Assessment of immediate and long-term functional results of percutaneous transluminal coronary angioplasty

Maximal myocardial perfusion by videodensitometry in the assessment of the early and late results of coronary angioplasty: relationship with coronary artery measurements and left ventricular function at rest

In the assessment of the acute results of percutaneous transluminal coronary angioplasty (PTCA), myocardial perfusion at maximal vasodilatation theoretically has fewer limitations than the coronary flow reserve measurements and quantitative coronary angiography. The purpose of this study was to compare the myocardial perfusion to the measurements of the severity of the lesion (minimal luminal diameter and percent area stenosis) and to relate it to the changes of left ventricular function after PTCA. Regional myocardial perfusion was assessed during intracoronary papaverine, using the inverse mean transit time of contrast medium (1/Tmn), before, 15 min after, 18-24 hr after, and 6 months after successful single-vessel PTCA in 14 patients with stable angina. Left ventricular angiography (before angioplasty, 18-24 hr after, and 6 months later) was analysed by area-length and centerline methods. Immediately after PTCA, 1/Tmn increased from 0.14 +/- 0.07 sec-1 to 0.21 +/- 0.09 sec-1 (P = .001). Maximal myocardial perfusion remained higher than the pre-PTCA value the day after angioplasty (1/Tmn of 0.23 +/- 0.09 sec-1), while it reduced to near pre-PTCA values at follow-up (1/Tmn of 0.16 +/- 0.05 sec-1). Before PTCA, three out of ten patients had ejection fraction of < 65%, and seven had mild-to-moderate hypokinesis. The day after PTCA the ejection fraction and the regional dysfunction improved significantly. The change in ejection fraction 18-24 hr after PTCA did not correlate with minimal luminal diameter and percent area stenosis and correlated slightly with the improvement of perfusion (r = 0.54, P = .10). At follow-up left ventricular function deteriorated in the whole group, despite the persistence of angiographic success of PTCA, possibly because of changes in the loading condition. Coronary artery stenosis measurements and 1/Tmn failed to correlate with the left ventricular function. Given the difficulties in routine application of the analysis of time-density curves, the measurement of minimal luminal diameter remains a more practical assessment of the results of the intervention. However, the improvement of myocardial perfusion may give more information than coronary artery dimensions of the early recovery of left ventricular function.

Predictive value of reactive hyperemic response on reperfusion on recovery of regional myocardial function after coronary angioplasty in acute myocardial infarction

BACKGROUND

The objective of the study was to determine the coronary vasodilatory reserve in reperfused myocardium in patients with acute myocardial infarction and its relation to regional myocardial function.

METHODS AND RESULTS

The study population consisted of 22 patients with acute myocardial infarction who underwent successful coronary angioplasty. The vasodilatory reserve in the reperfused myocardium was assessed quantitatively using computer-assisted digital subtraction cine-angiography immediately after angioplasty and at follow-up angiography before hospital discharge. Myocardial contrast medium appearance time and density were determined before and after pharmacological hyperemia induced by an intracoronary injection of 12.5 mg papaverine. Global and regional left ventricular functions were determined from contrast angiography. After papaverine, the mean contrast medium appearance time decreased significantly from 3.5 +/- 0.7 to 2.7 +/- 0.7 cardiac cycles (P < .000005) immediately after successful coronary angioplasty and from 3.8 +/- 0.7 to 2.7 +/- 0.9 cardiac cycles (P < .000005) at angiography before hospital discharge. The mean contrast medium density increased significantly from 48.7 +/- 13.8 to 61.0 +/- 19.0 pixels (P < .003) and from 49.6 +/- 19.7 to 80.3 +/- 29.6 pixels (P < .000005), respectively. As a consequence, the calculated coronary flow reserve increased significantly from 1.8 +/- 0.7 to 2.6 +/- 1.0 (P < .0008). The global ejection fraction increased significantly from 52 +/- 12% to 58 +/- 14% (P < .03), primarily because of a significant improvement in the regional myocardial function of the infarct zone from 20.8 +/- 9.0% to 26.0 +/- 10.5% (P < .001). Coronary flow reserve correlated well with regional myocardial function both during the acute phase (R = .79, P < .002) and at follow-up angiography (R = .82, P < .000004). Interestingly, coronary flow reserve measurement on reperfusion, immediately after angioplasty, correlated significantly with regional myocardial function at follow-up angiography (R = .81, P < .00003).

