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CLINICAL STUDIES

Safety of deferring angioplasty in patients with normal coronary flow velocity reserve

^a Clinic of Internal Medicine III (Cardiology & Angiology & Intensive Care Medicine) Friedrich-Schiller-Universität, Jena, Germany
^* Clinic of Internal Medicine (Cardiology & Pulmonology) Georg-August-Universität, Göttingen, Germany

Manuscript received May 11, 1998; revised manuscript received August 19, 1998, accepted September 24, 1998.

Address for correspondence: Dr. H. R. Figulla, Klinik für Innere Medizin III, Friedrich-Schiller-Universität, Erlanger Allee 101, D-07740 Jena, Germany
figulla{at}polkim.med.uni-jena.de

	Abstract

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Background. In the catheter laboratory there is a need for functional tests validating the hemodynamic significance of coronary artery stenosis.

Objectives. It was the objective of our study to compare the long-term cardiac event rate and the clinical symptoms in patients with reduced coronary flow velocity reserve (CFVR) and standard PTCA with patients with normal CFVR and deferred angioplasty.

Methods. Our study included 70 patients with intermediate coronary artery stenoses (13 f, 57 m; diameter stenosis >50%, <90%) and an indication for PTCA due to stable angina pectoris and/or signs of ischemia in noninvasive stress tests. CFVR was measured distal to the lesion after intracoronary administration of adenosine using 0.014 inch Doppler-tipped guide wires.

Results. In 22 patients (31%), PTCA was deferred due to a CFVR 2.0 (non-PTCA group). In the remaining 48 patients (69%) mean CFVR of 1.4 ± 0.23 (p < 0.001) was measured (PTCA group). CFVR increased to 2.0 ± 0.51 after angioplasty. During follow-up (average 15 ± 6.0 months), the following major adverse cardiac events (MACE) occurred: in the PTCA group re-PTCA was performed in nine patients (18.8%) because of unstable angina, five patients (10.4%) suffered an acute myocardial infarction (MI) (two infarctions occurred during the angioplasty, three patients suffered an infarction during follow-up), two patients (4.2%) needed blood transfusions due to severe bleedings, two patients (4.2%) underwent bypass surgery and one patient (2.1%) died. In the non-PTCA group, angioplasty was necessary only in two cases (9.1%) during follow-up. We did not observe any MI in the non-PTCA group.

The overall rate of MACE was significantly lower in the non-PTCA group compared to the PTCA group (9.1% vs. 33.3%, p < 0.01). However, only 40% of the patients of the non-PTCA group were free of angina pectoris at stress. In the PTCA group, 63% did not complain of any symptoms at follow-up (p < 0.05).

Conclusions. We conclude that determination of the CFVR is a valuable parameter for stratifying the hemodynamic significance of coronary artery stenosis. PTCA can safely be deferred in patients with significant coronary stenosis but a CFVR 2.0. The total rate of MACE at follow-up was below 10% among these patients. However, if PTCA was deferred the number of patients who are free of angina is lower compared to those patients who underwent angioplasty.

Abbreviations and Acronyms   APV = average peak velocity   CABG = coronary artery bypass graft surgery   CAD = coronary artery disease   CCS = Canadian Cardiological Society   CFVR = coronary flow velocity reserve   FFR = fractional flow reserve   MACE = major adverse cardiac event   MI = myocardial infarction   NYHA = New York Heart Association   PTCA = percutaneous transluminal coronary angioplasty   QCA = quantitative coronary angiography   RFVR = relative coronary flow velocity reserve   SPECT = single-photon emission computed tomography

Angiography alone is an imperfect method for determining the physiologic relevance of coronary lumen narrowing (5). In addition, noninvasive stress tests have an imperfect specification (6). In the interest of optimization of coronary artery disease therapy, there is a need for more physiological tests to define prospectively the group of patients whose coronary vessel flow capacity is sufficient despite a stenosis, and therefore PTCA seems unnecessary. Measurements of translesional pressure-flow velocity measurements and of the fractional flow reserve (FFR) have already been established by clinical studies (5,7). The registration of coronary flow velocity reserve (CFVR) can easily be performed. Recent studies have demonstrated a correlation between CFVR after angioplasty and the clinical outcome (8). However, the value of the CFVR to evaluate the indication for PTCA has not been proven so far in a prospective study. Therefore, we tested the hypothesis that CFVR is able to distinguish those patients who may benefit from an angioplasty procedure from those for whom PTCA seems unnecessary.

