Pacemaker therapy in hypertrophic obstructive cardiomyopathy: still awaiting the evidence.

Correspondence: W.J. McKenna, MD, The Heart Hospital, University College London Hospitals, 16-18 Westmoreland Street, London W1G 8PH, United Kingdom E-mail: [email protected] The initial descriptions of hypertrophic cardiomyopathy (HCM) focused on the presence of left ventricular (LV) outflow tract obstruction as a defining feature of the condition.1-6 The use of echocardiography, which emerged as the gold standard technique for non-invasive assessment of the heart from the 1970s onwards, subsequently suggested that only a minority of patients have evidence of LV outflow tract obstruction at rest.7,8 However, more recent studies have shown that up to 70%-75% of patients with HCM have obstruction either at rest (25%-30%) or upon provocation.9,10 This observation has important clinical implications. First, it is well recognized that LV outflow tract obstruction can cause symptoms, including exertional dyspnoea, angina, and syncope or presyncope, resulting from acute reductions in cardiac output, with elevated left ventricular filling pressures and myocardial ischaemia. Symptoms in obstructive HCM are most commonly exertional therefore, the non-invasive evaluation of LV outflow tract obstruction should include provocation manoeuvres such as upright exercise or Valsalva. Furthermore, patients with LV outflow tract obstruction have worse overall, HCMrelated and sudden death-free survival than those without obstruction.11-13 The abolition/reduction of LVOTO, and the relief of symptoms associated with it, is therefore a key feature of the management of patients with HCM. Mechanism of left Ventricular Outflow Tract Obstruction