A pacemaker is an implanted device that delivers electrical impulses to the heart, primarily to manage a slow or irregular heart rhythm. This technology influences the heart’s electrical system, affecting its mechanical pumping action. Whether the device can also improve the heart’s pumping efficiency depends entirely on the type of device and the specific heart condition it treats. The critical measurement for assessing heart function is the Ejection Fraction (EF). While some pacemakers merely maintain a safe heart rate, others are specifically designed to restore the efficiency of the heart’s pump.
Understanding Ejection Fraction
Ejection Fraction (EF) is a measurement that helps doctors assess the heart’s ability to pump blood out to the body. It is expressed as a percentage and represents the amount of blood pumped out of the main pumping chamber, the left ventricle, with each contraction. Think of the left ventricle like a sponge; the EF is the percentage of water squeezed out with every squeeze.
A healthy heart typically has an EF between 55% and 70%, meaning more than half the blood in the ventricle is ejected during a heartbeat. When the EF drops below 40%, it is considered heart failure with reduced ejection fraction. Measuring the EF is a primary way to diagnose the severity of heart failure and track the effectiveness of any treatment, including device therapy.
Standard Pacing Versus Specialized Devices
The effect a pacemaker has on Ejection Fraction depends on whether it is a standard device or a specialized system. Traditional pacemakers are designed to treat bradycardia, or a slow heart rate, by placing a lead in the right ventricle to ensure a minimum safe heart rate. This method of pacing is rate-driven, not efficiency-driven.
Standard pacing can sometimes create an unnatural electrical activation pattern, causing the ventricles to contract out of sync. Long-term pacing of the right ventricle, especially in patients who rely heavily on the device, can induce ventricular dyssynchrony. This may lead to pacing-induced cardiomyopathy, which can cause a small reduction in the Ejection Fraction over time. Specialized devices, conversely, are designed to correct mechanical synchronization issues rather than simply manage heart rate.
Cardiac Resynchronization Therapy and EF Improvement
The technology specifically designed to increase Ejection Fraction is Cardiac Resynchronization Therapy (CRT). This system uses biventricular pacing, involving three leads placed in the right atrium, the right ventricle, and a vein on the surface of the left ventricle. By pacing both the left and right ventricles simultaneously, the CRT device restores the coordinated, synchronized contraction of the heart muscle.
This synchronization is particularly beneficial for patients with heart failure who also have an electrical conduction delay, such as a Left Bundle Branch Block (LBBB) pattern. When the ventricles contract together, the heart’s pumping efficiency improves, reducing the volume of blood left behind after each beat. For suitable patients, typically those with an Ejection Fraction of 35% or less, CRT can lead to a significant increase in EF. Clinical studies report an average EF improvement of 8 to 10 absolute percentage points, for example, increasing the EF from 27% to 37% within six months.
Monitoring Results and Expected Outcomes
Following the implantation of a CRT device, a patient’s progress is carefully monitored to determine if they are a “responder” to the therapy. The primary tool for assessing improvement is a transthoracic echocardiogram, which is used to measure the Ejection Fraction and evaluate the heart’s size and function. This assessment is typically performed around three to six months after the device is activated.
A positive response is defined by an increase in Ejection Fraction and a reduction in the size of the left ventricle, known as reverse remodeling. While most patients experience functional improvement, such as better exercise tolerance, within the first few weeks, the structural changes that increase the EF take longer to develop. About 30% of patients may not show a significant increase in EF, but even non-responders can still experience an improvement in their heart failure symptoms.