Hypertrophic cardiomyopathy in adults: Supraventricular tachycardias including atrial fibrillation

INTRODUCTION — Hypertrophic cardiomyopathy (HCM) is a genetically determined heart muscle disease caused by mutations in one of several sarcomere genes that encode components of the contractile apparatus. (See "Hypertrophic cardiomyopathy: Gene mutations and clinical genetic testing".)

HCM is characterized by left ventricular hypertrophy (LVH) of various morphologies (figure 1) and is commonly associated with atrial arrhythmias.

The evaluation and management of supraventricular tachycardias, primarily atrial fibrillation (AF), in patients with HCM will be reviewed here.

Other aspects of the clinical manifestations, diagnosis, and management of HCM in adults are discussed separately:

●(See "Hypertrophic cardiomyopathy: Natural history and prognosis".)

●(See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation".)

●(See "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

●(See "Hypertrophic cardiomyopathy: Management of patients without outflow tract obstruction".)

●(See "Hypertrophic cardiomyopathy: Gene mutations and clinical genetic testing".)

●(See "Hypertrophic cardiomyopathy: Management of ventricular arrhythmias and sudden cardiac death risk" and "Hypertrophic cardiomyopathy: Risk stratification for sudden cardiac death".)

EPIDEMIOLOGY — In patients with HCM, the prevalence of AF appears to be four- to sixfold higher than similarly aged patients in the general population, with an incidence in the range of 2 to 5 percent per year [1-3]. AF is rare in young patients with HCM who are less than 30 years of age. AF is paroxysmal in approximately two-thirds of patients and persistent or permanent in the remaining one-third:

●In a cohort of 4591 patients from the Sarcomeric Human Cardiomyopathy Registry (SHaRe) who were followed for a mean of 5.4 years, 20 percent developed AF at some point (no data were presented to determine paroxysmal versus permanent AF or burden of AF) [4].

●In a cohort of 1558 consecutive patients with HCM who were followed at a referral center for an average of 4.8 years, AF occurred in 304 patients (20 percent), with 74 percent being paroxysmal AF and 26 percent developing permanent AF [5].

●In a case-control study of 104 patients with HCM (52 case patients with HCM and AF at some point during follow-up, 52 controls with HCM and normal sinus rhythm) diagnosed between 1960 and 1985, AF was present in approximately 5 percent of patients at the time of diagnosis of HCM and developed in an additional 10 percent during the five years following diagnosis [1].

●In a retrospective study of 75 patients with HCM with a dual-chamber implantable cardioverter-defibrillator (ICD) but no known history of AF, 21 patients (28 percent) developed AF over an average follow-up of five years [3]. Eighteen of the 21 patients developed asymptomatic AF episodes (ie, clinically silent), most of which lasted less than one hour; however, 13 of the 18 patients with clinically silent AF had more than one episode, and 8 of the 18 ultimately developed symptoms attributed to AF. Nonfatal embolic stroke occurred in 1 patient associated with asymptomatic AF and without other risk factors.

PATHOPHYSIOLOGY — HCM is associated with a thick and noncompliant LV resulting in some degree of diastolic dysfunction in nearly all patients. Thus, patients with HCM are thought to be particularly dependent on the contribution of atrial systole to provide optimal LV filling and cardiac output. Diastolic dysfunction significantly impacts affected patients’ tolerance of AF and other atrial tachyarrhythmias. AF, with loss of atrial kick and associated rapid ventricular rates results in reduced diastolic LV filling time and LV filling, which contributes to increased heart failure symptoms. (See "Heart failure with preserved ejection fraction: Clinical manifestations and diagnosis" and "Hemodynamic consequences of atrial fibrillation and cardioversion to sinus rhythm", section on 'Adverse hemodynamics in AF'.)

Thus, diastolic dysfunction has a significant impact on a patient's ability to tolerate AF and other atrial tachyarrhythmias. (See "Hemodynamic consequences of atrial fibrillation and cardioversion to sinus rhythm".)

