EVOLUTION OF THE CARDIAC PACEMAKER

Cardiac pacemakers have been around since the 1960s. They have become a cornerstone of treatment for complete heart block and sick sinus syndrome.^1-2 Patients who used to have recurrent syncope or giddiness could now live normal lives. Indeed, many patients with complete heart block and sick sinus syndrome continue to work and lead very active lives after their pacemaker implantation.

Over the years, the size of the pacemaker has shrunk and the electronics within have increased in complexity and function, mirroring the advance in microelectronics. However, the overall form of the pacemaker has not changed significantly – till now.

Pacemakers traditionally consist of 2 major components – the pulse generator (which contains the battery and electronics) and the leads (insulated wires that connect the pulse generator to the heart). Many patients, however, find the pulse generator bulge unsightly and cardiologists have to manage the leads that malfunction.

NEXT GENERATION OF PACEMAKERS

Recently, a new type of pacemaker has been developed^3-5 that is about the size of a large capsule placed directly in the heart – the leadless pacemaker. It can be implanted via a femoral vein puncture in about 30 minutes – half the time of the traditional pacemaker.

The leadless pacemaker no longer leaves a scar or unsightly bulge over the chest of patients as it is located fully within the right ventricle. It is also less prone to infection – minimising one of the most common complications of pacemaker implantation. National Heart Centre Singapore (NHCS) was the first in Singapore to begin implanting the leadless pacemaker in patients last August.

Currently the leadless pacemaker is most suitable for older patients who require only right ventricular pacing or in patients with bilateral occluded subclavian veins. As the technology matures, this new device will likely become the preferred option for more patients.

VENTRICULAR FIBRILLATION AND SUDDEN CARDIAC ARREST

In the past, patients who developed ventricular fibrillation (VF) cardiac arrest would have to be very fortunate to survive.
These patients would require:

1. A passer-by or family member to realise that they have collapsed
2. Cardiopulmonary resuscitation (CPR) to be started early (often within a few minutes of VF)
3. A defibrillator be placed early to detect patient’s VF and defibrillation administered in a timely manner – the cardiac life support ’chain of survival‘

It is therefore not surprising that only 2% of sudden cardiac arrest patients in Singapore survive.⁶ In recent years, attempts have been made to improve this figure by training more members of the public with CPR and having automated external defibrillators widely available.

Implantable Cardioverter Defibrillator (ICD)
Amongst patients already known to be at high-risk of VF however, there is a technology that has been proven to save lives² – the implantable cardioverter defibrillator (ICD).

This device is implanted in the same way as a traditional pacemaker, monitors a patient’s heart rhythm all the time (24 hours, 7 days a week), detects VF and delivers a life-saving shock automatically. Some ICDs have a battery life of more than 10 years. Over the past decade, the number of patients undergoing ICD implantation has increased.⁷

New Generation of ICD
In the past few years, a new version of the ICD has been developed⁸ that does not require placement of an intravascular lead – the entirely subcutaneous ICD.⁹

This new development reduces the risk of systemic infection and eliminates the need for central venous access. The entirely subcutaneous ICD can be implanted in most hospitals in Singapore, and has been performed at NHCS over the past 4 years.

CASE STUDY

Mr RHL is a 60-year-old store manager with hypertension, hyperlipidaemia and diabetes mellitus for the past 6 years. He saw his GP for recurrent lower limb swelling and shortness of breath. In view of his recurrent symptoms, he was referred to a cardiologist.

An echocardiogram was performed which showed a reduced left ventricular ejection fraction (LVEF) of 25%. Coronary angiogram showed only minor coronary artery disease – insufficient to account for his poor heart function.

RHL was eventually diagnosed with non-ischaemic cardiomyopathy after a complete work-up. When his LVEF did not improve after a year on medical therapy, he agreed to an ICD implant.

Three months after his implant, he woke up in the middle of the night after some chest discomfort, but did not think much about the event. He returned to work the next morning. It was only at his subsequent device check clinic visit that he realised he had received the life-saving therapy for ventricular tachycardia. His medications were optimised further and he remains on follow up with his GP and cardiologist.

CONCLUSION

There have been rapid advances in electronic technology that has resulted in a new generation of pacemakers and implantable defibrillators. The appropriate use of these technologies has the potential to save many patients’ lives.

Primary care doctors can help by being aware of the increasing number of patients on these cardiac implantable electronic devices. GPs also have a critical role to play in referring appropriate patients for further cardiac assessment and management.

GPs can call for appointments through the GP Appointment Hotline at 6704 2222

References

Adj Asst Prof Daniel Chong is a Senior Consultant with the Department of Cardiology at the National Heart Centre Singapore (NHCS). He is also Deputy Director, Residency Programme in the Cardiovascular Sciences Academic Clinical Programme. His subspecialty interest is in electrophysiology and pacing.