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Episodic syncope in hypertrophic cardiomyopathy: evidence for inappropriate vasodilation
  1. K Prasad1,
  2. L Williams1,
  3. R Campbell1,
  4. P M Elliott2,
  5. W J McKenna2,
  6. M Frenneaux1
  1. 1
    Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham, UK
  2. 2
    The Heart Hospital, London, UK
  1. Dr Lynne Williams, Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; l.k.williams{at}bham.ac.uk

Abstract

Symptoms of impaired consciousness (syncope and pre-syncope) occur in 15–25% of patients with hypertrophic cardiomyopathy (HCM).1 In young patients a history of recurrent syncope is associated with an increased risk of sudden death.25 Syncope usually occurs without warning or symptoms suggestive of the cause. Detailed investigations identify a probable mechanism in a minority, usually paroxysmal atrial fibrillation or ventricular tachycardia. In the majority however no likely mechanism is found despite repeated 24-hour ambulatory echocardiography (ECG) or patient-activated monitoring, exercise testing and invasive electrophysiological studies.1 6 Empirical treatment with amiodarone, a pacemaker or an implantable cardioverter-defibrillator is commonly employed, but is often unsuccessful in relieving the symptoms.

We have previously observed that approximately 30% of patients with HCM have abnormal blood pressure response during maximal upright exercise.7 8 This was due in the majority of patients to an exaggerated fall in systemic vascular resistance, possibly arising from abnormal activation of stretch-sensitive left ventricular mechanoreceptors,9 10 by a mechanism similar to that described in aortic stenosis.11 However, in some patients an inadequate cardiac output response to exercise may be responsible.12 We hypothesised that abnormal vasodepressor-mediated hypotension may also occur during daily life in patients with HCM, and that this may be an important mechanism of syncope when conventional investigations fail to reveal a cause.

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Footnotes

  • Funding: The study was supported by the British Heart Foundation, London, UK.

  • Competing interests: None.

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