The heart sleeve, also known as the myocardial sleeve or atrial myocardial sleeve, is an extension of heart muscle tissue, typically from the atria, into adjacent large veins. Though small, this anatomical feature can impact heart function.
Understanding the Heart Sleeve
The heart sleeve is primarily found extending from atrial muscle tissue into the pulmonary veins, which carry oxygen-rich blood from the lungs to the left atrium. Most individuals have four pulmonary veins, two connected to each lung. These sleeves average about 9 millimeters in length but can range up to 38 millimeters from the vein-atrial junction. Superior pulmonary veins typically have longer sleeves.
This sleeve consists of cardiomyocytes, or heart muscle cells, arranged in circular and longitudinal patterns. The transition from the atrial to the venous wall is gradual, with myocardial sleeves from the left atrium overlapping the smooth muscle cells of the venous walls. While most common in pulmonary veins, these sleeves can also extend into the vena cava, the large veins returning deoxygenated blood to the right atrium. Their thickness is not uniform, often being thickest at the venoatrial junction and thinning distally.
How the Heart Sleeve Functions
The heart sleeve participates in the heart’s electrical conduction system. It contains specialized heart muscle cells that generate and conduct electrical impulses. These cells contribute to the coordinated contraction of the atria, ensuring efficient blood flow into the ventricles.
The cells within the myocardial sleeves of the pulmonary veins exhibit properties similar to the heart’s natural pacemaker, the sinoatrial node. They can undergo spontaneous depolarization, generating electrical impulses without external stimulation. This inherent electrical activity allows the heart sleeve to contribute to the heart’s overall rhythm and pumping action.
When the Heart Sleeve Causes Problems
The heart sleeve’s unique electrical properties and anatomical structure make it a common site for abnormal heart rhythms, especially atrial fibrillation (AFib). AFib is the most common abnormal heart rhythm, characterized by an irregular and often rapid heartbeat. Ectopic beats, which are extra or abnormal heartbeats, often originate from the myocardial sleeves of the pulmonary veins.
These ectopic beats can trigger or sustain AFib due to the irregular arrangement of muscle fibers and potential for disorganized electrical activity. Abnormal calcium regulation within sleeve cells can also contribute to spontaneous arrhythmogenic activity. When these electrical impulses are not properly coordinated, they can lead to a chaotic atrial rhythm.
Symptoms of AFib originating from the heart sleeve vary; some individuals experience no symptoms. Common symptoms include heart palpitations, described as a racing, pounding, fluttering, or skipping sensation in the chest. Other symptoms may include fatigue, dizziness, shortness of breath, and chest discomfort. AFib prevalence increases with age.
Approaches to Managing Issues
Diagnosing heart rhythm problems originating from the heart sleeve involves several tools. An electrocardiogram (ECG or EKG) records the heart’s electrical activity. For intermittent issues, a Holter monitor records heart rhythm over 24 hours or longer. An electrophysiology (EP) study is a specialized procedure where thin wires are threaded through blood vessels to the heart to map its electrical activity and pinpoint arrhythmia sources.
For treatment, catheter ablation, specifically pulmonary vein isolation (PVI), is a primary strategy. This procedure neutralizes problematic electrical activity within the heart sleeve. During PVI, a catheter delivers heat (radiofrequency ablation) or cold (cryoablation) energy to create small scars around the openings of the pulmonary veins. This scar tissue blocks abnormal electrical signals from the myocardial sleeves, preventing them from disrupting the heart’s rhythm.