The term "Schirm" would appear to refer to the shape of the device. Schirm can also be translated as shield (cf. Reuter/Reuter, WB Medizin), and again, a shield has a similar shape.

For a relatively generic term, I'd use Amplatzer occluder or Amplatzer occlusion device.

See the illustratins in these 2 references:
[PDF] www.smw.ch/pdf/2000_18/2000-18-148.pdf
... Jahren [2035] und 7 Kinder proximale Schirm im pulmonalen Ende des PDA (Abb ... Schirme),
2 «Coils» (Abb. 1), 2 «Amplatzer-Devices» (Abb. möglich, falls die ...
Text version - Ähnliche Seiten

www.aeksh.de/SHAE/med_wissen/012000/seite_33.htm
(The picture shown in this particular reference looks very much like an umbrella)

A special device called, Amplatzer, would be delivered through the catheter at the site of the defect and the hole sealed. The dumb-bell shaped device was made of nitinol mesh covered with dacron and expanded to completely occlude the defect, he added.
www.indiaserver.com/thehindu/1999/03/31/stories/0431210l.ht...

and Amplatzer duct occlusion devices (SS 1903b), 1391. ... detector (DirectRay(tm)) and conventional screen-film systems (SS 513), 416. ...
www.ecr.org/T/ECR99/sciprg/aux99l.htm

Here are some Google hits:

"Amplatzer Septal Occluder

The Amplatzer Septal Occluder is a percutaneous, transcatheter, atrial septal defect closure device designed for the occlusion of atrial septal defects in secundum position."

"...covers transcatheter closure of atrial septal defects (ASDs) using the Amplatzer septal occluder when the ASD diameter measured by echocardiography is less ... "

"Schirm" always makes reference to a protective instrument, also in the sense of "screening" or "warding off".

"Schirm" always makes reference to a protective instrument, also in the sense of "screening" or "warding off". Strictly speaking, should it not be anti-occlusion device? In this case it could be simply a "stent", which opens like an umbrella, the meaning of which is the German "Schirm".