PREDISPOSING FACTORS — Several factors appear to be associated with risk for development of AF in patients with HCM, including [2,6,7]:

●Increased left atrial diameter (eg, left atrial dimension >45 mm) and volume

●Increasing age

●Left atrial dysfunction

●Severe and diffuse hypertrophy

●LV ejection fraction (LVEF), particularly when LVEF <50 percent (end-stage HCM)

In contrast to these risk factors, the presence or severity of an LV outflow tract gradient does not appear to be associated with an increased incidence of AF [8].

There are limited data on atrial pathology in HCM, but some studies have shown extensive atrial fibrosis similar to that seen in patients with long-standing HF [7]. Myocyte disarray, present in the ventricular myocardium, has not been reported in the atria, and the expression of sarcomeric protein mutations in atrial tissue has not been studied.

CLINICAL MANIFESTATIONS — While AF is often poorly tolerated in HCM and may be associated with significant symptoms and clinical deterioration, its impact of morbidity and mortality can be significantly mitigated with modern AF management [1,2,5,9]. While most patients with HCM who develop AF have prominent symptoms, not all patients are symptomatic. The clinical manifestations of AF in patients with HCM can be divided into acute symptoms and long-term consequences.

●Acute presentation – For many patients with HCM, acute symptoms associated with AF are similar to symptoms of AF in patients without HCM such as palpitations, dyspnea, and chest pain. However, some patients with HCM and AF, especially those with LV outflow tract (LVOT) obstruction or severe diastolic dysfunction, develop symptomatic hypotension with lightheadedness, presyncope, or syncope. These symptoms are caused by decreased LV diastolic filling time during the tachycardia, which may also provoke or worsen an LVOT gradient. As an example, in a series of 52 patients with HCM who developed AF, the acute onset of AF was associated with worsening of functional class in 89 percent of patients [1]. With reversion to sinus rhythm or, to a lesser extent, with control of the ventricular rate, nearly all patients returned to their baseline functional class.

●Long-term sequelae – The long-term studies of patients with HCM of both paroxysmal and persistent/permanent AF have been most strongly linked to an increase in limiting symptoms and an increase in risk of thromboembolic stroke, with less evidence linking AF to increasing heart failure-related death [1,2,10,11]. Unlike ventricular arrhythmias, AF and other atrial tachyarrhythmias are generally not associated with an increased risk of sudden cardiac death, though there are case reports in which AF with a rapid ventricular response has degenerated into ventricular tachycardia and ventricular fibrillation [9,12,13]. (See 'Prognosis' below.)

Conflicting data on the impact of AF on stroke and functional status in patients with HCM have been reported, which can be largely attributed to the application of contemporary therapies to treat AF, including advancement in catheter ablation techniques as well as surgical intervention with Cox-Maze and increasing recognition for low burden of AF to recommend anticoagulation for stroke prophylaxis:

●In a cohort of 480 patients, 22 percent of whom had paroxysmal or chronic AF, stroke risk was markedly increased in the patients with AF compared with those in sinus rhythm (21 percent for patients with AF versus 3 percent without AF; ) [2]. Additionally, the development of AF was associated with an increased risk of severe functional limitation (odds ratio 2.8 for developing NYHA class III/IV symptoms). The risk of stroke and deterioration of functional status was highest in patients with LVOT obstruction.

●In a cohort of 1558 patients, among whom 304 patients (20 percent) developed AF over a mean follow-up of 4.8 years, only 18 patients with AF (6 percent) experienced an embolic event, with only two deaths directly attributable to the embolic event (annual mortality of 0.1 percent due to thromboembolism) and no evidence to support the assertion that AF leads to long-term deterioration in functional status, including risk for progressive heart failure [5]. The risk of stroke was significantly higher among patients with AF not on long-term antithrombotic therapy (14 versus 2 percent).