CONCLUSIONS

The results indicate that there is a pharmacologically inducible vasodilatory reserve in reperfused ischemic myocardium after successful coronary angioplasty in patients with acute myocardial infarction and that this is increased at 10-day follow-up angiography. More important, the degree of reactive hyperemic response on reperfusion has a predictive value regarding the ultimate degree of recovery of regional myocardial function. Quantitative assessment of reperfusion may be useful in investigating the role of coronary reperfusion and salvage of myocardial function.

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.

Restenosis revisited: insights provided by quantitative coronary angiography

In this editorial, the problem of restenosis after coronary balloon angioplasty and other transluminal interventions is reviewed from the perspective of quantitative coronary angiography. The review is largely based on the experience of the Thoraxcentre in the application of quantitative angiography to the study of restenosis over the past decade, with incorporation and discussion of relevant and significant contributions from other groups. Current discrepancies in the angiographic definition of restenosis are highlighted and the use of percent diameter stenosis or MLD as the measurement parameter of choice is objectively addressed. Perspectives on the pathologic paradigm of restenosis are briefly reviewed as a basis from which to evaluate quantitative angiographic information provided by various studies. Particular attention is then paid, in chronologic fashion, to discussion and elaboration of insights to the restenosis process provided by quantitative angiographic studies, which have led to the introduction of some new methodological approaches to the comparison of short- and long-term angiographic luminal changes after various interventions. A word of caution on the potential pitfalls of quantitative angiographic studies is provided and counterbalanced with a discussion of clinical correlations of quantitative angiographic measurements. Finally, a proposal is made for the application of quantitative angiographic measurements to randomized clinical trials for the purpose of comparing new interventional devices.

Inability of coronary blood flow reserve measurements to assess the efficacy of coronary angioplasty in the first 24 hours in unselected patients

To determine functional and anatomic changes in the first 24 hours after coronary angioplasty, we studied at random 15 patients (9 men, mean age 60 years) who underwent coronary angioplasty of 16 coronary arteries. Quantitative coronary angiography and coronary flow reserve measurements from digitized coronary angiograms were performed before, immediately after, and 24 hours after coronary angioplasty. Calculated were the minimal luminal diameter, obstruction area, and percentage diameter stenosis from two preferably orthogonal projections. Prior myocardial infarction in the myocardial region of interest was present in four patients. Seven patients had multivessel disease. Collateral vessels supplying the compromised flow region were observed in three patients. Six patients had refractory unstable angina pectoris. After coronary angioplasty, angiographically visible dissection was noted in six patients, whereas side branch occlusion was observed in one. Minimal luminal diameter before, immediately after, and 24 hours after was 0.93 +/- 0.18 mm, 1.53 +/- 28 mm, and 1.53 +/- 0.21 mm, respectively; obstruction area was 0.70 +/- 0.26 mm2, 1.92 +/- 0.69 mm2, and 1.87 +/- 0.51 mm2, respectively; diameter stenosis was 60.4 +/- 8.0%, 36.8 +/- 11.4%, and 37.6 +/- 5.3%, respectively. The coronary flow reserve (lower limit of normal with this technique 3.4) was essentially the same before and immediately after coronary angioplasty (1.26 +/- 0.59 vs 1.30 +/- 0.42, p = NS) with a slight improvement to 1.78 +/- 0.90 (p less than 0.05) 1 day later. Coronary artery dimensions correlated poorly with coronary blood flow reserve before and after angioplasty.(ABSTRACT TRUNCATED AT 250 WORDS)

Coronary restenosis: what have we learned from angiography?

Coronary restenosis remains a major problem for interventional cardiology not only by virtue of its frequency, but also because of the current inability to prevent it. Symptomatic status and non-invasive evaluation have been used to study restenosis, but both lack specificity and sensitivity, particularly in patients with multivessel disease. Angiography remains the reference standard. Several arbitrary definitions have been used, some related to visual estimates of coronary stenosis and others to quantitative angiographic techniques. In another approach, linear modeling is used to assess minimal luminal diameter of lesions on restudy. Although angiographic studies have been essential in the study of restenosis, questions concerning the underlying mechanism and pathophysiology remain. The development of animal models that closely resemble human restenosis should allow evaluation of pathophysiologic mechanisms and development of new strategies to prevent the problem.

Radionuclide methods to evaluate percutaneous transluminal coronary angioplasty

Radionuclide angiocardiography and myocardial perfusion imaging with exercise are valuable methods to assess patients undergoing percutaneous transluminal coronary angioplasty. Successful angioplasty results in improvement in ventricular systolic and diastolic function and regional perfusion. Complications of angioplasty, such as periprocedural infarction and side branch occlusion, can be documented noninvasively. Radionuclide methods have also been demonstrated to be of prognostic value in predicting coronary artery restenosis and recurrent cardiac symptoms. However, to avoid underestimating the success of coronary revascularization, studies must be scheduled long enough following angioplasty to allow transient abnormalities associated with artery dilation to resolve.

