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Enlarged left atrium, atrial fibrillation and adverse outcome in hypertrophic cardiomyopathy: is there a difference between apical and non-apical phenotype?
  1. Yuichiro Minami,
  2. Nobuhisa Hagiwara
  1. Department of Cardiology, Tokyo Women’s Medical University, Tokyo, Japan
  1. Correspondence to Dr Yuichiro Minami, Department of Cardiology, Tokyo Women’s Medical University, 8-1 Kawada-cho, Shinjuku-ku, Tokyo 162-8666, Japan; yuichiro24{at}celery.ocn.ne.jp

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Apical hypertrophic cardiomyopathy (HCM) was first described in 1976 by Sakamoto and colleagues as a novel cardiac condition characterised by a spade-shaped left ventricular cavity, apical hypertrophy and giant negative T waves.1 Contemporary reports of apical HCM describe it as a phenotypic variant of HCM in which hypertrophy is localised to the left ventricular apex with or without midsegment involvement. Apical HCM is observed worldwide, although it is traditionally reported more frequently in Asian countries (20%–40% of all HCMs) compared with Western countries (3%–11% of all HCMs). In general, patients with apical HCM exhibit mild symptoms and follow a more benign course with a lower mortality rate compared with other forms of HCM. However, numerous case reports and studies suggest considerable overlap between apical hypertrophy, midventricular obstruction and apical aneurysm. Further, our prior study and a report by Maron and colleagues demonstrated a largely unfavourable clinical course for patients with HCM with midventricular obstruction and/or apical aneurysm.2 3 Thus, the clinical course of patients with apical HCM may not always be benign, and the risk stratification of these patients is of great interest.

In this issue of Heart, Lee and colleagues report the clinical impact of atrial fibrillation (AF) in patients with apical HCM (n=306).4 They showed that AF occurred in 25.2% of patients with apical HCM (annual incidence of 4.6%) and was independently predicted by an older age and enlarged left atrial diameter (>45 mm). During a follow-up of 5.5 years, patients with AF had a higher incidence of death and stroke, and those with AF still had an increased risk for death and stroke after adjustment for age and gender. Thus, it was concluded that AF should be carefully managed in patients with apical HCM. Despite being based on a selective retrospective cohort of patients with HCM from a single tertiary referral centre, these results provide additional epidemiological information regarding the relationship between AF and outcome in patients with apical HCM. The prevalence, annual incidence, predictive factors and prognostic effects of AF in this apical HCM cohort are almost consistent with those of previous studies in the entire HCM cohort.5 6

Since its original description in 1958, prevention of sudden cardiac death and reduction of left ventricular outflow tract gradient have been the primary focus of clinical management and research in HCM. However, AF represents the most common sustained supraventricular arrhythmia, and is more prevalent than either sudden cardiac death or medically refractory outflow tract obstruction in the HCM population. In addition, AF is associated with an increased risk of stroke, heart failure and death in patients with HCM. AF in patients with HCM appears to be 4–6-fold more common than in the general population, with a reported prevalence ranging from approximately 10% to 30% in numerous studies.5 These differences in prevalence between studies may be related to multiple factors, including racial differences, phenotypic disparities, selection bias or differences in the recognition of subclinical, asymptomatic paroxysmal AF. The diagnosis of paroxysmal AF can be difficult in clinical practice, as patients without documented AF may nonetheless have asymptomatic (silent) paroxysmal AF. Surprisingly, a recent study showed that short atrial arrhythmias detected by a device occurred in 29 of 114 (25%) patients with HCM with cardiac implantable electronic devices during 2.8 years of follow-up, resulting in a high annual incidence of 7.0%.7 Indeed, the study by Lee and colleagues reported that AF was detected before the time of stroke only in approximately 50% of patients with apical HCM with both AF and stroke.4 In this respect, it is worth considering the possibility that under-recognition of subclinical, asymptomatic paroxysmal AF may contribute to the elevated stroke risk in this population. Further, a previous study reported that AF was not previously documented in more than half of patients with HCM with stroke and systemic embolic events, and among these patients without previously documented AF, enlarged left atrium diameter (≥48 mm) was an independent determinant of these events.8

As shown in figure 1, the cause of left atrial enlargement in patients with HCM is likely multifactorial. Diastolic dysfunction, left ventricular intracavitary obstruction, mitral regurgitation, elevated left ventricular filling pressures and AF lead to left atrial remodelling and dilation. Additional factors may include background AF risks unrelated to HCM, such as ageing and hypertension. Accordingly, patients with HCM with an enlarged left atrium are thought to be predisposed to the development of AF—whether an asymptomatic paroxysmal episode or a first episode of AF—which in turn may cause further left atrial enlargement and adverse events even in patients without previously documented AF. The European Society of Cardiology guidelines recommend that 48 hours of ambulatory electrocardiography monitoring should be performed every 6–12 months in patients with HCM with an enlarged left atrial diameter ≥45 mm (class IIa). However, it is not entirely clear whether left atrial enlargement develops antecedent to the development of AF, rather than as a secondary phenomenon. There are many points to be clarified, and further studies are required to determine the relationship between left atrial size, AF and adverse outcome in patients with apical and non-apical HCM.

Figure 1

Left atrial remodelling and dilatation, development of atrial fibrillation and adverse outcome in patients with hypertrophic cardiomyopathy.

The management of AF in patients with HCM is also important. Although the relative benefit of rhythm versus rate control in the management of AF is unclear, patients with HCM may develop highly symptomatic AF, particularly in the presence of a rapid ventricular response, and will benefit from restoration of sinus rhythm. There are limited data on the safety and efficacy of antiarrhythmic agents in patients with HCM, and the current choices (mainly disopyramide and amiodarone) may be suboptimal. Thus, the use of catheter ablation for AF is an attractive strategy, although evidence for the efficacy of AF ablation in this population is also limited. A recent meta-analysis showed that outcomes were less favourable for patients with HCM than for the general population, with a twofold higher risk of relapse, more frequent need of repeat procedures and concomitant use of antiarrhythmic drugs.9 Nevertheless, the meta-analysis also suggested that ablation is a valuable option for symptomatic drug-refractory patients with HCM with paroxysmal AF and a smaller left atria, with a low observed complication rate.9 In addition, a recent single-centre retrospective study showed that AF ablation was similarly effective in patients with apical HCM compared with non-apical HCM.10 Data on anticoagulant use in HCM are also limited, although observational data suggest a lower incidence of stroke in patients with AF treated with warfarin compared with those on antiplatelet therapy or no treatment. Unfortunately, the prevention of stroke by prophylactic anticoagulation in patients with HCM at high risk of developing AF (ie, patients with enlarged left atrium without previously documented AF) has not been studied.

As Lee and colleagues concluded, the development of AF should be carefully monitored, and AF should be carefully managed in patients with apical HCM, as for those with non-apical HCM. However, this study did not address the prevalence and prognostic implications of AF in the remaining patients with non-apical HCM (n=779) from the same cohort. As there are racial differences and selection bias regarding the phenotype of HCM, a comparison between apical and non-apical phenotype is preferable in the same cohort rather than with past studies. In this regard, it is not entirely clear whether there is a difference between the apical and non-apical phenotype with respect to the prevalence and prognostic effect of AF, and further study on this issue is needed. Finally, to improve the prognosis of patients with apical and non-apical HCM, further optimisation of risk stratification, screening methods and management strategies for AF remains a clinical challenge.

References

Footnotes

  • Contributors This article was written by YM in collaboration with NH.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.

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