DIAGNOSIS — The diagnosis of AF is usually suspected in a patient with palpitations, dyspnea, or chest pain with an irregularly irregular pulse present on physical examination. However, not all patients with AF are symptomatic, but AF should be suspected in an asymptomatic patient with an irregularly irregular pulse on physical examination. In these situations, an electrocardiogram (ECG) should be promptly performed to verify the diagnosis.

Since left atrial (LA) size is a strong independent predictor of future AF, European guidelines recommend that all patients with HCM and LA diameter ≥45 mm undergo 48-hour ECG monitoring every 6 to 12 months to detect episodes of "silent" AF [14]. This recommendation is based on expert opinion with no published data on the efficacy of screening for AF with ECG monitoring. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation", section on 'Electrocardiogram'.)

Patients with intermittent symptoms suggestive of paroxysmal AF may not be in AF at the time of the examination and initial ECG. In such patients, ambulatory monitoring for up to four weeks can aid in making the diagnosis. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation", section on 'Additional cardiac testing' and "Ambulatory ECG monitoring".)

TREATMENT

Atrial fibrillation — In general, the therapeutic options for AF in patients with HCM are similar to those for patients without HCM (algorithm 1), with some caveats [15,16]. Since patients with HCM are frequently less tolerant of AF than patients without HCM, we favor a more aggressive approach to the maintenance of sinus rhythm in patients with HCM than in other settings. In addition, patients with HCM and AF are at an increased risk of thromboembolic events, including stroke, and the threshold to introduce anticoagulation should generally be low [15,16]. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation".)

Initial management — The initial management of AF in patients with HCM is similar to that for any patient with AF [16-19].

●In patients who are asymptomatic or have only mild to moderate symptoms, initial therapy includes slowing the ventricular rate and concurrent initiation of anticoagulation therapy (algorithm 1). Beta blockers and nondihydropyridine calcium channel blockers (ie, verapamil and diltiazem) are preferred as first-line agents in most patients, and intravenous preparations are preferred to oral preparations when rapid control of rate is necessary. Digoxin should be avoided as a rate control agent in patients with HCM. (See 'Rate control' below.)

●In patients with severe symptoms or who are hemodynamically unstable related to AF, urgent cardioversion should be performed.

The management of new-onset AF is discussed separately. (See "Atrial fibrillation: Overview and management of new-onset atrial fibrillation".)

Long-term management

Rhythm control — In the majority of patients with HCM, AF is not well tolerated, often producing severe, limiting symptoms. A rate control strategy is a reasonable first option for all patients. However, given how symptomatic many patients with HCM are when they develop AF, and the low efficacy in controlling these symptoms with AV nodal blocking agents, greater weight should be given to pursuing an early rhythm control strategy. Notably, in patients with HCM who have asymptomatic paroxysmal or chronic AF, there are no clinical trials addressing the benefits of a rate versus rhythm control strategy. In this clinical scenario, expert opinion has generally supported rate control for AF in patients with HCM who are asymptomatic. (See 'Rate control' below.)

Rhythm control in patients with HCM and AF can be accomplished with either chemical or electrical cardioversion to restore sinus rhythm and antiarrhythmic drugs to suppress recurrences of AF, with catheter or surgical ablation in special circumstances (algorithm 1). The 2014 American Heart Association/American College of Cardiology/Heart Rhythm Society (AHA/ACC/HRS) AF guidelines and the 2014 European Society of Cardiology (ESC) HCM guidelines, as well as the 2016 ESC AF guidelines and the 2020 AHA/ACC HCM guidelines, concluded that the weight of evidence or opinion was in favor of the usefulness of antiarrhythmic drugs to prevent recurrent AF, although there are no randomized controlled trials evaluating the efficacy of either antiarrhythmic drug therapy or catheter ablation for preventing long-term recurrence of AF in patients with HCM [17,19,20].

