The human heart can continue beating even when separated from the body. This capability stems from the organ’s inherent electrical system and specific conditions required for its function, both naturally and through medical intervention.
The Heart’s Internal Rhythms
The heart’s capacity to beat independently stems from its intrinsic electrical system, not direct signals from the brain. Specialized cells in the sinoatrial (SA) node, the heart’s natural pacemaker, govern this system. The SA node, located in the upper right chamber, generates regular electrical impulses that spread throughout the cardiac muscle.
These electrical signals cause the heart’s chambers to contract in a coordinated rhythm, pumping blood. While the brain and nervous system can influence heart rate, they do not initiate each beat. The SA node continuously produces these action potentials, allowing the heart to maintain its pumping action even after being disconnected from the body.
Key Factors for Heart Survival
Without external support, a heart removed from the body can beat for only a short duration, typically a few minutes. The most immediate factor limiting its survival is the rapid depletion of oxygen. Heart cells require a constant oxygen supply for contraction, and without blood flow, this supply quickly vanishes.
Temperature influences how long the heart remains viable. Warmer temperatures accelerate metabolic processes and energy consumption, leading to faster deterioration. Conversely, colder temperatures slow these activities, preserving the heart’s energy and delaying cellular damage. While glucose and other nutrients are important for cellular function, oxygen deprivation is the primary immediate constraint.
Heart Preservation in Medicine
Medical science employs techniques to extend a donor heart’s viability outside the body for transplantation. Static cold storage is a widely used method, involving rapidly cooling the heart to reduce its metabolic rate and oxygen demand. This process, known as cold ischemia, slows cellular degradation.
Specialized preservation solutions, such as University of Wisconsin (UW) solution, Celsior, and Custodiol (HTK), are flushed through the heart. These solutions provide essential nutrients, protect cells from damage, and buffer against metabolic waste products. Using these methods, a donor heart can be preserved for 4 to 6 hours for transplantation.
More advanced techniques, like machine perfusion, further extend this preservation window by keeping the heart metabolically active. In machine perfusion systems, the heart is continuously perfused with an oxygenated, blood-based solution, allowing it to remain viable for over 12 hours in some cases. This technology extends transport time and allows for continuous assessment of the heart’s function before transplantation.