbB2 signaling has a critical role in cardiomyocyte physiology, based mainly on findings that blocking ErbB2 for cancer therapy is toxic to cardiac cells. However, consequences of high levels of ErbB2 activity in the heart have not been previously explored.

METHODOLOGY/PRINCIPAL FINDINGS

We investigated consequences of cardiac-restricted over-expression of ErbB2 in two novel lines of transgenic mice. Both lines develop striking concentric cardiac hypertrophy, without heart failure or decreased life span. ErbB2 transgenic mice display electrocardiographic characteristics similar to those found in patients with Hypertrophic Cardiomyopathy, with susceptibility to adrenergic-induced arrhythmias. The hypertrophic hearts, which are 2-3 times larger than those of control littermates, express increased atrial natriuretic peptide and β-myosin heavy chain mRNA, consistent with a hypertrophic phenotype. Cardiomyocytes in these hearts are significantly larger than wild type cardiomyocytes, with enlarged nuclei and distinctive myocardial disarray. Interestingly, the over-expression of ErbB2 induces a concurrent up-regulation of multiple proteins associated with this signaling pathway, including EGFR, ErbB3, ErbB4, PI3K subunits p110 and p85, bcl-2 and multiple protective heat shock proteins. Additionally, ErbB2 up-regulation leads to an anti-apoptotic shift in the ratio of bcl-xS/xL in the heart. Finally, ErbB2 over-expression results in increased activation of the translation machinery involving S6, 4E-BP1 and eIF4E. The dependence of this hypertrophic phenotype on ErbB family signaling is confirmed by reduction in heart mass and cardiomyocyte size, and inactivation of pro-hypertrophic signaling in transgenic animals treated with the ErbB1/2 inhibitor, lapatinib.

CONCLUSIONS/SIGNIFICANCE

These studies are the first to demonstrate that increased ErbB2 over-expression in the heart can activate protective signaling pathways and induce a phenotype consistent with Hypertrophic Cardiomyopathy. Furthermore, our work suggests that in the situation where ErbB2 signaling contributes to cardiac hypertrophy, inhibition of this pathway may reverse this process.

PQ interval in patients with Fabry disease

Fabry disease (FD) is an X-chromosomal inherited lysosomal storage disease resulting in intracellular storage of globotriaosylceramide. Cardiac involvement is most frequently manifested as left ventricular hypertrophy. However, patients with FD may also have from various conduction abnormalities particularly affecting atrioventricular (AV) conduction. The present study was designed to analyze primarily AV conduction abnormalities on baseline electrocardiograms of patients with FD and to investigate the correlation with echocardiographic findings. Electrocardiograms at rest of 207 patients with FD were compared to echocardiograms. PQ-interval shortening and first-degree AV block could be found in only 29 cases (14%) and 3 cases (1.4%), respectively. No echocardiographic differences could be found in patients with and without PQ-interval shortening, including left ventricular hypertrophy, atrial size, and diastolic parameters. Furthermore, no correlation of the PQ interval with any echocardiographic parameters was detected. There was no difference between men and women in baseline clinical and electrocardiographic parameters. In conclusion, shortening of the PQ interval was not a common electrocardiographic finding in patients newly diagnosed with FD. Furthermore, no correlation with typical echocardiographic findings or disease stage in FD at baseline could be found.

Electrophysiological study in a patient with Fabry disease and a short PQ interval

A short PQ interval is a common finding in patients with Fabry disease. However, there have been few electrophysiological studies in Fabry disease, and it is not clear whether the short PQ interval that is present in this disease results from preexcitation or enhanced atrioventricular nodal conduction. We present a case of a 43-year-old man with syncope, sick sinus syndrome, a PQ interval of 80 ms, and palpitations. Electrophysiological study showed PA, AH, and HV intervals of 24, 32, and 34 ms, respectively, and features of enhanced atrioventricular nodal conduction. The presence of an atrioventricular accessory pathway was excluded. We conclude that the short PQ interval in Fabry disease can result from accelerated conduction in the atrioventricular node.