Percutaneous coronary rotational angioplasty: preliminary clinical and quantitative imaging results

To determine anatomical and functional changes within the first 24 hours after percutaneous coronary rotational angioplasty (PCRA-ROTABLATOR, Biophysics International, USA), we studied 5 patients (4 men) with a mean age of 55 years (range 52-59) using quantitative coronary angiography, coronary flow reserve from digitized coronary angiograms, quantitative left ventricular angiography, and 99mTechnetium-MIBI SPECT imaging before PCRA, immediately after, and 24 hours after. The minimal luminal diameter and obstruction area showed a moderate increase immediately after PCRA, with a substantial further improvement after 24 hours. The mean coronary flow reserve before PCRA and 24 hours after (1.65 +/- 0.31 vs. 1.81 +/- 0.37; p = NS) remained unchanged. Although the global ejection fraction showed slight impairment immediately after PCRA, this was restored 24 hours later. Only the contribution to regional ejection fraction in the regions supplied by the treated coronary artery attributed to the decrease of global ejection fraction. Before and after PCRA, Tc-99m MIBI tomography performed at rest revealed no perfusion defects in the myocardial regions related to the coronary arteries undergoing the intervention.

Concept of maximal flow ratio for immediate evaluation of percutaneous transluminal coronary angioplasty result by videodensitometry

BACKGROUND

In the setting of percutaneous transluminal coronary angioplasty (PTCA), immediate information about the result of the intervention is important, whereas morphological parameters are often less reliable than in diagnostic coronary arteriography. Recently, a new videodensitometric method was introduced and validated in animal experiments, which allows accurate comparison of maximal myocardial perfusion between situations with different degrees of stenosis. This method uses mean transit time (Tmn) of the contrast agent at maximal hyperemia as a parameter for maximal flow and is strictly in accordance with indicated dilation theory.

METHODS AND RESULTS

In 40 patients with angina pectoris, single-vessel disease, and a positive exercise test at the time of acceptance for PTCA, this approach was applied for evaluation of the improvement of maximal flow achieved by the PTCA. Maximal vasodilation was induced immediately before and 15 minutes after PTCA by intracoronary administration of papaverine, and digital angiographic studies were performed. By special breath-holding instruction, almost motionless, triggered image acquisition was possible during 15-20 heartbeats. Excellent subtraction images could be obtained, and reliable determination of Tmn at maximal hyperemia was possible in 33 patients both before and after PTCA. The ratio between maximal flow after and before PTCA, called maximal flow ratio (MFR), was represented by the ratio between Tmn before and after the intervention and compared with the results of exercise testing 24-48 hours before and 7-10 days after the procedure. After correction for pressure changes, MFR was 2.2 +/- 1.5 for the 33 dilated vessels and 1.0 +/- 0.2 for 25 normal vessels serving as a control. In 94% of all patients, an MFR value of more than 1.6 or less than 1.6 discriminated between presence or absence of reversal of exercise test result from positive to negative. If on-line judgment of success was based upon angiographic parameters or measurement of trans-stenotic pressure gradient, the relation with noninvasive functional improvement was present only in 66% and 74% of all patients, respectively. A definite range of what can be called normal Tmn at maximal hyperemia could be distinguished, and post-PTCA values for successfully dilated arteries returned completely to this normal range.

CONCLUSIONS

Accurate comparison of maximal myocardial perfusion before and after PTCA is possible in man, improvement of maximal flow is highly related to functional improvement as indicated by exercise test results, and, therefore, this method provides a straightforward way for on-line evaluation of the result of the intervention.

Coronary atherectomy. Clinical, angiographic, and histological findings and observations regarding potential mechanisms

Between August 5, 1988 and August 1, 1989, we attempted percutaneous directional coronary atherectomy of 76 lesions, including 42 primary lesions and 34 restenosis lesions that developed after one or more prior interventions. The procedure was successful in 67 lesions (88%), with a decrease in diameter stenosis from 80 +/- 11% to 5 +/- 15% after atherectomy (p less than 0.01). One or more complications occurred in six patients (9%), including non-Q wave myocardial infarction (three patients, 4.5%), femoral arterial injury requiring surgical repair (two patients, 3%), and proximal dissection leading to emergency bypass surgery (one patient, 1.5%). Despite these favorable acute results, the 6-month lesion restenosis rate was 30% by life-table analysis. Light microscopy of retrieved tissue revealed atherosclerotic plaque in 94%, media in 67%, and adventitia in 27%. Intimal proliferation was present in 97% of the restenosis lesions but was also evident in 33% of primary lesions. Tissue weight from 27 lesions averaged 18.5 mg (range, 5.8-45.1 mg), which is not adequate to explain the entire angiographic improvement. Thus, part of the improvement in lumen diameter appears to be due to mechanical dilatation rather than to tissue removal alone. Atherectomy can predictably treat selected coronary lesions with overall safety comparable to that of conventional balloon angioplasty, although the procedure as currently performed does not derive all of its benefit from tissue removal and does not appear to prevent restenosis.

