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Eur J Cardiothorac Surg 1998;13:404-409
© 1998 Elsevier Science NL

Non-invasive evaluation of mammary artery flow reserve and adequacy to increased myocardial oxygen demand¹

^a Department of Cardiac Surgery, Catholic University, Largo A. Gemelli 8, 00168 Rome, Italy
^b Department of Angiology, Catholic University, Rome, Italy
^c Department of Nuclear Medicine, Catholic University, Rome, Italy
^d Department of Cardiology, Catholic University, Rome, Italy

Received 29 September 1997; received in revised form 15 December 1997; accepted 6 January 1998.

Corresponding author. Tel.: +39 6 3058181; fax: +39 6 3058181.

	Abstract

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Objective: To evaluate the flow reserve and adequacy to meet myocardial requests in stress conditions of mammary artery-left anterior descending (IMA-LAD) grafts using a non-invasive method. Methods: Patients (20) with angiographic evidence of normofunctioning left IMA-LAD grafts were submitted to dypiridamole Tl²⁰¹ myocardial scintigraphy and concomitant transthoracic echo-doppler evaluation of the IMA flow at a mean interval of 32.5 months after surgery. Results: Under basal conditions, the mean peak and end flow velocities in systole were 0.39 and 0.06 m/s, respectively. In diastole, the mean peak and end flow velocities were 0.27 and 0.02 m/s and mean tele-diastolic flow velocity was 0.14 m/s, with a mean systolic/diastolic ratio of 1.51. After dypiridamole infusion, mean systolic velocities were 0.47 (peak) and 0.23 (end) m/s, respectively +20 and +283%, whereas mean diastolic velocities were 0.56 (peak) and 0.06 (end) m/s, +107 and +200%, respectively. Mean tele-diastolic flow velocity increased to 0.32 m/s (+128%) and the systolic-diastolic index changed to 0.85. In all cases no significant scintigraphic evidence of induced ischemia was demonstrated in the LAD region. Conclusions: Transthoracic echo-doppler evaluation combined with Tl²⁰¹ myocardial scintigraphy is a useful tool for the assessment of IMA flow reserve and adequacy to stress conditions. In the late postoperative period, the IMA shows the possibility of increasing the flow velocity, almost 2-fold; the increase in flow is prevalently diastolic and leads to a complete reversal of the physiological systolic/diastolic flow ratio. The flow reserve of IMA is always able to meet the augmented myocardial oxygen demand after dypiridamole infusion.

Key Words: Internal mammary artery • Echo-Doppler • Tl²⁰¹ myocardial scintigraphy • Flow reserve

	Introduction

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The possibility of a simultaneous study of the flow reserve and adequacy to augment myocardial oxygen demands of coronary artery bypass grafts would be of obvious interest in clinical research. However, until now no method for this concomitant evaluation has been reported.

Transthoracic echo-Doppler has been widely applied in clinical practice for the non-invasive assessment of mammary artery graft patency [1] [2] [3], and more recently, this technique has been used to study the modifications of graft flow in different conditions [4] [5].

Herein is reported a preliminary experience with an original non-invasive method who combines dypiridamole Tl²⁰¹ myocardial scintigraphy and transthoracic echo-Doppler in order to offer the possibility of assessing both the hemodynamic characteristics of the increase of IMA flow under stress conditions and the adequacy of this flow to an augmented myocardial O₂ request.

	Materials and methods

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Patient population
This study protocol involves 20 patients who underwent single IMA-LAD grafting at our institution and in whom post-operative angiography revealed a normofunctioning IMA graft. These twenty cases were selected among the 194 patients who underwent postoperative angiography at our Institution from January to December 1996; selection was based on a perfect postoperative angiography (all graft widely patent) and the willingness of the patient to undergo the dypiridamole study.

Main clinical and angiographic data of the patients are shown in Table 1. Each patient gave his/her informed consent before either the post-operative angiography and the scintigraphic, echo-Doppler evaluation.

The left IMA was usually detected in the third intercostal space in parasternal position; in 4 patients the IMA could be detected only in the supraclavicular position. In 3 of these patients, endovenous infusion of an echo-contrast medium (suspension of microparticles of galactose and palmitic acid 300 mg/ml; Levovist, Schering AG, Germany) was also necessary in order to ameliorate the vascular imaging. The artery could be visualized in all our cases.

Colour-doppler imaging was obtained using a constant angle of 60° between the ultrasound beam and the long axis of the vessel. Under colour-Doppler guidance a pulsed Doppler evaluation of the flow velocity in the IMA using a sample volume of 1 mm³ and taking into consideration the angle between the ultrasound beam and the axis of the vessel was performed.