There are few data to support the selection of a particular antiarrhythmic agent for maintenance of sinus rhythm in patients with HCM [17,19]. While data are limited, for maintenance of sinus rhythm in most patients with HCM and AF, our experts generally use sotalol as first-line antiarrhythmic therapy. Sotalol should be started on an inpatient basis, regardless of whether the patient has an ICD or not, monitoring over several doses for clinically significant prolongation of the QT interval or proarrhythmia. As an alternative initial therapeutic option, disopyramide may be used but is considered less effective in suppressing AF than sotalol, and due to the possibility that disopyramide may accelerate atrioventricular (AV) conduction, it must be given in combination with an AV nodal blocking agent, such as a beta blocker or a nondihydropyridine calcium channel blocker [17,21]. In addition, the use of disopyramide should be confined to patients with left ventricular outflow tract obstruction (where it has been demonstrated to be safe), as its use in nonobstructive patients can increase filling pressures and may cause heart failure symptoms. One exception to the use of sotalol (or disopyramide) in suppressing AF would be to consider amiodarone initially in those patients with HCM in whom long-term use of the drug is unlikely based on the patient's advanced age or if a short-term duration of antiarrhythmic therapy is planned. If sotalol is not efficacious or not well tolerated, dofetilide could be considered, but limited data exist on its safety in HCM [22], and therefore in most circumstances its use should be confined to those patients with ICDs. (See "Antiarrhythmic drugs to maintain sinus rhythm in patients with atrial fibrillation: Recommendations".)

In selected cases, for patients with nonobstructive HCM who have recurrent AF resulting in worsening symptoms and functional status, catheter-based radiofrequency ablation may be most appropriate, while isolated maze could be considered as an alternative option. Catheter ablation of AF with a technique of pulmonary vein isolation appears to be safe and effective for patients with HCM, with outcomes that may be similar to patients with other forms of structural heart disease who have AF [23-30]. As examples:

●Among a single-center cohort of 79 patients with HCM and AF refractory to antiarrhythmic medications who underwent catheter ablation, 71 percent of patients had no documented recurrent AF over an average of 35 months following the ablation [26]. However, in a different cohort of 49 patients who underwent 72 catheter ablation procedures, freedom from AF at one-year post-ablation was only 44 percent, dropping to 32 percent at three-years post-ablation [5].

●In a systematic review and meta-analysis that included 531 patients from 15 nonrandomized trials, with significant heterogeneity among the various patient cohorts, freedom from AF following a single procedure (at the latest available follow-up which ranged between 11 and 54 months) averaged 46 percent, which increased to 66 percent following repeat ablation procedures [28]. Similar results were reported in a separate systematic review and meta-analysis that included 139 patients from six studies, in which the freedom from AF was 39 percent after a single procedure [29].

Catheter ablation of AF is discussed in detail separately. (See "Atrial fibrillation: Catheter ablation".)

Similarly, in patients with obstructive HCM who are undergoing surgical myectomy and who have symptomatic AF, an adjunctive surgical Cox-Maze procedure for AF ablation should be considered as a possible therapeutic option that has been shown to be safe and effective only in case reports and small series of patients [5,14,31-33]. Among a single-center cohort of 62 patients who underwent surgical Cox-Maze IV procedure at the time of septal myectomy between 2004 and 2015, freedom from AF at one-, three-, and five-year post-procedure was 85, 69, and 64 percent, respectively [33]. (See "Atrial fibrillation: Surgical ablation".)

Rate control — Because of the lack of controlled data demonstrating a benefit from maintaining sinus rhythm in patients with HCM and AF, and also because of the potential side effects associated with antiarrhythmic drugs, some patients and clinicians will select a rate control strategy, particularly in asymptomatic or minimally symptomatic patients (algorithm 1). For patients in whom a rate control strategy is selected, we recommend the use of beta blockers, calcium channel blockers, or the two drugs in combination, rather than digoxin.

