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Multi-site Pacing

The first pacemaker was invented in the 1950s to compensate for an electrical cardiac deficiency. Until the end of the 1990s, the only reason to implant a pacemaker was heart conduction diseases. A Parisian team, from the Clinique du Val d’or, associated with the Cardiology Department of the hospital of Rennes, had the idea to use the pacemaker to resynchronize the right side and the left side of the heart so as to optimize the cardiac results of patients with congestive heart failure. That was the creation of multi-site pacing.

How does it work?
When a patient has cardiac insufficiency, it means that the cardiac muscle is weakened. Most of the time, it is caused by a myocardial infarction, but there are other causes. Sometimes, on top of the weakening of the heart, there can be a “desynchronization” between the different contractile segments of the heart: part of the heart, most often the lateral wall of the left ventricle, contracts a few milliseconds late. This phenomenon adds up with the overall weakness of the heart and diminishes even more the cardiac output. This desynchronization has a direct deleterious effect on the cardiac muscle itself. Correcting desynchronization can improve heart contraction in the long run. In a nutshell, the aim is to stimulate almost at the same time the left side and the right side of the heart. A lead therefore needs to be implanted in the right heart (right ventricle) and another in the left heart (left ventricle).

In practical terms, what is done?
Setting a lead into the right ventricle is fairly easy: it has been done for many years in standard heart stimulation through the vein system. The main problem is that of the left lead. Usually, setting a stimulation lead in the left ventricle needs an arterial catheterism. We use the arterial system to get into the left heart, exposing the patient to peri-surgical embolic complications, the most famous of which is the cerebral ischemic accident. Fortunately, there is another solution.

There is a vein system at the surface of the heart which collects oxygen-poor blood to recycle it towards the lungs. The vein system is born in the upper part of the right heart (right atrium) and is called “coronary sinus”. The purpose of this process is to stimulate the left heart as the blood passes through the vein system of the coronary sinus. In practical terms, this process is difficult because several obstacles must be overcome. The first one is that of the catheterism at the entrance (“the ostium”) of the coronary sinus. Once in the vein system, you have to get into the “target vein” which faces the desynchronized wall. To finish, when the lead/wire is in place, it needs to be stable and the stimulation threshold has to be “acceptable”. As my male-nurse often tells me in the operating room at the hospital, “it’s as if you wanted to paint the corridor through the mailbox!”

What can I expect from this technique?
Many international scientific studies have proven how useful this technique can be. The beneficial effects were first demonstrated on the patients’ quality of life. Today, it is well established that it also enables to improve the patients’ survival expectancy. In the days and the months that follow the implantation, many symptoms should diminish, if not disappear: fatigue, breathlessness at rest and maybe even during efforts… Unfortunately, despite all our efforts, 20 to 30% of the patients are not responder to the technique. That is why a pre-surgery check-up is necessary. It enables us to pick the best candidates. When we do not obtain the improvements we were expecting, we must consider reprogramming the pacemaker. In some cases, changing the stimulation site can turn out to be necessary. When it cannot be done through intravascular tracts, we can discuss resorting to heart surgery can be discussed.

What are the complications of this process?
This technique has been used for 10 years throughout the world (since 2000 in our Department). Much progress has been made on the equipment at our disposal, which enabled us to increase significantly the success rate of our implantations, which now exceeds 85%.

Even if the complication rate remains higher than a standard implantation, it has substantially decreased and now reaches acceptable levels. The complications include the usual heart stimulation complications, and also dissection of the coronary sinus, arrythmias and conduction disorders, and renal failure.

The dissection of the coronary sinus is the perforation of the veinous system during the procedure. It leads to the leaking of blood around the heart in the pericardium. The treatment is surgical drainage. It should be kept in mind that we are working on weakened, fragile hearts. During the procedure, severe conduction disorders and arrhythmias, especially ventricular arrhythmias, can happen, threatening the patient’s vital prognosis. Renal failure is due to the toxicity of the contrasting product used to see the coronary sinus. If the patient is insufficiently hydrated or the product has been used excessively, there can be a dysfunction of the kidneys which usually stops after rehydration. Resorting to dialysis as an emergency remains extremely rare.

Multisite pacing can be combined to defibrillation in the case of “multisite defibrillation” which presents the advantages of both devices.

As we have seen, this technique is long and difficult. It often entails long sessions of catheterism for the patient (and the practitioner). It may therefore cause complications. If you also take into account the state of the heart of the patient, it can be easily understood that this technique requires the practitioner to be a dab hand and the patient to be carefully chosen. If not, the patient is exposed not only to unsatisfactory results but, more seriously, to complications which could turn out to be lethal.

A lot remains to be achieved however, and not a day goes by without some new studies being published somewhere in the world.

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