Effects of Body Mass Index on the Hyperemic Response to Regadenoson

We will test the hypothesis that a single dose of Regadenoson will produce equivalent degrees of coronary hyperemia in patients of widely different body size. This will be a prospective, open-label, comparative trial using MRI to measure myocardial perfusion reserve (ratio of myocardial blood flow with vasodilator to myocardial blood flow at rest) during sequential administration of the coronary vasodilators adenosine and regadenoson. Non-invasive MRI measurements of resting myocardial blood flow, and sequential measurements of blood flow during adenosine infusion (weight adjusted dosing) and then blood flow during regadenoson infusion (single, fixed dose. Blood flow measurements will be obtained sequentially and in the same sequence in each subject during a two hour MRI exam. 32 subjects will be recruited for this study. The first 2 will be for testing of the protocol. Inclusion criteria: 2 subjects for initial protocol evaluation, then 30 subjects with body mass index (BMI) between 18 and 40. Exclusions are pregnancy, renal dysfunction and claustrophobia.

Introduction: Regadenoson (Lexiscan) is currently recommended for use as a targeted vasodilator in myocardial perfusion studies and is available as a single, fixed dose for all patients. Here we propose to compare the hyperemic response measured with MRI in subjects with a wide range of BMI 18-40.

MRI is an ideal test to compare the effects of regadenoson in patients with different body mass indices (BMIs). No radiation is used and multiple perfusion tests can be performed in close temporal sequence. Importantly, a number of researchers have shown the ability to obtain quantitative stress and rest myocardial blood flow values in the heart with MR imaging. This allows the calculation of myocardial perfusion reserve (MPR). Flow reserve measurements also can be done with dynamic PET, but not with SPECT. PET has the disadvantage of radiation exposure.

Regadenoson may be a more desirable agent for use with MRI than is adenosine. Adenosine requires the use of 2 intravenous lines, and the use of either a specialized, expensive, MRI-compatible infusion pump to deliver the drug, or long lengths of tubing to run to a pump outside the scanner room. Neither solution is ideal. Regadenoson does not require any such pumps or the starting of a second i.v.. The work here would accomplish 2 goals: 1) to demonstrate the feasibility of performing quantitative MRI perfusion measurements with regadenoson, and 2) to test whether a single dose of regadenoson produces maximal coronary hyperemia across a wide range of body sizes.

Study Design: This will be a prospective, open-label, study. The design is single group, one arm, 2 interventions in which we will compare MPR measured sequentially during adenosine and regadenoson using MRI. Non-invasive MRI measurements of resting flow, flow at adenosine stress, and flow at regadenoson stress will be obtained sequentially in each subject during a single two hour MRI exam. Each drug will be given in the same order to all subjects.

32 subjects will be recruited for this study. The first two subjects will be imaged only with resting perfusion, in order to determine optimal acquisition parameters for the study, and will not be used in the analysis. The main outcome measure is MPR with each agent.

Eligibility Criteria:
Inclusion Criteria:

* BMI 20-40 kg/m\^2
* age 18-88

Exclusion Criteria:

* critically ill patients, patients on ventilators, patients with hypotension, asthmatics, and other patients whose medical care or safety may be compromised from undergoing an MRI examination will be excluded.
* Patients with claustrophobia will also be excluded.
* Also, anyone with contraindications to MRI (pacemaker, ICD, metal implants), pregnant subjects, minors, and prisoners will be excluded from this study.
* If subjects are over 60 or have any suspicion of abnormal kidney function, a blood test to determine GFR will be performed prior to imaging.
* Subjects with GFR \< 30 will be excluded from the study.