7th March 2024

Investigations

The ECG findings of HCM are normally relatively striking and most patients will have an abnormal ECG, though the findings on ECG do not correlate well with clinical outcome.

ECG can show:

• Voltage criteria for left ventricular hypertrophy (S wave in V1 + tallest R wave in V5-V6 >35mm)
• Left atrial enlargement (p mitrale (bifid p waves))
• Short PR intervals (accessory pathways are more common in patients with HCM)
• Atrial fibrillation and supraventricular tachycardias are common
• Giant T wave inversions seen in the precordial leads
• Narrow, “dagger-like” q waves in the inferior and lateral leads

Echocardiography is the most common confirmatory diagnostic test. This will typically show asymmetric septal hypertrophy with a ratio of septal wall to posterior wall thickness >1.4:1. The LV is typically non-dilated and systolic function is preserved as measured by left ventricular ejection fraction, though deformation parameters are often reduced. Systolic anterior motion of the anterior mitral leaflet can also be seen. A velocity gradient across the left ventricular outflow tract can be seen, and in the absence of this being found despite typical myocardial hypertrophy, echocardiography while performing Valsalva manoeuvre or an exercise test should be considered to assess for dynamic left ventricular outflow tract obstruction.

Cardiac MRI can provide similar information to echocardiography but with better tissue characterisation and may be better at identifying areas which are difficult to image on echo due to impaired echocardiographic windows.