Episodic syncope in hypertrophic cardiomyopathy: evidence for inappropriate vasodilation.
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.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 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.
Prasad
K
K
Department of Cardiovascular Medicine, University of Birmingham, Edgbaston, Birmingham, UK.
Williams
L
L
Campbell
R
R
Elliott
P M
PM
McKenna
W J
WJ
Frenneaux
M
M
D000293:Adolescent; D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002312:Cardiomyopathy, Hypertrophic / Q000150:complications* / Q000503:physiopathology; D004108:Dilatation, Pathologic / Q000503:physiopathology; D015444:Exercise / Q000502:physiology; D006801:Humans; D007022:Hypotension / Q000209:etiology; D011311:Pressoreceptors / Q000502:physiology; D013575:Syncope / Q000209:etiology* / Q000503:physiopathology; D018667:Tilt-Table Test