Assessing the Risks Associated with MRI in Patients with a Pacemaker or Defibrillator

BACKGROUND The presence of a cardiovascular implantable electronic device has long been a contraindication for the performance of magnetic resonance imaging (MRI). We established a prospective registry to determine the risks associated with MRI at a magnetic field strength of 1.5 tesla for patients who had a pacemaker or implantable cardioverterdefibrillator (ICD) that was "non-MRI-conditional" (i.e., not approved by the Food and Drug Administration for MRI scanning). METHODS Patients in the registry were referred for clinically indicated nonthoracic MRI at a field strength of 1.5 tesla. Devices were interrogated before and after MRI with the use of a standardized protocol and were appropriately reprogrammed before the scanning. The primary end points were death, generator or lead failure, induced arrhythmia, loss of capture, or electrical reset during the scanning. The secondary end points were changes in device settings. RESULTS MRI was performed in 1000 cases in which patients had a pacemaker and in 500 cases in which patients had an ICD. No deaths, lead failures, losses of capture, or ventricular arrhythmias occurred during MRI. One ICD generator could not be interrogated after MRI and required immediate replacement; the device had not been appropriately programmed per protocol before the MRI. We observed six cases of self-terminating atrial fibrillation or flutter and six cases of partial electrical reset. Changes in lead impedance, pacing threshold, battery voltage, and P-wave and R-wave amplitude exceeded prespecified thresholds in a small number of cases. Repeat MRI was not associated with an increase in adverse events. CONCLUSIONS In this study, device or lead failure did not occur in any patient with a non-MRIconditional pacemaker or ICD who underwent clinically indicated nonthoracic MRI at 1.5 tesla, was appropriately screened, and had the device reprogrammed in accordance with the prespecified protocol.St. Jude Medical; Biotronik; Boston Scientific; Hewitt Foundation for Medical Research6 month embargo; first published: February 23, 2017This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Variable performance of individuals: the role of population density and endogenously formed landscape heterogeneity

1.   Individuals can show positive correlations in performance (e.g. growth and reproduction) through time beyond the effects of size or age. This ‘performance autocorrelation’ has been attributed previously to traits that differ among individuals or to extrinsic generators of environmental heterogeneity. 2.   A model of mobile consumers on a dynamic resource showed that consumer foraging gave rise to resource heterogeneity that in turn generated autocorrelation in growth in consumers. 3.   Resource heterogeneity and growth autocorrelation were most pronounced when consumers were poorer foragers, moving locally and with an imperfect ability to identify the highest resource cells. 4.   The model predicted that lowered population density enhanced resource heterogeneity and the strength of growth autocorrelation. 5.   Consistent with model predictions, an experiment with tidepool limpets demonstrated that autocorrelation in growth changed with population density, with individuals in lower density tidepools showing stronger temporal correlations in growth. 6.   Our model and empirical results contrast with those of previous studies with plants, where dominance and suppression increases with increasing density. 7.   Our results suggest that growth autocorrelation can occur without invoking size-dependent advantages, intrinsic trait differences or extrinsic generators of environmental heterogeneity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/74301/1/j.1365-2656.2003.00742.x.pd