Mean transit time for videodensitometric assessment of myocardial perfusion and the concept of maximal flow ratio: a validation study in the intact dog and a pilot study in man

Over the last decade it has become more and more obvious that besides anatomical information about the severity of coronary artery stenoses, information about coronary and myocardial blood flow is necessary to understand the functional significance of these obstructions and to evaluate the result of an intervention. Several methods have been proposed for this purpose, each of these having their particular limitations. In this study a new method is shortly described which allows the accurate calculation of relative maximal myocardial perfusion by ECG-triggered digital radiography (videodensitometry), using mean transit time (Tmn) as time parameter; this technique is based on the original physiologic principles of indicator dilution theory. This method was validated in 8 instrumented dogs in which an excellent linear relation was present between 1/Tmn and flow (r = 0.96 +/- 0.03). Although this method does not allow assessment of resting flow and therefore coronary flow reserve (CFR), it provides a means for the reliable comparison of maximal myocardial flow in different situations and it is independent of most factors affecting coronary flow reserve. The ratio between maximal flow after and before an intervention is called maximal flow ratio (MFR) and this concept was applied in a pilot study in man to evaluate PTCA results in 10 patients undergoing elective angioplasty. MFR was compared with the result of exercise testing 24 hours before and 10 days after the angioplasty. MFR greater than or equal to 1.5 was always accompanied by reversal of exercise test result from positive to negative. We conclude that the accurate calculation of relative maximal perfusion of the myocardium is possible by videodensitometry and suggest that comparison of maximal flow after and before an intervention can be valuable in man for functional evaluation of the result of the intervention.

Reproducibility of mean transit time for maximal myocardial flow assessment by videodensitometry

In the assessment of myocardial perfusion by ECG-triggered digital radiography, time parameters are calculated from the time density curve (TDC) and related to blood flow. Recently we developed a method which uses mean transit time (Tmn) as time parameter, and which is in accordance with the original principles of indicator dilution theory. In this approach, variability in vascular volume is excluded and Tmn-1, determined at maximal hyperemia, showed an excellent correlation with maximal flow in animal validation studies. For calculation of Tmn, however, a large part of the descending limb of the TDC has to be known for reliable extrapolation, and especially this part of the curve is subject to variability in image quality in man. Therefore we tested reproducibility of Tmn in 30 arteries in 20 patients. Tmn was derived from the TDCs, obtained from paired studies under identical circumstances with an interval of 10 minutes. Satisfactory images could be obtained in all but one patient. Image processing was performed in an identical way in the paired studies. Reproducibility proved to be excellent for all three coronary arteries. The absolute value of the relative differences between the first and second determination was 7 +/- 7% for the LAD, 6 +/- 3% for LCx and 4 +/- 2% for the RCA (mean +/- SD). Correlation coefficients between both measurements were 0.97, 0.95 and 0.95 for the respective arteries. Therefore, it is concluded that, using this approach, Tmn at maximal hyperemia can be determined reproducibly in man and used for maximal myocardial flow assessment.

Intravascular ultrasound cross-sectional arterial imaging

In this paper we review the current status of intravascular ultrasound. Data from qualitative and quantitative studies is presented. Our experimental findings and those of other investigators are reviewed. Intravascular ultrasound has been shown to delineate normal and abnormal arterial morphology as well as to identify and differentiate fibrous, lipid-rich, calcified plaques and complicated plaques. Quantitative studies show strong correlations between ultrasound and histology for lumen area, wall thickness, and plaque area. In vivo studies from our experimental work and clinical laboratory as well as the work of other researchers is presented. This data supports the potential of ultrasound imaging for guidance of intravascular intervention. The potential advantages and limitations of this new technology are discussed. This methodology shows promise for the assessment of the extent and severity of atherosclerosis, monitoring its progression and regression and guiding intravascular plaque ablation technologies.

