Does a Pacemaker Increase Ejection Fraction?

A standard pacemaker that stimulates the right ventricle does not increase ejection fraction and, in many patients, gradually lowers it. The story changes dramatically with cardiac resynchronization therapy (CRT), a specialized form of pacing that can boost ejection fraction by ten or more percentage points in the right candidates. Whether a pacemaker helps or hurts your heart’s pumping ability depends almost entirely on the type of device, where its leads are placed, and how much pacing your heart actually needs.

Why Conventional Pacing Tends to Lower Ejection Fraction

Most traditional pacemakers work by sending an electrical impulse to the tip of the right ventricle, a spot called the right ventricular apex. This keeps the heart from beating too slowly, which is the device’s primary job. But the electrical signal that spreads from that single point doesn’t travel the same route the heart’s natural wiring uses. Instead of both ventricles contracting in a coordinated squeeze, the left ventricle contracts slightly out of sync, and over months or years that dyssynchrony takes a toll on pumping efficiency.

Research tracking patients with normal ejection fractions before pacemaker implantation has shown that chronic right ventricular apical pacing produces measurable dyssynchrony early on, and that dyssynchrony predicts a later decline in ejection fraction.¹ A study using 3D echocardiography confirmed that right ventricular pacing led to drops in ejection fraction over both short and long follow-up periods.² The damage isn’t always dramatic, but when the heart relies heavily on pacing to maintain its rhythm, the cumulative effect can push someone toward heart failure, a condition sometimes called pacing-induced cardiomyopathy.

Even the pacing rate matters. In patients with normal heart size, increasing the ventricular pacing rate caused a steady, linear decline in stroke volume and ejection fraction. Patients who already had enlarged hearts responded differently: their ejection fraction dropped significantly only at the higher pacing rates, and their best cardiac output occurred within a narrow band of 70 to 90 beats per minute.³ In other words, conventional pacing is not a one-size-fits-all therapy even in its most basic parameters.

How Much Pacing Is Too Much

Not everyone with a right ventricular pacemaker develops a weaker heart. A key variable is pacing burden, the percentage of heartbeats that are initiated by the device rather than by the heart’s own electrical system. The adverse effects of right ventricular pacing appear to be directly related to this burden and are worse in patients who already have some left ventricular dysfunction before the device goes in.⁴

One study found that patients paced more than 40% of the time experienced a statistically significant drop in ejection fraction, while those paced less than 40% of the time did not.⁵ Larger analyses echo this pattern: high right ventricular pacing burden, especially above 50%, is one of the strongest predictors of later heart failure hospitalization in patients who started out with preserved ejection fractions.⁶

This is why modern pacemaker programming emphasizes minimizing unnecessary ventricular pacing whenever possible. If your own heart can conduct signals from the atria to the ventricles, even with occasional delays, algorithms in the device try to step aside and let your natural conduction do the work. The pacemaker fires only when it detects a true gap. For people who need pacing only occasionally, like those with intermittent heart block, this approach keeps the pacing burden low and protects the ejection fraction.

Cardiac Resynchronization Therapy and Ejection Fraction Recovery

CRT represents the opposite end of the pacing spectrum. Rather than pacing one spot on the right ventricle, CRT places leads in both ventricles (or uses the heart’s own conduction system) to coordinate their contraction. The goal is to correct the very dyssynchrony that conventional pacing can cause or that occurs naturally in patients with conditions like left bundle branch block.

The landmark MADIT-CRT trial, published in the New England Journal of Medicine, demonstrated that CRT significantly reduced left ventricular volumes and improved ejection fraction in patients with mild heart failure symptoms.⁷ A European study tracked the response over 12 months and found that ejection fraction improved by roughly 10.6 percentage points on average across the entire population studied, with similar gains in elderly and younger patients alike.⁸

The mechanism is straightforward in principle: by restoring coordinated electrical activation, CRT improves contractility, reduces mitral valve leakage, and shrinks the dilated left ventricle back toward a more normal size, a process cardiologists call reverse remodeling.⁹ In the best-case scenarios, the improvement can be extraordinary. A published case report described a patient whose ejection fraction climbed from 15% to 60% after one year of CRT, essentially normalizing a heart that had been failing severely.¹⁰

Who Responds Best to CRT

Not every patient fitted with a CRT device sees that kind of turnaround. Roughly a third of CRT recipients are considered non-responders, meaning they don’t achieve a clinically meaningful improvement. At the other extreme, some patients are classified as “super-responders” whose hearts remodel far beyond what average numbers would suggest.

