Episodic Syncope in Hypertrophic Cardiomyopathy – Evidence for inappropriate vasodilation
Krishna Prasad 1, LYNNE WILLIAMS 2*, Ross Campbell 2, Perry M Elliott 1, William J McKenna 1 and Michael Frenneaux 2
1 The Heart Hospital, London, United Kingdom
2 University of Birmingham, United Kingdom
* To whom correspondence should be addressed. E-mail: l.k.williams{at}bham.ac.uk.
Accepted 15 July 2008
 | Abstract |
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Symptoms of impaired consciousness (syncope and pre-syncope) occur in 15 – 25% of patients with hypertrophic cardiomyopathy[1]. In young patients a history of recurrent syncope is associated with an increased risk of sudden death[2-5]. 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 ECG or patient-activated monitoring, exercise testing and invasive electrophysiological studies[1;6]. Empiric 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[8;9]. 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[8;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.
