Purpose. The trauma induced by balloon angioplasty has an impact on the outcome of coronary interventions, such as stent procedures. However, balloon inflation for PTCA is not yet standardized even though procedural and long-term outcomes might be affected. Methods. During routine PTCA, a total of 454 patients [mean age, 60.9 ± 9.0 years; 162 (35.7%) with 1-vessel disease; 159 (35%) with 2-vessel disease; 133 (29.3%) with 3-vessel disease] were allotted to computer-assisted dilatation (CAPS) with a pressure slope of 0.2 bar/s (CAPS 0.2; n = 149 patients), 1.0 bar/s (CAPS 1.0; n = 154 patients) or to standard inflation with a hand-driven pump (n = 151 patients). Angiographic follow-up rates after 4.1 ± 3.2 months were 88.1% for the hand-driven pump, 94% for CAPS 0.2 and 87.7% for CAPS 1.0. Results. Flow reducing (1.3–2.0%) and non-flow reducing (12.6–14.9%) dissections were equally distributed among all groups as were major adverse cardiac events (2.6–4.0%). The stent rate was 1.3% with the hand-driven pump, 0.7% with CAPS 0.2 and 1.3% with CAPS 1.0. Angiographic restenosis rate was 48.9% with the hand-driven pump, 44.3% with CAPS 0.2 and 32.6% with CAPS 1.0. (hand-driven pump versus CAPS 1.0, p < 0.007; CAPS 0.2 versus CAPS 1.0, p < 0.049). Conclusions. The pressure slope during balloon inflation in PTCA has a significant impact on restenosis. The impact on stent procedures has yet to be determined.

       Stents have proven their benefits in an increasing number of transluminal coronary interventions.1,2 However, stents increase procedural costs and have the inherited problem of in-stent restenosis, particularly in patients with small-vessel disease, for which the optimal treatment modalities have not been settled.3–7 Moreover, after stand-alone angioplasty, there seem to be particular variables, such as optimal result after angiography,8,9 guidance by Doppler flow wire,10,11 guidance by intracoronary Doppler and quantitative angiography,12 and assessment by intravascular ultrasound,13,14 that achieve comparable restenosis rates to primary stenting. On the other hand, the vessel wall trauma that results with the process of balloon inflation plays a crucial role in determining long-term results15–19 even with the combination of stents and brachytherapy.20
       The current mode of inflation using a hand-driven pump precludes a standardized inflation process. Controlled widening of the vessel wall, which limits traumatization of the vascular wall, is possible with a computer-assisted percutaneous transluminal coronary angioplasty system (CAPS), the reliability of which has been published elsewhere.21

METHODS

       Design. The primary endpoint of this single-center, prospective, randomized trial was the binary restenosis rate. Secondary endpoints at 6 months were acute success; target site revascularization; acute ischemic, vascular, and hemorrhagic complications; and angiographic late and percent minimal lumen diameter. Safety endpoints were combined late cardiac events [death, myocardial infarction (MI), and revascularization].

       Inflation devices. A computer-assisted PTCA system (CAPS) has been developed for controlled dilatation and has been described elsewhere.21 Conventional balloon catheters are connected to a pressure sensor, which is connected to a readily available syringe. The syringe is clamped to a plastic housing which hosts the step motor for inflation and deflation. Pressure slope (0.1–1.0 bar/second), maximal pressure (0.1–20.0 bars) and inflation time (1–180 seconds) are preselected by means of a laptop computer (>= 386 SX 20 processor) which also displays the inflation process by a pressure/volume curve online. On a separate cart, the electronic components (e.g., the microcontroller, etc.) allow for adjustment of the parameters in closed loop mode 40 times per second. Extensive in vitro testing demonstrated the system’s technical reliability, high reproducibility of the inflation process, and safety.21
Hand-driven (manual) balloon inflation was performed by means of various readily available inflation pumps commonly used in clinical practice.

