What are the possible complications of sick sinus syndrome?

Syncope and death. The sinus node is a bundle of heart cells concentrated in the right atrium that normally sets off each heart beat for life. Arteriosclerosis may slowly, or rapidly in a heart attack, destroy these cells and lead to very abnormal, usually very slow, heart rates. If the rate slowed down to perhaps 30's, one may pass out, if worse, one may not wake up. Once the diagnosis is clear, need pacemaker.
a few things. Sick sinus syndrome results in the top chamber being unable to effectively regulate its rate. It can also occur in the setting of atrial fibrillation. With this combination, both extremely fast and extremely slow heart rates are possible. Symptoms can include dizziness lightheadedness or palpitations, chest pains, exercise intolerance, or even feelings as though you might pass out.