Echocardiographic evaluation of Coronary Arteries

Dr Raghu Kishore Galla

Clinical applications

• Visualization of the epicardial coronary arteries by echocardiography istechnically challenging.

• Resolution of transthoracic echo using a 2.5-3.5MHz probe is only 2mmwhile the diameter of the epicardial coronary arteries ranges from 1.5 to4mm.

• Epicardial coronaries are relatively superficial in the chest, so they lie innear field of the ultrasound waves.

• Translational and rotational motion of the coronary arteries in the AVgrooves poses a challenge in obtaining stable Doppler signals.

• Relatively low velocity of coronary flow compared to the flow velocity inthe ventricles makes color signals hard to discern.

• Tomographic nature of the echocardiographic study makesdifferentiation between adjacent vessels e.g. the LAD and the diagonalbranches extremely difficult.

• Direct transthoracic visualization of the coronary arteries was attemptedin children and occasionally in adults with coronary artery anomalies,arterio venous fistulas, and aneurysms (Harada et al., 1999; Hiraishi et al,2000; P.C. Frommelt & M.A. Frommelt, 2004)

• Using dedicated high-frequency probes made assessment of the left maincoronary, the LAD and even the posterior descending branch of the RCAfeasible in a large proportion of patients (Hozumi et al., 1998).

• Transthoracic and transesophageal echo can provide data regardingcoronary patency, the presence of coronary stenosis or coronary ectasia(Iliceto S, et al., 1991, Kozakova M, et al., 1997, Lambertz et al., 2000).

• With improvements in ultrasound machines and introduction of harmonicimaging and high frequency transducers, direct visualization of longsegments of all three coronary arteries is now possible.

• Although the entire artery cannot be reconstructed, multiple segmentscan be visualized and flow velocity can be measured, thus enabling us toobtain useful anatomic and physiologic information.

• Careful evaluation of coronary flows can translate into a wide variety ofclinical applications

Technical Considerations

• A high quality ultrasound machine gives good quality imaging forcoronaries.

• The 5.0 or 3.5 MHz narrow-band sector transducers in second harmonicmode are used for B-mode examination.

• Color Doppler mapping and spectral Doppler coronary flow velocityassessment are performed at 2.5 or 2 MHz

• After obtaining good quality B-mode image, coronary segments should besearched, using color flow with or without the use of harmonics.

• Sample size of color Doppler should be at minimum, velocity range shouldbe set with a low Nyquist limit (15–20 cm/s), and filters should bedecreased.

• Some ultrasound systems provide special color maps for coronary arteryevaluation including second or third harmonics of B-mode and color, lowNyquist limit, special gain for B-mode, and Doppler mode, etc.

CORONARY FLOW AND DOPPLER ANALYSIS

• Normal antegrade coronary flow is predominant diastolic with a smalldome like systolic component (Heinz Lambertz et al., 2004).

• Systolic flow is less important and is a less stable measure as it can beeven retrograde. The maximal flow velocities in non stenosed proximalparts of LAD, Cx, and RCA is in the range of 0.7 m/s

• It is difficult to record both diastolic and systolic flow in the same cardiaccycle in all patients, because of cardiac motion that displaces the coronaryartery from the ultrasound beam in systole.

• Diastolic flow is antegrade in both epicardial and intramural vessels,whereas systolic flow is antegrade in epicardial but retrograde inintramural vessels, because blood is squeezed backwards by myocardialcontraction(Vernon Anderson H et al., 2000).

• As a result of the two opposite forces, the magnitude of systolic flowvelocity may change along the coronary tree and close to the origin of aperforator there might be a watershed area with stagnation of systolicflow.

• The epicardial anterograde systolic flow is mainly a capacitance, ratherthan a nutrient flow, and may not reflect myocardial perfusion.

PARAMETERS TO BE ASSESSED

• Diastolic flow velocity

• Systolic flow velocity

• Diastolic Deceleration time

• Coronary flow reserve

• The baseline coronary flow velocity may change from one beat to the otherof even 5–10 cm/s. Controls with normal CAGs and normal LV function had apeak diastolic velocity in the distal LAD in the range of 21.2 ± 7.9 cm/s.

• Elevated resting flow velocities may occur in tachycardia, anemia,hyperthyroidism, severe LVH etc ( Czernin J er al, 1993, Voci P et al., 2004).

• Coronary vasodilators increase the diameter of the epicardial artery andreduce baseline flow velocity.

• Analysis of the coronary Doppler waveform can provide useful informationabout vessel patency and the presence of severe stenosis or moderatestenosis

Method of examination

• The size of the area where color Doppler examination is carried out shouldbe kept at minimum.

