Form a recent review:
Most clinicians would recommend ICD therapy if any one of the five major risk factors is present, although recent debate has focused on whether at least two risk factors are required…
Previous cardiac arrest/ventricular tachycardia (secondary prevention)Family history of premature sudden cardiac deathLeft ventricular wall thickness greater than or equal to 30 mmPrevious episodes of documented NSVT (greater than or equal to 3 beats, rate greater than or equal to 120 bpm)Unexplained syncope
Concerning treatment in general:
Many treatment options are currently available for HCM patients. This ranges from no treatment; lifestyle modifications, e.g. avoiding competitive sports in all patients with HCM; use of pharmacological agents e.g. beta blockers, calcium channel blockers, and diuretics; to surgical septal myectomy and transcoronary alcohol septal ablation of the myocardium (i.e. the creation of a limited septal infarct by direct injection of alcohol into a septal perforator artery) for individuals with significant left ventricular outflow tract obstruction with symptoms unresponsive to drug therapy. The single most important advance in the clinical management of HCM has involved the use of ICD therapy in the prevention of sudden death  . Recent studies indicate that treatment of individuals at highest risk of sudden death with an ICD is the most definitive form of therapy in preventing sudden death and easily surpasses empirically-based preventative strategies previously used in HCM, e.g. amiodarone and beta blockers.