Routine orthostatic LVOT gradient assessment in patients with basal septal hypertrophy and LVOT flow acceleration at rest: please stand up

Abstract

A 70-year-old female with exertional dyspnoea was found to have basal septal hypertrophy (BSH), or a 'basal septal bulge', with evidence of mild left ventricular outflow tract obstruction (LVOT) at rest on her initial echocardiogram. She was usually fit and well with no significant past medical history. She had no history of hypertension. She had never smoked. There was no family history of hypertrophic cardiomyopathy (HCM). A cardiac MRI did not demonstrate any typical features of HCM. ECG showed sinus tachycardia with a rate of 101 bpm but was otherwise unremarkable. She was referred for exercise echocardiography to assess for latent LVOT obstruction. Prior to commencing exercise, her LVOT gradient was re-assessed at rest. Her LVOT gradients were 30 mmHg at rest, 49 mmHg during Valsalva and 91 mmHg on standing. A diagnosis of significant latent LVOT obstruction was made and the patient was started on bisoprolol, a cardioselective beta-blocker. Bisoprolol was slowly uptitrated from 1.25 mg to 5 mg once daily, following which the patient reported a significant improvement in her symptoms with an improved exercise capacity. Follow-up echocardiography demonstrated a dramatic reduction in LVOT gradient, with a maximum of 11 mmHg assessed both with Valsalva and on standing. This case is a reminder that patients with a 'common' basal septal bulge can develop significant LVOT obstruction, the symptoms of which may respond to pharmacological therapy. Orthostatic assessment of LVOT gradient using echocardiography should be considered during standard LVOT obstruction provocation manoeuvres such as a Valsalva. Learning points: Differentiation between basal septal hypertrophy (BSH) and hypertrophic cardiomyopathy (HCM) may be challenging. Key factors favouring HCM include a positive family history of HCM or sudden cardiac death, septal thickness >15 mm/posterior wall thickness >11 mm, systolic anterior motion of the anterior mitral valve (SAM), late gadolinium enhancement on cardiac MRI, a causative genetic mutation associated with HCM and an abnormal ECG. Significant LVOT obstruction may develop in patients with BSH and is potentially responsive to pharmacotherapy. Standing reduces venous return, resulting in decreased LV volume. Compensatory mechanisms to maintain cardiac output involve sympathetic nervous system activation leading to increased LV contractility and subsequent increased LVOT gradient. Significant LVOT obstruction may be unmasked by an orthostatic posture. Orthostatic LVOT gradient assessment should be part of the routine echocardiographic assessment of all patients with an increased LVOT gradient at rest. The post-prandial state has been associated with increased LVOT gradient due to splanchnic dilatation and the consequent increased cardiac output required to maintain blood pressure. Post-prandial status should therefore be considered when assessing LVOT gradient.

Keywords: basal septal hypertrophy; latent LVOT obstruction; orthostatic LVOT assessment; provocable gradient.

Figure 1

12 lead electrocardiogram at initial presentation.

Figure 2

Continuous wave Doppler through the left ventricular outflow tract (A) at rest (B) on standing (C) with Valsalva and the (D) parasternal long axis view with measurements.

Figure 3

Continuous wave Doppler through the left ventricular outflow tract following the introduction of bisoprolol 2.5 mg (A) at rest (B) on standing.