What is the main source of energy for cardiac muscle?

RRB Staff Nurse Mumbai-2015

Biochemistry & Nutrition

Easy

Appeared in: RRB Staff Nurse Mumbai-2015

Explanation

The heart is a highly aerobic organ that requires a constant supply of energy to function continuously.
Under normal resting conditions, the primary fuel source for cardiac muscle is the oxidation of fat (specifically free fatty acids).
Fatty acids are very energy-dense and provide approximately 60% to 90% of the ATP (energy) required by the resting heart.
This preference for fatty acids ensures a reliable and efficient energy supply for continuous cardiac contraction.

Option A: While glucose is an important energy source for the heart, it is secondary to fatty acids under normal resting conditions, contributing only about 10% to 40% of the total energy.
Option C: Proteins and their building blocks, amino acids, are not a primary or significant source of energy for the heart under normal physiological conditions. Their main role is structural and functional.
Option D: Lactic acid (lactate) is not the main source of energy for the heart at rest. It is a substrate that the heart can use, but its contribution is variable and generally low in a resting state.

Visual 1: Diagram: A pie chart showing the percentage contribution of different fuel sources (Fatty Acids, Glucose, Lactate/Ketones) to cardiac energy metabolism at rest. This visually reinforces the dominance of fatty acids.
Visual 2: Flowchart: Illustrating the metabolic pathways within a cardiomyocyte, showing how fatty acids, glucose, and lactate are converted to Acetyl-CoA to enter the Krebs cycle and produce ATP.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Cardiac muscle metabolism and primary fuel sources as background academic context rather than a clinical decision trigger.
Understanding cardiac fuel preference is crucial in managing ischemic heart disease. During a heart attack (myocardial infarction), limited oxygen impairs fatty acid oxidation, forcing the heart to rely on less efficient anaerobic glycolysis of glucose, which leads to lactic acid buildup and reduced ATP production.
In heart failure, the heart's metabolism often shifts away from fatty acid oxidation towards more glucose utilization, a change that is a target for some investigational therapies.
What if? If a patient has uncontrolled type 1 diabetes with ketoacidosis, the heart adapts to use the abundant ketone bodies as a major fuel source, sometimes even preferring them over fatty acids and glucose.

How to Approach the Question

This is a factual recall question about organ-specific metabolism.
First, identify the key terms in the question: 'main source of energy' and 'cardiac muscle'.
Recall the unique metabolic profile of the heart. Unlike the brain (which prefers glucose), the heart has a strong preference for a different fuel at rest.
Remember that the heart's continuous, high-energy demand is best met by the most energy-dense fuel available, which is fat (fatty acids).
Evaluate the options: Glucose and lactate are used, but are secondary to fats at rest. Protein is a structural component, not a primary fuel.
Select the option representing the fuel source that provides the largest percentage of energy to the heart in a resting state.

Concept Tested & Keywords

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