Supraventricular Arrhythmias

Supraventricular arrhythmias are common in HCM. They are related to left atrial enlargement and fibrosis developing in the context of chronically elevated filling pressures as a consequence of obstruction, diastolic dysfunction, and/or mitral valve dysfunction."8 Paroxysms of supraventricular tachycardia (SVT) and AF can be detected on Holter monitoring in up to 30% of adults, although the incidence in the young is closer to 5-10%. Sustained or symptomatic episodes are much less common and warrant treatment with amiodarone, which is usually effective in reducing recurrences and attenuating the development of permanent AF.11 The threshold for starting anticoagulation should be low to minimise embolic complications."17

Established AF is uncommon in the young, while in adults the prevalence can be up to 30%.11 It is more common in elderly HCM patients and has been associated with a poorer overall prognosis, an enlarged atrial size, and increased risk of thromboembolism including stroke.611 w17 w18 Its onset is associated with an acute deterioration in symptoms that usually reverses with control of the ventricular response.11 The long term outlook, with appropriate treatment to control heart rate and prevent emboli, is usually good.12 w17 w19 Repeated cardioversions to restore sinus rhythm are not warranted. In most HCM patients the contribution of atrial systoles to stroke volume is negligible by the time AF develops—that is, patients have a palpable atrial beat but no fourth heart sound.

A slurred upstroke to a broad QRS complex is a common surface ECG finding in HCM patients. In less than 5% of these

Table 10.2 The recognised markers of risk in HCM and their sensitivity, specificity, positive and negative predictive accuracy (PPA and NPA)

Risk factor

Sensitivity (%)

Specificity (%)

PPA (%)

NPA (%)

Abnormal blood pressure response: <40 years old19

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