The heart is a muscle that needs an electrical current to make it contract. That electrical current is generated and conducted around the heart from an area at the top of the heart called the Sino-atrial node. The Sino-atrial node therefore is the heart’s pacemaker. The pacemaker’s job is to generate a heart rate commensurate with the physiological needs of the body at any given time. When this god-given pacemaker starts malfunctioning, and is therefore unable to generate an adequate heart rate for the body’s demands, the individual may start noticing symptoms in keeping with a reduced amount of blood getting round the body and the combination of symptoms with evidence of the pacemaker not functioning adequately at the time is termed as sick sinus syndrome.
Who gets it?
Anyone can get it but it is definitely far more prevalent as people get older eg in their 7th-8th decades of life. In addition, patients with persisting heart disease, high blood pressure and people with a high body mass index are more susceptible.
Why does it happen?
In sick sinus syndrome, you can have problems either with production of the electrical impulse (which is termed sinus arrest) or problems with conduction of that impulse to the rest of the heart (which is termed sinoatrial conduction block or delay). Very often you have problems with both. The basic mechanisms why the sinus node starts failing boil down to 3 main processes:
There are several causes:
- Sinus node fibrosis: This happens usually just due to wear and tear and aging.
- Medications and toxins may cause sinus node dysfunction but in my experience often unmask rather than cause sinus node disease. Medications which do so include beta blockers, calcium blockers, Digoxin. Antiarrhythmic medications and also medications known as acetylcholinesterase inhibitors (which are particularly relevant as some may be used for the treatment of Alzheimer’s disease). There are other medications too which can do this including Lithium, Ivabradine, even cimetidine.
- Infiltration conditions where there is deposition of abnormal proteins/calcium within the heart – such as Amyloidosis, Sarcoidosis, Scleroderma, and haemochromatosis.
- Inflammatory conditions such as infections can cause sinus node dysfunction such as Rheumatic fever, Diptheria, pericarditis and chaga’s disease.
- The pacemaker has a blood supply. This is usually from the right coronary artery in the majority of patients but sometimes comes from the left circumflex. If there is a narrowing or blockage of these vessels, then you can get development of sinus node dysfunction.
- Trauma such as during a cardiac operation can also lead to this
- Finally conditions such as hypothermia, hypothyroidism, muscular dystrophies and low oxygen levels can all contribute.
The natural history:
Pacemaker malfunction in its early stages is rarely constantly present. Often it comes and goes. When it is present and the heart is not beating effectively for long enough, the patient may develop symptoms such as blackouts, falls, transient dizziness and lightheadedness. I think whenever an older person complains of a sudden vacant spell or an unheralded fall or blackouts, this would be the foremost diagnosis in my mind that i would want to consider and exclude. As time progresses the episodes of pacemaker malfunction get more frequent and the patient may develop more symptoms. Sometimes progression can take several years whereas sometimes it can take just months.
Sometimes, we pick up a sick pacemaker incidentally on the ECG or a heart monitor. The findings that help us confirm this is if we sinus arrest, long pauses of more than 3 seconds and an exceptionally slow heart rate during waking hours.
Is it dangerous?
The answer is yes. It may be dangerous for the patient in several ways:
- It can substantially increase the risk of falls and injury. As it can happen without warning, there is a high likelihood of injury which in itself in an elderly patient may be catastrophic. In addition it can be catastrophic if it happens when the patient is driving or swimming etc.
- It is difficult to know if it is associated with sudden death because often patients tend to be elderly and have associated comorbidities and it is simply not possible to make the diagnosis on post-mortem because even if the pacemaker looks fibrotic one can not assume that it malfunctioned – however in the elderly injury itself can be very dangerous.
- A significant number of patients with sick sinus syndrome will also develop atrial fibrillation or atrial flutter which in this age group substantially increases the risk of strokes.
How do you make the diagnosis:
- Sometimes just a simple ECG can give us the answer but more often than not, patients require prolonged heart monitoring. In my experience the best way to do this is to implant a little monitoring device under the skin of the chest – this device is known as a REVEAL device and it can stay on the patient for 2 years and is usually very effective in helping confirm the diagnosis where you ideally want to see evidence of pacemaker malfunction at the same time as when the patient is experiencing symptoms. If you have a relative who gets sudden lightheadedness or falls, it is well worth insisting on having a REVEAL device. The advantage of having a REVEAL device is that it may also pick up silent episodes of AF which may then allow the patient to be anticoagulated.
What is the treatment:
Once a diagnosis is confirmed, a pacemaker is recommended and this will then act to generate an impulse if the natural pacemaker fails to do so and will stop the heart slowing down excessively. Remember a pacemaker will only stop the heart going too slow. If fast heart rates are observed because of episodes of AF, then the patient may require medications to slow the heart down (although the heart will never slow down too much as the pacemaker will prevent this). The patient may also require anticoagulation if atrial fibrillation is obsereved.
With pacemakers, most patients go back to their normal quality of lives without any inconvenience.
I hope you found this useful. I would love to hear your thoughts.
Keywords: Pacemaker; Sick sinus syndrome; pacemaker malfunction; syncope