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Left mamary artery flow in coronary mamary by-pass.

Orlandi Fábio; Grossmann Rosana; Hublard Ernesto Luiz; Cortese Marcelo; Nakajima Eliza; Capellini Luis Fernando; Mangione José Armando; Beltrão Pedro; Cividanes Gil Vicente; Puig Luis Boro; Gebara Otávio; Del Castillo José Maria.

Instituto de Cardiologia de São Paulo, Hospital Santa Paula.
São Paulo, SP, Brasil

Material and Methods

Purpose: Determine the best line of access to evaluate the coronary mamary by-pass through transtoracic echocardiography (TTE) and determine the internal mamary artery (IMA) pattern of flow in cases without stenosis, with stenosis, and with occlusion.
Material and methods: It has been studied 32 consecutive patients revascularized by coronary mamary by-pass, all males , average age 56 years. It has also been studied, as controls, 10 individuals who had never been submitted to coronary by-pass surgery, all males, average age 47 years. All patients have been submitted to digital coronary angiography. It has been visualized by TTE the internal mamary artery (IMA). Its diameter was measured, its flow has been registered and it has been calculated the diastolic integral velocity, systolic integral velocity and the resistance index.
Results: IMA satisfactory visualization and arterial flow register has been obtained in 26 patients (81%) and in 6 controls (60%) . Controls had high resistance flow patterns (systemic artery pattern) while in the revascularized patients the flow patterns varied from bifasic with diastolic prevalence (cases without stenosis or with mild/moderate stenosis) to bifasic with systolic prevalence (cases with severe degree of stenosis). In revascularized patients the best line of examination has been paraesternal incidence in third or fourth intercostal spaces, while in controls the best line has been the supra or infraclavicular route.
Conclusion: TTE, with the use of high frequency transducers, is a good method to assess IMA flow patterns in patients with coronary mamary by-pass. Left paraesternal incidence is the best line of examination. The IMA flow pattern allows the diferenciation of patients with severe stenosis and patients without stenosis or mild/moderate stenosi



Left mammary artery, branch of left subclavian artery is thoroughly used for myocardium revascularization, mainly for revascularization of the left anterior descending coronary and its branches.
Due to the fact of being a muscle irrigating artery its pattern of flow is triphasic, systolic and of high resistance. When we use it as by-pass its flow must adjust to the flow pattern found in the coronary system: biphasic and predominantly diastolic.
This adaptation of the internal mammary artery flow to the coronary flow pattern may be used to assess wheter the mammary coronary by-pass is pervious or not, as well as to predict the conditions of the coronary bed distal to anastomosis and the presence of stenosis in the very anastomosis.
The use of high frequency probes like the ones used to vascular ultrasound, permits the visualization of internal mammary artery in its origin and between the intercostal spaces as well as the flow detection, thereby being an important diagnosis method to the assessment of revascularized patients with mammary coronary by-pass. This kind of assessment was previously available only through invasive methods (cardiac catheterism).



Determine, through transthoracic echocardiography with high frequency emission probes, the most appropriate way of access to evaluate mammary coronary by-passs, the left internal mammary artery diameter and its pattern of flow in cases without stenosis, with stenosis and with occlusion..


Material and Methods: 

It has been studied 32 consecutive revascularized patients with anastomosis between left internal mammary artery and left coronary artery (25 anastomosis to the anterior descending branch and 7 anastomosis to the marginal or diagonal branch). 29 patients (91%) were male and mean of ages was 56 years (standard deviation 9 years).
As control group it has been studied 10 non-revascularized patients, all males, with mean of ages of 47 years (standard deviation 7 years). All patients, controls and revascularized, have been submitted to digital angiography in the same day of the echocardiographic study.
To the echocardiographic study a HP Sonos 1000 equipment with linear 7.5MHz and arterial flow analysis protocol has been used. The examinations have been recorded in VCR tapes for subsequent assessment and measurement.
With the 7.5MHz probe left internal mammary artery has been identified, either in its origin (through supraclavicular way of access) or along the 2nd to 4th intercostal spaces, parasternal line. Second intercostal space was also called infraclavicular way of access. It has been measured the vessel diameter in its best sight point and has been gotten its flow spectral recording (Figure 1) . It has been measured the systolic velocity peak, the diastolic velocity peak (in cm/s) and the integral velocity ( in cm). With such data , Pourcelot’s resistivity index (IR) has been computed with the following formula:

IR = systolic velocity - diastolic velocity/ systolic velocity

Figure 1

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Fig. 1: Left: Ultrasonographic B-mode of the left mammary artery through supraclavicular approach. Right: Doppler spectral curve of the left mammary artery flow. ASE: left subclavian artery; AMIE: left mammary artery; ATI: thyrcervical trunk; AVE: left vertebral artery; Sist: systolic peak velocity; Diast: diastolic velocity; I.R.: resistivity index; VTI: integral velocity.

