Pacemaker: Get it Going Fast!

How Your Heart Beats

Your heart is a muscular pump consisting of four chambers, two on the left side and two on the right. The chambers are contracted according to signals from your heart’s electrical system to keep it beating at appropriate rates —typically 60 to 100 beats per minute in a resting adult.

A specialized set of cells in your heart, your electrical conduction system, governs your heartbeat, starting from a focus in the right atrium (SA node) and spreading all over the heart, making it contract and pump blood. Several conditions like aging, muscle damage by a previous heart attack, some drugs, and certain genetic conditions can cause your heart rhythm to get abnormal.

What is a Pacemaker?

A pacemaker is precisely what its namesake indicates – it essentially determines the pace or the rate which will constitute the heart rate. As mentioned earlier, the body has a couple of pacemakers of its own, but when these malfunction, your cardiologist may opt to go for an artificial pacemaker, which will extrinsically give electrical signals through electrodes to stimulate cardiac muscle and thereby set your heart rate and keep it regular.

Types of Pacemakers

There are two types of artificial pacemakers that the cardiac electrophysiologist may recommend.

1. 1. Fixed-rate pacemakers – they discharge at a pre-determined rate no matter what your intrinsic cardiac activity is. They act as a separate focus generating a cardiac impulse. So, they have the risk of causing ventricular fibrillation due to an abnormal discharge of cardiac muscle while waiting for the depolarization wave.

• Non-competitive

1. 1. Demand: this detects any intrinsic ventricular activity which could abnormally depolarize the heart and set off an arrhythmia, and suppresses it.
   2. Stand-by: also called ventricular-triggered pacemakers – they sense each intrinsic ventricular beat, both normal and abnormal, and discharges into the refractory period of the electrical cycle. But this would mean that the patient is at a theoretical risk when around other electrical waves.

But all non-competitive pacemakers take away the risk of ventricular fibrillation.

How does a Pacemaker Work?

The pacemaker is a tiny lightweight device (weighing around 1 ounce), and can be implanted under the skin. In the past, it was also inserted into the abdomen, but it is less common now. It has a generator with a little battery and information on controlling the heartbeat as well as electrodes that connect the heart to the generator and carry the relevant electrical signals.

The procedure takes about an hour, and it is considered a day surgery unless the patient develops significant complications.

When Would I Need a Pacemaker?

Pacemakers are mainly needed to control the 

• Rate – Bradycardia: due to sinus node disease or heart block, or tachycardia
• Rhythm of the heart – when medical management for arrhythmias fail, and a long-term maintenance of the rate is important.

It can also be used in heart failure – these are called biventricular pacemakers because the electrodes are placed over both ventricles allowing the coordination of beating of both chambers. As an added advantage, they can provide a larger electrical impulse, which is commonly called a “shock,” and reverts the heart back into sinus rhythm right at the beginning of a new arrhythmia. So, they are called Implantable Cardioverter defibrillators (don’t worry – it isn’t as deadly as the defibrillator used by health care professionals!)

What Complications Should I Expect?

Some of the complications that may occur during the surgery are:

• Arrhythmias – as you go into surgery without being as healthy as you are expected to be, your heart is prone to developing abnormal rhythms with interventions as well as with anesthetic drugs.
• Voice changes – because we are tampering with the recurrent laryngeal nerves
• Bleeding – in case the procedure punctures and artery. If it punctures a coronary vessel, it could cause cardiac tamponade. Bleeding may also be expected if the patient is on anticoagulant drugs or antiplatelet medication.
• Pneumothorax – this essentially means there is air in the pleural cavity, introduced by puncture of the pleura when performing surgery
• Infection risk – while inserting the pacemaker, and if it remains untreated, it could go on to be infective endocarditis.
• Malposition of the pacemaker after insertion
• Additionally, it may puncture the lung, but these are all rare complications

What is the Outlook for Me after a Pacemaker?

The pacemaker battery will last about 6-15 years, depending on the brand, and various other factors. However, if it is regularly checked and replaced, you will be able to keep your heart rate and a rhythm at a safe level and expect a normal lifespan.

References

1. WRIGHT K, MCINTOSH H. Artificial Pacemakers. Circulation. 1973;47(5):1108-1118. doi:10.1161/01.cir.47.5.1108
2. Pacemakers. Bhf.org.uk. https://www.bhf.org.uk/informationsupport/treatments/pacemakers. Published 2021. Accessed September 14, 2021.
3. Pacemaker – Mayo Clinic. Mayoclinic.org. https://www.mayoclinic.org/tests-procedures/pacemaker/about/pac-20384689. Published 2021. Accessed September 14, 2021.
4. Encyclopedia M, pacemaker H. Heart pacemaker: MedlinePlus Medical Encyclopedia. Medlineplus.gov. https://medlineplus.gov/ency/article/007369.htm. Published 2021. Accessed September 14, 2021.