From the Guidelines
Milrinone should be used with extreme caution in patients with Wolff-Parkinson-White (WPW) syndrome, as it can potentially accelerate conduction through accessory pathways, leading to dangerously rapid ventricular rates and increased risk of ventricular fibrillation. Milrinone is a phosphodiesterase-3 inhibitor that increases cardiac contractility and causes vasodilation, which can enhance conduction through the accessory pathway, bypassing the AV node's normal delay 1. This medication may increase the ventricular response during atrial fibrillation or flutter in WPW, potentially precipitating ventricular fibrillation or other dangerous tachyarrhythmias.
Key Considerations
- The risk of developing atrial fibrillation (AF) over 10 years in patients with WPW syndrome is estimated at 15% 1.
- Approximately 25% of patients with WPW syndrome have accessory pathways with short anterograde refractory periods (<250 msec), which are associated with a risk of rapid ventricular rates and ventricular fibrillation 1.
- Patients with multiple accessory pathways are also at greater risk of ventricular fibrillation 1.
Management
If milrinone must be used in a WPW patient due to heart failure or low cardiac output, close cardiac monitoring is essential, and the lowest effective dose should be employed. The typical dosing is a loading dose of 50 mcg/kg over 10 minutes followed by a continuous infusion of 0.375-0.75 mcg/kg/min, but this may need adjustment based on the patient's condition 1. Having antiarrhythmic medications readily available (such as procainamide or amiodarone) and access to emergency defibrillation equipment is prudent.
Underlying Mechanism
The underlying mechanism of concern is that milrinone's positive inotropic effects and increased sympathetic tone can enhance conduction through the accessory pathway, bypassing the AV node's normal delay and potentially leading to dangerously rapid ventricular rates 1.
Recommendations
- Catheter ablation of the accessory pathway should be considered for most symptomatic patients with AF who have WPW syndrome, particularly those with syncope due to rapid heart rate or those with a short bypass tract refractory period 1.
- Immediate electrical cardioversion should be performed to prevent ventricular fibrillation in patients with WPW in whom AF occurs with a rapid ventricular response associated with hemodynamic instability 1.
From the Research
Milrinone and Wolf Parkinson White Syndrome
- There is no direct evidence in the provided studies regarding the use of milrinone in patients with Wolf Parkinson White (WPW) syndrome.
- WPW syndrome is a disorder characterized by the presence of at least one accessory pathway that can predispose people to atrial/ventricular tachyarrhythmias and even sudden cardiac death 2.
- Management of WPW syndrome may include pharmacological treatment, such as antiarrhythmic drugs, or radiofrequency ablation 2, 3.
- The choice of treatment depends on various factors, including the presence of symptoms, the location and conduction properties of the accessory pathway, and the patient's overall health status 3, 4.
- Some studies have investigated the use of adenosine-sensitive accessory pathways in patients with WPW syndrome, which may have implications for treatment 5.
- Novel assessment methods, such as multi-extrastimulus pacing, have been proposed to better evaluate accessory pathway function in patients with WPW syndrome 6.