The Guanacaste Volcanic Arc Sliver of Northwestern Costa Rica.

Recent studies have shown that the Nicoya Peninsula of northwestern Costa Rica is moving northwestward ~11 mm a-1 as part of a tectonic sliver. Toward the northwest in El Salvador the northern sliver boundary is marked by a dextral strike-slip fault system active since Late Pleistocene time. To the southeast there is no consensus on what constitutes the northern boundary of the sliver, although a system of active crustal faults has been described in central Costa Rica. Here we propose that the Haciendas-Chiripa fault system serves as the northeastern boundary for the sliver and that the sliver includes most of the Guanacaste volcanic arc, herein the Guanacaste Volcanic Arc Sliver. In this paper we provide constraints on the geometry and kinematics of the boundary of the Guanacaste Volcanic Arc Sliver that are timely and essential to any models aimed at resolving the driving mechanism for sliver motion. Our results are also critical for assessing geological hazards in northwestern Costa Rica.

Acute Management of Refractory and Unstable Pediatric Supraventricular Tachycardia.

OBJECTIVE: To characterize the management of acute pediatric supraventricular tachycardia (SVT), placing special emphasis on infants, patients refractory to adenosine (refractory SVT), and patients with hypotension, poor perfusion, or altered mental status (unstable SVT). STUDY DESIGN: Retrospective cohort study of patients 0-18 years of age without congenital heart disease who presented to our pediatric hospital from January 2003 to December 2012 for the treatment of acute SVT. Multiple logistic regression was applied to identify whether age was a risk factor for different SVT therapies. Model fit and residuals also were examined. RESULTS: We identified 179 episodes for SVT. First dose of adenosine was effective in 72 (56%) episodes, and a second dose was effective in 27 of 54 (50%) episodes, leaving 27 (15%) episodes with refractory SVT. The response to the first dose of adenosine increased proportionally with age (OR 1.13, 95% CI 1.05-1.2). Only 1 of 17 episodes in infants responded to the first dose of adenosine. Refractory SVT was more frequent in infants vs older children (χ2 = 5.9 [1 df], P = .01). Unstable SVT was present in 13 episodes and was treated with adenosine and antiarrhythmics. Synchronized cardioversion was performed on 3 patients, 2 patients with unstable SVT, and 1 with refractory SVT. CONCLUSION: In children with SVT, young age is associated with decreased response to the first dose of adenosine and increased odds of adenosine-refractory SVT. In the treatment of unstable SVT, medical management with various antiarrhythmics before cardioversion may have a role in a subset of patients. Synchronized cardioversion rarely is performed for acute SVT.