• Usually, a small part of the artery is seen at first,then by movingstep - by - step up and down the course of the vessel, the entire artery (orits long part) may be assessed.

• The Doppler angle should not exceed 60°

• The color doppler pattern in the normal coronary artery is uniformlyconsistent with laminar flow. At the site of stenosis, focal flow accelerationand turbulence may be detected as aliasing zone.

• The Doppler velocity should be measured at the point of focal aliasing.

• Krzanowski et al. and Saraste et al. showed that a local peak diastolic flowvelocity >2.0 m/s could be used as a sign of diameter reduction of >50% forall three main coronary arteries.

• Since LM and proximal LAD segment are almost horizontal and exceedthis angle, we rely on mosaic flow to determine significant stenosis inthese segments.

• A local maximal flow velocity >1.5 m/s is also a reasonably accurate sign ofstenosis.

• Hozumi et al. have observed localized aliasing by color flow mapping in100% of patients with LAD restenosis of >50% after coronary angioplastyand 56% of patients without restenosis.

• Noninvasive doppler has advantages over IVUS/FFR.

• Echocardiography avoids contact with the coronary artery, which may bereactive during myocardial infarction.

• Echo also measures velocities in regions inaccessible to IVUS such as theseptal perforators.

• The most important limitation of transthoracic doppler measurement is thedifficulty of obtaining accurate adjustment of the Doppler beam parallel tothe coronary flow.

• If the angle between the Doppler beam and the coronary artery is > 60°,diastolic flow velocity could be underestimated

Segmental Evaluation of Coronary Arteries

• Standard parasternal short and long axis views from second or thirdintercostal space or low parasternal long or short axis views from fourth orfifth intercostal space should be used.

• Coronary arteries appear as linear intra myocardial color segments ofapproximately 0.5–2.5 cm in length and 2–4 mm in diameter.

• Initially, after obtaining a short segment, step-by-step movement of thetransducer along the course of the vessel will bring longer segments intoview.

LMCA and proximal segments of the left and right coronary arteries

• With the patient in left lateral decubitus position,parasternal short axis view of the great vessels isobtained.

• First obtain the classic PASX view at the level of theaortic valve, then make slight clockwise rotationand anterior tilt of the transducer to visualize theleft main trunk.

• In the plane immediately below the pulmonarytrunk, left main (LM) and proximal left anteriordescending (LAD) can be visualized.

• The LM has approximately 1–3 cm length and isusually visualized along its entire course

Proximal part of left coronary artery in B-mode, modified parasternal short axis view.

• Color Doppler imaging of thecoronary flow in the proximal portionof the left coronary artery istechnically difficult for two reasons

-The almost orthogonal alignment ofcoronary flow to the ultrasoundbeam

-The interposition of the rightventricular outflow tract andpulmonary artery.

• The LMCA can also be imaged froman apical transducer position.

• From the classical five chamberview, the transducer is carefullyangled more anteriorly until theascending aorta is visualized.

• With slight tilting and rotation ofthe transducer, the left and the rightcoronary arteries can be recorded inone imaging plane.

• The orifice of the left coronaryartery is located approximatelythree O’clock.

• The orifice of the RCA can bedetected at approximately tenO’clock

Visualization of the middle segment of the LAD

• The middle and distal portion of the leftanterior descending artery lies in theanterior ventricular groove close to theanterior chest wall.

• Due to the proximity of the middle anddistal LAD to a precordially locatedtransducer, these coronary segmentsare ideal for transthoracic echo.

• From the classic PSAX at the level ofthe papillary muscles, a lateraldisplacement of the transducer by 2-3cm allows the visualization of theanterior interventricular groove.

• With caudal displacement of the transducerof 1-2 intercostal spaces, Color Doppler isused to identify the coronary flow in theanterior groove.

• Once a predominant diastolic flow signal isdetected from a vessel within the anteriorinterventricular groove, activate the zoommode while keeping the Doppler box smallwith adjustment of the velocity range at 12-24cm/s.

• From the previous view, the transducer isrotated 70 to 90º to obtain the best LADlong axis view.

• For measurement of the coronary flowvelocity, pulsed wave Doppler is used with asample size of 3mm and care should betaken to avoid an angle exceeding 35 to 45º.

Visualization of the distal segment of the LAD • The distal part of the LAD can be recorded in a

modified foreshortened three-chamber viewfrom an apical window.

• From the conventional apical 2 chamber view thetransducer is rotated anti-clockwise to obtain anapical long axis view, showing the LV and leftventricular outflow tract.

