Detecting myocardial ischaemia using miniature ultrasonic transducers--a feasibility study in a porcine model.
BACKGROUND
Detection of myocardial ischaemia during and after cardiac surgery remains a challenge. Echocardiography is more sensitive in ischaemia detection than echocardiography (ECG) and haemodynamic monitoring, but demands repeated examinations for monitoring over time. We have developed and validated an ultrasonic system that permits continuous real-time assessment of myocardial ischaemia using miniature epicardial ultrasound transducers.


METHODS
In an open-chest porcine model (n=8), prototype ultrasound transducers were fixed on the epicardium in the left anterior descending and circumflex coronary artery supply regions, providing continuous measurement of transmural myocardial velocities. Peak systolic velocity and post-systolic velocity were recorded simultaneously with ECG, left ventricular pressure and arterial pressure. Two-dimensional (2D) echocardiographic strain was used as a reference. Global changes were induced by infusing fluid, epinephrine, nitroprusside and esmolol. Regional changes were induced by occluding the left anterior descending coronary artery (LAD). Subsequent LAD stenosis was performed in a subgroup, with flow reduction to 50% of baseline level and further to occlusion.


RESULTS
Systolic velocity in the LAD region decreased during LAD occlusion (0.9+/-0.1 to 0.1+/-0.1 cm s(-1), P<0.01), whereas post-systolic velocity increased (0.3+/-0.1 to 2.3+/-0.1 cm s(-1), P<0.01). No changes occurred in the circumflex coronary artery (CX) region. Severe ischaemia was confirmed by reduction in 2D echocardiography strain calculations. Changes in myocardial velocities assessed by miniature transducer during ischaemia differed from changes during all global interventions. Significant reduction in systolic velocity occurred at 50% LAD flow (0.9+/-0.1 to 0.5+/-0.1 cm s(-1), P=0.02) with further decrease on following occlusion (0.0+/-0.0 cm s(-1), P<0.01). Post-systolic velocity increased both from baseline to 50% LAD flow, and further to occlusion.


CONCLUSIONS
The epicardial transducers provided continuous assessment of regional myocardial function and detected ischaemia with high sensitivity and specificity. Further development of this system may provide a useful tool for myocardial monitoring during and after cardiac surgery.
Espinoza
Andreas
A
The Interventional Centre, Rikshospitalet University Hospital, Oslo, Norway. andreas.espinoza@rr-research.no
Halvorsen
Per Steinar
PS
Hoff
Lars
L
Skulstad
Helge
H
Fosse
Erik
E
Ihlen
Halfdan
H
Edvardsen
Thor
T
D000818:Animals; D006348:Cardiac Surgical Procedures / Q000009:adverse effects; D023921:Coronary Stenosis / Q000000981:diagnostic imaging / Q000503:physiopathology; D004195:Disease Models, Animal; D004562:Electrocardiography; D004812:Epidemiologic Methods; D005260:Female; D006439:Hemodynamics; D008297:Male; D008904:Miniaturization; D017202:Myocardial Ischemia / Q000000981:diagnostic imaging* / Q000209:etiology / Q000503:physiopathology; D012815:Signal Processing, Computer-Assisted; D034421:Sus scrofa; D014159:Transducers; D014463:Ultrasonography