Stress-only Tc-99m myocardial perfusion imaging in an emergency department chest pain unit.

BACKGROUND: Stress-only myocardial perfusion imaging (MPI) saves time by eliminating rest imaging, which is important for emergency department (ED) throughput but has not been studied in an ED population. STUDY OBJECTIVE: To determine the prognosis of a normal stress-only MPI study compared to a normal rest-stress MPI and establish its effectiveness in an ED setting. METHODS: All patients evaluated in the ED over 6.5 years who underwent a stress-only technetium-99m gated MPI were compared to those who had a rest-stress study. All-cause mortality was determined using the Social Security Death Index. Survival was analyzed in patients with normal and abnormal MPI results. RESULTS: A total of 4145 studies (2340 stress-only, 1805 rest-stress) were performed. Patients' average age was 57.9 years, 38.5% were male, and most had an intermediate or low pretest risk of coronary artery disease (87.7%). Average follow-up was 35.9 ± 20.9 months. In patients with normal perfusion, at 1 year of follow-up there were 11 deaths in the stress-only group (0.5% 1-year mortality), and 13 deaths in the rest-stress cohort (1.1% 1-year mortality). At the end of follow-up, the stress-only group had a lower all-cause mortality (p < 0.0001) and similar risk adjusted all-cause mortality (p = 0.10) than the rest-stress cohort. Patients with abnormal perfusion demonstrated the expected differential prognosis based on total perfusion deficits in both groups. CONCLUSIONS: A normal stress-only MPI study has a benign 1-year prognosis similar to a rest-stress study when performed in the ED. The ability to triage patients more rapidly and reduce radiation exposure represents an attractive alternative for low-risk patients.

Repetitive firing triggers clustering of Kv2.1 potassium channels in Aplysia neurons.

The Kv2.1 gene encodes a highly conserved delayed rectifier potassium channel that is widely expressed in neurons of the central nervous system. In the bag cell neurons of Aplysia, Kv2.1 channels contribute to the repolarization of action potentials during a prolonged afterdischarge that triggers a series of reproductive behaviors. Partial inactivation of Aplysia Kv2.1 during repetitive firing produces frequency-dependent broadening of action potentials during the afterdischarge. We have now found that, as in mammalian neurons, Kv2.1 channels in bag cell neurons are localized to ring-like clusters in the plasma membrane of the soma and proximal dendrites. Either elevation of cyclic AMP levels or direct electrical stimulation of afterdischarge rapidly enhanced formation of these clusters on the somata of these neurons. In contrast, injection of a 13-amino acid peptide corresponding to a region in the C terminus that is required for clustering of Kv2.1 channels produced disassociation of the clusters, resulting in a more uniform distribution over the somata. Voltage clamp recordings demonstrated that peptide-induced dissociation of the Kv2.1 clusters is associated with an increase in the amplitude of delayed rectifier current and a shift of activation toward more negative potentials. In current clamp recording, injection of the unclustering peptide reduced the width of action potentials and reduced frequency-dependent broadening of action potentials. Our results suggest that rapid redistribution of Kv2.1 channels occurs during physiological changes in neuronal excitability.