	Methods

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Patient selection.   Between July 1994 and December 1996, 2,760 PTCAs were performed in our clinic. In this prospective trial we consecutively included 70 patients who were referred for elective angioplasty during certain terms of this period. All patients met the inclusion criteria as shown in Table 1. They were referred for coronary angioplasty due to a de novo lesion of >50%. In addition, they reported chest pain at stress and/or they showed signs of ischemia in noninvasive stress tests. Precatheterization stress tests were performed by bicycle exercise testing or thallium scintigraphy in a standard manner without antianginal drugs. All patients had to reach at least 85% of their maximum heart rate during exercise. Bicycle stress test was considered positive if ST-segment depression of 0.2 mV in two standard leads was measured. Scintigraphy was considered positive if thallium storage was reversibly diminished in at least two regions in the area of interest. Patients were excluded if more than one lesion had to be treated, collateral flow was present, the left main was stenosed, the patient had unstable angina or angina at rest. Further exclusion criteria were previous myocardial infarction or reduced coronary blood flow (<TIMI III) in the vessel of interest.

Study protocol.   Coronary angiography was performed in standard manner by femoral approach with 7F Judkins guiding catheter. After intracoronary injection of 0.2 mg of nitroglycerin, quantitative coronary angiography (QCA) of the target lesion was obtained. QCA was performed by Philips DCI automated coronary analysis using the 7F guiding catheter as reference standard (9). The lesion severity was determined by percent diameter stenosis relative to angiographically normal diameter.

A 0.014'' Doppler guide wire (FlowWire^TM, Cardiometrics, Mountain View, California) was placed 1–2 cm distal to the stenosis after intravenous administration of 10,000 IU of heparin. The 175 cm long wire has an integrated piezoelectric ultrasound transducer in the tip. The signal of the 12 MHz pulsed Doppler was analyzed by a computer system (FlowMap^TM, Cardiometrics, Mountain View, California) using fast Fourier transformation. The validity of these Doppler wire measurements has been demonstrated in various settings (10,11). The mechanical and electrical characteristics of this Doppler guide wire are reported in detail elsewhere (12). The average peak velocity (APV) 4 mm distal of the tip of the Doppler wire was obtained from the spectral signals averaged over two cardiac cycles. After registration of APV at rest, adenosine was injected through the guiding catheter to induce coronary hyperemia. We used 12 µg for the right and 18 µg for the left coronary artery. The coronary flow velocity reserve (CFVR) was computed as the ratio of hyperemic to basal APV. In those patients who had CFVR 2, PTCA was deferred and they were allotted to the non-PTCA group. In the remaining patients with CFVR <2, balloon angioplasty was performed in standard manner (PTCA group) after administration of an additional 5,000 IU of heparin. Balloon inflation or stent implantation was performed until an angiographically satisfying result was achieved in all patients of the PTCA group (degree of stenosis <30%).

In addition, all 70 patients received optimal medication consisting of aspirin, nitrates, beta-adrenergic blocking agents, ACE-inhibitors and lipid lowering drugs as appropriate to each individual. Patients with stents received ticlopidine 250 mg bid for four weeks.

Clinical follow-up.   We defined as major adverse cardiac event (MACE) the occurrence of severe bleeding requiring blood transfusion, repeated PTCA or primary PTCA in the non-PTCA group, acute myocardial infarction, coronary bypass surgery, cardiac death during angioplasty or during follow-up period. A myocardial infarction was considered if an increase of creatine kinase to more than twice the normal value was measured and a Q-wave developed in at least two leads of standard ECG recordings. Severe bleeding was defined as blood loss requiring transfusion of blood or surgical intervention. Follow-up period was at least six months. All patients underwent physical examination and noninvasive stress tests (bicycle exercise testing or thallium scintigraphy) in our clinic. The same stress test protocol was used at follow-up examination as at the beginning of the study. All patients had to cycle until at least 85% of their maximum heart rate was reached. In those patients who reported new onset or aggravation of angina or showed pathological results in noninvasive stress test at follow-up, reangiography was performed.

Statistical analysis.   Data are reported for 70 patients. They were divided into two groups after measurement of coronary flow velocity reserve. All values are expressed as mean ± SD and the percentage in each group. P values were calculated using paired Student t tests for statistical analysis of continuous variables within a group. Associations between the two groups were tested for, using two-tailed unpaired Student t tests for continuous data after F-test determination of standard distribution or chi-square (²) test without continuity adjustment for categorical data. A p value <0.05 was considered statistically significant.

	Results

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The clinical data of the 70 patients are shown in Table 2. Angiographic characteristics are summarized in Table 3. Age, gender, NYHA class, CCS class, extent of coronary artery disease, results of stress tests and incidence of angina pectoris were comparable between the two groups at the time of inclusion (Fig. 1).

