The percentage of an external current flowing in the body from arm to arm that will pass through the myocardium is about:

The correct choice indicates that approximately 0.1% of an external current flowing through the body from arm to arm will pass through the myocardium. This value highlights the relatively small proportion of electrical current that reaches the heart compared to the total current flowing through the body.

Understanding why this is the case involves knowledge of the body's electrical pathways and the resistance presented by different tissues. The myocardium is surrounded by layers of non-conductive tissue, such as skin and fat, which naturally resist the flow of electrical current. When a current enters the body, it tends to take pathways that offer the least resistance. Since the myocardium is deeper and encased by more resistive structures than superficial tissues, only a fraction of the current will ultimately affect it.

This concept is critical in biomedical engineering and safety because it underscores why low levels of current can be hazardous, especially during procedures involving electrocautery or defibrillation, where the current may inadvertently flow through the heart. Understanding these percentages is vital for the design and testing of medical equipment to ensure patient safety and effective operation.