Early CT Abnormalities in Acute Stroke
Early CT Abnormalities in Acute Stroke
Evolution of stroke therapies appears to be paralleling the path of intervention for acute myocardial infarction. Thrombolytic therapy for acute ischemic stroke appears to be beneficial, though not without somewhat daunting risks, if administered within a six-hour time window. These authors suggest that very subtle early CT changes, termed "hypoattenuation," are associated with the greatest degree of benefit from thrombolytics (tissue plasminogen activator). Hypoattenuation denotes irreversible ischemia to a parenchymal area of the brain and appears as a small localized area in the first few minutes after onset of ischemia. Concomitant PET scanning among those patients demonstrating hypoattenuation on CT reveals that hypoattenuation is a marker for much more diffuse cerebral ischemia, indicating a large adjacent "at-risk" body of tissue, not yet infarcted. This at-risk tissue is the area most likely to be salvaged by prompt thrombolytic therapy.
Using a combination of CT and PET scanning in 23 patients clinically suffering acute strokes of less than three hours’ duration, the authors note that 90% of patients demonstrating hypoattenuation went on to develop infarcts. Of patients presenting with clinical stroke but without hypoattenuation on CT, their ischemia did not progress to infarct in more than 55% of cases. The authors comment that this finding of hypoattenuation on CT indicates an area of irreversible ischemia but that this "tip of the iceberg" may help select those individuals most likely to benefit from early reperfusion.
Grand M, et al. Lancet 1997;350: 1595-1596.
Clinical Scenario: A healthy 30-year-old woman was seen in the office for her "routine city physical." An irregular heart beat was heard on cardiac auscultation. Can you explain the irregularity of her rhythm that is seen in the figure?
Hint: The tracing in the figure was obtained at the same visit as the rhythm strip shown in last month’s ECG Reviewfrom the same asymptomatic 30-year-old woman.
Interpretation: The rhythm strip in the figure is clearly irregular. Nearly half of the beats are widened and abnormal in appearance. The easiest way to approach interpretation of this complex arrhythmia is to try to identify the underlying rhythm first; then assess each abnormal beat.
Focusing attention on lead II, it can be seen that the QRS complex of beats #1, 2, 4, 6, and 8 is narrow and preceded by a fairly similar appearing (upright) P wave with constant PR interval. This defines the underlying rhythm in the figure as sinus.
Beats #5, 7, and 9 are all preceded by premature P waves. Support that the small upright deflections in front of beats #5, 7, and 9 truly are premature P waves is forthcoming from analysis of simultaneously recorded lead III, which shows similar deflections in front of these three widened beats. This defines these widened beats as premature atrial contractions (PACs). As noted in last month’s ECG Review (Intern Med Alert 1998;20:8), most aberrant beats are conducted with a pattern of either left or right bundle branch block and/or a hemiblock. The morphologic appearance of the QRS complex of beats #5 and 9 is consistent with a bifascicular pattern of aberrancy (i.e., the S wave of beats #5 and 9 in lead I is consistent with right bundle branch block; the marked negativity in leads II and III is consistent with left anterior hemiblock). Note, however, that the QRS complex of premature beat #7 is slightly less wide than the QRS of beats #5 and 9 and that the S wave in lead I of beat #7 is missing! This is because the QRS complex of this PAC (beat #7) is conducted with a left anterior hemiblock pattern of aberrancy, but without right bundle branch block.
The final two points to explain in this tracing relate to the relative pause between beats #1 and 2, and the different morphology of premature beat #3. Once again, the lesson from last month’s ECG Review holds true: When there are some PACs, there will often be more! Careful inspection in lead III of the T wave of beat #1 shows notching that confirms the presence of a hidden and "blocked" PAC. Peaking of the T wave that precedes beat #3 in lead III confirms that beat #3 is also a PAC, in this case conducted with the bifascicular pattern of right bundle branch block and left posterior hemiblock aberration. Thus, as was the case last month, the rhythm in the figure is atrial bigeminy in which PACs are either blocked or manifest differing patterns of aberrant conduction.
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