Imaging Left Ventricular Muscarinic Receptor Heterogeneity

Abstract

As pointed out by Mazzadi et al1 in this issue of Circulation: Cardiovascular Imaging , parasympathetic tone plays a critical role as modulator of the cardiac sympathetic nervous system in both health and disease. Decreased tone, as reflected by decreased heart rate variability (HRV), has an important role in prognosis after myocardial infarction (MI).2 HRV is also associated with worse outcome in some patients with heart failure.3,4 Sudden increases in parasympathetic tone, identified by increase in HRV, may precipitate ventricular fibrillation in selected individuals.5 Other investigators have not found any of a multitude of HRV components to be predictive of outcome.6 The predictive value of HRV is insufficient to be used alone and must be part of a multivariate assessment. Article see p 365 Given the wealth of data demonstrating that HRV and its derivatives provide useful but not highly predictive clinical information and at a relatively low cost, what added value is gained by the use of a complicated and expensive imaging method? There are limitations to measurement of HRV that generally require the patient to be in sinus rhythm without sinoatrial dysfunction, to have ≤20% ectopic beats, have good quality tracings and, ideally, at least 24 hours of recording.2 The requirement for sinus rhythm limits it application in the largest population in which it is most likely beneficial, those with heart failure. Also, imaging of presynaptic sympathetic function has been shown to better predict adverse events.6 The results of the Mazzadi et al1 study suggest that imaging of parasympathetic function also may be predictive. Probably the most important rationale for the use of imaging to measure muscarinic cholinergic function relates directly to the regional heterogeneity of myocardial perfusion and sympathetic and parasympathetic function. As noted by Mazzadi et al,1 …