Mean transit time for the assessment of myocardial perfusion by videodensitometry

The intrinsic limitations of coronary arteriography to predict the physiological effects of coronary obstructions are well known. Therefore, more direct assessments of the functional significance of coronary stenoses are becoming increasingly important. Study of contrast passage by electrocardiogram-triggered digital radiography has been proposed as a way of assessing changes in myocardial perfusion. The main problems in this approach are the limited time for motionless image acquisition, the potential alteration of vascular volume between different states, and the changing flow pattern induced by contrast agents. This has led to empiric substitution of mean transit time (Tmn) by other time parameters and to representation of vascular volume by maximal contrast intensity (Dmax). To avoid these problems, intact dogs were studied during almost motionless image acquisition of 20-25 consecutive paced heart beats obtained with synchronous radiographic pulses. In this way, unequivocal and reproducible determination of Tmn was possible. Constant and maximal vascular volume was created by continuous infusion of dipyridamole, and it was proved that coronary flow in this model was not influenced by contrast injections. Flow in the circumflex artery was measured by a ring mounted and calibrated Doppler probe. In each dog, flow in the circumflex artery was varied by a balloon occluder in 12 small steps (range, 0-174 +/- 42 ml/min). Inverse appearance time (1/Tapp), Dmax, Dmax/Tapp, inverse time of maximal intensity (1/Tmax), and 1/Tmn were calculated and the relations of these parameters to measured flow were investigated. Tmn proved to be the most reliable parameter for this purpose (r = 0.97 +/- 0.02; mean +/- SD), followed by Tmax (r = 0.93 +/- 0.04). Dmax failed to represent vascular volume but, in fact, showed a moderate correlation with flow (r = 0.78 +/- 0.22), as did Tapp (r = 0.64 +/- 0.18, 0.75 +/- 0.27, and 0.59 +/- 0.26 for the three definitions of Tapp used in this study). Dmax/Tapp correlated better with flow than either component separately. Our results indicate that the mean transit time calculated by videodensitometry can be used to accurately assess changes in myocardial perfusion strictly according to the original principles of indicator dilution theory.

Variability of coronary flow reserve obtained immediately after coronary angioplasty

Coronary flow reserve (CFR) improves in most patients immediately following coronary angioplasty (PTCA). The degree of improvement, however, may be variable and its predictive value for a favorable long-term angiographic result is unknown. To evaluate these issues, we used digital subtraction angiography to measure CFR in 15 patients before and immediately after PTCA. Minimum coronary diameter improved and percent diameter stenosis was reduced immediately following PTCA (from 0.75 +/- 0.35 mm to 2.19 +/- 0.56 mm, and from 74 +/- 12% to 27 +/- 15%, respectively; p less than 0.001). While CFR improved in patients immediately following PTCA (from 1.49 +/- 0.75 to 2.68 +/- 1.73; p less than 0.05), a substantial variability in CFR measurements (range 0.80 to 8.33) was present. At repeat arteriography 2.9 +/- 0.6 months later, 4 patients demonstrated restenosis. Compared with the 11 patients without restenosis, those with restenosis had similar coronary dimensions and CFRs immediately following PTCA. We conclude that coronary flow reserve, determined by digital subtraction angiography, improves in most patients immediately after PTCA but the degree of improvement is variable. Its ability to predict long-term angiographic outcome remains uncertain.

Estimation of coronary flow reserve by intracoronary Doppler flow probes and digital angiography

This prospective study investigated two different methods used clinically to estimate coronary flow reserve during cardiac catheterization. First, the relationship between simultaneous digital angiography and intracoronary Doppler velocity measurements was determined in 61 patients. The correlation coefficient for 233 simultaneous pairs of papaverine-induced flow reserve was 0.70 (Doppler = 0.41 digital + 0.93, P less than 0.0001). Repeated basal flow determinations showed little variability (Doppler: 2 +/- 5% (mean +/- 95% confidence intervals); digital: 3 +/- 10%). Repeated hyperemic flow estimates by the Doppler technique were more reproducible (10 +/- 2%) than those by the digital method (26 +/- 6%). Second, estimates of coronary flow reserve by side-mounted and end-mounted Doppler catheters were compared in vitro and in patients. In vitro measurement of blood velocity was linear for both catheter designs and was highly correlated with volume flow determined by electromagnetic flow meter (r = 0.99 side-mounted; r = 0.96 end-mounted). In patients (n = 20), average coronary flow reserve for the side-mounted Doppler crystal was 2.64 +/- 0.15 and for the end-mounted Doppler crystal was 2.40 +/- 0.14 (P less than 0.02). When flow reserve was determined twice for each catheter, there was greater variability in repeated measurements using the side-mounted Doppler crystal (21 +/- 10%, n = 14) than using the end-mounted Doppler crystal (12 +/- 4%, n = 32).(ABSTRACT TRUNCATED AT 250 WORDS)