Medical device history (cardiology): Identify Dr. Paul Zoll's 1952 invention in Massachusetts. Full question: What did cardiologist Dr. Paul Zoll invent in 1952 in Massachusetts—an innovation used to maintain a patient's heart rhythm noninvasively? Choose the correct option.

Given data

• Year and place: 1952, Massachusetts.
• Inventor: Dr. Paul Zoll (cardiologist).
• Domain: Devices to manage cardiac rhythm.

Concept/Approach
Zoll pioneered external transthoracic cardiac pacing, applying electrical impulses through chest electrodes to maintain heart rate—decades before fully implantable pacemakers became routine.

Why other options are incorrect
ICD: implantable defibrillators arrived later. Coronary stent: 1980s innovation. Heart-lung machine: developed by Gibbon and others earlier in the 1950s, but not Zoll's 1952 Massachusetts milestone.

Final Answer
External cardiac pacemaker (noninvasive transthoracic pacing).