The following parameters were calculated: Peak systolic velocity (m/s) (PSV); end systolic velocity (m/s) (ESV); peak diastolic velocity (m/s) (PDV); end diastolic velocity (m/s) (EDV); tele-diastolic velocity (TDV), time average mean velocity (m/s) (TAMV); resistance index, (PSV-EDV)/PSV (RI); pulsatility index, (PSV-EDV)/TAMV (PI); systolic-diastolic peak velocity ratio (SDR). The TAMV was defined as the area between the line traced on the Doppler wave and the base line, and represents the mean velocity corrected for the duration of the velocity curve, electronically calculated by the computer by tracing the area of the curve. The diameter of the IMA was calculated using internal electronic calipers on frozen frame images from the B-mode recording.

Flow (F) was obtained using the formula: F (ml/min)=TAMV (cm/s)x(r²x60) where r is half the internal diameter of the IMA expressed in cm.

Vasodilatory protocol
The left IMA flow was evaluated in all patients at rest and after e.v. administration of dypiridamole 0.84 mg/kg (Persantin, Boehringer Mannheim, Germany).

Echo-Doppler evaluation of IMA flow was started immediately after administration of dypiridamole and continued without interruption for 15 minutes. Flow measurements were made when the vasodilator effect was judged to be maximal by the operator. All patients suspended all vasoactive medications two days before the test.

Scintigraphic evaluation
Tallium²⁰¹ myocardial scintigraphy was performed in all patients immediately after the dypiridamole test (in concomitance with the echo-Doppler evaluation) in order to verify if the increase of left IMA blood flow was sufficient to meet the augmented myocardial oxygen demand. 370 MBq of Tc99m-Sestamibi was injected intravenously 2–3 min after completion of Dipyridamole infusion. Image acquisition was started 30–60 min later (DYP-SPET). After 3–4 h, 1110 MBq of Tc99m-Sestamibi was injected at rest (REST-SPET). Image acquisition was started 30–60 min later. Imaging was performed by a rotating rectangular single head gamma-camera (Starcam 3200i, General Electric, USA) equipped with a low-energy high resolution parallel hole collimator. Energy discrimination was achieved by a 20% window centred over the 140 KeV photopeak of 99mTc; zoom factor was 1.33x, acquisition matrix was 64x64. The camera was rotated in 6° increments, collecting 32 views for 50 s each. Image reconstruction was accomplished by filtered back-projection with a Butterworth filter with a cut-off frequency of 0.35 cycles/pixel and a power factor of 5. No attenuation or scatter correction was performed. From transverse axial tomograms encompassing the whole heart, sagittal and oblique slices parallel to the long axis and short axis of the left ventricle were obtained. From the DYP-SPET and REST-SPET studies of each patient three short axis slices (apical, mid-ventricular and basal) one horizontal long axis (mid-ventricular) and one vertical long axis slice (mid-ventricular) were selected. The tomograms were divided into 20 segments ( Fig. 1 ). Eight segments (numbered 1, 2, 5, 6, 9, 10, 13 and 15) were attributed to the distribution territory of the LAD. Two experienced observers blinded to patients conditions and to each other assigned to each of these segments a score according to the local perfusion conditions: 0=normal perfusion; 1=mild defect; 2=severe defect. Disagreements were resolved by consensus after a common reevaluation.

View larger version (14K): [in this window] [in a new window]   Fig. 1. Division of tomograms for SPET evaluation.

	Results

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Detailed results of the echo-doppler measurement are shown in Table 2.

In general, due to the peculiar characteristics of the coronary circulation, dypiridamole administration led to a marked increase of the end-systolic and diastolic flow velocities and to a less evident increase of the systolic velocity and the IMA diameter ( Fig. 2 ).

View larger version (69K): [in this window] [in a new window]   Fig. 2. Echo-Doppler evaluation of left IMA flow at rest (a) and after dypiridamole infusion (a): the increase of diastolic peak velocity (V3) is even superior to the increase in systolic peak velocity (V1) (V2, end-systolic velocity; V4, end-diastolic velocity).

In four cases minimal scintigraphic evidence of induced ischemia was demonstrated in the LAD region (all the 4 patients had diseased diagonal or antero-lateral branches who were not grafted at surgery because of the poor quality and/or small diameter of the vessels); in the remaining 16 patients no inducible ischemia could be demonstrated ( Fig. 3 ) and the mean ischemia index was 1.5±0.5 (Table 3).

View larger version (83K): [in this window] [in a new window]   Fig. 3. Scintigraphic evaluation after dypiridamole infusion: absence of inducible ischemia in the LAD region.

	Discussion

Top Abstract Introduction Materials and methods Results Discussion References

 
The possibility of evaluating coronary artery bypass flow reserve and adequacy to meet augmented myocardial oxygen demands simultaneously would be of obvious interest in clinical research. However, until now a concomitant study of graft flow and myocardial perfusion has never been attempted and the two evaluations have always been performed in different settings. Moreover, flow studies have usually been possible only by mean of invasive, catheter-based methods and their extensive application has been limited by both economical and ethical reasons. The recent validation of transthoracic echo-Doppler for the study of IMA flow variations provided a new non-invasive tools for graft flow study [4] [5].

