From the Guidelines
Isoproterenol is effective in shortening the QT interval by increasing heart rate and accelerating cardiac repolarization, and its use is recommended in emergency situations for patients with torsades de pointes or other dangerous arrhythmias associated with QT prolongation, as stated in the 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death 1.
Mechanism of Action
Isoproterenol works by stimulating beta-adrenergic receptors in the heart, which increases calcium influx and enhances the outward potassium currents responsible for repolarization.
Dosage and Administration
When administered intravenously, isoproterenol is typically dosed at 2-10 mcg/min, titrated to effect, as mentioned in the 2010 American Heart Association guidelines for cardiopulmonary resuscitation and emergency cardiovascular care 1.
Side Effects and Precautions
Side effects of isoproterenol include tachycardia, hypotension, tremors, and anxiety. Isoproterenol should be used with caution in patients with coronary artery disease, as it increases myocardial oxygen demand. Continuous cardiac monitoring is essential during administration.
Clinical Use
The QT-shortening effect of isoproterenol occurs rapidly after administration begins and diminishes when the medication is discontinued, making it a temporary intervention rather than a long-term solution for QT prolongation. According to the 2018 guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death, isoproterenol can be effective in restoring/maintaining sinus rhythm in the setting of electrical storm with refractory VF and short QT syndrome 1.
From the Research
Isoproterenol's Effect on QT Interval
- Isoproterenol has been shown to shorten the QT interval in various studies 2, 3, 4.
- In a study published in Circulation, isoproterenol shortened the ventricular paced QT interval from 386 +/- 8 ms to 348 +/- 6 ms (p < 0.001) 2.
- Another study published in the International Journal of Cardiology found that isoproterenol infusion shortened the QT interval and decreased the Transmural Dispersion of Repolarization (TDR) in a patient with Amiodarone-induced Long QT Syndrome (LQTS) 3.
- Isoproterenol has also been used to prevent torsades de pointes in patients with acquired LQTS, and it has been shown to shorten the QT interval and eliminate pauses that precipitate torsades 4.
Mechanism of Action
- The exact mechanism of isoproterenol's effect on the QT interval is not fully understood, but it is thought to be related to its ability to increase the generation of signals from the beta-Adrenergic Receptor (beta-AR) and enhance the I(Ks) function 3.
- Isoproterenol may also affect the ventricular effective and functional refractory periods, which can contribute to its shortening effect on the QT interval 2.
Clinical Implications
- Isoproterenol's ability to shorten the QT interval makes it a useful tool in the treatment of torsades de pointes and other arrhythmias associated with LQTS 4.
- However, its use should be carefully considered, as it can also have pro-arrhythmic effects in certain situations 5, 6.
- Further studies are needed to fully understand the effects of isoproterenol on the QT interval and its clinical implications.