Article • Experts explore the future of CSP, CRT, ICD

Implantable cardiac devices: which techniques are ready for prime time?

Opposing views on new implantable cardiac devices were aired in a Great Debate session at the European Society of Cardiology’s annual 2024 congress in London. Experts discussed emerging techniques and technologies and debated whether they are actually ready for clinical application. At the core of the session was the issue of whether conduction system pacing (CSP) should replace cardiac resynchronisation.

Report: Mark Nicholls

Speakers firstly discussed the pros and cons of whether CSP – a cardiac pacing technique that uses the heart’s natural conduction system to help the ventricles activate in a physiological way via leads in the organ’s conduction system – should replace cardiac resynchronisation, a treatment for heart failure (HF) that involves implanting a device to help the heart’s ventricles pump in a coordinated way.

A second element to the Great Debate focused on whether patients with an ICD (implantable cardioverter-defibrillator) but no indication for bradycardia pacing should receive an extravascular ICD (EV-ICD), where the lead is placed below the breastbone and is outside of the heart.

CSP: A proximal solution for a proximal problem

Arguing the case for CSP to replace cardiac resynchronisation therapy (CRT), Dr Jacqueline Joza from McGill University Health Centre in Montreal in Canada, felt the debate should actually focus on whether CSP should replace biventricular (BV) pacing as both methods resynchronise the heart. Her key points were to suggest that the HIS-Purkinje system was meant to conduct rapidly and synchronously (so it should be used); that the block in LBBB (left bundle branch block) occurs most often at a location within the HIS (the cardiac muscle cells that transmit electrical impulses), so it is a case of delivering a proximal solution for a proximal problem; and that BV-CRT is an inefficient and dyssynchronous method of delivering CRT.

Joza conceded: ‘The only time BV-CRT may be a better fit is when there is no HIS-Purkinje disruption at all.’ But she added that CSP performs well in patients with RBBB (right bundle branch block) and HF indication for pacing.

Just a ‘new kid on the block’ in need of evidence

Portrait photo of Professor Kevin Vernooy

Putting the case against CSP replacing CRT was Cardiologist-Electrophysiologist Professor Kevin Vernooy from Maastricht University Medical Centre in the Netherlands. He argued that there are many trials that show BV pacing is much better than just an ICD in these patients¹ with much evidence to suggest that BV in patients with LBBB and HF is an ‘awesome therapy.’²^,³^,⁴

While acknowledging CSP in HF is a ‘new kid on the block’, he expressed surprise that clinicians seem to be moving towards it ‘without evidence’ when he believes there is such a good existing pacing therapy. ‘We have so much evidence that biventricular pacing is doing a good job,’ added Vernooy. ‘Even though CSP is theoretically an alternative for BV pacing, the implantation requires new skills and knowledge with limited success rates in patients with heart failure with the current tools. Therefore, we still need BV as a bail-out strategy, so I think we should not go too quickly.’

He concluded that while CPS is a ‘promising’ pacing strategy, clinical routine is shifting towards it ‘without evidence’; that training, education and EP understanding is ‘essential’; and that CSP does not seem to be the ‘optimal strategy’ in many patients.

Transvenous leads: only for those that need them

Portrait photo of Professor Lucas Boersma

In a second debate in the session, Professor Lucas Boersma from St Antonius Hospital in Nieuwegein, the Netherlands, argued the case for patients with an ICD but no indication for bradycardia pacing, receiving an extravascular ICD (EV-ICD).

While acknowledging that ICDs save lives and the Transvenous ICD (TV-ICD) has become the ‘workhorse’ over the last 3-4 decades in everyday clinical care for Sudden Cardiac Death (SCD), he said TV-ICD therapy comes with a price of morbidity and mortality and that leads can become infected or break down.⁵ ‘We used to take that for granted because there was no alternative,’ he said. ‘But if we place the lead outside the vasculature, that may avoid unnecessary complications.’

S-ICD (subcutaneous) was an important first step but he pointed to further advantages of EV-ICD: smaller devices, lower defibrillator energy, greater longevity, pacing with a single device, anti-tachycardia pacing, asystole pacing support and post-shock-pacing. Boersma concluded by pointing out that EV-ICD and S-ICD have high conversion rates and similar efficacy for transforming ventricular arrhythmias back to sinus rhythms and they avoid harmful vascular complications. ‘For patients that do not need pacing, these devices with no transvenous lead in the heart are the way to the future; we should not give transvenous leads to patients that don’t need them.’

TV-ICD: ‘still a lot to offer’

Portrait photo of Professor Jeanne Poole

Offering the opposing view was Professor Jeanne Poole from the University of Washington in Seattle. Her institution is a high user of S-ICD, which has been FDA approved for 14 years, so she suggested it is already ‘prime time’ in appropriate patient groups, whereas EV-ICD has only been recently approved in the United States and has not been adequately tested in real world prospective registries or randomised controlled trials. ‘So, categorically, it is not ready for prime time,’ she said.

The expert discussed the risk of lead fracture, though acknowledged future transvenous leads are likely to be more robust and smaller, and that infection rates are now significantly lower. Pointing to additional considerations in favour of TV-ICD systems, she said they still have the lowest inappropriate shock rates and set a ‘high bar’ with tens of thousands of patients enrolled in clinical studies. There is also excellent sensing with endocardial leads, expanded diagnostics, long battery life, well-established surgical techniques, no need for general anaesthesia, painless ATP for patients, and offer flexibility in programming.

In summary, Prof. Poole said that all patients with an ICD indication but no indication for bradycardia pacing should categorically not receive an EV-ICD. ‘Transvenous ICD systems still have a lot to offer, they are the only option for many ICD indicated patients and they will be around for many years,’ she concluded.

References:

Profiles:

Dr Jacqueline Joza is an associate professor of medicine and cardiac electrophysiologist at the McGill University Health Centre, Canada. Her research focuses on CSP, atrial fibrillation and syncope.

Professor Kevin Vernooy is the medical director of the heart and vascular center and chairs the Department of Cardiology at the Maastricht University Medical Center in the Netherlands. His research focuses on the invasive treatment of cardiac arrhythmias in patients with heart failure.

Professor Lucas Boersma is an Electrophysiologist at St Antonius Hospital in the Netherlands and was Head of the Cardiology Department from 2008-2016. He is the past chairman of the Committee for Science & Innovation of the Netherlands Society of Cardiology and endowed Professor of Cardiology at the University of Amsterdam since 2017.

Professor Jeanne Poole is an electrophysiologist and the Section Head of Electrophysiology at the University of Washington in Seattle, US, and is Editor-in-Chief for the Heart Rhythm O² Journal.

05.12.2024