Symptomatic patient with LBBB

F. Mut, M. Beretta

Nuclear Medicine Service, Asociacion Española

Montevideo, Uruguay

Clinical history

• Woman 66 y.o., no known risk factors for CAD.

• Asthmathic, atypical chest pain.

• Chronic LBBB.

• Had bronchospasm when submitted for MPS with

dipyridamole, so she was switched to exercise.

Myocardial perfusion study

Quantitative results

How would you describe the findings?

a) Septal fixed defect.

b) Septal reversible defect.

c) Septal partially reversible defect.

d) No defect, normal study.

How would you describe the findings?

a) Septal fixed defect.

b) Septal reversible defect.

c) Septal partially reversible defect.

d) No defect, normal study.

There is a septal defect which clearly

shows partial reversibility, with no complete

normalization (septal wall is still thinner than

lateral wall at rest).

stress

rest

How would you interpret the findings?

a) Ischemia.

b) Infarction.

c) Ischemia + infarction.

d) Inconclusive, defect possibly due to LBBB.

How would you interpret the findings?

a) Ischemia.

b) Infarction.

c) Ischemia + infarction.

d) Inconclusive, defect possibly due to LBBB.

• LBBB produces septal defects believed to represent a

relative perfusion deficit because myocardial perfusion

should be maximum during diastole and this can be impaired

since the relaxation phase is compromised.

What stress test would you have

primarly selected?

a) Physical exercise.

b) Adenosine / dipyridamole.

c) Dobutamine.

d) Regadenoson.

What stress test would you have

primarly selected?

a) Physical exercise.

b) Adenosine / dipyridamole.

c) Dobutamine.

d) Regadenoson.

• Perfusion defects due to LBBB can be exaggerated with

increased heart rate, so vasodilators are preferred, but the

patient is asthmatic.

• Regadenoson is a selective A2A receptor agonist with no

effect on bronchial smooth muscle.

Follow up

• Since the patient remained symptomatic and the

myocardial perfusion result was inconclusive, she

underwent cardiac catheterization.

• The result: normal coronary arteries.

• Patients with LBBB or ventricular pacemaker should undergo vasodilator

stress because exercise often produces a false-positive perfusion defect

in the interventricular septum.

• The defect is probably related to abnormal septal contractility,

accompanied by an relative fall in coronary flow to the septum.

• Exercise stress or any cause of tachycardia tends to enhance this

heterogeneous perfusion by increasing the flow proportionately more in

the normally contracting myocardium, resulting in a reversible perfusion

defect on imaging.

• Vasodilator stress has been shown to overcome the coronary flow

misbalance, resulting in a more homogeneous perfusion pattern.

Teaching points

• Regadenoson is a pharmacologic agent approved by the FDA in 2008 as

an agent for use in stress testing and can also be used in combined

protocols with exercise.

• Regadenoson produces maximal hyperemia quickly after IV injection as

a bolus and maintains it for an optimal duration, practical for myocardial

perfusion imaging.

• Regadenoson is an agonist with low affinity for the A2A adenosine

receptor, and at least a 10-fold lower affinity for the A1 adenosine

receptor. In addition, it has relatively weak affinity for the A2B and A3

adenosine receptors.

• Coronary vasodilation and an increase in coronary blood flow (CBF)

results from activation of the A2A adenosine receptor by regadenoson.

Teaching points

References • Cerqueira MD, Nguyen P, Staehr P, et al. Effects of age, gender, obesity,

and diabetes on the efficacy and safety of the selective A2A agonist

regadenoson versus adenosine in myocardial perfusion imaging

integrated ADVANCE-MPI trial results. JACC Cardiovasc Imaging 2008;

1:307-16.

• Koepfli P, Wyss CA, Gaemperli O, et al. Left bundle branch block causes

relative but not absolute septal underperfusion during exercise. Eur

Heart J 2009; 30:2993-9.

• Botvinick EH. Current methods of pharmacologic stress testing and the

potential advantages of new agents. J Nucl Med Technol 2009; 37:14-

25.

• Ross MI, Wu E, Wilkins JT, et al. Safety and feasibility of adjunctive

regadenoson injection at peak exercise during exercise myocardial

perfusion imaging: The Both Exercise and Regadenoson Stress Test

(BERST) trial. J Nucl Cardiol 2013; 20:197-204.