Pacing and Cardiac Function When Ejection Fraction Is Preserved
A preserved left ventricular ejection fraction (LVEF) is often interpreted as evidence of satisfactory cardiac performance. In patients who require permanent pacing, however, a normal EF does not remove the possibility of clinically important ventricular dyssynchrony, impaired relaxation, rising filling pressures, or progressive heart failure symptoms. Systolic function measured at rest may remain stable while pacing alters the timing and efficiency of contraction.
The relationship between pacing and cardiac function is therefore more nuanced than a simple comparison of baseline and follow-up EF. Lead position, pacing burden, atrioventricular timing, intrinsic conduction, ventricular geometry, atrial rhythm, and comorbidities all influence outcomes. Patients with preserved EF may tolerate conventional pacing for years, while others develop exertional intolerance, atrial fibrillation, or a decline in myocardial performance.
A contemporary assessment should combine imaging, electrical data, symptoms, and device interrogation. This approach helps clinicians identify patients who need closer surveillance, programming changes, conduction system pacing, or a more advanced resynchronization strategy.
Why Preserved Ejection Fraction Can Mislead
LVEF describes the proportion of blood ejected from the left ventricle during systole, but it does not fully capture myocardial strain, mechanical synchrony, diastolic function, or cardiac reserve. A patient can have an EF above 50% while showing reduced longitudinal strain or impaired relaxation. These abnormalities may become evident during exercise, tachycardia, anemia, or increased blood pressure.
Right ventricular pacing can create an activation pattern resembling left bundle branch block. Electrical stimulation begins outside the normal His–Purkinje network, producing delayed activation of sections of the left ventricle. This may increase regional workload, reduce contraction efficiency, and promote adverse remodeling. The effect is influenced by pacing percentage and site, as well as the patient’s underlying substrate.
Preserved EF also varies with loading conditions. Hypertension, valve disease, obesity, renal dysfunction, and atrial fibrillation can raise filling pressures without immediately reducing systolic output. Consequently, new breathlessness or exercise limitation after pacemaker implantation should not be dismissed because the echocardiographic EF remains normal.
How Ventricular Pacing Affects Cardiac Mechanics
The most relevant physiological issue is ventricular activation sequence. Right apical pacing may produce a broad paced QRS and interventricular or intraventricular dyssynchrony. Septal motion can become abnormal, and the lateral wall may contract later than regions activated earlier. Over time, this uneven distribution of myocardial stress can contribute to pacing-induced cardiomyopathy in susceptible individuals.
The risk is not determined by pacing burden alone. A high percentage of ventricular pacing is a recognized concern, but the clinical impact also depends on baseline conduction disease, scar, ischemic heart disease, age, ventricular dimensions, and the presence of atrial or valvular pathology. Some patients with frequent pacing maintain stable function, whereas others experience symptoms or ventricular remodeling at a lower burden.
Atrioventricular timing adds another layer. If the paced or sensed atrial-to-ventricular interval is poorly matched to ventricular filling, atrial contraction may occur too early or too late. This can reduce preload, increase atrial pressure, and produce pacemaker syndrome. Programming should therefore be evaluated alongside lead location and QRS duration rather than treated as a separate technical issue.
Selecting A Pacing Strategy
For patients with preserved ventricular function who require pacing, the initial decision should reflect the expected pacing burden and the reason for implantation. Individuals with intermittent atrioventricular block and reliable intrinsic conduction may benefit from algorithms that minimize unnecessary ventricular pacing. These features can reduce exposure to dyssynchronous activation, although they must be used carefully in patients with long PR intervals, intermittent block, or symptoms related to irregular conduction.
His-bundle pacing and left bundle branch area pacing aim to preserve or restore more physiological ventricular activation. These approaches may narrow the paced QRS and improve electrical synchrony compared with conventional right ventricular pacing. Their use requires operator expertise, careful assessment of capture thresholds, and long-term follow-up because lead performance and capture stability can vary.
Cardiac resynchronization therapy is generally established for selected patients with reduced EF, prolonged QRS duration, and symptomatic heart failure. Its role in preserved EF is more individualized. Patients with a high anticipated pacing burden, baseline conduction abnormalities, or early evidence of pacing-related dysfunction may be considered for a physiologic pacing approach before substantial remodeling occurs. The decision should be based on clinical risk rather than EF alone.
A broad electrophysiology perspective is valuable when pacing is part of a complex arrhythmia history. For example, patients with ventricular tachycardia and structural disease may require coordinated decisions about ablation, defibrillator therapy, and pacing; reviews of epicardial ablation techniques illustrate how procedural planning depends on anatomy, substrate, and long-term rhythm management.
Monitoring Function Beyond Ejection Fraction
Echocardiography remains central to follow-up, but serial EF should be complemented by other measurements. Global longitudinal strain may identify subclinical deterioration before a meaningful EF reduction occurs. Left atrial volume, transmitral flow, tissue Doppler indices, pulmonary pressures, and right ventricular function can help explain symptoms that are not reflected by the left ventricular EF.