• Using the color Doppler, the distal segment ofthe LAD, located in the apical part of theinterventricular groove can be detected close tothe apex of the left ventricle.

• From this view, the transducer is shifted 1 to 2intercostal spaces cranially with anterior tilt tovisualize the peripheral epicardial segments ofthe LAD

Detection of the septal branches of the LAD

• In immediate proximity of the mid and distalportion of the left anterior descendingartery, septal side branches with varyingcaliber can be seen by color Doppler analysis.

• Frequently, the vessel course can befollowed over a longer distance within theventricular septum.

• Diagonal branches or a dominantintermediate branch can’t always be clearlydifferentiated from the left anteriordescending artery, as they may haveapproximately the same diameter and analmost parallel course.

Visualization of LCx• Proximal LCx is visualized in the left parasternal

position and a modified short-axis view of greatvessels with the slight caudal tip of the transducer.

• The normal anterograde blood flow in proximal LCx isidentified as a blue linear color signal on color Dopplermap, reflecting the direction of the flow from thetransducer .

• Visualization of mid and distal segments of the LCx isvery difficult and possible in a few patients only.

• As the mid and distal Cx are located in the coronarysulcus at the border between LA and LV, theangulation from heart basis to apex at the level ofpapillary muscles is usually required

Detection of the left circumflex artery

• The posteriorpapillary muscle can beused as a symbolic border between midand distal LCx.

• The first or second obtuse marginalbranches (OMB) presenting distal partsof the LCx can be assessed from fourth-and fifth intercostal spaces in the apicallong-axis position in a modified four- orfive chamber view at either lateral orinferior wall of the left ventricle B – mid LCx (mCx); the left parasternal position, a modified

parasternal short-axis view at the level of papillary muscles; C – the first obtuse marginal branches (OMB) presenting distal Cx, the apical long-axis position, a modified five-chamber view

Visualization of the RCA• To visualize the posterior descending branch

of the RCA, the left ventricle is first imaged ina conventional apical two-chamber view.

• From this position, the transducer is slightlyrotated anti-clockwise and carefully tiltedanteriorly.

• Using color Doppler, coronary blood flow inthe posterior interventricular groove can beidentified.

• After detection of the characteristicpredominant diastolic blood flow in thebasal part of the posterior interventriculargroove, the sample volume (2.0-3.5mm) ispositioned for spectral Doppler analysis ofcoronary blood flow.

Proximal part of right coronary artery (RCA) in, modified apical 5C view

Duplex examination of proximal part of the RCA in modified apical 5C view

Distinction between the posteriordescending coronary artery (PDA)and concomitant posterior cardiacvein (PCV):

A – the PDA is slighter, located closer tothe left ventricle and demonstrates abiphasic predominantly diastolic flowwithout respiratory variations

B – the PCV is larger, located closer tothe right ventricle and demonstrates athree-phase predominantly systolic flowwith high respiratory variations;

C- simultaneous image of the PDA andPCV.

Success rate of the detection of main coronary arteries by TTE (%) (Boshchenko et al,2008

Success rate of the detection of one and more segments of each coronary artery by TTE (%) (Boshchenko et al

Success rate in visualizing distal coronary arteries by TTE

Detection of the left internal mammary artery

• The proximal mammary artery is bestvisualized from a supraclavicular view usinghigh frequency transducer (8 MHz lineartransducer).

• A patent mammary artery graft is recognizedby its typical baseline spectral Doppler flowprofile, showing considerably higher diastolicblood flow velocity compared to the othervessels originating in close proximity to thesubclavian artery

Transesophageal echocardiography

• The best way to image the proximal segmentof the coronary artery is a transesophagealshort axis view at the level of the aortic bulbwith a slight anteflexion of the probe.

• From this view the left main stem and theproximal LAD can be visualized in about 70 to90% of patients.

• The success rate in imaging the proximalsegment of the left circumflex is even higher(75 to 90%).

• The best way to visualize the ostium of theright coronary artery is a sagittal scanningplane showing the ascending aorta in along axis (Lambertz H et al., 2000).

• With a slight clockwise rotation of theprobe,a short segment of the rightcoronary artery originating from the aorticbulb can be imaged from the majority ofpatients

• Transesophageal echocardiography, with or without contrast, is a low costmethod and easily repeatable, which can be used to evaluate coronarycirculation in selected patients.

• This approach has less clinical importance in evaluating the hemodynamicrelevance of a left anterior descending artery stenosis.

