Double apical impulse is seen in-

pulsus bisferiens, , is a sign where, on palpation of the pulse, a double peak per cardiac cycle can be appreciated. Bisferious means striking twice. Classically, it is detected when aoic insufficiency exists in association with aoic stenosis, but may also be found in isolated but severe aoic insufficiency and hyperophic obstructive cardiomyopathy. Normally, aerial pulses are best felt in radial aeries but character is better assessed in carotid aery. Pulsus bisferiens is best felt in brachial and femoral aeries. Ref Harrison 20th edition pg 1486