View larger version (15K): [in this window] [in a new window]   Figure 1 Severity of angina pectoris (according to Canadian Cardiac Society) of patients who reported angina at stress before angioplasty, at discharge and after follow-up of 15 months. (n.s.: t test not significant).

Acute results.   In 22 patients angioplasty was deferred due to a CFVR 2.0 (non-PTCA group). No acute complication was observed among this group. New York Heart Association (NYHA) and angina pectoris status have been improved by optimization of medical therapy.

In the PTCA group, the CFVR increased from 1.4 to 2.0 after angiographically successful angioplasty (p < 0.001). The degree of stenosis was reduced from 76.5% to 16.5% (p < 0.001). NYHA class was also improved in the PTCA group. The incidence of angina pectoris was reduced nearly one class according to CCS (Canadian Cardiac Society). Among those who underwent PTCA, two patients (4.2%) suffered an acute myocardial infarction. Another patient (2.1%) underwent emergency coronary bypass surgery after dissection into the left main. In two patients (4.2%) bleeding occurred at the femoral puncture site requiring blood transfusion; surgical intervention was necessary in one of these cases. In total, we noticed major adverse cardiac events (MACE) related to the initial PTCA in five patients in the PTCA group (10.4%).

Follow-up results.   The follow-up period was 15 ± 6.0 months (range: 6 to 30 months). At follow-up, there was no difference in medical treatment between the PTCA and the non-PTCA group (data not presented). In the non-PTCA group, we found progression of CAD with an aggravation of angina in two patients (9.1%). In these two patients, PTCA was performed after 11 and 12 months, respectively, both in an outside institutions while measuring the CFVR.

Among those with an initially normal CFVR in the target vessel, three other patients (13.6%) underwent angiography during follow-up. They showed abnormalities during stress ECG in different leads as before angiography. However, they did not require PTCA. The degree of coronary diameter narrowing remained unchanged in those five patients of the non-PTCA group who were restudied by coronary angiography. Neither an acute myocardial infarction nor cardiac death was observed in this group. Thirteen patients of the non-PTCA group (59.1%) reported chest pain at follow-up examination. Eight patients (36.4%), including those two who were dilated, showed signs of ischemia in noninvasive stress tests. Considering PTCA, MACE occurred in two patients of the non-PTCA group (9.1%) during follow-up.

In the PTCA group, three patients (6.3%) suffered myocardial infarction during follow-up. Two of them underwent re-PTCA, one patient had emergency coronary bypass surgery two years after initial angioplasty due to occlusion. Other than the two emergency PTCAs, an additional seven patients (14.6%) underwent re-PTCA for relevant restenosis. Another 15 patients (31.25%) underwent angiography during follow-up because of new onset or aggravation of angina or suspect results in noninvasive stress tests. They did not require reintervention. Eighteen patients (37.5%), including the seven patients who had re-PTCA, reported angina at stress at follow-up. Eight of them, plus 10 other patients who were free of angina showed signs of ischemia in noninvasive stress tests among the PTCA group (37.5%).

One patient (2.1%) died of ventricular fibrillation four months after initial angioplasty. Since autopsy was denied, it was unclear whether he had an acute myocardial infarction in the vessel of interest. In summary, 11 patients of the PTCA group (22.9%) had MACE during the follow-up period. The total MACE rate in the PTCA group at follow-up was approximately 30%.

	Discussion

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In this prospective study, we tested the method of deferring PTCA in patients with significant coronary stenosis yet sufficient CFVR. Deferring angioplasty was safe and had a favorable outcome in 22 patients with CFVR 2. The rate of MACE was significantly elevated in those patients who had CFVR <2 and underwent PTCA compared to the patients with normal CFVR and deferred angioplasty (Fig. 2). Despite angina pectoris at stress, we did not observe any disadvantage in the non-PTCA group after deferred angioplasty compared to the PTCA group.

View larger version (17K): [in this window] [in a new window]   Figure 2 The slopes reflect the relation between risk of major adverse cardiac event (MACE: severe bleeding, re-PTCA, acute myocardial infarction, coronary bypass surgery, sudden cardiac death) and benefit (number of patients who are free of angina pectoris) in the PTCA subgroup (n = 48) and the non-PTCA subgroup (n = 22).