• Most of the left anterior descending artery stenoses are located distal tothose left anterior descending artery segments that can be visualized byTransesophageal echocardiography.

• Approximately 20% to 30% of the patients cannot be investigated byDoppler because of respiration, obesity, chest deformity andemphysema, acute changes in cardiac volume, or inadequately stableposition of the Doppler signal.

• Flow in the branches could be erroneously interpreted as the flow in themain trunk.

• This could happen for LAD in the two-chamber or in the short axis view,where a long diagonal branch or the first septal perforator might also bevisualized.

Clinical utilization of echocardiographic coronary imaging…

Coronary artery patency

• In situation of acute myocardial infarction, a non-invasive way tovisualize the LAD should be of great help to diagnose the success ofreperfusion.

• In this setting, the sensitivity, specificity, PPV, NPV and accuracy of thetransthoracic echo Doppler in the noninvasive assessment of the LADreperfusion with 2.5MHz transducer were 81.6%, 64%, 90.7%, 54% and78% respectively (H. Farouk et al.,2010).

• Detection of the distal LAD flow by TTDE was significantly correlatedwith the reperfusion as assessed by coronary angiography.

• Epicardial coronary flow is not always synonymous with cellular myocardialperfusion as seen in the no-reflow phenomenon.

• Visualization of septal perforator flow can be a more reliable marker ofreperfusion.

• Voci et al ( 2004) considered a myocardial segment to be reperfused whenat least two of the predicted four to five perforators could be visualized bytransthoracic echo after acute MI.

RECANALISATION SCORE

• A recanalization score (RS) of 1 to 4 was used—where 1 = LAD closed, noperforators; 2 = LAD open, no perforators; 3 = LAD open, 1 to 2segments with perforators; 4 = LAD open, 3 to 4 segments withperforators.

• RS discriminated recovery of ventricular function better than TIMI flow.

• The RS was the best single multivariate predictor (p < 0.0001) of percentchanges in wall motion score index and the ejection fraction

Diastolic deceleration time

• Antti Saraste et al, (2005) found that diastolic deceleration time of the LADflow velocity correlated with myocardial fluorodeoxyglucose uptake in theLAD territory.

• Diastolic deceleration time was markedly longer in patients with viablemyocardium than partially viable or non-viable myocardium.

• A DDT < 190ms is always associated with nonviable myocardium.

Total Coronary Occlusion

• The absence of coronary flow on color Doppler map is not a reliable sign of totalocclusion.

• At present, TTE is not a suitable method to diagnose acute coronary occlusions.However, chronic total occlusions (CTO) can be picked up by identifying coronarycollaterals.

• Watanabe et al. proposed the reversal of coronary flow in epicardial collateralvessels to be the main ultrasound sign of CTO.

• Retrograde flow in distal LAD is a good marker of total LAD occlusion with 88%sensitivity and 100% specificity and retrograde flow in PDA is a good marker ofRCA occlusion with 67% sensitivity and 100% specificity.

• Identifying intramyocardial collateralsin the interventricular septum hasincreased the sensitivity in the CTOdetection from 88% to 96% for theLAD and from 67% to 80% for the RCA.

• Identifying collateral flow ininterventricular septum is a vital clueto diagnose anomalous left coronaryartery origin from pulmonary artery.

Left Main Coronary Artery Stenosis

• Using the criteria of either color aliasing or apeak diastolic flow velocity of >1.5 m/s, LMstenosis of >50% could be diagnosed with asensitivity of 85% and specificity of 88%.

• LM flows should be specifically assessed byTTE in patients with rest angina, familialhypercholesterolemia, Takayasu disease(aortoarteritis), and also in patients whoundergo LM stenting to assess stent patency.

• Prior knowledge of LM stenosis will enable theangiographer to take precautions whileengaging the LM ostium during coronaryangiography

Severe coronary stenosis

• Coronary artery stenosis could be identified with color Doppler as localspot of turbulence.

• An abnormal maximal-to-prestenotic blood flow velocity ratio greaterthan 2.0 would signify a critical stenosis.

• This has an overall sensitivity of 82% and specificity of 92%.

• The sensitivity and specificity were, respectively, 73% and 92% for LAD,63% and 96% for RCA, and 38% and 99% for LCx stenoses.

Recanalized LAD after Thrombolysis

• Anjaneyulu A, Raghavaraju , Johann C, Krishnamraju P, Rajagopalaraju A, etal. had attempted to show reperfusion after thrombolysis in LAD in 12patients of acute anterior wall MI.

• In seven patients, flow could be demonstrated in LAD within 15 min to 6 hafter initiating thrombolysis.