For the majority of patients with HCM, onset of AF results in an acute development of limiting symptoms (or worsening of existing symptoms), which often substantially impacts the patient's quality of life. For this reason, the goal is often maintenance of sinus rhythm, as restoration of atrial contribution to stroke volume is so important. However, in the minority of patients with HCM and AF who are asymptomatic, a rate control strategy can be considered initially or in those patients who have failed efforts at rhythm control and who are not candidates for an ablation procedure.

Ventricular rate control can be achieved with pharmacologic or nonpharmacologic means. Beta blockers, nondihydropyridine calcium channel blockers (ie, verapamil and diltiazem), or the two drugs in combination are usually adequate to control the ventricular rate [14,17,18,20]. Although there are no data on the use and safety of digoxin as a rate control agent in HCM, based on expert opinion and standard practice, digoxin should not be used in patients with AF and HCM, since it can increase inotropy, which could exacerbate heart failure symptoms in the majority of patients with HCM who have preserved systolic function. (See "Control of ventricular rate in patients with atrial fibrillation who do not have heart failure: Pharmacologic therapy".)

When the ventricular rate cannot be controlled with medications and the patient is not considered a candidate for catheter or surgical ablation of AF, AV nodal ablation with pacemaker implantation will provide definitive control of the ventricular rate [14].

Anticoagulation — Limited evidence is available to guide anticoagulant therapy in patients with HCM and AF. Patients with HCM and AF are at significant risk of thromboembolism, although risk factors for thromboembolism have not been well defined [2,14,17,20]. Since patients with HCM were not included in most clinical trials of thromboprophylaxis in AF, the CHA₂DS₂-VASc score cannot be applied to patients with this condition to determine the risk of thromboembolism.

For symptomatic AF — For patients with HCM and symptomatic AF, we recommend chronic oral anticoagulation (algorithm 1). This recommendation applies for symptomatic AF, regardless of the duration of episodes of AF. Either a direct oral anticoagulant (DOAC; eg, dabigatran, rivaroxaban, apixaban, edoxaban) or warfarin (with a target international normalized ratio [INR] of 2 to 3) can be chosen as the initial thrombotic regimen in patients with HCM and AF [15,19].

Support for this approach to comes from a study of 304 HCM patients with AF followed for a mean of 4.8 years [5]. Embolic events occurred in only 2 percent of patients taking anticoagulation therapy compared with 14 percent among HCM patients with AF not taking anticoagulation. Only two deaths were directly attributable to an embolic event (annual mortality of 0.1 percent due to thromboembolism).

Whether a threshold amount of AF exists to recommend anticoagulation is uncertain, and, since patients with HCM are not included in most clinical trials of thromboprophylaxis in AF, the CHA₂DS₂-VASc score cannot be applied to patients with this disease to determine the benefit of anticoagulation.

Several studies have documented the increased risk of thromboembolic events in patients with HCM and AF [2,17,19,34,35]. In a series of 480 patients with HCM, of whom 22 percent had paroxysmal or chronic AF, stroke risk was markedly increased in the patients with AF compared with those in sinus rhythm (odds ratio 17.7) [2]. The elevated risk of thromboembolic events includes patients treated with rhythm control who appear to be in normal sinus rhythm, given the risk of recurrent AF with minimal or no symptoms. (See "Atrial fibrillation in adults: Use of oral anticoagulants".)

Specific antithrombotic regimens in patients with HCM have not been studied in randomized trials. Both warfarin therapy (with a target INR of 2 to 3) and the DOACs (eg, dabigatran, rivaroxaban, apixaban, edoxaban) have been shown to be efficacious in other populations without HCM. Data from observational studies suggest that both warfarin and DOACs are safe and effective in reducing thromboembolic risk.

●Among 2397 patients with HCM and AF treated with anticoagulation who were enrolled in a nationwide Korean database between 2013 and 2016 and followed for 1.6 years, rates of embolic ischemic stroke and bleeding complications were significantly lower among patients treated with a DOAC compared with warfarin [36].

