Paramedic interpretation of prehospital lead-II ST-segments

OBJECTIVE

To determine the reliability of ST-segment interpretation by paramedics from lead-II rhythm strips obtained in the prehospital setting.

DESIGN

Prospective, blinded study of 127 patients transported by an urban/rural emergency medical services system with complaints consistent with ischemic heart disease.

METHODS

Emergency department physicians asked emergency medical technician-paramedics (EMT-P) via radio to evaluate ST-segments for elevation or depression and grade it as "mild," "moderate," or "severe." Then, this rhythm strip was interpreted blindly by emergency physicians who also interpreted the lead-II obtained from a 12-lead electrocardiogram (ECG) obtained in the emergency department (ED). The field interpretation was compared with the subsequent readings and the final in-patient diagnosis using positive predictive value (PPV), negative predictive value (NPV), and the Kappa statistic. Markedly discrepant interpretations were analyzed separately.

RESULTS

Using physician interpretation as the reference standard, paramedic interpretation of the lead-II ST-segments obtained in the prehospital setting was correct (within +/- 1 gradation) in 113 out of 127 total cases (89%). Of 105 patients for whom final hospital diagnosis was available, the ST-segment on the rhythm strip obtained in the prehospital setting, had a positive predictive value of 74% and a negative predictive value of 85% for myocardial ischemia or myocardial infarction (MI) (p < 0.001, Kappa = 0.59). Discordant interpretations between the paramedics and emergency physicians often were related to a basic misunderstanding of rhythm strip morphology.

CONCLUSION

Field interpretation of ST-segments by paramedics is fairly accurate as judged both by emergency physicians and correlation with final patient outcome, but its clinical utility is unproved. A small but clinically significant number of outliers, consisting of markedly discrepant false positives, reflects paramedic uncertainty in identifying the deviations of the ST-segment.

Expression of ricin B chain in Spodoptera frugiperda

DNA encoding ricin B chain was derived from preproricin genomic DNA and ligated into the baculovirus transfer vector, pAcGP67A. Co-transfection of Spodoptera frugiperda Sf9 cells with BaculoGold DNA was followed by limiting dilution purification of recombinant baculovirus. Infection of SF9 cells at a multiplicity of infection of 1 in the presence of 25 mM lactose produced 3 mg/l of soluble, glycosylated, 34 kDa protein immunoreactive with monoclonal and polyclonal antibodies to ricin B chain. The recombinant ricin B chain had similar lectin-binding activity to plant ricin B chain. The recombinant protein reassociated with ricin toxin A chain similarly to ricin toxin B chain and the recombinant heterodimers had similar cell cytotoxicity to ricin.

Expression of oligohistidine-tagged ricin B chain in Spodoptera frugiperda

DNA encoding ADPGH6G was fused to the 5'-end of RTB DNA and subcloned as a BamHI-EcoRI DNA cassette into the baculovirus transfer vector, pAcGP67A. Spodoptera frugiperda Sf9 cells were cotransfected with pAcGP67A-ADPGH6G-RTB DNA and BaculoGold AcNPV DNA, and recombinant baculovirus was isolated by two cycles of limiting dilution assay followed by dot blot analysis with 32P-dCTP random primer labeled RTB DNA. Recombinant virus was purified and amplified to obtain stocks at titers of 10(7) infectious particles/mL. Sf9 cells grown in serum-free medium were then infected at an moi of 3 in the presence of 25 mM alpha-lactose. After 5 days, supernatants and cell pellets were harvested and assayed by an asialofetuin ELISA for recombinant RTB protein. Fusion RTB protein was produced in the supernatant at 5 mg/L and in the cell pellet at 1 mg/L. Recombinant protein was purified to > 80% homogeneity using either a monoclonal antibody affinity matrix with alkaline elution or a Ni(2+)-NTA matrix with imidazole elution. The purified protein bound asialofetuin similarly to plant RTB. N-terminal sequencing confirmed the oligohistidine tag. SDS-PAGE confirmed the 1,000 Da increase in mass relative to "wild-type" recombinant RTB produced in Sf9 cells. Immunoblots confirmed reactivity with polyclonal and monoclonal antibodies to plant RTB. The fusion protein reassociated with plant RTA similarly to plant RTB.(ABSTRACT TRUNCATED AT 250 WORDS)