Researchers from Mount Sinai School of Medicine are pioneering newultrasound techniques that provide the first characterization ofmultidirectional blood flow in the heart. By focusing on fluiddynamics - specifically, the efficiency with which blood enters andexits the heart's left ventricle - the researchers believe they candetect heart disease even when traditional measures show no sign of trouble. In addition to improving diagnoses, this shift in focus from musclemechanics to fluid mechanics could lead to more effectivetherapeutic interventions. The work is described in a studypublished by two Mount Sinai cardiologists and a team ofinternational collaborators in a recent issue of JACC Cardiovascular Imaging , a journal of the American College of Cardiology. |
The ultrasound tools cardiologists use today often fail to detectchanges in the heart until there is overt dysfunction. Blood flowimaging, however, may provide better clues in diagnosing heart failure . Sinai investigators reason that flow should be immediatelyaffected by changes in cardiac function - such as those revealed inimage analysis by the chaotic behavior of tiny whirlpools. The computer-aided visual study of these abnormalities coulddramatically improve the assessment of patients with heart failureand lead to a fresh understanding of normal and abnormal pumpingand circulatory function.
Visual blood-flow analysis could alsoyield improved therapies for arrhythmias and other disorders requiring cardiac synchronization. Researchersare actively exploring applications in aortic atherosclerosis,before and after valve replacement, and congenital abnormalities. "With visualization, we are looking at the ultimate measure of theefficiency of the heart - how the blood is brought in and how it issent out," said Jagat Narula, MD, PhD, Director of CardiovascularImaging at Mount Sinai and the senior author of the paper. "Today,cardiologists place great weight on a gauge called the squeezefraction, or ejection fraction - the portion of blood pumped fromthe ventricle with each heartbeat.
What we are doing is a completedeparture from the view of the heart as a squeezing,pressure-generating chamber." Mount Sinai researchers and their collaborators have experimentedwith a range of imaging techniques to grasp the characteristics ofnormal and abnormal blood flow. The approaches includephase-encoded MRI, cardiac magnetic resonance (CMR) and severalforms of ultrasound-based imaging known as echocardiographicparticle imaging velocimetry. "The most effective technique involves injecting a stream ofbubbles that behave exactly like red blood cells and usingechocardiography to track their path through the left ventricle,"said Partho Sengupta, MD, Director of Cardiac Ultrasound Researchat Mount Sinai, and the first author, with Narula, of the JACC paper. In these investigations, the computer-enhanced video outputdepicts normal and turbulent flow in vivid detail, with arrowsplotting the direction as the bubbles swirl through the heartchamber. "Not only are you following the path of the blood, but you canactually identify the amount of energy that is being distributed,"said Dr.
Sengupta. "Like other forms of ultrasound, that meanslow-cost heart tests using this technology could be performed on asimple outpatient basis." The echocardiography technology pioneered by Sengupta and Narulasheds light on diagnostic discrepancies that have puzzledcardiologists relying on pressure measurements. "After sustaining significant damage, a patient's heart may nothave the greatest squeeze, but there could be good trafficking ofblood through the heart and the patient could remain asymptomatic,"Sengupta explained. "The normal ejection fraction is around 60percent, but we sometimes see a patient with 20 percent walkingaround and playing golf. Other people who are at 50 percent may beshort of breath.
Flow visualization is one way to capture theessence of why the patient is or is not symptomatic." Diagnosing cardiac disease by looking for structural defects in theheart is like analyzing highway traffic by examining the road, Dr.Narula said. "The structure may not be great, but how does thataffect the cars that are actually traveling on the road? It's thesame thing if you fail to look at the blood." Likewise, a plumber's investigation of pipes in a house onlymatters or makes sense in relation to how the water flows, claimsSengupta. A new study these investigators have submitted forpublication zeros in on specific correlations between blood flowand cardiac pathology. "We will be able to demonstrate thatefficiency may be lost even though the structure is maintained,"said Senguptra. "In other words, the fa ade is good, but inside,you have lost it." Sengupta points out that the combined visualization and computationtechniques in the JACC paper are still new and require further work, includingdevelopment of appropriate flow-based indexes for applications invarious cardiac pathologies.
Forces acting on flow are exceedinglycomplex and dynamic, the researchers said. Pumped by the heart at arate of 8 pints to 16 pints per minute, blood interacts with thecontours of the myocardium, valves, vessels, and other features,which are also in motion. The flow is multidirectional - curling,spinning, and forming eddies that are affected in countless ways bystructural changes in heart tissue. As with any new observationaltechniques, data from novel cardiac visualizations in complexenvironments are subject to interpretation. "We have started using these imaging techniques in clinicaltrials," Narula said.
"They will require careful evaluation." Additional References Citations.
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