Usefulness of the Myocardial Infarction and Cardiac Arrest Calculator as a Discriminator of Adverse Cardiac Events After Elective Hip and Knee Surgery.

The 2014 American College of Cardiology and American Heart Association guidelines on perioperative evaluation recommend differentiating patients at low risk (<1%) versus elevated risk (≥1%) for cardiac complications to guide appropriate preoperative testing. Among the tools recommended for estimating perioperative risk is the National Surgical Quality Improvement Program (NSQIP) Myocardial Infarction and Cardiac Arrest (MICA) risk calculator. We investigated whether the NSQIP MICA risk calculator would accurately discriminate adverse cardiac events in a cohort of adult patients undergoing elective orthopedic surgery. We retrospectively reviewed 1,098 consecutive, elective orthopedic surgeries performed at Hershey Medical Center from January 1, 2013, to December 31, 2014. Adverse cardiac events were defined as myocardial infarction or cardiac arrest within 30 days of surgery. The mean estimated risk for adverse cardiac events using the NSQIP MICA risk calculator was 0.54%, which was not significantly different (p = 1) compared with the observed incidence of 0.64% (7 of 1,098 procedures). The c-statistic for discriminating adverse cardiac events was 0.85 (95% CI 0.67 to 1) for the NSQIP MICA risk calculator and 0.9 (95% CI 0.75 to 1) for the Revised Cardiac Risk Index. In conclusion, the NSQIP MICA risk calculator is a good discriminator of adverse cardiac events in patients undergoing elective hip and knee surgery, performing comparably to the Revised Cardiac Risk Index.

ExbB cytoplasmic loop deletions cause immediate, proton motive force-independent growth arrest.

The Escherichia coli TonB system consists of the cytoplasmic membrane proteins TonB, ExbB, and ExbD and multiple outer membrane active transporters for diverse iron siderophores and vitamin B12. The cytoplasmic membrane proteins harvest and transmit the proton motive force (PMF) to outer membrane transporters. This system, which spans the cell envelope, has only one component with a significant cytoplasmic presence, ExbB. Characterization of sequential 10-residue deletions in the ExbB cytoplasmic loop (residues 40 to 129; referred to as Δ10 proteins) revealed that it was required for all TonB-dependent activities, including interaction between the periplasmic domains of TonB and ExbD. Expression of eight out of nine of the Δ10 proteins at chromosomal levels led to immediate, but reversible, growth arrest. Arrest was not due to collapse of the PMF and did not require the presence of ExbD or TonB. All Δ10 proteins that caused growth arrest were dominant for that phenotype. However, several were not dominant for iron transport, indicating that growth arrest was an intrinsic property of the Δ10 variants, whether or not they could associate with wild-type ExbB proteins. The lack of dominance in iron transport also ruled out trivial explanations for growth arrest, such as high-level induction. Taken together, the data suggest that growth arrest reflected a changed interaction between the ExbB cytoplasmic loop and one or more unknown growth-regulatory proteins. Consistent with that, a large proportion of the ExbB cytoplasmic loop between transmembrane domain 1 (TMD1) and TMD2 is predicted to be disordered, suggesting the need for interaction with one or more cytoplasmic proteins to induce a final structure.

Deletion and substitution analysis of the Escherichia coli TonB Q160 region.

The active transport of iron siderophores and vitamin B(12) across the outer membrane (OM) of Escherichia coli requires OM transporters and the potential energy of the cytoplasmic membrane (CM) proton gradient and CM proteins TonB, ExbB, and ExbD. A region at the amino terminus of the transporter, called the TonB box, directly interacts with TonB Q160 region residues. R158 and R166 in the TonB Q160 region were proposed to play important roles in cocrystal structures of the TonB carboxy terminus with OM transporters BtuB and FhuA. In contrast to predictions based on the crystal structures, none of the single, double, or triple alanyl substitutions at arginyl residues significantly decreased TonB activity. Even the quadruple R154A R158A R166A R171A mutant TonB still retained 30% of wild-type activity. Up to five residues centered on TonB Q160 could be deleted without inactivating TonB or preventing its association with the OM. TonB mutant proteins with nested deletions of 7, 9, or 11 residues centered on TonB Q160 were inactive and appeared never to have associated with the OM. Because the 7-residue-deletion mutant protein (TonBDelta7, lacking residues S157 to Y163) could still form disulfide-linked dimers when combined with W213C or F202C in the TonB carboxy terminus, the TonBDelta7 deletion did not prevent necessary energy-dependent conformational changes that occur in the CM. Thus, it appeared that initial contact with the OM is made through TonB residues S157 to Y163. It is hypothesized that the TonB Q160 region may be part of a large disordered region required to span the periplasm and contact an OM transporter.