• Furthermore, a focal area of color turbulence could be shown in thesepatients in LAD after the reappearance of flow , which correlated with thesite of significant stenosis on coronary angiography.

Recanalized left anterior descending flow 60 min after thrombolysis. (a) Focal area of mosaic flow in mid LAD. (b)Coronary angiogram in the same patient showing severe stenosis (90%) in mid LAD

In-stent Restenosis

• Direct assessment of stent flow is possiblein LM and proximal LAD segments. Anyturbulence with increased flow velocities>1.5 M/s would suggest restenosis.

• Indirect assessment of LAD and RCA stentscan be done by evaluating coronary flowreserve (CFR). A CFR value of <2 afterintravenous adenosine in distal LAD wouldsuggest significant in-stent restenosis inproximal or mid-LAD.

• A similar finding in PDA would suggestin-stent restenosis in RCA.

Ischemic Cardiomyopathy

• When a diagnosis of dilated cardiomyopathy is made by TTE, thepresence of mosaic flow pattern in proximal coronary arteries (LM, LAD,or LCx) is a strong pointer to ischemia as the cause for myocardialdysfunction.

• It is worthwhile to interrogate the proximal coronary segments by TTE todiagnose ischemic cardiomyopathy, in which myocardial dysfunction canbe improved with revascularization

Coronary Flow Reserve (CFR)

• CFR is defined as the ability of coronary blood flow volume to increase undermaximal coronary hyperemia when compared with flow volume at rest.

• TDE-CFR is defined as hyperemic diastolic mean (or peak) flow velocity divided bybaseline flow velocity.

• Intracoronary Doppler with adenosine or papaverine infusion remains to be thereference standard for the assessment of CFR.

• Hozumi et al. performed the first validation of TTE comparing CFR in the LAD withsimultaneous intracoronary doppler guidewire assessment.

• TTE reflected the invasive measurement of coronary flow velocity and CFRaccurately, and the agreement between the two methods was 0.98 for diastolicpeak velocity and 0.97 for CFR.

• CFR assessment may be performed at the bedside within a few minutes.

• Adenosine should be infused intravenously at the rate of 140 mcg/kg/minfor 2 min. Coronary flow velocities are measured before and immediatelyafter the cessation of adenosine infusion.

• Distal LAD is the preferred site for assessment of flow velocities. Thenormal range of CFVR for both men and women is ≥2.7

• The cutoff value for CFR is generally accepted to be 2.0 for predictingsignificant LAD stenosis in patients, for decision making regardingintervention, after intracoronary intervention, and with in-stent restenosis

• The feasibility of TDE-CFR for LAD artery is very high, with more than 90%in experienced hands, and nearly 100% with the use of intravenouscontrast agents (Caiati C et al., 1999).

• The feasibility is less in the PDA artery, between 54and 86% due totechnical limitations (Hozumi T et al., 1998, Lethen H et al., 2003, Ueno Yet al., 2002).

• The measurements of TDE-CFR, in the LAD as in the PDA arteries, areclosely correlated with invasive measurements using a Doppler flow wire.

• The feasibility of TDE-CFR in the circumflex artery is more challenginggiven the particular anatomy of this artery and the poor resolution of thelateral wall.

• In one study by Pizzuto F et al. CFR with a cutoff value <2.0 was asignificantly better predictor (90% sensitivity and 96% specificity) of LADstenosis than multidetector computed tomography (80% sensitivity and93% specificity).

• A transthoracic CFR in the LAD <2.0 provided data consistent with thoseobtained by single-photon emission computed tomography for physiologicestimation of stenosis severity with 94% sensitivity and 100% specificity(Hirate)

Conclusion

• TTE with the help of harmonic imaging, contrast agents, andhigh-frequency transducers can be used for the diagnosis of coronarystenosis as a noninvasive, inexpensive, non-X-ray, high time resolutiontechnique.

• Doppler TTE assessment of coronary flows in CAD patients can provide alot of useful functional information with a wide range of clinicalapplications.

• Echocardiography can be used to visualize the epicardial coronary arteries directly in a large proportion of patients.

• The success is greatest in children, ostia of the left and right coronaryarteries and in the LAD.

• It is unlikely, at least in the near future, that echo can provide completeanatomical assessment of the coronary tree.

• X-ray bases modalities, angiography and CT are still superior in providinganatomical details.

• In some clinical situations, echo can provide very useful data regardingcoronary patency, severe stenosis, moderate coronary lesions, the state ofthe microcirculation and congenital coronary anomalies.

Thank you