Author: Dr Hitesh Patel
Worldwide cardiologists and doctors alike are vested in therapies to combat heart failure and explore measures to improve the quality of life for patients – new implanted device based therapies are under active investigations- including devices that can modulate cardiac contractility, and multiple other modes to alter vagal tone. In an ever-evolving landscape of treatment devices, here Dr Hitesh Patel hones in on cardiac resynchronisation, an established therapy for selected patients with heart failure and reduced ejection fraction, he explains what it involves, that some patients are super responders, but not all obtain the same benefit.
Cardiac resynchronisation therapy – also referred to as biventricular and multisite ventricular pacing – involves implanting a device to simultaneously pace the heart’s right and left ventricles. For those patients with a dilated cardiomyopathy and left bundle branch block with a widened QRS –cardiac resynchronisation aims to reinstate left ventricular synchrony.
“The magnitude of the benefit from resynchronisation therapy does depend on how wide the left bundle branch block is,” explains Dr Hitesh Patel. “People who benefit the most are the ones with non-ischemic cardiomyopathy with a very wide QRS left bundle branch block, greater than 150 milliseconds.”
Although not a new therapy measure – the first case was reported over 20 years ago – successful cardiac resynchronisation still rests on successful pacing of both ventricles.
The technique
“What you have to do, is put in standard pacing leads in the right heart (a right atrial and a right ventricular lead). To pace the left ventricle, still via the same access site in the subclavian vein, you pass a wire into the right atrium and then enter the coronary sinus of the heart, and you have to pass the pacemaker lead into the coronary veins, into one of the posterior lateral branches,” explains Dr Patel.
Thus, you have three leads in the venous system- two into the right heart and one to the left ventricle via the coronary sinus.
“Sometimes when we are sending people for cardiac surgery, they have left bundle branch block and if we think there is a very high chance the person is going to end up needing one of these devices, we’ll ask the surgeons to put an epicardial lead at the time of surgery. So, what they do is put a lead on the heart – on the left side – to avoid us having to implant a lead through the coronary sinus.”
Heart matters aren’t always self-explanatory and in the early days many cardiologists thought that if the septum was not moving, it was dead and was never going to start working again, explains Dr Patel.
“In fact, it’s just moving in the opposite direction. It’s like you are playing tug of war and if your team members are not pulling at the same time, you are not going to win the battle and this is what happens with the heart,” he says.
“If you have dyssynchrony and the different walls of the heart are not coming in together, your heart is not as efficient as it is going to be.”
As with many treatment methods, response to cardiac resynchronisation is variable.
A study titled ‘Cardiac resynchronisation therapy: predictive factors of unsuccessful left ventricular lead implant’, headed by Alfonso Marcias and nine authors, and published in the European Heart Journal, Volume 28, followed 212 heart therapy patients, of whom 186 achieved successful implantation and 26 patients experienced complications.
These included:
- Failure to cannulate the coronary sinus.
- High threshold to chronic pacing.
- Impossibility to obtain a stable lead placement.
- Failed cardiac synchronisation.
The complication rate of this particular study is not dissimilar to those of other resynchronisation studies – MIRACLE (13%) and the COMPANION trial (9.9%).
The authors of this study concluded that the presence of permanent atrial fibrillation can predict unsuccessful pacing from the cardiac synchronisation, and that stable chronic cardiac synchronisation lead pacing was achieved in more than 85% of cases, and was associated with a relatively low rate of complications.
The super responder
Some patients are ‘super responders’, says Dr Patel – demonstating this with a clinical case. The patient has a non-ischemic cardiomyopathy, left branch block, low ejection fraction and a dyssynchronous heart – despite medical therapy.
“This guy is very fit but his ventricle was absolutely huge – 8.2cm at the base in end-diastole measured– and it looked like a big football on the echocardiogram,” says Dr Patel. “However, he can still exercise for over nine minutes on the Bruce Protocol – it was a bit borderline whether he met the criteria to have a resynchronisation device – but it didn’t seem right to leave this guy with a football-size heart.”
He received a synchronisation device and after six months his heart wasn’t beating completely normally but it had shrunk in size. The left ventricular ejection fraction improved from being severely impaired to 50% to 55%.
“He went from having a huge ventricle with an EDD of 8.2cm and now his end diastolic dimension is more like 5.6cm, coupled with his increased ejection fraction.”
However, not everyone has a spectacular a response when implanting a resynchronisation device, in fact people who don’t respond might be harmed, says Dr Patel.
“These are the people with narrow QRS who don’t have a left bundle branch block and if you implant these devices in them they don’t benefit.”