Scar tissue, known as fibrosis, represents the body’s natural response to injury, where damaged tissue is replaced by a fibrous, non-contractile material. While this process provides structural support in various organs, its formation in the heart presents unique challenges. Unlike other tissues that can regenerate, the specialized muscle cells of the heart, called cardiomyocytes, have a limited capacity for self-repair. When heart muscle is damaged, it is often permanently replaced by stiff, non-functional scar tissue, significantly impacting the heart’s ability to function.
Formation of Scar Tissue in the Heart
The most common cause of scar tissue formation in the heart is a myocardial infarction, commonly known as a heart attack. During a heart attack, a blockage in the coronary arteries restricts blood flow to a region of the heart muscle, depriving it of oxygen. This lack of oxygen leads to the death of cardiomyocytes, resulting in irreversible damage.
Over several days to weeks following the injury, the dead heart muscle cells are gradually replaced by collagenous scar tissue. This healing process involves an inflammatory phase, followed by a fibrotic phase where fibroblasts, a type of connective tissue cell, proliferate and secrete proteins, primarily collagens, to form the scar. While this fibrous replacement helps maintain the structural integrity of the heart wall and prevents rupture, the scar tissue lacks contractile ability.
Beyond heart attacks, other conditions can also lead to scar tissue in the heart. Chronic hypertension, or high blood pressure, can impose persistent stress on the heart walls, leading to thickening of the heart muscle and eventually fibrosis. Inflammation of the heart muscle, known as myocarditis, can also damage cardiac tissue, leading to scar formation. Cardiomyopathies, diseases affecting the heart muscle, and even the natural aging process, can contribute to myocardial scarring.
Mechanical Impairment of Heart Function
Scar tissue impairs the heart’s ability to pump blood efficiently due to its rigid, non-contractile nature. Healthy heart muscle contracts rhythmically to propel blood throughout the body. Scar tissue, however, lacks this contractile ability, directly reducing the heart’s overall pumping efficiency.
The presence of scar tissue can lead to increased stiffness within the heart chambers, particularly in the ventricles. This stiffness impairs the heart’s ability to relax and fill properly with blood during diastole, the relaxation phase of the cardiac cycle. Consequently, less blood can enter the ventricles, reducing the volume available for pumping.
During systole, the contraction phase, the non-contractile scar tissue can bulge outwards, further diminishing the heart’s effective pumping action. This localized bulging means that some pressure generated by healthy muscle is wasted on expanding the scarred area instead of propelling blood forward. This increases pressure within the heart chambers and reduces blood flow to the body, forcing the remaining healthy heart muscle to work harder.
Disruption of Electrical Signals
The heart relies on a precise electrical system to coordinate its contractions. Normal electrical impulses propagate through specialized pathways, ensuring synchronized pumping of the atria and ventricles. Scar tissue, however, interferes with this electrical rhythm.
Scar tissue can act as an electrical insulator, blocking or slowing the normal propagation of electrical signals. This creates areas of delayed or absent conduction, forcing electrical impulses to navigate around the scarred regions. These detours can lead to abnormal electrical pathways, causing the impulses to re-enter and re-excite parts of the heart, disrupting the synchronized contraction of heart chambers.
Fibroblasts within scar tissue are understood to play an active role in disrupting electrical activity. These scar-forming cells can communicate directly with cardiac muscle cells, promoting electrical excitability and contributing to irregular heartbeats. This abnormal electrical activity can manifest as various arrhythmias, some of which can be life-threatening and may lead to sudden cardiac death.
Progressive Heart Conditions
The combined effects of mechanical impairment and electrical disruption caused by scar tissue can lead to the development or worsening of several chronic heart conditions. The reduced pumping efficiency and increased workload on the remaining healthy heart muscle can progressively weaken the heart over time. This ongoing strain can result in the development of heart failure, a condition where the heart is no longer able to pump enough blood to meet the body’s demands.
Heart failure symptoms, such as shortness of breath, fatigue, and swelling in the lower body, reflect the body’s reduced blood supply. Electrical instability caused by scar tissue can also lead to recurrent and increasingly severe arrhythmias. These irregular heartbeats can further compromise the heart’s ability to pump effectively and, in severe cases, can be fatal. Scar tissue also correlates with a higher risk of sudden cardiac death.