Device interrogation provides essential context. Clinicians should review ventricular pacing percentage, paced QRS duration, atrial arrhythmia burden, rate response, heart rate trends, lead function, and stored episodes. A rising pacing burden or progressive QRS widening may prompt closer imaging surveillance. Changes in activity levels, thoracic impedance, or patient-reported exertion can add useful longitudinal information where available.
Symptoms should be interpreted with care. Fatigue, reduced walking distance, exertional dyspnea, edema, and orthopnea may indicate pacing-related dysfunction, but they can also arise from pulmonary disease, ischemia, anemia, deconditioning, chronotropic incompetence, or medication effects. A structured evaluation prevents premature attribution to the pacemaker and supports targeted intervention.
| Clinical feature | Potential concern | Useful assessment | Possible response |
|---|---|---|---|
| High right ventricular pacing burden | Dyssynchrony and adverse remodeling | Device interrogation, paced QRS, serial echocardiography | Minimize unnecessary pacing or consider physiologic pacing |
| New exertional dyspnea with preserved EF | Diastolic dysfunction, poor AV timing, or chronotropic limitation | Doppler study, exercise assessment, programming review | Optimize settings and investigate alternative causes |
| Declining global longitudinal strain | Early myocardial dysfunction | Speckle-tracking echocardiography | Intensify surveillance and review pacing strategy |
| Atrial fibrillation after implantation | Loss of atrial contribution and irregular filling | Device diagnostics, ECG, rhythm monitoring | Address rhythm control, rate control, and anticoagulation |
| Widening paced QRS | Less coordinated ventricular activation | Twelve-lead ECG and lead review | Assess lead position, capture, and conduction system options |
| Persistent symptoms despite stable imaging | Functional limitation without obvious remodeling | Exercise testing, laboratory evaluation, comorbidity review | Treat the underlying cause and reassess pacing parameters |
Special Considerations In HFpEF
Patients with heart failure with preserved EF (HFpEF) are particularly sensitive to changes in filling time and ventricular interaction. Their symptoms often reflect elevated filling pressures, impaired relaxation, arterial stiffness, or limited ability to increase stroke volume during activity. A pacing rate that is adequate at rest may fail to meet demand during exertion if chronotropic response is impaired.
Atrial systole can make an important contribution to ventricular filling in patients with stiff ventricles. Loss of atrial contraction during persistent atrial fibrillation, or poorly timed ventricular pacing during sinus rhythm, may therefore produce a disproportionate clinical effect. Device programming should account for age, activity, atrial rhythm, PR interval, and symptoms rather than relying on nominal settings.
Right ventricular function and ventricular interdependence also deserve attention. Excessive right ventricular pacing can alter septal motion and affect left ventricular filling, while pulmonary hypertension and tricuspid regurgitation may worsen after lead implantation. Assessment of the entire circulation is more informative than concentrating exclusively on LVEF.
Applying A Patient-Centered Follow-Up Plan
Before implantation, clinicians should estimate the likelihood of substantial ventricular pacing and document baseline electrical and mechanical function. A 12-lead ECG, echocardiogram, symptom profile, rhythm history, and anticipated conduction status provide a foundation for later comparison. In selected patients, strain imaging or cardiac magnetic resonance may clarify myocardial reserve and scar burden.
After implantation, early review should confirm capture, lead integrity, programmed intervals, pacing percentage, and symptom response. A later assessment should compare paced QRS duration, ventricular volumes, EF, strain, atrial size, and functional capacity with baseline findings. The timing of repeat imaging can be individualized, but new symptoms or a substantial rise in pacing burden should prompt earlier review.
Treatment decisions should balance expected benefit with procedural risk. Reprogramming is often the least invasive first step, while a lead revision or upgrade requires a clear clinical rationale. Conduction system pacing may be attractive when conventional pacing is likely to be harmful, but it should be offered within a framework that includes operator experience, patient anatomy, venous access, infection risk, and future device needs.
Practical Priorities For Clinical Care
- Estimate ventricular pacing burden before implantation and reassess it during every meaningful device review.
- Use paced QRS duration, strain, diastolic indices, and symptoms alongside EF to detect early dysfunction.
- Optimize atrioventricular timing and rate-response settings when fatigue, breathlessness, or exercise intolerance develops.
- Consider conduction system pacing or resynchronization in carefully selected patients at elevated risk of pacing-related remodeling.
- Investigate non-pacing causes of symptoms, including ischemia, anemia, pulmonary disease, valve disease, atrial fibrillation, and medication effects.
Research in this area continues to refine which patients benefit from physiologic pacing while ventricular function is still preserved. Prospective studies that combine imaging biomarkers, device data, exercise performance, and patient-reported outcomes may improve risk prediction. Clinicians and investigators can find relevant educational resources, current research, and publication information through the Journal of Arrhythmia contact page.
The central clinical principle is straightforward: preserved EF should be treated as a starting point for surveillance, not proof that pacing is physiologically neutral. Thoughtful lead selection, individualized programming, and multimodal follow-up can protect cardiac performance while addressing the rhythm problem that made pacing necessary. Explore current evidence in cardiac electrophysiology and apply these principles to patients whose symptoms, device data, or imaging suggest that pacing deserves closer attention.