●Among 2198 patients with HCM and AF treated with anticoagulation who were identified from a United States commercial insurance database between 2010 and 2015, rates of embolic ischemic stroke and bleeding were similar between warfarin and DOACs over short-term follow-up [37].

Either approach can be considered as the initial antithrombotic regimen in patients with HCM and AF [14,17,20]. (See "Direct oral anticoagulants (DOACs) and parenteral direct-acting anticoagulants: Dosing and adverse effects".)

For asymptomatic AF — In patients with HCM, asymptomatic or subclinical AF can be detected by external monitoring or device downloads. There are limited data on the prevalence of subclinical AF in HCM.

●Among 30 patients with HCM, 14 were noted to have evidence of subclinical AF over a follow-up of 595 days [38].

●Among 114 patients with HCM followed for 2.8 years, subclinical AF detected by device download occurred at a rate of 4 percent per year [39].

●In a retrospective study of patients with HCM with a dual-chamber ICD but no known history of AF, patients developed asymptomatic AF episodes (ie, clinically silent), most of which lasted less than one hour; however, 13 of the 18 patients with clinically silent AF had more than one episode [3].

There is debate regarding the burden of subclinical AF necessary to recommend DOACs for stroke prophylaxis. Extrapolating from non-HCM studies, episodes of subclinical AF >24 hours were associated with increased stroke risk compared with shorter episodes [40]. For this reason, the 2020 AHA/ACC HCM guidelines recommend DOAC therapy for patients with HCM detected with subclinical AF >24 hours duration [19]. For shorter episodes of >5 minutes to 24 hours, it would also be reasonable to consider DOAC therapy while also taking into consideration important clinical variables, such as length and burden of AF episodes, and the strengths and limitations of long-term anticoagulation therapy, including bleeding risk, for an individual patient.

Atrial flutter and other supraventricular tachycardias — The approach to the management of atrial flutter in patients with HCM is similar to the approach in patients without HCM. Given the high success rates for radiofrequency ablation in eliminating atrial flutter, this should be considered early in patients with HCM. (See "Atrial flutter: Maintenance of sinus rhythm", section on 'RF catheter ablation'.)

Nonsustained supraventricular tachycardias (SVTs) are commonly found during ambulatory electrocardiographic monitoring in patients with HCM. The majority of these events are asymptomatic and self-limited. Up to 25 percent of patients with HCM will have such arrhythmias, but they rarely require therapy [41]. (See "Narrow QRS complex tachycardias: Clinical manifestations, diagnosis, and evaluation" and "Overview of the acute management of tachyarrhythmias".)

PROGNOSIS — In addition to the symptoms associated with AF and the risk of worsening heart failure and stroke, mortality is higher in adults with HCM who develop AF [2,42,43].

●In a single-center cohort of 3673 patients with HCM evaluated between 1975 and 2012, 650 patients (18 percent) had AF; patients with AF were older and more often symptomatic, and AF was associated with increased total mortality (adjusted hazard ratio 1.5, 95% CI 1.3-1.7) [43].

●In a cohort of 202 Italian adults with HCM who were followed for up to 30 years (mean 10 years), the 57 patients (28 percent) with AF had a significantly higher mortality at 15 years (24 versus 3 percent in patients with HCM and no AF) [42].

●In a cohort of 480 adults with HCM from the United States and Italy who were followed for an average of 9.1 years, intermittent or permanent AF significantly increased the rate of HCM-related death, primarily due to heart failure deaths and not sudden cardiac death [2]. The risk of death was associated with the presence of left ventricular outflow tract obstruction and AF onset before age 50 years.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Atrial fibrillation" and "Society guideline links: Cardiomyopathy".)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5^th to 6^th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10^th to 12^th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

●Basics topic (see "Patient education: Hypertrophic cardiomyopathy in adults (The Basics)")

●Beyond the Basics topic (see "Patient education: Hypertrophic cardiomyopathy (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

●Epidemiology – In patients with hypertrophic cardiomyopathy (HCM), the prevalence of atrial fibrillation (AF) appears to be four- to sixfold higher than in similarly aged patients in the general population, with an incidence in the range of 2 percent per year. (See 'Epidemiology' above.)

