New defibrillator can be implanted without putting electrodes into heart

Latest defibrillator can be implanted without putting electrodes into the heart, writes Jeanette Wang

PUBLISHED : Monday, 05 May, 2014, 9:42am
UPDATED : Monday, 05 May, 2014, 9:42am

A new defibrillator that detects arrhythmias and shocks the heart back into normal rhythm - yet has no wires that touch the heart - has been successfully implanted in two patients in Hong Kong, the first in Asia.

A team from the University of Hong Kong's Li Ka Shing Faculty of Medicine performed the surgeries and both patients are making satisfactory progress in rehabilitation.

"The greatest advantage of the new defibrillator is that the implantation can be conducted without putting any electrodes into the heart through blood vessels, leaving the heart untouched," says Professor Tse Hung-fat, William MW Mong Professor in Cardiology and Chair Professor of department of medicine at the faculty.

The risk of heart perforation after the surgery will drop to zero per cent
Professor tse hung-fat

"Hence, the risk of heart perforation, and/or infection of the heart after the surgery will drop to zero per cent."

Three incisions over the patient's left chest are made and the device, called a subcutaneous implantable cardiac defibrillator (S-ICD), is placed under the skin of the chest wall, over the ribs and sternum.

A wire runs under the skin along the left side of the breast bone. The surgery for implanting the device takes around an hour, compared to up to two hours for a conventional device, thereby reducing the time a patient is anaesthetised.

Apart from a highly significant reduction in the risk of developing severe complications, the S-ICD can also be placed solely by anatomical landmarks without using X-ray, hence reducing patients' radiation exposure.

Further, replacing worn-out electrodes in the new device needs only a simple surgery, says Tse. With a conventional defibrillator, more complicated surgery must be used to replace worn-out electrodes, which may cause heart injuries.

Tse says the S-ICD costs HK$200,000, similar to a mid-range conventional ICD, which costs between HK$140,000 and HK$300,000. However, the new device has only a five-year battery life, compared to seven to 10 years for the conventional device.

In Hong Kong, about 200 patients install defibrillators every year. They provide immediate help to patients at critical moments to avoid sudden cardiac arrest because of an insufficient outflow of blood from the heart.

First introduced to clinical practice in 1980, the implantable cardiac defibrillator has improved the survival rate of patients at high risk for sudden cardiac death. Randomised, multicentre studies have shown a relative risk reduction in total mortality of up to 54 per cent and an arrhythmic mortality reduction of 50 per cent to 70 per cent.

However, the most frequent complications associated with the conventional device involve the transvenous leads. The S-ICD was initially developed for patients who were not candidates for these conventional ICDs, such as those with some congenital heart abnormalities or no venous access.

"With the failure rate of transvenous leads variably reported as 28 to 40 per cent at eight years, a subcutaneous approach could substantially reduce risks associated with lead extraction and is particularly suited to young patients with a long life expectancy and higher lead failure rates due to active lifestyles," wrote Christopher P. Rowley and Michael R. Gold in their paper published in June 2012 in the journal Circulation: Arrhythmia and Electrophysiology.

Due to the advantages of the subcutaneous approach, for some patients, it may be a preferred approach for the prevention of sudden cardiac death than simply an alternative to transvenous ICDs, added Rowley and Gold.

Tse notes that the new device is not for everyone: "The S-ICD can replace the most important function of conventional ICD, that is, defibrillation, but cannot perform long-term cardiac pacing to maintain heart rate."

Patients who will benefit most from the new device include those with structural heart diseases in whom the leads cannot be implanted; those with high risk of infection, such as those on hemodialysis or immunosuppression; those with high risk of lead complication; and those who require primary prevention of sudden cardiac death and do not require pacing, especially those with inherited cardiac arrhythmic syndrome or cardiomyopathy.

The S-ICD is made by US company Boston Scientific and has been used in Europe and New Zealand since 2009. It was approved by the US Food and Drug Administration in 2012, following an extensive review of data obtained from pilot studies and the European EFFORTLESS S-ICD Registry.

In a study funded by the device's maker and published last August in the American Heart Association journal Circulation, 314 patients using the device were followed for an average of 11 months. Three quarters of the participants were male, with an average age of 52.

Over the first 180 days following implantation, 21 patients had 38 episodes of abnormal rhythms that precede cardiac arrest - ventricular fibrillation or ventricular tachycardia. In each case, the device restored the heart to a normal rhythm.

During this time, 99 per cent of the patients had no complications from the device. But 41 patients (13 per cent) received an inappropriate shock.

The ongoing European EFFORTLESS registry has confirmed these positive results.