       Study population. After informed consent was obtained, a total of 454 unselected patients (82.6% men; mean age, 60.9 ± 9.0 years) scheduled for routine PTCA were assigned by computer-generated randomization to either computer-assisted dilatation with 0.2 bar/second (CAPS 0.2), 1.0 bar/second (CAPS 1.0) or standard inflation with a hand-driven pump (H).
       Inclusion criteria consisted of patients of either sex, aged 20–85 years, with the indication for PTCA in a native coronary artery with a significant lesion of >= 70% occlusion and <= 20 mm in length (measurements determined by “visual estimation”). No minimal reference diameter was required. The patient had to be a candidate for bypass surgery.
       Exclusion criteria consisted of ejection fraction < 20%; New York Heart Association class IV; unprotected left main; serum creatinine > 2.5 mg/dl; contraindication to both aspirin and ticlopidine; contraindication for emergent bypass operation; cerebral stroke < 6 month prior; and a limited overall prognosis (e.g., end-stage malignancy). Demographic data (Table 1), risk factors (Table 2) and lesion characteristics (Table 3) were similar between the 3 groups.

       Operator technique. The procedures were performed by three operators with an annual volume of about 1,000 interventions each. The procedure consisted of the administration of 200 IU/kg body weight of heparin after introduction of the sheath, and was supplemented by 100 IU/kg body weight in prolonged procedures. Following intracoronary injection of nitroglycerin (> 100 µg), baseline angiography of the involved vessel was performed in at least two near-orthogonal views, showing the target lesion free of foreshortening or vessel overlap, using an 8 French guiding catheter. The target lesion was crossed with a 0.014´´ exchange-length guidewire and dilated with an appropriately sized balloon (balloon/artery ratio, 1:1). Assessment of lesion severity and lesion length (and therefore, choice of the balloon) was based on visual estimation.
       The procedure was judged successful if the remaining diameter was less than or equal to 30%. Angiographic images were acquired pre-procedure, post-procedure and at 4-month follow-up examination. 35-mm cine angiography films, as well as the case report forms, were evaluated by the center’s angiographic core lab. The investigators only received the cine films and were thus blinded to the mode of balloon inflation. Regarding the number of balloon inflations, there was no significant difference in the maximal pressure or in the time span for which this pressure was exerted (i.e., peak pressure time) (Table 4).

       Concomitant medical therapy. All patients received aspirin 100 mg/day both pre-procedure and throughout the follow-up period. If aspirin was not tolerated, ticlopidine (250 mg twice daily) was given.

       Angiographic assessment.Angiograms were reviewed by two of the center’s angiographic core laboratory investigators using qualitative morphologic and quantitative angiographic methods by means of the CAAS II System (Pie-Medical, 6227 AJ Maastricht, The Netherlands). The contrast-filled diagnostic or guiding catheter served as the calibration standard, while the reference and minimal lumen diameters were determined using an automated edge-detection algorithm. Reference vessel diameters were calculated by selecting a smooth arterial segment 10 mm proximal and distal to the lesion. The reference vessel diameter, minimal lumen diameter, and percent diameter stenosis were taken from the worst view using a validated edge-detection algorithm.

       Follow-up. Follow-up procedures included baseline electrocardiogram, white blood cell count, hematocrit, hemoglobin, creatinine (CK) and CK-MB, repeat visit, exercise tolerance test, and catheterization at 4 months. Abrupt closure was defined as significantly reduced flow (TIMI grade 0 or 1) due to mechanical dissection, coronary thrombus, or severe microvascular spasm that resulted in either unplanned transluminal reintervention, emergent surgery, controlled MI or death. Acute myocardial infarction was defined as CK-MB levels >= 2 times the normal with significant CK-MB levels with or without electrocardiogram changes. Major vascular complications at the access site included those which required transfusion or surgery and pseudoaneurysms.
       Patient follow-up consisted of a repeat visit, an exercise tolerance test and catheterization at 4 months. The binary restenosis definition (> 50% reduction in lumen diameter at follow-up) was used. The referring cardiologist was contacted for follow-up data on patients.

       Statistical analysis. The Kolmogorov-Smirnov test was used to check the assumption of a Gaussian distribution. Mean and standard deviation were used to describe Gaussian distributions, whereas non-Gaussian distributions were described by median and range. Discriminant variables were evaluated with the 2-sided exact Fisher test using two-by-three contingency tables containing the three treatment groups. For all tests, the significance level a was 0.05.

RESULTS

       Procedural outcome. For the patients with computer-assisted inflation at slow pressure increase (CAPS 0.2), procedural success was achieved in all but 2 (1.3%); due to severe dissections of NHLBI type F,22 these patients proceeded to emergent coronary bypass operation and had uneventful recoveries. Although acute MIs were most frequent in patients with conventional hand-driven inflation (4% versus 1.3% in CAPS 0.2 patients and 2.6% in CAPS 1.0 patients), total major adverse coronary events occurred in 4.6–8.6% in all groups (p = not significant). Flow reducing and non-flow reducing dissections were equally present in all groups (Table 5).