Cardiac involvement in Fabry disease

Fabry disease is a rare X-linked defect of the lysosomal enzyme alpha-galactosidase A. The disease is characterized by progressive intracellular accumulation of neutral glycosphingolipids. The storage occurs within various tissues and cells, including cardiocytes, the cardiac conduction system, and valvular fibrocytes. Cardiac involvement may be the sole manifestation of the disease, particularly in individuals with residual enzyme activity. In general, hemizygous men are more seriously affected than heterozygous women. The main cardiac manifestations include myocardial hypertrophy, which, in some patients, mimics hypertrophic cardiomyopathy. Conduction system involvement leads to PR shortening or, in later stages, to AV blocks. Arrhythmias presenting with variable severity also appear to be common. Valvular involvement is frequently noted but generally mild and clinically non-significant. Newly available enzyme replacement therapy has produced promising results in preventing further functional deterioration of affected organs and possibly also in reversing impaired function.

CONCLUSIONS

With the advent of effective enzyme replacement therapy, early diagnosis of Fabry disease may be crucial for patient prognosis.

Isolated cardiac manifestations in Fabry disease: the UK experience

Cardiac abnormalities are common in patients with Fabry disease, and may be the only clinical manifestation of the disease in some patients. At St George's Hospital Medical School, a national referral centre for hypertrophic cardiomyopathy in the UK, a study of 153 consecutively referred male patients revealed that 4% had Fabry disease. This increased to 6% in patients over 40 years of age. All these patients had electrocardiographic (ECG) abnormalities, most of which were consistent with those found in patients with classic Fabry disease: left ventricular hypertrophy, repolarization abnormalities and a prolonged QRS complex. A study of heterozygote females with Fabry disease also showed ECG and echocardiographic abnormalities in most patients.

CONCLUSIONS

Fabry disease should be considered in the differential diagnosis of otherwise unexplained cardiac disease.

Cardiac manifestations in Fabry disease

Fabry disease is an X-linked recessive genetic disorder of glycosphingolipid metabolism, due to deficiency of the lysosomal enzyme alpha-galactosidase A. The disease is characterized by the progressive intracellular lysosomal accumulation of neutral glycosphingolipids throughout the body, including the cardiovascular system. It has been reported that cardiac involvement could be the sole manifestation of the disease in some patients. Myocardial abnormalities are characterized mainly by left ventricular (LV) wall thickening without significant cavity dilatation, the most frequent abnormal structural pattern being concentric LV hypertrophy (LVH). In some patients the disease mimics a typical hypertrophic obstructive cardiomyopathy. According to our experience, systolic function is largely preserved in a large majority of affected individuals. In contrast, mild to moderate impairment of diastolic filling is a relatively common finding, representing probably the most important cause of dyspnoea in patients with Fabry disease. However, in a relatively large population of affected patients, severe diastolic dysfunction, typical of restrictive cardiomyopathy, was not found. Valvular structural abnormalities are frequent due to valvular infiltration. In several patients, hypertrophy of papillary muscles and/or systolic anterior motion of the mitral leaflets associated with LV outflow obstruction may aggravate the mitral valve dysfunction. We did not confirm the previously reported high prevalence of mitral valve prolapse. Valvular regurgitation seems to be relatively frequent but mostly non-significant. Electrocardiographic changes in Fabry disease are multiple and include atrioventricular (AV) conduction abnormalities (abbreviation of the P-R interval or AV blocks), signs of LVH and repolarization abnormalities. Our observations suggest that conduction defects and repolarization changes are present predominantly in subjects with LV structural abnormalities. Cardiac symptoms in patients with Fabry disease include shortness of breath on effort (related to LV diastolic dysfunction), vasospastic and/or exertional angina pectoris (due to LVH, endothelial dysfunction and/or fixed coronary artery stenosis) and syncope (related to AV blocks or LV outflow obstruction). The extent of cardiac involvement, in particular LV mass assessment, could represent an ideal surrogate endpoint for evaluating the efficacy of specific therapies.