Lacosamide (Vimpat) is a medication used to manage partial-onset seizures in adults and children. While effective as an anti-epileptic drug, it can affect the heart’s electrical system, influencing the speed and coordination of the heart’s rhythm. Because of this potential cardiac safety profile, monitoring and a careful assessment of individual risk factors are important parts of treatment.
Understanding How Lacosamide Affects Heart Rhythms
Lacosamide’s influence on the heart centers on its ability to alter the timing of the electrical signals that regulate the heartbeat. The most consistently observed effect is the prolongation of the PR interval, which represents the time it takes for an electrical impulse to travel from the atria, the heart’s upper chambers, to the ventricles, the lower chambers. This delay in electrical communication is typically dose-dependent, meaning higher doses are more likely to cause a greater change in the interval length.
A prolonged PR interval can manifest as a first-degree atrioventricular (AV) block. Although first-degree AV block often causes no symptoms, more significant conduction delays, such as second- or third-degree AV block, have been reported in rare cases and can lead to a slow heart rate, or bradycardia. The Food and Drug Administration (FDA) has noted these potential cardiac conduction abnormalities as a risk associated with the drug. Some patients have also experienced other rhythm disturbances like atrial fibrillation or flutter, especially those with pre-existing heart conditions or diabetic neuropathy.
The Electrical Mechanism Behind Cardiac Effects
The cardiac effects of lacosamide occur because the drug interacts with voltage-gated sodium channels, which are present in both nerve cells and heart muscle tissue. These channels allow sodium ions, which carry electrical charge, to enter the cell and propagate an electrical signal. Lacosamide works by selectively enhancing the slow inactivation of these sodium channels.
Enhancing slow inactivation means the drug holds the sodium channels in a closed state for a slightly longer duration than normal. In the heart’s conduction system, particularly the atrioventricular (AV) node, this action subtly disrupts the swift, synchronized flow of sodium ions needed for rapid signal transmission. This minor interference with the normal cardiac electrophysiology leads to the measurable delay in the electrical signal passing through the heart, which is recorded as the PR interval prolongation.
Factors That Increase Vulnerability
Several patient characteristics and co-existing medications can increase the risk of experiencing heart-related side effects from lacosamide. Pre-existing cardiac conditions, such as AV block, sick sinus syndrome, or severe heart disease like heart failure, make the heart more susceptible to the drug’s conduction-slowing effects. Patients with structural heart disease or a genetic predisposition to heart rhythm problems, known as sodium channelopathies, are also at higher risk.
Advanced age is another factor, as older adults may have slower drug clearance and an increased incidence of underlying cardiac issues. Impaired kidney or liver function can also lead to higher concentrations of lacosamide remaining in the bloodstream for longer periods, intensifying the drug’s impact on the heart. Furthermore, taking other medications that also prolong the PR interval, such as beta-blockers or calcium channel blockers, can have an additive effect, compounding the risk of a significant conduction delay.
Safety Monitoring and When to Seek Medical Attention
To manage potential cardiac adverse effects, healthcare providers recommend specific monitoring procedures before and during lacosamide treatment. Obtaining a baseline electrocardiogram (ECG) is suggested before starting the medication to check for any pre-existing conduction abnormalities. Follow-up ECGs are important after the dosage is increased or when the drug reaches a steady-state level in the body to monitor for significant PR interval prolongation.
Patients should watch for symptoms that could indicate a serious conduction issue and necessitate immediate medical consultation. These warning signs include new-onset dizziness, lightheadedness, or feeling faint, especially when standing up. Other symptoms requiring prompt attention are palpitations, which feel like a fluttering or pounding in the chest, and severe fatigue or shortness of breath. Patients must never stop taking lacosamide abruptly without first consulting their healthcare provider, as this can lead to an increase in seizure activity.