       Follow-up. Angiographic follow-up after 4.1 ± 3.2 months in 408/454 patients (89.9% of all patients and 90.3% if adjusted for the two patients who proceeded to emergent bypass operation) revealed similar binary restenosis rates of 65/133 (48.9%) in the hand-driven group and 62/140 (44.3%) in the CAPS 0.2 group. With rapid balloon inflation (CAPS 1.0), the recurrence rate of 32.6% (44/135) was significantly lower in comparison to manual inflation (p < 0.049) and to CAPS 0.2 (p < 0.007) (Table 6). A post hoc power calculation for the difference in this primary outcome parameter was determined to be > 70%.
       Twelve out of 454 patients (2.6%) who presented neither with angina pectoris nor ischemia during the symptom-limited exercise stress test refused follow-up angiography. One patient (0.2%) with 3-vessel disease died from sudden cardiac death. Thirty-three out of 454 patients (7.3%) were lost to follow-up.

DISCUSSION

       Stents have become the treatment of choice in most percutaneous transluminal coronary interventions despite several disadvantages, including in-stent restenosis, risk of sidebranch occlusion, unsatisfactory results in bifurcational lesions, long lesions, and the treatment of small vessels; at this point, these issues remain unsolved.1,2 Moreover, after stand-alone balloon angioplasty, the optimal result as assessed angiographically,8,9 by Doppler flow-wire,10,11 by intracoronary Doppler and quantitative angiography,12 or by intravascular ultrasound13,14 was predictive of similar restenosis rates compared to primary stenting. In addition, the enhanced costs per procedure may not be covered by all of the patients. These issues still justify plain old balloon angioplasty as the treatment of choice in many patients.
       It is well known that the damage to the vessel wall following interventional procedures plays a crucial role in the occurrence of restenosis23–25 even after the application of brachytherapy.20 However, the mode of balloon inflation is not yet standardized. It is also unknown which mode of balloon angioplasty would be most suitable for a particular type of lesion.26–28 A lesion’s morphologic characteristics do not seem to determine the acute morphologic result. Intravascular ultrasound analysis did not reveal any significant relationship between pre-interventional plaque characteristics such as composition features and eccentricity, and the incidence, location, and extent of post-interventional dissections.29
       As a first step, the present trial supports the hypothesis of vascular injury to determine the long-term outcome of PTCA15–18,24,30 and revealed another parameter8–14 which might identify subsets of patients in whom provisional stenting would result in a recurrence rate similar to primary stenting. The possible benefits and risks of two reproducible modes of balloon inflation were compared to the generally accepted, although non-standardized, hand-driven mode of PTCA. The reproducibility of inflation was ascertained by a computer-assisted system, the absolute reliability and safety of which has been reported elsewhere.21
       In non-selected patients, there were no differences in minor or major procedural and post-procedural complications between the treatment groups, which is in accordance with previous results.26 At 4-month follow-up exam, however, the rapid pressure increase (1.0 bar/second) demonstrated a significant reduction in recurrence rates (32.6%) when compared to hand-driven balloon angioplasty (48.9%; p < 0.007) and to the slow pressure increase (44.3%; p < 0.049), respectively. Since the inclination of 0.2 bar/second was chosen to match with hand-driven inflation, the long-term results of CAPS 0.2 and manual inflation showed only minor differences, which is in accordance with the more recent literature.31,32 Balloon material, as well as diameter and length of the balloons, has been reported to influence the mechanical properties of the balloon, the interactions between the balloon and the artery, and thus the vascular trauma.15–19,33 However, there was no difference between the balloons used in the samples. Peak pressure time and peak pressure were also the same in the three groups.
       Predictors known to influence restenosis, such as dilatation of the proximal left anterior descending coronary artery, residual stenosis after PTCA, and unstable angina,30,34–38 were equally distributed among the patient groups as well. There were also no differences in risk factors that may influence restenosis rates, such as diabetes,38–41 hypercholesterolemia42–45 and smoking habits.39
       Theoretically, the lesion’s mechanical properties, composed of morphological and functional components, influence the acute and long-term results of angioplasty. Balloon inflation builds up a certain pressure which translates into a radial force to the vessel wall — a force that is created at random by the hand-driven pump. It has been demonstrated in vitro, in necropsy segments and in the rabbit that different types of stenoses translate into different pressure-volume curves.27,46–50
