Quantitative assessment of stenotic aortic valve area by using intracardiac echocardiography: in vitro validation and initial in vivo illustration

The QuantumCor device for treating mitral regurgitation: an animal study

OBJECTIVES

The mitral annular contraction achieved could help reduce mitral regurgitation (MR), and with appropriate modifications, be applied to human subjects providing a potentially effective percutaneous method of valve repair.

BACKGROUND

MR is an important source of morbidity and is an independent predictor of mortality. A variety of percutaneous approaches are being developed to address this issue. We introduce a novel potential method utilizing radiofrequency (RF) energy to heat and shrink the mitral valve annulus in an animal model.

METHODS

In open-heart procedures in 16 healthy sheep (six with naturally occurring MR), we used a malleable probe (QuantumCor, Lake Forest, CA) that conforms to the annular shape to deliver RF energy via a standard generator to replicate a surgical mitral annular ring. Seven sheep were followed chronically and their mitral annulus dimensions measured serially.

RESULTS

All sheep underwent intracardiac echocardiography or direct circumferential measurement of the mitral annulus before and after RF therapy. RF therapy was administered in less than 4 min in each case, and the mean anteroposterior (AP) annular distance was reduced by a mean of 23.8% (AP diameter reduction 5.75 +/- 0.86 mm, P < 0.001) acutely. In the six sheep with nonischemic MR, regurgitation was eliminated. Acute histopathology (HP) demonstrated no damage to the leaflets, coronary sinuses, or coronary arteries. At the end of the intended 6-month period of the chronic part of the study, four of the seven animals survived. The four treatment animals showed significant reductions in mitral A-P dimension, with a percent diameter reduction of 26.4% (AP diameter reduction 7 +/- 2.3 mm).

CONCLUSION

The application of RF directly to heat the mitral annulus has resulted in sustained contraction of the annulus in this limited preclinical animal study. With further study and possible modifications, it holds promise for future application in human subjects with MR.

New applications of intracardiac echocardiography: assessment of coronary blood flow by colour and pulsed Doppler imaging in dogs

OBJECTIVE

To explore the application of a new 10 French intracardiac echocardiography (ICE) catheter with phased array and Doppler capable transducer for the assessment of epicardial and intramyocardial coronary blood flow.

METHODS

The coronary arteries were detected by cross sectional imaging in seven closed chest dogs, and coronary blood flow visualised by colour Doppler. Blood flow velocities were recorded by pulsed Doppler at baseline for reproducibility of repeated measurements, and during hyperaemia for coronary flow reserve measurements. Comparisons were made with Doppler guide wire data obtained simultaneously. Intramyocardial coronary artery blood flow was assessed by colour flow mapping, and the blood flow velocities recorded using pulsed Doppler at baseline and during hyperaemia.

RESULTS

Seven left main, six left anterior descending, seven left circumflex, and five right coronary arteries were visualised in the seven animals by cross sectional or colour Doppler imaging. Repeated measurements of coronary flow velocity showed a good correlation (mean diastolic velocity, r = 0.93, n = 22, p < 0.0001; peak diastolic velocity, r = 0.96, n = 22, p < 0.0001, respectively). Intraobserver/interobserver variability was satisfactorily low. Coronary flow reserve from ICE correlated highly with the value obtained from the Doppler guide wire (r = 0.90, n = 26, p < 0.0001). Intramyocardial coronary blood flow was identified in all seven dogs, and flow velocities were recorded at baseline and during hyperaemia in four animals.

CONCLUSIONS

This new ICE catheter provides high quality diagnostic resolution. It is useful for coronary blood flow assessment.

Intracardiac echocardiography: newest technology

Intracardiac echocardiography, defined as ultra-sonographic navigation and visualization within large blood-filled cavities or vessels of the cardio-vascular system, has recently undergone refinement as a clinical tool through technologic advances in transducer miniaturization. Intra-cardiac ultra-sound catheters image at lower frequencies than current conventional intravascular ultrasound catheters used for intracoronary imaging. The lower imaging frequency enables greater tissue penetration, permitting whole-heart evaluation from a right-sided catheter position. Newer devices are steerable, have variable imaging frequency (5.5 to 10 MHz), and full Doppler capability (pulsed, continuous wave, and tissue Doppler). These advances have made intracardiac high-resolution imaging as well as hemodynamic assessment possible. A historical perspective, current capabilities and limitations, and potential clinical and research applications of this new imaging technique are discussed.

Transvascular Imaging: Feasibility Study Using a Vector Phased Array Ultrasound Catheter

BACKGROUND: Transvascular imaging is defined as the acquisition of anatomic and functional information of structures lying beyond the confines of a vascular conduit within which the imaging device resides. Interrogating structures surrounding the vascular conduit is the subject of this feasibility study using a novel underblood, phased array ultrasound-tipped catheter. METHODS: An intravascular catheter (10-F, 3.2-mm-diameter, four-way articulation) tipped with a 5.5- to 10-MHz frequency agile, vector phased array transducer with full Doppler capability (Sequoia, Acuson) was used. The imaging transducer has a wide range of tissue penetration (2 mm to >10 cm from the lens). The catheter was introduced via an 11-Fr femoral venous sheath into the inferior and superior vena cavae and right heart chambers. As the catheter was advanced, attention was directed to visualization of structures surrounding the vessel in which the catheter resided. RESULTS: From the cavae and femoral vein the thoracic, abdominal and femoral arteries could be easily imaged. Anatomy that was visualized included the liver, hepatic veins, gallbladder, and mesenteric vessels. Normal and pathological anatomy and Doppler physiology could be readily appreciated. Doppler (i.e., pulsed- and continuous-wave, color flow, and tissue Doppler) fostered unique transvascular physiological hemodynamic and flow assessment. CONCLUSION: Transvascular imaging is feasible in human subjects using this 10-Fr catheter tipped with a 5.5- to 10-MHz vector phased array transducer. Intravascular navigation to a desired location within the body and the performance of diagnostic or therapeutic procedures at a remote site under direct ultrasound visualization are possible. Full Doppler capability extends the concept of transvascular hemodynamic and physiological assessment.

