Efforts toward quantitation of coronary artery functional capacity

Digital angiographic assessment of the physiological changes to the regional microcirculation induced by successful coronary angioplasty

BACKGROUND

Impulse response analysis of digital coronary angiographic images calculates a parameter known as the mean transit time of the microcirculation (Tmicro). This has been shown to accurately assess the regional microcirculatory response to proximal stenosis in relation to flow. Our goal was to apply impulse response analysis to patients undergoing successful angioplasty and to quantify the induced physiological changes with respect to quantitative angiographic measurements of stenosis dimensions.

METHODS AND RESULTS

We studied 24 patients before and after successful single-vessel percutaneous transluminal coronary angioplasty (PTCA). Minimal luminal stenosis area was increased from 0.9 +/- 0.6 before PTCA to 4.1 +/- 1.3 mm2 after PTCA (P < .0001). In all patients this was accompanied by an increase in the inverse of Tmicro (Tmicro-1), from 8.5 +/- 3.0 to 26.5 +/- 9.0 min-1 (P < .0001) with a linear correlation between Tmicro-1 and minimal luminal stenosis area (r = .73; SEE = 7.74). Stenosis flow reserve, estimated by integration of stenosis dimensions, increased in all patients from 1.8 +/- 1.0 to 4.5 +/- 0.4 after PTCA (P < .01). A comparison of Tmicro-1 with stenosis flow reserve revealed a nonlinear relation. In 16 patients undergoing PTCA of the left anterior descending or circumflex artery, contrast injections into the left main stem allowed simultaneous measurements of Tmicro-1 in the adjacent, nonstenotic artery. Adjacent artery Tmicro-1 did not change after PTCA (25.8 +/- 6.2 compared with 25.6 +/- 6.8 min-1 before PTCA; P = NS); moreover, Tmicro-1 of the dilated artery measured after PTCA was equivalent to the nonstenotic adjacent artery, indicating normalization of microcirculatory responses.

CONCLUSIONS

These data suggest that Tmicro-1 determined by digital angiographic impulse response analysis of a single contrast injection under resting flow conditions may be a practical method to assess the regional microcirculatory response to changes in stenosis severity effected by coronary angioplasty.

Coronary flow reserve calculated from pressure measurements in humans. Validation with positron emission tomography

BACKGROUND

Experimental studies have shown that fractional flow reserve (defined as the ratio of maximal achievable flow in a stenotic area to normal maximal achievable flow) can be calculated from coronary pressure measurements only. The objectives of this study were to validate fractional flow reserve calculation in humans and to compare this information with that derived from quantitative coronary angiography.

METHODS AND RESULTS

Twenty-two patients with an isolated, discrete proximal or mid left anterior descending coronary artery stenosis and normal left ventricular function were studied. Relative myocardial flow reserve, defined as the ratio of absolute myocardial perfusion during maximal vasodilation in the stenotic area to the absolute myocardial perfusion during maximal vasodilation (adenosine 140 micrograms.kg-1 x min-1 intravenously during 4 minutes) in the contralateral normally perfused area, was assessed by 15O-labeled water and positron emission tomography (PET). Myocardial and coronary fractional flow reserve were calculated from mean aortic, distal coronary, and right atrial pressures recorded during maximal vasodilation. Distal coronary pressures were measured by an ultrathin, pressure-monitoring guide wire with minimal influence on the trans-stenotic pressure gradient. Minimal obstruction area, percent area stenosis, and calculated stenosis flow reserve were assessed by quantitative coronary angiography. There was no difference in heart rate, mean aortic pressure, or rate-pressure product during maximal vasodilation during PET and during catheterization. Percent area stenosis ranged from 40% to 94% (mean, 77 +/- 13%), myocardial fractional flow reserve from 0.36 to 0.98 (mean, 0.61 +/- 0.17), and relative flow reserve from 0.27 to 1.23 (mean, 0.60 +/- 0.26). A close correlation was found between relative flow reserve obtained by PET and both myocardial fractional flow reserve (r = .87) and coronary fractional flow reserve obtained by pressure recordings (r = .86). The correlations between relative flow reserve obtained by PET and stenosis measurements derived from quantitative coronary angiography were markedly weaker (minimal obstruction area, r = .66; percent area stenosis, r = -.70; and stenosis flow reserve, r = .68).

CONCLUSIONS

Fractional flow reserve derived from pressure measurements correlates more closely to relative flow reserve derived from PET than angiographic parameters. This validates in humans the use of fractional flow reserve as an index of the physiological consequences of a given coronary artery stenosis.

