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There are several issues involved –
Low platelet count
needs further investigation by a Haematologist...
Fast heart rate in spite of a pacemaker, especially with water in the lungs - is an indication for anti-arrhythmic drugs / and extensive investigation as to the cause – Pulmonary embolism
, atrial flutter
, VT and so on
You have not stated her personal habits, family history, or co-morbidities, even age ...which could influence the diagnosis and outcome...
The treating doctor alone can suggest based on his assessment of the situation.
Wishing speedy recovery