Bradycardia-tachycardia syndrome, or sick sinus syndrome (SSS), is actually a collection of diseases where the heart is no longer able to effectively perform its regular pacemaking duties. A small area of the heart located in its right upper chamber is composed of special fibers in what is called the sinus node. It is responsible for all the normal and regular heartbeats we have when no one is thinking about it, as well as speeding the heart up when necessary (as in exercise or increased blood flow needs) and slowing it down (in periods of rest or sleep). When the sinus node malfunctions, or wears out, or is prevented from performing its “command” function in keeping an appropriate and regular rhythm, the heart rate no longer is regular (arrhythmia) or appropriate to the stimulating action in the body. It may provide an inadequate heart rate response to stress or exercise which, needless to say, can lead to serious consequences if not attended to.
While primarily a disease of those in their seventies and older, SSS can occur in much younger ages. It’s estimated that more than one in every 600 cardiac patients over the age of 65 has this syndrome. The majority of cases involves a “remodeling” of the tissues of the sinus node, such that they may become hardened or fibrosed and, as a result, less and less effective at putting out a signal strong enough for the heart to march to. Often coexisting cardiac conditions such as heart failure, heart blockages near the area, or infiltrative diseases such as sarcoidosis or hemochromatosis may be involved. Intrinsic cases such as electrolyte and metabolic disturbances or the actions of certain cardiac medications that slow conduction in the heart can mimic SSS, but withdrawal of the medication or correction of the imbalance generally restores the sinus node function to normal.
Most sick sinus syndrome is progressive. In the beginning it may be picked up as an uncomfortable feeling by the affected individual, whether the heart is going too fast or too slow. Either case (when the heart is going too slowly and providing too little blood to the brain or too quickly and not having a chance to fill adequately before pumping) causes signs of what is called cerebral hypoperfusion. This lack of adequate blood flow to cerebral tissues can cause transient lightheadedness, confusion, palpitations, chest pain, heart failure or even stroke. An EKG generally shows either the very slow or very fast heart rate or the lack of progression from any activity of the sinus node to initiate a forceful and normal heart beat.
Generally it makes sense that a failing natural pacemaker in the heart would cause a slow rhythm and an escape heartbeat as some other part of the heart struggles to take over a function not natural for it. Without the pacemaker area taking its normal dominant role, fast rhythms may occur in up to 50 percent of those affected including very chaotic ones like atrial fibrillation—when it’s almost fireworks between different areas of the heart. If not immediately obvious on a single EKG tracing, a Holter monitor or prolonged cardiac monitoring makes the diagnosis, particularly in the evolutionary stage of SSS. Treatment of known SSS then generally involves the implanting of a permanent pacemaker, which relieves symptoms and improves quality of life, but again doesn’t reverse the primary process (whether it be aging or disease) of the rest of the heart. It does however help against potentially lethal outcomes of chaotic atrial rhythm such as embolism, thrombotic stroke and accidents from losing consciousness when heart rate slows and the brain does not receive sufficient oxygen at any given time.
Most people who end up with pacemakers or have SSS have an increased mortality over time and are rated higher if it occurs at younger ages, and certainly higher if there is other underlying heart disease to account for. Some cases may be offered at standard if there is a specific cause and all other investigations show cardiac function to be otherwise normal. Those in whom extrinsic factors cause SSS (like correctable medical conditions or medications that slowed heart conduction that were stopped) are looked upon more favorably as well.