Other functional tests.   Noninvasive tests for detecting myocardial ischemia are associated with a great number of false positive or negative results (6,13). There are several factors influencing the predictive value of noninvasive stress tests or reported angina pectoris at stress (14–16). Even invasive examination by quantitative coronary angiography remains an imperfect method to determine the impact of coronary artery stenosis (17,18). Measurements of translesional pressure gradient can also be used for analyzing the hemodynamic significance of coronary artery stenosis (19). In combination with analysis of flow velocity proximal to distal of the stenosis, it is a valid parameter for clinical decision making (5). Kern et al. showed the feasibility and safety of deferring angioplasty in patients with normal translesional pressure-flow velocity measurements in a study design similar to the one used in our investigation. The average CFVR in the patients with coronary artery stenosis of intermediate severity in whom PTCA was deferred due to the translesional pressure-flow velocity measurements was 2.0 ± 0.64. Although nearly half of their patients had CFVR below two, they did not observe any adverse outcome in patients with deferred PTCA.

Ideal coronary flow velocity reserve.   We took the cutoff value of 2.0 for "normal" CFVR due to findings in single-photon emission computed tomography (SPECT) (20,21). Although SPECT is an imperfect method for determination of the hemodynamic significance of coronary artery stenosis, 2.0 is a clear-cut value for decision making in daily clinical practice. The FACTS Study Group found a cut point for optimal sensitivity and specificity of CFVR at 1.7 in comparison with SPECT and Doppler flow velocity measurements in patients with moderate CAD (22). The DEBATE Study showed a cutoff of 2.5 for CFVR immediately after PTCA to predict the incidence of MACE in a retrospective analysis (8).

Thus, optimization of PTCA results according to a CFVR 2.5 might reduce the rate of MACE during follow-up, but this was not the aim of our study. However, the DEBATE Study also indicates that decision making by angiographic criteria is insufficient.

Safety and cost.   Our data demonstrate the safety, feasibility and clinical outcome of deferring angioplasty of coronary artery stenosis associated with "normal" CFVR. The risk of an adverse outcome was significantly lower among the 22 cases in whom PTCA was deferred due to normal CFVR compared with the patients who underwent angioplasty. The costs of Doppler guide wire compared with the resources which can be saved by deferring angioplasty in 30% of patients are much lower especially if the higher incidence of re-PTCA are taken into account.

Methodical limitations.   The patients with single vessel disease medical therapy showed better long term outcome, but in multivessel disease PTCA seems to be more favorable (4). We did not distinguish patients with single vessel disease from those with significant lumen narrowing in two or three vessels. It should be one aspect of bigger trials to test which patients will benefit from deferred PTCA on the basis of CFVR-detection.

Collateral flow can provide sufficient supply in the distal myocardium even if the CFVR is reduced. Since visible collateral flow in the vessel of interest was an exclusion criteria, the collateral flow was of minor importance for the flow velocity measurements in this study. Measurements of the (FFR) by intracoronary pressure wire may be superior in accurate determination of functional severity of coronary artery stenoses in vessels with relevant collateral flow (7,23–25).

Since reangiography was not performed in all patients, we are not able to quantify the degree of progression of CAD. On one hand there might be some nonsymptomatic restenosis in the patients who underwent PTCA, but on the other hand the CFVR may have decreased in some patients with deferred PTCA. Due to the unobtrusive clinical outcome, we failed to perform reangiography in these patients.

Recently it was suggested to take the relative CFVR (RFVR) to reduce the interindividual variations of CFVR (26). The RFVR is defined as the ratio of absolute CFVR of the diseased vessel divided by CFVR measured in an angiographically normal reference vessel (27). The RFVR might be able to consider microvascular disease better than CFVR without flow velocity measurements in a reference vessel.

Clinical relevance.   The rate of immediate PTCA during primarily diagnostic procedure is growing (28). Measurements of CFVR offer the opportunity to validate the indication for PTCA if noninvasive stress tests are missing and angina pectoris is untypical. Beyond this application there is sometimes a need to distinguish the relevant stenosis from those which do not require angioplasty in multivessel disease. A major number of patients in the catheter laboratory can benefit from functional testing of stenosis severity before elective PTCA. Measurements of CFVR can also be used to improve the result of PTCA beyond angiography (29). Physiologically guided angioplasty can help to reduce the incidence of major adverse cardiac events and the costs.

Conclusion.   We conclude that determination of the CFVR is a valuable parameter for stratifying the hemodynamic significance of coronary artery stenosis. A "normal" CFVR can be found in about 30% of patients with angiographically significant stenoses who show an indication for PTCA due to stable angina pectoris or positive noninvasive stress test. PTCA can safely be deferred in patients with significant coronary stenosis but CFVR 2.0.

	References

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