Our experience extends the application of transthoracic echo-Doppler studies and, by combining this method with dypiridamole Tl²⁰¹ myocardial scintigraphy, allows a concomitant evaluation of the increase in mammary artery flow and the adequacy of this flow to the augmented myocardial oxygen demand.

The fact that our results are concordant with those obtained using intravascular flow measurements and implantable Doppler probes [6] [7] confirms the reliability of our echo-Doppler technique. On the other hand, the sensitivity and specificity of dypiridamole Tl²⁰¹ myocardial scintigraphy in detecting myocardial ischemia has been proven to be extremely high [8] [9].

In our experience, the systolic/diastolic peak velocity ratio was consistently higher than that reported by Crowley and Shapiro in 1995 [3]. However, these authors used an echocardiographical method and detected the IMA in close proximity to the anastomosis, whereas we evaluated IMA flow at a considerably more proximal level (III intercostal space or even more proximal in the patients in whom a supraclavicular approach had to be used). Luise and colleagues, and Kern and co-authors, using intravascular Doppler have reported that the systolic/diastolic flow ratio varies along the course of the IMA graft, showing a predominant systolic component in the proximal part and a superior diastolic flow in proximity of the anastomosis [6] [10]. Moreover, Luise and colleagues found that the systolic/diastolic ratio is higher in a IMA graft with patent collaterals (i.e. in mammary arteries harvested without the use of specific devices through a minithoracotomy). As seven of our patients received a minimally invasive revascularization, it is obvious that the mean systo/diastolic peak velocity ratio in our series was higher than that reported by Crowley and Shapiro. In view of that, a systo/diastolic index >1 cannot be considered an absolute predictor of IMA malfunction (as suggested by Crowley and Shapiro) but should always be related to the level where the IMA graft was detected and flow measurements performed and to the type of graft studied.

Our method is likely to have extensive future application in clinical research: its use will probably be particularly useful in the evaluation of the questioned adequacy of composite grafts to stress conditions, in the assessment of the variations of gastroepiploic grafts flow according to the gastrointestinal status and, more in general, in the study of the flow reserve and adequacy to myocardial requests of pedicled grafts in different physiological and pathological conditions.

	Acknowledgments

 
The authors wish to acknowledge Mr Domenico Costantini for his technical assistance in editing the photographic material.

	Footnotes

 
Presented as a poster at the 11th Annual Meeting of the European Association for Cardio-thoracic Surgery, Copenhagen, September 28–October 1, 1997.

	References

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1. De Bono DP, Samani NJ, Spyt TJ, Hartshorne T, Thrush AJ, Evans DH. Transcutaneous ultrasound measurement of blood flow in internal mammary artery to coronary artery grafts. Lancet 1992;339:379-381.[Medline]
2. Van Son JAM, Skotnicki SH, Peters MBM, Pijls NHJ, Noyez L, Van Asten WNJC. Non-invasive hemodynamic assessment of the internal mammary artery in myocardial revascularization. Ann Thorac Surg 1993;55:404-409.[Abstract]
3. Crowley JJ, Shapiro LM. Non-invasive assessment of left internal mammary artery graft patency using transthoracic echocardiography. Circulation 1995;92(2):25-30.[Abstract/Free Full Text]
4. Canver CC, Armstrong VM, Cooler SD, Nichols RD. Assessment of internal thoracic artery vasoreactivity in response to sublingual nitroglycerin. Ann Thorac Surg 1997;63:1041-1043.[Abstract/Free Full Text]
5. Takemura H, Kawasuji M, Sakakibara N, Tedoriya T, Ushijima T, Watanabe Y. Internal thoracic artery graft function during exercise assessed by transthoracic Doppler echography. Ann Thorac Surg 1996;61:914-919.[Abstract/Free Full Text]
6. Luise R, Teodori G, Di Gianmarco G, D'Annunzio E, Palloscia L, Barsotti A, Gallina S, Contini M, Vitolla G, Calafiore AM. Persistence of mammary artery branches and blood supply to the left anterior descending. Ann Thorac Surg 1997;63:1759-1764.[Abstract/Free Full Text]
7. Takayama T, Suma H, Wanibuchi Y, Tohda E, Matsunaka T, Yamashita S. Physiological and pharmacological responses of aterial graft flow after coronary artery bypass grafting measured with an implantable ultrasonic doppler miniprobe. Circulation 1992;86(2):217-223.
8. Lakkis NM, MacMarian JJ, Verani MS. Exercise thallium 201 single photon emission computed tomography for evaluation of coronary artery bypass graft patency. Am J Cardiol 1995;76:107-111.[Medline]
9. Task Force. ACC/AHA Guidelines for clinical use of cardiac radionuclide imaging. J Am Coll Cardiol 1995;25:521-544.[Medline]
10. Kern MJ, Bach RG, Donohue TJ, Caracciolo EA, Wolford T, Aguirre FV. Role of large pectoralis branch artery in flow through a patent left internal mammary artery conduit. Catheter Cardiovasc Diagn 1995;34:240-244.[Medline]

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