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\begin{document}

\title{Surgical Unroofing a Long-Segment Myocardial Bridge of the Left Anterior
Descending Artery Leading to Complete Angiographic and Symptomatic
Improvement: A Case Report}



\author[1]{Christine Johnstad}%
\author[2]{Jason Smith}%
\author[2]{Mohun Ramratnam}%
\author[2]{Amy Fiedler}%
\affil[1]{Affiliation not available}%
\affil[2]{University of Wisconsin}%


\vspace{-1em}



  
  \date{May 29, 2024}


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\selectlanguage{english}
\begin{abstract}
A 52-year-old man presented to our institution with a one year history
of intermittent, progressive chest tightness with activity. He underwent
stress test which was positive. Coronary angiography revealed a long
segment myocardial bridge of the left anterior descending artery (LAD).
Initially, he was trialed on maximal medical therapy, however, symptoms
continued. As a result, he was brought to the operating room for
unroofing of the myocardial bridge with excellent clinical and
radiographic outcome. The diagnosis, medical, and surgical management of
myocardial bridge is complicated. Long-term data surrounding best
options for management is scarce.%
\end{abstract}%



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\textbf{Background:}

Myocardial bridging is an anatomical variant, occurring when an
epicardial coronary artery contains an intramyocardial segment that
becomes compressed during systole.\textsuperscript{1} Most commonly,
myocardial bridging occurs in the mid-portion of the LAD. The incidence
and prevalence vary widely due to variation in diagnostic methods and
definitions of myocardial bridging.\textsuperscript{2,3} Currently, no
diagnostic gold standard exists for clinically significant myocardial
bridging.

Longstanding debate surrounds the clinical significance of myocardial
bridging. Since myocardial perfusion occurs mainly during diastole, it
was thought that systolic compression in the setting of a myocardial
bridge would not have significant clinical impact. However, angiography
and intravascular ultrasound (IVUS) have shown that compression extends
into diastole, inducing symptoms from delayed diastolic relaxation and
decreased perfusion. Additionally, myocardial bridging may cause
persistent reduction in diastolic luminal diameter, retrograde systolic
flow, reduced coronary flow reserve, and increased velocity of blood
flow.\textsuperscript{2,4} Often, the tunneled artery segment in
symptomatic patients has endothelial dysfunction. The portion of the
artery proximal to the bridge may be prone to atherosclerosis due to
alterations in flow patterns. The bridged segment has a propensity
toward coronary spasm due to endothelial
dysfunction.\textsuperscript{1,3-5} Patient specific features such as
the depth and length of myocardial bridge, septal branch involvement,
and degree of systolic diameter reduction influence the clinical impact.

\textbf{Case Presentation:}

A 52-year-old man presented to our institution with a one year history
of~intermittent, progressive chest tightness. Past medical history was
notable for hypertension, hyperlipidemia, post-traumatic stress disorder
and family history of coronary artery disease (CAD). Prior to developing
symptoms,~he was quite physically active; however, became less so prior
to presentation due to symptomatic limitations.

He underwent an exercise stress test that showed good functional
capacity (exercise time of 9 min 47 seconds) but demonstrated 2-3 mm ST
depressions starting in Stage 2 of the bruce protocol in leads II, III,
aVF and V4-V6. The patient also expressed dypnea with exercise that
resolved 5 minutes into recovery. Coronary angiography was then
performed, demonstrating non-obstructive CAD . However, a long segment
myocardial bridge in the mid-LAD was observed (Figure 1) Transthoracic
echocardiogram (TTE) demonstrated normal left ventricular size, normal
systolic function and an estimated left ventricular ejection fraction of
60-65\%.

Initially, the patient was trialed on maximal medical therapy for
symptomatic relief, including amlodipine, aspirin and rosuvastatin. His
symptoms persisted.~ He was subsequently referred for cardiac surgical
evaluation.~ He was deemed an appropriate operative candidate, and was
brought to the operating room for surgical unroofing of the myocardial
bridge on April, 2020.

Standard aortic and dual stage venous cannulation was performed. The
aorta was cross clamped and the heart was arrested with antegrade Del
Nido cardioplegia. Upon surface inspection, a long segment of
intramyocardial LAD was easily identified (Figure 2).~ The LAD was
unroofed with the use of a 15-c blade over the course of 10 mm.~ The
aortic cross clamp was removed and the patient was easily separated from
cardiopulmonary bypass. He underwent coronary angiography on
post-operative day one to evaluate the results of the surgery
radiographically. Angiography revealed that the myocardial bridge had
been entirely relieved (Figure 3). The patient had an uneventful
post-operative course and was discharged home on postoperative day
number four. He was seen in follow-up one and two months post procedure
and is doing well without recurrence of symptoms.