Comparison of digital and cine coronary arteriography

Digital coronary arteriography has advanced from a curiosity to a powerful clinical tool. This development has been motivated by the new imaging demands of interventional cardiology, by the need for quantifying atherosclerotic disease, and by advances in computer and video technology. Digital imaging has now essentially replaced cinefilm for clinical decision making in some catheterization laboratories, although uncertainty remains regarding the diagnostic comparability of the two modalities. Therefore, we compared simultaneously acquired digital and cine arteriograms from 18 patients with multivessel coronary artery disease. Digital utilized pulse-progressive technique, a 512 x 512 pixel x 8 bit image matrix, and no post processing. Four angiographers interpreted the arteriograms, identifying 131 stenotic lesions for measurement with manual calipers. Measurements of percent diameter stenosis by digital and cine correlated closely (r = 0.88), but digital estimated stenoses to be significantly more severe than cine (p less than 0.0001). This difference was most significant in small (less than 2 mm diameter) arteries, in branch arteries, and with mild stenoses. The differences between digital and cine were not statistically significant for stenoses greater than 50% diameter narrowing. Interobserver variability was similar for digital and cine imaging. Thus, unprocessed digital and film-based coronary arteriography yield similar assessments of atherosclerotic stenoses, but the techniques may not be diagnostically interchangeable. This paper discusses the technical advances which have occurred in digital coronary arteriography, the comparability of digital and cine imaging, and the factors which may be responsible for observed differences between the two modalities.

Quantitative rotational thallium-201 tomography for identifying and localizing coronary artery disease

The purpose of this study was to develop and validate a method for quantifying the uptake, redistribution, and washout of thallium-201 (201Tl) obtained with rotational tomography. This method generates maximum count circumferential profiles of the short-axis slices of the left ventricle, translates them into polar coordinate profiles, and displays them as a bullseye plot, which consists of a series of concentric circles with the apex at the center and the base at the periphery. Normal limits were established for the distribution of 201Tl in 36 patients with a low (less than 5%) probability of coronary artery disease (CAD). Forty-five patients who had undergone coronary angiography were used as a pilot group to define criteria for the identification and localization of perfusion defects. The best agreement with the results of angiography was found when abnormal regions of the bullseye were defined as contiguous defects over 2.5 SDs below normal. These criteria were applied prospectively to 210 points (179 points with greater than 50% diameter stenosis and 31 with less than 50%). Visual, quantitative, and combined visual and quantitative analysis were compared for overall detection of disease and for detection of individual vessel involvement. The overall sensitivity for detection of disease by these methods was 97%, 95%, and 95%, respectively. The specificities were 68%, 74%, and 71% respectively. The sensitivity for detection of individual vessel involvement with the bullseye alone was 78% for the left anterior descending artery (LAD), 89% for the right coronary artery (RCA), and 65% for the left circumflex (LCx). For visual analysis, the results were 70%, 88%, and 50%, respectively, while the use of visual and quantitative analysis combined identified 75% of LAD, 87% of RCA, and 55% of LCx lesions. We conclude that quantitative analysis of rotational 201Tl tomographic images is a highly accurate technique for determining the presence and location of CAD.

Automated quantitative coronary arteriography: morphologic and physiologic validation in vivo of a rapid digital angiographic method

Quantitative coronary arteriography has been shown to be useful in assessing the extent of coronary disease, its functional significance, and its response to therapeutic interventions. Most current methods rely either on hand-drawn arterial contours or automatic edge-detection algorithms applied to 35 mm cineangiograms. To assess the performance in vivo of a new, fully automatic, rapid coronary quantitation program, dogs were instrumented with precision-drilled, plastic cylinders to create intraluminal stenoses in the left anterior descending and/or circumflex arteries, as well as with high-fidelity micromanometers and electromagnetic flow probes. Stenosis diameters ranged from 0.83 to 1.83 mm. Biplane, on-line, digital coronary angiograms and cineangiograms were recorded during standard selective coronary arteriography in the closed-chest preparation. The on-line digital images were analyzed in nonsubtracted and subtracted modes. Cineangiograms were digitized to allow coronary quantitation by the same computer program. There was an excellent correlation between known and measured minimal diameter stenoses (r = .87 to .98, SEE = 0.09 to 0.24 mm). Interobserver and intraobserver variability analysis showed high reproducibility (r = .90 to .97, SEE = 0.12 to 0.23 mm). The best results in both analyses were achieved by nonsubtracted digital imaging and the worst by cineradiography. Measures of percent diameter stenosis, percent area stenosis (geometric and videometric), and absolute minimal cross-sectional area (geometric and videometric) were all significantly correlated with independent measures of actual coronary flow reserve. This study provides direct anatomic and physiologic validation in vivo of a new and rapid coronary quantitation method suitable for analysis of both digital angiograms and cineangiograms.