Myocardial Bridging
Myocardial Bridging
| 🔢 No. | 🔍 Key Point |
|---|---|
| 1 | Myocardial bridging most commonly involves the left anterior descending (LAD) artery. |
| 2 | The bridged segment of the artery is located intramyocardially (within the heart muscle). |
| 3 | Systolic compression of the tunneled artery segment is the hallmark of myocardial bridging. |
| 4 | Often considered benign, but can cause ischemia or arrhythmias in some cases. |
| 5 | Angiographic ‘milking effect’ during systole is a classic finding. |
| 6 | Beta-blockers are the first-line treatment for symptomatic patients. |
| 7 | Nitrates are contraindicated, as they may worsen compression. |
| 8 | Associated with T wave inversions in anterior leads on ECG in some cases. |
| 9 | Coronary CT angiography is excellent for dynamic visualization of bridging. |
| 10 | Intravascular ultrasound (IVUS) can quantify degree of systolic compression. |
| 11 | Atherosclerosis is more common proximal to the bridged segment, not within it. |
| 12 | Surgical unroofing or CABG may be considered if medical therapy fails. |
| 13 | Myocardial bridging can trigger ventricular arrhythmias or even sudden cardiac death rarely. |
| 14 | Stress testing (e.g. dobutamine) can provoke signs of ischemia from bridging. |
| 15 | The tunneled artery segment does not typically develop atherosclerosis. |
| 16 | SPECT or PET perfusion imaging helps assess ischemia due to bridging. |
| 17 | Higher prevalence is noted in young males during autopsy studies. |
| 18 | Frequently asymptomatic and discovered incidentally on imaging. |
| 19 | May be mistaken for coronary artery spasm or stenosis on angiography. |
| 20 | Usually involves a short segment, but long or deep bridges are more likely symptomatic. |
🧠 Myocardial Bridging - IVUS Feature
| 🔢 No. | 🧠 IVUS Feature | 🩺 Description / Interpretation |
|---|---|---|
| 1 | Systolic Compression | Bridged segment shows marked luminal narrowing during systole. |
| 2 | Diastolic Restoration | The artery returns to near-normal luminal diameter in diastole, confirming dynamic obstruction. |
| 3 | 'Half-moon' Echo-free Space | Seen between bridged segment and epicardium — represents overlying myocardium (diagnostic clue). |
| 4 | Dynamic Phasic Compression Pattern | Degree of luminal narrowing varies with cardiac cycle — unlike fixed stenosis. |
| 5 | Absence of Atherosclerosis in Bridged Segment | IVUS typically shows smooth intima within the bridged portion — protective effect of intramyocardial course. |
| 6 | Atherosclerosis Proximal to Bridging | Commonly observed due to disturbed shear stress and turbulent flow proximal to the bridged segment. |
| 7 | Increased Wall Shear Stress Proximally | Leads to plaque formation proximal to the tunneled artery, while the tunneled segment remains spared. |
| 8 | Systolic Narrowing with 'Slit-like' Lumen | During systole, the artery may appear nearly collapsed in the bridged area. |
| 9 | Reproducible with Dobutamine or Stress | Systolic narrowing becomes more prominent with inotropic stimulation during IVUS. |
| 10 | Absence of Calcification in Bridged Segment | Bridged arteries are typically free of calcified plaque — IVUS confirms soft, compressible vessel. |
| 11 | Cross-sectional Area Reduction >50% in Systole | Indicates hemodynamically significant myocardial bridging. |
| 12 | Measurement of Percent Diameter Reduction | Calculated as: [(Diastolic Diameter - Systolic Diameter) ÷ Diastolic Diameter] × 100. |
| 13 | Tunica Media Appears Thicker | The muscular overburden overlying the artery can be visualized as thickened hypoechoic area. |
| 14 | Segment Length Evaluation | IVUS allows accurate measurement of the bridged segment’s length — longer segments may be symptomatic. |
| 15 | Tapered Appearance of Lumen | Sometimes the bridged segment appears tapered on cross-section due to dynamic compression. |
| 16 | Use of IVUS-Guided FFR Integration | Functional impact of bridging can be better assessed when IVUS is combined with physiological testing. |
| 17 | Eccentric Compression Pattern | Compression may not be concentric — often occurs eccentrically, more on the epicardial side. |
| 18 | Lack of Stent Expansion in Bridged Segment | If stented, the stent may not fully expand during systole, seen clearly on IVUS (risk of fracture). |
| 19 | Increased Resistance to Guidewire Passage | Mild resistance may be felt due to compression, though IVUS helps differentiate this from spasm. |
| 20 | Helps Plan Surgical Unroofing | Identifies exact location and extent of compression, aiding pre-surgical planning. |
Intravascular ultrasound (IVUS) findings in myocardial bridging (MB) typically reveal a characteristic "half-moon" or "halo" sign, indicating the intramural course of the coronary artery.
1. Systolic compression and diastolic relaxation
- Characteristic: IVUS clearly shows the systolic compression of the bridged segment of the coronary artery.
- Delayed Relaxation: Studies have shown delayed relaxation and reduced vessel lumen diameter even into diastole, affecting coronary blood flow during the predominant filling phase.
- Eccentric Compression: This compression is typically eccentric rather than concentric.
2. "Half-moon" sign
- Pathognomonic: A specific IVUS finding is the "half-moon" sign, an echolucent area representing the myocardial fibers overlying the coronary artery.
- Localization: This is observed throughout the cardiac cycle within the bridged segment, unlike normal segments.
3. Atherosclerotic plaques
- High Incidence: IVUS studies consistently show a high prevalence of atherosclerotic plaques in the coronary artery segment immediately proximal to the myocardial bridge.
- Importance: These plaques may not be visible on standard angiography, highlighting the superior sensitivity of IVUS for detecting them.
- Flow Disturbances: The development of proximal plaque is linked to hemodynamic disturbances, specifically dynamic retrograde blood flow caused by compression of the bridged artery.
What is the finger-tip phenomenon?
The finger-tip phenomenon, also described as a "spike-and-dome" pattern, is a specific flow pattern seen in the intracoronary Doppler imaging of myocardial bridges. It's characterized by:
- Abrupt early diastolic flow acceleration: A sudden increase in blood flow velocity during the initial part of diastole (heart muscle relaxation).
- Rapid mid-diastolic deceleration: A sharp decrease in flow velocity during the middle of diastole.
- Mid-to-late diastolic plateau: A period of relatively stable blood flow during the latter part of diastole.
This pattern is thought to arise from the combined effects of:
- Reduced distal coronary resistance.
- Delayed relaxation of the myocardial muscle fibers surrounding the artery, which causes some degree of compression to persist into early diastole.
- An increase in the pressure gradient at the beginning of diastole as the artery starts to decompress and blood rushes through.
In addition to the fingertip phenomenon, other characteristic findings associated with myocardial bridging when using Intracoronary Doppler include:
- Reduced or absent antegrade systolic flow: Little or no forward blood flow during systole.
- Retrograde flow in the proximal segment: Blood flowing backward in the segment just before the bridge, particularly noticeable after intracoronary nitroglycerin injection.
What is the finger-tip phenomenon?
Finger-tip phenomenon, also described as a "spike-and-dome" pattern, is a specific flow pattern seen in the intracoronary Doppler imaging of myocardial bridges