●Risk factors – Several factors predispose to the development of AF in patients with HCM, including increased left atrial diameter and volume, left atrial dysfunction, increasing age, and left ventricular ejection fraction (LVEF), particularly when LVEF <50 percent (end-stage HCM). In contrast to these risk factors, the presence or severity of an LV outflow tract (LVOT) gradient does not appear to be associated with an increased incidence of AF. (See 'Predisposing factors' above.)

●Clinical manifestations – While most patients with HCM who develop AF have fairly prominent symptoms, not all patients will be symptomatic. The acute symptoms associated with AF in patients with HCM, which may include palpitations, dyspnea, and chest pain, are similar to the symptoms of AF in patients without HCM. However, patients with HCM, especially those with an LVOT gradient, are also at risk for hypotension, lightheadedness, presyncope, and syncope. (See 'Clinical manifestations' above.)

The long-term consequences of both paroxysmal and persistent/permanent AF in patients with HCM include an increase in limiting symptoms and risk of thromboembolic stroke, as well as decreased overall functional status. Unlike ventricular arrhythmias, however, AF is not clearly associated with an increased risk of sudden cardiac death. (See 'Clinical manifestations' above.)

●Diagnosis – The diagnosis of AF is usually suspected in a patient with palpitations, dyspnea, or chest pain with an irregularly irregular pulse present on physical examination and confirmed by obtaining an ECG. (See 'Diagnosis' above.)

●Initial management – In patients who are asymptomatic or have only mild to moderate symptoms, the initial management of AF is similar to other patients with AF and includes slowing the ventricular rate and concurrent initiation of anticoagulation therapy (algorithm 1). (See 'Initial management' above and "Atrial fibrillation: Cardioversion" and "Cardioversion for specific arrhythmias".)

In patients with severe symptoms or who are hemodynamically unstable related to AF, urgent cardioversion should be performed.

●Long-term management

•Rhythm versus rate control – In symptomatic patients with HCM and paroxysmal or persistent AF, we suggest a rhythm control strategy (Grade 2C). This can be accomplished with either chemical or electrical cardioversion to restore sinus rhythm and antiarrhythmic drugs to suppress recurrences of AF. Although various professional society guidelines have concluded that the available data were insufficient to recommend one antiarrhythmic drug over another, our experts generally use sotalol (rather than amiodarone or disopyramide). In selected cases, catheter-based radiofrequency ablation or a surgical maze procedure may be appropriate. (See 'Rhythm control' above.)

A rate control strategy is also reasonable. For patients in whom a rate control strategy is selected, we recommend the use of beta blockers, calcium channel blockers, or the two drugs in combination, rather than digoxin (Grade 1B). (See 'Rate control' above.)

If rate control is not achieved with medications and catheter or surgical ablation is not an option, patients may undergo atrioventricular (AV) nodal ablation with placement of a permanent pacemaker for definitive rate control. (See 'Rate control' above.)

•Anticoagulation – The CHA₂DS₂-VASc score has not been studied in patients with HCM and therefore cannot be applied to patients with AF and HCM to determine need for anticoagulation.

For patients with HCM and clinical AF and subclinical AF >24 hours duration, we recommend chronic oral anticoagulation (Grade 1A). Either warfarin (with a target international normalized ratio [INR] of 2 to 3) or one of the direct oral anticoagulants (DOACs; eg, dabigatran, rivaroxaban, apixaban) can be chosen as the initial thrombotic regimen in patients with HCM and AF. For patients with shorter episodes of subclinical AF, anticoagulation therapy may be reasonable. (See 'Treatment' above and "Atrial fibrillation in adults: Use of oral anticoagulants".)