\textbf{Discussion:}

The Schwarz classification is used for guiding therapeutic
considerations in patients with an identified myocardial bridge. This
classification is broken down into types A, B, and C. Type A patients
have an incidental finding of myocardial bridging on angiography without
objective signs of ischemia and do not require treatment. Type B
patients demonstrate ischemia during stress testing and should receive
treatment with beta-blockers or calcium-blockers. Type C patients have
significantly altered intracoronary hemodynamics, with objective signs
of ischemia, including symptoms. These patients should be managed with
medical therapy initially, and if that fails, operative intervention
should be pursued.\textsuperscript{6}

Beta-blockers are useful in patients with myocardial bridging due to
their negative inotropic and chronotropic effects coupled with reduced
sympathetic drive, allowing for increased length of diastolic coronary
filling and reduced compression. Calcium-channel blockers can be used as
an alternative. Nitrates should be used with caution in these patients,
as they increase systolic compression within the bridge while
vasodilating the proximal segment. These altered hemodynamics may
exacerbate retrograde flow thereby reducing the threshold for myocardial
ischemia.

In patient's refractory to medical therapy, stenting may be considered.~
However, significant rates of in stent restenosis have been identified
small numbers of patients. Additional concerns surrounding stenting
include stent fracture, thrombosis, and increased risk of perforation
during deployment, all of which has limited the utility of this
treatment.\textsuperscript{4,5}

A surgical gold standard has not been established for patients with an
isolated myocardial bridge and refractory symptoms due to the infrequent
finding of need for surgical intervention. Coronary artery bypass graft
(CABG) with use of the left internal mammary artery (LIMA) to the LAD
has been described. Concerns regarding the ability of the CABG graft to
remain open due to competitive flow in a patient with non-obstructive
CAD limits enthusiasm for this approach. Alternatively, the literature
suggests that for patients with isolated myocardial bridge, the surgeon
may carefully unroof the intra-myocardial component of the affected
vessel. A perceived benefit of unroofing is that it can be done in
isolation or in combination with CABG if necessary. The unroofing
technique has been shown to be safe and effective in improving symptoms
in a small number of patients. Interestingly, very little is in the
literature regarding the actual angiographic outcome of patients who
undergo surgical unroofing of a myocardial bridge as a result of
significant symptoms. This case report demonstrates complete unroofing
as confirmed by post-operative angiography in addition to significant
symptomatic improvement.

\textbf{Conclusion:}

In young patients with exertional chest pain, myocardial bridging should
be considered in the differential diagnosis.~ While many patients with
myocardial bridge respond well to medical therapy, those who do not
should explore surgical options for symptomatic improvement and
treatment.

The surgical management of a symptomatic patient with an isolated
myocardial bridge is debated. CABG has been performed, however concerns
regarding graft patency in the setting of non-obstructive CAD is
warranted.~ Unroofing of the bridge has been described and performed in
case reports throughout the literature, however post-operative
symptomatic improvement and angiographic demonstration of complete
bridge relief have been infrequently reported. Here, we describe a
patient with a symptomatic myocardial bridge involving the LAD for which
medical therapy was ineffective. Our patient underwent successful
surgical unroofing of a long segment myocardial bridge, leading to total
symptomatic improvement and complete resolution on post-operative
coronary angiography.

Multi-institutional registries and randomized clinical trials are
warranted to shed light on optimal strategies for patients with
myocardial bridging refractory to medical therapy.

\textbf{References} :

\begin{enumerate}
\tightlist
\item
  Hemmati P, Schaff HV, Dearani JA, Daly RC, Lahr BD, Lerman A. Clinical
  Outcomes of Surgical Unroofing of Myocardial Bridging in Symptomatic
  Patients. \emph{The Annals of Thoracic Surgery}. 2020;109(2):452-457.
  doi:10.1016/j.athoracsur.2019.07.005.
\item
  Murtaza G, Mukherjee D, Gharacholou SM, et al. An updated review on
  myocardial bridging. \emph{Cardiovascular Revascularization Medicine}.
  2020. doi:10.1016/j.carrev.2020.02.014.
\item
  Tarantini G, Migliore F, Cademartiri F, Fraccaro C, Iliceto S. Left
  Anterior Descending Artery Myocardial Bridging. \emph{Journal of the
  American College of Cardiology}. 2016;68(25):2887-2899.
  doi:10.1016/j.jacc.2016.09.973.
\item
  Corban MT, Hung OY, Eshtehardi P, et al. Myocardial bridging:
  contemporary understanding of pathophysiology with implications for
  diagnostic and therapeutic strategies. \emph{J Am Coll Cardiol}.
  2014;63(22):2346-2355. doi:10.1016/j.jacc.2014.01.049
\item
  Sara JD, Corban MT, Prasad M, et al. Prevalence of myocardial bridging
  associated with coronary endothelial dysfunction in patients with
  chest pain and non-obstructive coronary artery
  disease.\emph{EuroIntervention}. 2020;15(14):1262-1268.
  doi:10.4244/eij-d-18-00920.
\item
  Schwarz ER, Gupta R, Haager PK, et al. Myocardial Bridging in Absence
  of Coronary Artery Disease: Proposal of a New Classification Based on
  Clinical-Angiographic Data and Long-Term Follow-Up. \emph{Cardiology}.
  2009;112(1):13-21. doi:10.1159/000137693
\end{enumerate}\selectlanguage{english}
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\includegraphics[width=0.70\columnwidth]{figures/Pre-op-cath/Pre-op-cath}

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\includegraphics[width=0.70\columnwidth]{figures/Post-op-cath/Post-op-cath}

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