UMEM Educational Pearls

Just scan ‘em? Should everyone with unexplained out-of-hospital cardiac arrest get whole-body CT/CTA?

Background: Determination of the cause and subsequent management of out-of-hospital cardiac arrest is clinically challenging in those patients who survive to hospital admission without a clear diagnosis. CT imaging is often used to ascertain the cause of an arrest, find potentially intervenable etiologies, and assess for neurological injury but this practice and diagnostic yield are inconsistent and not well studied.

Study and Methods: The CT FIRST study is a single center cohort study using head-to-pelvis contrasted triple phase CT within 6 hours for cardiac arrest without obvious cause (sudden death CT or SDCT) studied in a before and after manner compared to usual care to determine the influence of early pan CT on diagnostic yield and outcomes. The primary outcome was diagnostic yield following SDCT and secondary outcomes include time to diagnosis of “time critical” findings and survival to discharge.  104 patients undergoing SDCT were compared to 143 historical controls after study implementation. Patients deemed to have a clear cause or are too unstable for CT were among exclusions.

Results: For the primary outcome of diagnostic yield: 92% of SDCT cohort received a separately adjudicated diagnosis for the arrest compared to 75% of the control cohort (p = 0.001). With time to such diagnosis of 3.1hrs in SDCT versus 14.1hrs of controls, with 39% versus 17% being made by CT. Time critical diagnoses including MI, PE, aortic dissection, pneumonia, embolic or hemorrhagic CVA and abdominal catastrophe were identified in 32% versus 24% (non significant) of the cohorts with delay greater than 6hrs to diagnosis reported in 12% in SDCT versus 62% in usual care (p=0.001).

There was no difference in survival to hospital discharge and no difference in safety measures and no evaluation reporting changes to and timing of patient managements.

The SDCT cohort had 100% scan rate compared to usual care where 81% received early head CT with chest CT and abdominal CT done in 36% and 18%, respectively. Notably there were no CT reported diagnoses that were later reversed on adjudication in either cohort. The planned economic and resource analysis was not reported in this study.

Discussion: There was a notable increase in diagnostic yield based on the study design with faster time to potentially time sensitive diagnoses.  There were, however, no differences in mortality and it was not clear the degree to which these diagnoses influenced patient management given the limited numbers in this study and diverse set of diagnoses associated with cardiac arrest. Like previous studies of selective versus whole body CT in trauma populations, the increased diagnostic yield was not associated with reduced mortality or reported changes in management. The yield numbers suggest increased confidence by exclusion as much as positive findings of the cause. As always, the caveats of a relatively small single center before-and-after cohort study apply. 

An interesting twist is that no CT diagnosis pointing to the cause of the arrest was reversed on subsequent review, this may speak to the accuracy of modern CT and radiology interpretation, but I sometimes worry that this can also be reflective of diagnostic fixation, especially with “objective” tests, as well as nihilism about the utility of clinical diagnosis.

That said, non-selective CT has many potential benefits for many critically ill and unexaminable populations with diagnostic uncertainty, as demonstrated here, which must be balanced against risks of intrahospital transport and of resource utilization as we do not yet have clear data that patients benefit from the practice despite increased diagnostic yield.

 

References