Rethinking How We PACE the Heart

by admin on September 1, 2011

DrSamGirgis.com has the pleasure of hosting the following post by guest blogger, Dr. Richard Andraws MD, who is a Board Certified Cardiologist

 

Ah! lacharmante chose,

Quitter un pays morose,

Pour Paris!

Paris joli,

Qu’un jour dûtcréerl’Amour.

                                                   –Guillaume Apollinaire, Voyage à Paris

 

It’s fitting that the European Society of Cardiology convenes its annual Congress in Apollinaire’s delightful city every few years. He would have us believe it was created by Love as a respite from the dreariness that exists everywhere else. And Love’s throne is surely the heart.

This year’s Congress brings us two year follow-up data from the Pacing to Avoid Cardiac Enlargement (PACE) trial, whose preliminary resultswere reported in the New England Journal of Medicine in 2009.Worldwide an estimated 600,000 pacemakers are implanted yearly to treat dangerously slow heart rates that can lead to fatigue, loss of consciousness, and death. About the size of a silver dollar, they generate small electrical impulses that are conducted to the heart via wires known as “leads.” Usually two leads are placed inside the heart: one in the upper chamber on the right (the atrium) and one in the lower chamber (the ventricle). The impulses cause contraction of the heart muscle and prevent the rate of pumping from falling below a preset value.

Unfortunately, pacing the right side of the heart, while sometimes necessary, can have deleterious effects. The spread of electricity through the heart is significantly different when pacing as compared with normal activation. This leads to unnatural stress on the heart, which can cause it to weaken. In fact, patients with heart failure often develop this abnormal electrical pattern because of disease. It’s been shown in select heart failure patients that “biventricular” pacing (i.e. placing a third pacing lead on the left side of the heart) actually improves symptoms and can strengthen the heart.

So the tantalizing question is, why not put “Bi-V” pacemakers into all patients who will need to be paced most of the time? All the benefits of pacing without the side effects.

The PACE Investigators randomized 117 patients with normal heart function and need for a pacemaker to conventional right-sided pacing (RVP) and biventricular pacing (BiVP). Both groups were paced more than 90% of the time. Other baseline characteristics were similar. At 2 years, the BiVP group appeared to have healthier hearts, with better pumping function and less evidence of adverse “remodeling.” Interestingly, though, patients did not have better exercise tolerance or subjectively feel better regardless of how they were paced. And there was no benefit in terms of heart failure hospitalizations.

Thus, there’s a discrepancy here: BiVP preserves heart function based on the numbers, but this does not appear to translate into significant clinical benefit. Reasons for this may include the modest size of the trial and the fact that it wasn’t designed to assess clinical endpoints primarily. BiV pacemakers are more expensive devices, are more challenging to implant (with possible higher complication rates), and state-of-the-art “regular” pacemakers are now smart enough to safely minimize how much they pace. So BiVP for all is probably not ready for primetime despite the intriguing data presented by Yu and colleagues. More research to elucidate whether there yet may be clinical benefit on the throne of Love (and so much else that makes us human) is warranted. 

REFERENCES

PACE: Biventricular pacing superior to right ventricular pacing in bradycardia patients with preserved systolic function: two-year results of PACE trial (Available at URL:http://www.escardio.org/congresses/esc-2011/congress-reports/Pages/710-2-PACE.aspx)

Wood MA, EllenbogenKA. Cardiac pacemakers from the patient’s perspective. Circulation 2002; 105: 2136-38.

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