Analysis from the MADIT-CRT trial identified six factors that predicted a super-response: female sex, no prior heart attack, a wider QRS duration on the electrocardiogram (at least 150 milliseconds), left bundle branch block, a body mass index under 30, and a smaller left atrium at baseline.¹¹ A separate study found that patients with dilated cardiomyopathy (as opposed to cardiomyopathy caused by blocked arteries) and patients who had previously undergone right ventricular apical pacing were more likely to achieve a super-response.¹²

That last detail is worth pausing on. Patients whose ejection fractions had dropped specifically because of right ventricular pacing often recover impressively once they are “upgraded” to CRT. Their hearts weren’t inherently diseased; they were dyssynchronized by the prior device. Remove the cause of the dyssynchrony and the heart bounces back. This is quite different from someone whose heart muscle is scarred from a major heart attack, where the tissue damage limits how much recovery is possible regardless of how well the pacing is coordinated.

Sex Differences in CRT Response

Women consistently derive more benefit from CRT than men, a finding that has shown up across multiple trials and registries. The BIO|WOMEN trial reported that women gained an average ejection fraction improvement of about 14.7 percentage points compared to 11.5 in men, and that female sex independently predicted a greater response even after accounting for other baseline differences.¹³ Women also showed higher rates of reverse remodeling, better quality-of-life scores, and a larger proportion meeting the threshold for a clinically meaningful response.

The reasons aren’t entirely settled, but several biological differences likely contribute. Women tend to have smaller hearts and less coronary artery disease, both of which are associated with better CRT outcomes. Their hearts are also more likely to be affected by left bundle branch block, the electrical pattern that CRT is specifically designed to correct. Some researchers have suggested that women’s hearts may simply have more viable muscle tissue available to recover, because they are less frequently scarred by ischemic damage. Whatever the explanation, the clinical implication is clear: CRT guidelines may undercount the women who would benefit, because the qualifying criteria (particularly QRS width thresholds) were developed largely in male-majority trial populations.

Conduction System Pacing as an Alternative

A newer approach, called conduction system pacing, tries to use the heart’s own electrical highway instead of bypassing it. Rather than placing a lead at the ventricular tip, the lead is positioned at the His bundle (the main junction in the heart’s wiring) or along the left bundle branch. Because the signal travels through the heart’s built-in conduction system, both ventricles activate more naturally.

His bundle pacing has shown the ability to preserve ejection fraction in patients who would be at high risk for pacing-induced cardiomyopathy. In one study, patients who received His bundle pacing maintained their ejection fraction (60% before and 60% after), while a comparison group that received standard right ventricular pacing saw a significant drop from 59% to 56%.¹⁴ When used therapeutically in patients with heart failure and left bundle branch block, His bundle pacing produced earlier and greater improvements in ejection fraction and ventricular volumes than traditional biventricular CRT.¹⁵

Left bundle branch area pacing, a close cousin of His bundle pacing, has also been gaining traction. A meta-analysis comparing left bundle branch pacing CRT to traditional biventricular CRT found that the newer approach achieved greater QRS narrowing and greater ejection fraction improvement.¹⁶ These conduction system approaches are still evolving, and long-term data is thinner than for conventional CRT, but the early results suggest that pacing through the heart’s native wiring may become the default strategy for patients who need high amounts of ventricular pacing.

Leadless Pacemakers and Ejection Fraction

Leadless pacemakers, the small capsule-shaped devices implanted directly into the right ventricle through a catheter, have drawn attention for their lower complication rates compared to traditional lead-based systems. But from an ejection fraction standpoint, they face the same fundamental problem as any right ventricular pacing device: they deliver the electrical impulse from a single point in the right ventricle, producing the same dyssynchronous contraction pattern.

