Heart Health: Understanding The Function Of Pacemakers

By Dr. Ajay Sharma, Cardiologist, Lahey Hospital and Medical Center; Southern New Hampshire Medical Center

Pacemakers are a brilliant combination of engineering and medicine. It is important to understand the concept when the need arises. The heart has a specified site called sinus node in the right upper chamber (right atrium) which gives rise to an electrical impulse (at a rate of 60-100 beats per minute at baseline) which is transmitted through the conduction system to the lower chambers (ventricles).

The lower chambers respond by contracting and this pumps blood to the rest of the body. Nature has given this electrical spontaneity not only to sinus node but to other sites too. This assumes importance in case of failure of sinus node to generate impulse or ‘electrical block’ which is non-conduction of electrical impulse from upper chambers to lower chambers.

However, the other sites pace at a lower rate which is not enough to provide blood supply for normal bodily functions. This may bring out symptoms of dizziness, passing out, shortness of breath and in extreme cases, death. This is something which can be easily detected with the help of an ECG. To overcome this, pacemaker initiates an impulse in the lower chambers bypassing the need for the command from sinus node. Understandably, this improves quality of life.

Additionally, the lower chambers beat synchronously and this is achieved by electrical bundles. The left bundle assumes much higher importance as the left ventricle has to generate significant pressure to pump blood against gravity to the brain and to the tip of toe. If the left bundle gets affected, may be after heart attack or by degeneration or other rare processes, it may lead to heart failure. In this case, we use a distinct device called bi-ventricular pacemaker to deliver resynchronization therapy. This can improve the pumping function and lead to improvement/ resolution of symptoms and even decrease in hospitalization and mortality.

Another device that we use is called an ICD (Implantable Cardiac Defibrillator) which may be used separately or in conjunction with a pacemaker. This shocks the heart if it develops an arrhythmia of the lower chambers (ventricles) which is not compatible with life. This is life saving and has proven results in setting of severe heart failure or arrhythmogenic focus.

The batteries for pacemakers/ defibrillators can last up to 10 years and need a change after that. The information stored in the generators can be easily extracted by devices kept over the chest wall or remote transmission.  They can detect arrhythmias of the upper chambers (atrial fibrillation/ flutter) which may need blood thinners to decrease the risk of stroke.

Nowadays, leadless pacemakers are being used in appropriate cases which do not need leads/ wires. Pacemakers are usually day procedures and patients may be discharged home the same day or the next day. There are precautions to be taken in use of the arm for a few days after which normal functions can be resumed. There are pacemaker banks which provide pacemakers from deceased patients to be used in patients from countries with inability to pay for the cost of the device.

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