For predominantly diastolic flow it has been considered a negative resistivity index (Figure 2). For all measures it has been determined the mean and the mean standard deviation.
Between the revascularized patients and the control group have been analyzed differences between the left internal mammary artery, systolic, diastolic and integral velocities and the resistivity index. Thus, Student "t" test for independent samples has been used with a 5% significant level (p<0,05).
Revascularized patients have been grouped according the coronary angiography results in normal (anastomosis without stenosis), with light stenosis (<50%), with mild stenosis (from 51% to 75%) and with important stenosis (>75%). Such parameters have been analyzed through variance analysis.
It has been detrmined the variability for two independent observers through the correlation coefficient.

Figure 2

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Fig. 2: Left: Doppler spectral curve of the left mammary artery flow in non-revascularized patient (control group) showing high resistance, triphasic flow pattern. Right: Doppler spectral curve of the left mammary artery flow in non-stenotic revacularized patient (normal group) showing biphasic flow pattern with prevalence of diastolic component and negative resistivity index (I.R.)



The left internal mammary artery register has been satisfactorily obtained in 26 (81%) of 32 revascularized patients and in 6 (60%) of 10 patients of the control group, with the following particularity: in the majority of revascularized patients the best way of access was left parasternal, with 7 registers obtained in the 2nd intercostal space, 6 registers obtained in the 3rd intercostal space and 13 registers obtained in the 4th intercostal space. In the control group mammary artery has been seen in 2 patients through the supraclavicular way of access, in the 2nd intercostal space in 3 patients and in a patient in the 3rd intercostal space.
Table 1 shows obtained results in revasculrized patients and in the control group and the "t" test comparison. Table 2 shows results in revascularized patients grouped according the the stenosis degrees and control group patients and variance analysis between the parameters.
Figure 3 show the systolic and diastolic velocities in revascularized patients grouped according the degrees of stenosis and in the control group patients. Figure 4 shows the resistivity index in those patients.
The interobserver variability for two independent observers was satisfactory, presenting this method good reproductivity.

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Table 2
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Figure 3

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Fig. 3: Systolic and diastolic flow velocities in revascularized patients grouped according to the anastomosis stenosis and in the non-revascularized control group. Normal: anastomosis without stenosis; Leve: anastomosis with light stenosis (<50%); Moderada: anastomosis with mild stenosis (51-75%); Importante: anastomosis with important stenosis (>75%); Controle: non-revascularized control group; F: variance analysis value; p: significance.

Figure 4

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Fig. 4: Left mammary artery resistivity index in revascularized patients grouped according to the anastomosis stenosis and in the non-revascularized control group. For abbreviations see Figure 3.



Left internal mammary artery flow detection presents technical difficulties that will propably be minimized with the learning curve and with the equipment technical improvement. This could be the reason for the relatively low visualization index in control group where the internal mammary artery is a vessel of relatively few functional importance. However, it has not been found significant differences between internal mammary artery diameter of revascularized patients and the control group. In the revascularized patients this artery increase of flow due of by-pass probably contributed for a better visualization index, particularly of the vessel distal part. It also attracts our atention the fact of not being able to register the mammary internal flow in any female patient, probably due to the greater anterior thoracic wall thickness.
Systolic velocity was significantly greater in control group than in revascularized patients, the opposing occurring with diastolic velocity. The resistivity index, high in control group, thus proving the systolic prevalence, was negative in the majority of revascularized patients, except in the group which presented important by-pass stenosis (Figure 5) . This means that important obstructions of mammary coronary by-pass or of the distal bed of the revascularized artery change the coronary flow pattern which increases progressively the systolic component (high resistance pattern). This is important because it can suggest the anastomosis obstruction by non-invasive means. It seems there is not a significant relationship between the flow velocity variations and the resistivity mammary artery index in the group without stenosis and the groups with light or mild stenosis, although there is a trend to progressively reduce the diastolic velocity with the stenosis degree increase. One should attempt the small number of studied subjects. The integral velocity has not showed significant differences in revascularized patients grouped according the by-pass stenosis and the control group , thus not contributing for the patients partition.

Figure 5

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Fig. 5: Left mammary artery Doppler spectral flow in revascularized patients. Left: non-stenotic patient showing biphasic flow pattern with diastolic predominance and negative resistivity index. Center: mild stenosis in the revascularized branch showing biphasic flow pattern with equalization of the systolic and diastolic components. Right: total by-pass occlusion showing high resistance flow pattern.



One can obtain the left internal mammary flow with high frequency probing transthoracic echocardiography in a relatively high number of mammary coronary by-pass revascularized patients.
The left internal mammary flow pattern analysis allows to identify the patients with important stenosis or mammary coronary by-pass occlusions. The light or mild anastomosis stenosis are more difficult to identify. One should study greater patients series to obtain more exact results.
The low parasternal way of access (3rd or 4th intercostal space) seems to be technically easier and more appropriate for left internal mammary artery visualization in revascularized patients.


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