A study of leadless pacemaker recipients found that average ejection fraction dropped from about 52% to 48% after implantation, and roughly a quarter of patients experienced an absolute drop of 10% or more.¹⁷ The “leadless” part solves problems related to leads (infections, fractures, vein occlusion) but does not solve the electrical dyssynchrony problem that drives ejection fraction decline. If you need a pacemaker primarily for slow heart rate and your own conduction system is intact enough to keep pacing burden low, a leadless device can work well. If you’re expected to need near-constant ventricular pacing, the choice between leadless and lead-based doesn’t change the risk to your ejection fraction; what matters is whether the pacing strategy itself is synchronized.

The Ablate-and-Pace Strategy in Atrial Fibrillation

Some patients with persistent atrial fibrillation and uncontrollable heart rates undergo a procedure called “ablate and pace,” in which the junction between the upper and lower chambers is deliberately destroyed with a catheter and a pacemaker is implanted to maintain the ventricular rate. Because the chaotically fast signals from the atria can no longer reach the ventricles, heart rate becomes regular and controllable, and symptoms typically improve.

But does ablate-and-pace actually improve ejection fraction? An updated meta-analysis found a small, non-significant improvement in ejection fraction compared with drug therapy alone, averaging about 1.1 percentage points.¹⁸ Observational studies showed a trend toward greater improvement, but the randomized trials were essentially neutral. The strategy does appear to reduce mortality and hospitalization, however, so even without a large ejection fraction boost, the benefit may come from stabilizing the heart rate and relieving the burden of rapid, irregular rhythms. When CRT is used as the pacing device after ablation rather than a standard right ventricular pacemaker, the outcomes tend to be better, which fits with everything discussed above about synchronized versus non-synchronized pacing.

Pacing-Induced Cardiomyopathy in Children

Pacing-induced cardiomyopathy is not limited to adults. Children who require chronic ventricular pacing after congenital heart surgery face similar risks. A published case report described a child who developed heart failure with an ejection fraction of 37% after chronic left ventricular apical pacing following surgery for a congenital heart defect. After the pacing strategy was changed to a resynchronization approach and appropriate heart failure medications were added, the child’s ejection fraction recovered to 54% within ten months.¹⁹

Pediatric patients present unique challenges because their hearts are growing, they face decades of cumulative pacing burden, and the anatomy of congenital heart disease can make lead placement difficult. But the core principle remains the same: dyssynchronous ventricular pacing can weaken the heart, and restoring synchrony through CRT or conduction system pacing can reverse the damage. Pediatric cardiologists are increasingly watchful for early signs of pacing-induced dysfunction so that device upgrades can happen before the heart remodels too far in the wrong direction.

What Your Cardiologist Thinks About When Programming Your Device

Given all these trade-offs, device programming is where theory meets the individual patient. For someone with a dual-chamber pacemaker and functioning conduction between their atria and ventricles, the top priority is keeping right ventricular pacing as low as possible. For someone with complete heart block who has no choice but to pace every beat, the conversation shifts to whether conduction system pacing or CRT would preserve or improve their ejection fraction better than a conventional right ventricular lead.

CRT devices themselves can be optimized after implantation. The timing delays between the atrial signal and the ventricular pacing, and between the left and right ventricular leads, can be fine-tuned using echocardiography or device-based algorithms. While routine optimization protocols aren’t recommended for every CRT patient, they can be valuable for non-responders who haven’t seen the expected improvement.²⁰ In some cases, simply adjusting these intervals or changing the pacing vector can convert a non-responder into a responder, unlocking the ejection fraction gains that should have appeared earlier.

For patients already living with a pacemaker and wondering whether their ejection fraction is at risk, the practical steps are straightforward: ask about your pacing percentage at every device check, request periodic echocardiograms to track ejection fraction over time, and discuss with your cardiologist whether your current pacing strategy is the most physiological option available for your specific situation. A declining ejection fraction in a heavily paced patient is not something to wait on; it is often the signal that a device upgrade or lead repositioning should be considered before the heart remodels further.