       Most likely, the vascular injury must have differed with the rapid pressure increase compared to a lower slope, although it is currently unknown which type of trauma is less prone to instigate the processes of restenosis. In 20 patients who died between several hours and up to 4 years post-angioplasty,24 the proliferative response was significantly greater in lesions with evidence of medial or intimal tears. However, in an analysis of 293 human samples,30 the restenosis rate was significantly lower when a tear extended into the media or adventitia.
       The importance of dissection has also remained controversial. Uncomplicated intimal dissections may either be less prone to restenosis32,51 or may not influence recurrence rates,52 whereas major dissections enhance restenosis rates.25 These conflicting results may be attributed to factors such as preparation artifacts or spontaneous tears and cracks which are observed in untreated cadaveric arteries as well.53
       Unfortunately, there are comparable data from other groups. Rapid pressure slope compared with gradual incremental increase showed a significantly higher dissection rate (59% versus 36%; p < 0.01).27 This discrepancy can be explained by a variety of different methodological approaches in both trials. Ilia et al. performed the procedures by conventional hand-driven pumps with rapid inflation to 6 atm, whereas gradual inflation started at 3 bars and was followed by 0.05 bar/second until the desired pressure was achieved. Thus, the difference between slow and rapid inflation was more pronounced than in our trial.
       The devices of the present study were also more sophisticated and standardized. The ACS Sulp II™ (Guidant Corporation, Temecula, California) catheter used by Ilia et al. was mechanically different in comparison to today’s balloons. Furthermore, vascular dimensions were assessed only by quantitative coronary angiography in our trial. Procedural success (<= 50% residual stenosis, minimal reduction >= 20%) was achieved by 5.4 ± 0.3/5.5 ± 0.3 inflations in the aforementioned work and thus differ considerably with the definition of success (<= 30% residual stenosis) and the number of inflations (2.6 ± 1.6, 3.0 ± 1.7, and 2.7 ± 1.4) in our study. Follow-up data were not provided by Ilia and colleagues. Jain et al., who dilated 48 lesions by means of an electromechanical system, focused on and identified differences in lesion characteristics rather than the long-term outcomes.54
       Theoretically, the low stent rate would be regarded as inadequate by the present standards; a higher figure, however, would have obscured the different effects of the various inflation techniques.
       The present trial was not designed to explain the mechanisms of restenosis. The most likely cause for the differences in recurrence rates is the trauma to the vessel wall. The focus was also not on the assessment of the nature of the lesions which were dilated, since in vitro observations with CAPS failed to demonstrate sufficient specificity for this issue. One reason for this disadvantage is that deflation by use of common balloon catheters is accomplished by suction. Suction, however, will not evacuate the system completely. The remaining microbubbles with dissolution and air compression, as well as the compliance of the shaft, blunt the hydraulic transmission of rapid pressure changes as in the cracking of calcified lesions. All of the aforementioned research groups could translate morphologic findings into characteristic pressure-volume curves.27,47,54,55 However, the authors did not comment on the type of balloon catheters they were using. Hence, it cannot be concluded whether or not catheters with an antegrade deflation system (“vent”), which were quite common in the late eighties, were used. Evacuation of this balloon type resulted in complete evacuation in comparison to the current balloon catheters.
       To interpret the results morphologically, intravascular ultrasound apparently would have been required. However, the sensitivity of intravascular ultrasound is 80% to detect histologically proven damage,56 75% for dissections, and as low as 59% for media rupture.57 Since the present trial was planned as a preliminary assessment of whether the mode of inflation would translate into different outcomes, employment of today’s refined imaging methods may be justified and deferred to future investigations.
       Our study is limited by the relatively short follow-up period. Thus, different possible time courses of the restenosis process may have been obscured. Computer-assisted inflation is characterized by a linear pressure increase, whereas the pressure rises discontinuously by manual inflation. This aspect could have also influenced the outcome. Since there are no differences in acute and long-term results between the conventional and computer-assisted slow pressure increase, both with apparently the same pressure slope, this issue may be ruled out.
       In conclusion, the present data suggest that the procedure of balloon angioplasty itself seems to determine the mid-term outcome of plain old balloon angioplasty and thus may present another predictive variable to justify provisional stenting rather than primary stent deployment.

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