Could ivabradine challenge be helpful for the diagnosis of intermittent sinoatrial node dysfunction in suspected patients?

Sinoatrial node dysfunction (SND) is an important cause of syncope in the elderly. Though the diagnosis can be relatively straightforward in the persistent form of SND, it can be elusive when the dysfunction is intermittent. For intermittent SND, the diagnosis may require prolonged electrocardiographic recordings with an external or internal loop recorder, or an invasive electrophysiologic study. Ivabradine, an If inhibitor that slows sinoatrial discharge rate, is widely used for the treatment of chronic angina or heart failure. Though the drug is contraindicated in patients with known SND as it may exacerbate symptoms, we propose that a simple ivabradine suppression test, followed by a 24-h monitorization of heart rhythm, could be valuable to aid diagnosis of intermittent SND. The test we propose could be used prior to prolonged electrocardiographic monitoring in patients with suspected SND, but both the diagnostic accuracy and the safety should be evaluated with studies prior to implementation.