Potential applications of intracardiac echocardiography in the assessment of the aortic valve from the right ventricular outflow tract

Intracardiac echocardiography (ICE) is a developing technology and a promising method for visualizing intracardiac structures. However, its applications are currently limited to guidance during mitral valvuloplasty, catheter ablation, or electrophysiologic examination. The goal of this study was to observe the aortic valve, measure the annular diameter of the valve by ICE through a right-sided approach, and compare the results by ICE with those by transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE). We studied 18 patients (9 men, 9 women, aged 19 to 72 years) with various heart diseases, including 15 patients with mitral or aortic valvular disease. An imaging catheter was advanced through a long sheath into the outflow tract of the right ventricle. We obtained good longitudinal views of the aortic valve in all patients. Two of the 18 patients had poor image quality by TTE. The annular diameter by ICE correlated more closely with TEE than with TTE. In conclusion, right-sided ICE is a safe, simple, and useful procedure for observing the aortic valve during cardiac catheterization without additional discomfort in the patients. Right-sided ICE is superior to TTE in observing the aortic valve and measuring the annular diameter of the valve. The annular diameter can be measured by ICE as precisely as by TEE.

Three-dimensional surface area of the aortic valve orifice by three-dimensional echocardiography: clinical validation of a novel index for assessment of aortic stenosis

BACKGROUND

A direct and accurate method of assessing aortic valve area (AVA) in patients with aortic stenosis (AS) is desirable because of the well-known theoretical and practical limitations of the currently available methods. We assessed the clinical feasibility and accuracy of a novel index, the 3-dimensional surface area (3-DSA) of the aortic valve orifice by 3-dimensional transesophageal echocardiography (3-DTEE) in patients with AS.

METHODS

Intraoperative 3-DTEE was performed in 23 consecutive patients (mean age 58 +/- 15 years) with valvular AS using a Toshiba SSA-380A system with a multiplane TEE probe and a TomTec EchoScan system. The 3-DTEE acquisition, processing and reconstruction were conducted and the aortic valve orifice presented using a "surgeon's aortotomy view" (aortic valve orifice as if viewed through an open aortic root). The 3-D images were videotaped and calibrated and the 3-DSA measured by planimetry of the inner surface of the aortic valve leaflets at the maximal systolic opening using the dynamic 3-D images. For comparison, the 2-D cross sectional area (2-DCSA) of the aortic valve was also determined by 2-DTEE. The 3-DSA and 2-DCSA were compared with the AVA by the invasive Gorlin formula and the Doppler continuity equation method by transthoracic echocardiography.

RESULTS

The 3-DSA and 2-DCSA measurements were feasible in all but one patient. Both 3-DSA and 2-DCSA correlated moderately well with the AVA by the Gorlin formula (n = 17, r = 0.66, standard error of the estimate [SEE] = 0.3 cm2, P <.05 for 3-DSA and r = 0.61, SEE = 0. 5 cm2 P <.05 for 2-DCSA, respectively). They also correlated well with the AVA by Doppler continuity equation method (n = 22, r = 0.90, SEE = 0.1 cm2, P <.05 for 3-DSA and r = 0.83, SEE = 0.3 cm2, P <.05 for 2-DCSA, respectively). There was no statistically significant difference between the 3-DSA and AVA by both the Gorlin formula (Delta = 0.1 +/- 0.3 cm2, P =.3) and the Doppler continuity equation (Delta = -0.0 +/- 0.3 cm2, P =.7). In contrast, the 2-DCSA significantly overestimated AVA by the Gorlin formula (Delta = 0.5 +/- 0.5 cm2, P <.005) and by the Doppler continuity equation (Delta = 0.5 +/- 0.6 cm2, P <.0001).

CONCLUSIONS

Planimetry of 3-DSA of the aortic valve orifice by 3-DTEE is a clinically feasible and relatively accurate technique for assessment of AVA and is superior to 2-DCSA by 2-DTEE.

Quantification of the aortic valve area in three-dimensional echocardiographic data sets: analysis of orifice overestimation resulting from suboptimal cut-plane selection

BACKGROUND

Our study was designed to determine the feasibility of three-dimensional echocardiographic (3DE) aortic valve area planimetry and to evaluate potential errors resulting from suboptimal imaging plane position.

METHODS AND RESULTS

Transesophageal echocardiography with acquisition of images for 3DE was performed in 27 patients. Aortic valve orifice was planimetered in two-dimensional echocardiograms (2DE) and in two-dimensional views reconstructed from 3DE data sets optimized for the level of the cusp tips. To evaluate the errors caused by suboptimal cut-plane selection, orifice was also measured in cut-planes angulated by 10, 20, and 30 degrees or shifted by 1.5 to 7.5 mm. Planimetered orifice areas was similar in 2DE and 3DE studies: 2.09 +/- 0.97 cm2 versus 2.07 +/- 0.92 cm2. Significant overestimation was observed with cut-plane angulation (0.09, 0.19, and 0.34 cm2 at 10 degree increments) or parallel shift (0.11, 0.22, 0.33, 0.43, and 0.63 cm2 at 1.5 mm increments). Three-dimensional echocardiographic measurement reproducibility was very low and superior to that of 2DE.

CONCLUSIONS

Three-dimensional echocardiography allows accurate aortic valve area quantification with excellent reproducibility. Relatively small inaccuracy in cut-plane adjustment is a major source of errors in aortic valve area planimetry.