Saturday
15
February
No 8790
1992
ORIGINAL ARTICLES
Transcutaneous ultrasound measurement of blood-flow in internal mammary artery to coronary
artery grafts
Transcutaneous doppler ultrasound was used to examine internal-mammary-artery (IMA) bloodflow in 26 patients with I MA coronary bypass grafts. The ungrafted right IMA could be seen in all of 19 patients, the grafted left IMA in 16 of 26, and the grafted right IMA in 3 of 7. The velocity profile recorded from the proximal part of the grafted IMA is distinct from that of an ungrafted artery, with a systolic peak which reflects graft capacitance in the face of high intramyocardial resistance, and a diastolic peak which represents graft conductance when intramyocardial resistance is low. Total graft blood-flow can be estimated from the mean velocity and the measured vessel diameter; resting flows ranged from 22 to 79 ml/min. In recently grafted patients, resting graft blood-flow correlated with myocardial "run-off" estimated from preoperative arteriograms; graft blood-flow increased appropriately with exercise. This simple, non-invasive technique to measure IMA graft blood-flow may find applications for routine postoperative follow-up of patients with IMA grafts and for studies on the physiology and pharmacology of coronary artery blood-flow.
Introduction The internal mammary (or internal thoracic) artery is now preferred source for bypass grafts to the left anterior descending coronary artery In some patients, the right internal mammary artery (IMA) may also be used as a graft to the right or circumflex coronary arteries. A simple, repeatable, and non-invasive technique to assess IMA graft blood-flow would be useful for clinical follow-up of patients the
with such grafts, and for the study of coronary physiology and pharmacology. Duplex ultrasound has been extensively used to measure blood-flow in peripheral and cerebral blood vessels;’ we describe use of this technique in the assessment of IMA graft function.
Patients and methods 26 consecutive patients (25 men, 1 woman) were studied as part of routine follow-up in a cardiology clinic at intervals from 6 weeks to 12 months after coronary artery bypass surgery in which at least one IMA was grafted. Informed consent was obtained and the study was approved by the local ethics of medical research committee. The proximal IMA was imaged with transcutaneous ultrasound by use of a 7-5 MHz mechanical sector probe with 3 MHz offset doppler (Diasonics, Bedford, UK). The two transducer positions used were lateral to the upper sternal margin just below the clavicle, and above the clavicle with the ultrasound beam angled downwards and forwards. For intracoronary doppler studies we used a monorail 20 MHz catheter tip transducer (Schneider, Beulach, Switzerland) during routine coronary angiography. Preoperative coronary arteriograms were recorded on 35 mm cine-film and reported according to the Green Lane (Auckland) semi-quantitative analysis scheme,4 which assigns a "myocardial score" for the distribution of individual vessels as well as incorporating an assessment of the degree of stenosis. From the original reports of -the preoperative arteriograms we aggregated myocardial scores for all vessels supplied by the IMA graft downstream of the principal native vessel stenosis: for example, a sequential graft to the left anterior descending and two diagonal coronary arteries would aggregate the myocardial scores of all these vessels. The myocardial score was modified to take account of competing native coronary flow by multiplying the score by 1 in the case of total proximal occlusion, by 05 if proximal occlusion was by a single stenosis of or below 70% normal vessel diameter, and by 0-75 if the proximal stenosis showed more than 70% occlusion but was not complete. This "run-off" score was compared with measured IMA graft flow. Statistical comparisons were made with the Mann Whitney test, Wilcoxon’s test for paired observations, and Spearman’s correlation coefficient. Results are presented as median (range) for flow data, and as mean (standard deviation) for vessel diameter and flow per beat, for which data distribution was close to a normal distribution.
ADDRESSES: Departments of Cardiology (Prof D. P de Bono, MD, N. J. Samani, MRCP), Surgery (T. J. Spyt, FRCS), and Medical Physics (T. Hartshorne, A. J. Thrush, MSc, D. H. Evans, PhD), University of Leicester, Leicester, UK. Correspondence to Prof David de Bono, Clinical Sciences Wing, Glenfield General Hospital, Leicester LE3 9QP, UK.
380
Results Flow in the non-grafted IMA was detected in all 19 who had a unilateral IMA graft. The doppler sonogram (which represents instantaneous axial blood-flow velocities, calculated from doppler frequency shift, plotted against time) from this vessel (fig 1) resembles that of other medium-sized systemic arteries such as the external carotid artery. Flow in the proximal part of an IMA grafted to a left anterior descending coronary artery was identified in 16 of 26 patients (61%) who had had this procedure; a characteristic grafted-IMA doppler sonogram is shown in fig 2. The main difference between ungrafted and grafted IMA sonograms is that the grafted IMAs show substantial forward flow during diastole. Integration of the velocity derived from the intensityweighted mean doppler-shift frequency with respect to time allows the proportion of total flow that occurs in systole and diastole to be calculated independently of any measurement of vessel diameter, provided this size remains approximately the same in systole and diastole. For ungrafted right IMAs most flow occurred during systole (median 72% [range 57-83%]). With grafted left IMAs the proportion was reversed; the median systolic proportion of flow was only Grafted right IMAs showed a 34% (22-43%; p
15
February
No 8790
1992
ORIGINAL ARTICLES
Transcutaneous ultrasound measurement of blood-flow in internal mammary artery to coronary
artery grafts
Transcutaneous doppler ultrasound was used to examine internal-mammary-artery (IMA) bloodflow in 26 patients with I MA coronary bypass grafts. The ungrafted right IMA could be seen in all of 19 patients, the grafted left IMA in 16 of 26, and the grafted right IMA in 3 of 7. The velocity profile recorded from the proximal part of the grafted IMA is distinct from that of an ungrafted artery, with a systolic peak which reflects graft capacitance in the face of high intramyocardial resistance, and a diastolic peak which represents graft conductance when intramyocardial resistance is low. Total graft blood-flow can be estimated from the mean velocity and the measured vessel diameter; resting flows ranged from 22 to 79 ml/min. In recently grafted patients, resting graft blood-flow correlated with myocardial "run-off" estimated from preoperative arteriograms; graft blood-flow increased appropriately with exercise. This simple, non-invasive technique to measure IMA graft blood-flow may find applications for routine postoperative follow-up of patients with IMA grafts and for studies on the physiology and pharmacology of coronary artery blood-flow.
Introduction The internal mammary (or internal thoracic) artery is now preferred source for bypass grafts to the left anterior descending coronary artery In some patients, the right internal mammary artery (IMA) may also be used as a graft to the right or circumflex coronary arteries. A simple, repeatable, and non-invasive technique to assess IMA graft blood-flow would be useful for clinical follow-up of patients the
with such grafts, and for the study of coronary physiology and pharmacology. Duplex ultrasound has been extensively used to measure blood-flow in peripheral and cerebral blood vessels;’ we describe use of this technique in the assessment of IMA graft function.
Patients and methods 26 consecutive patients (25 men, 1 woman) were studied as part of routine follow-up in a cardiology clinic at intervals from 6 weeks to 12 months after coronary artery bypass surgery in which at least one IMA was grafted. Informed consent was obtained and the study was approved by the local ethics of medical research committee. The proximal IMA was imaged with transcutaneous ultrasound by use of a 7-5 MHz mechanical sector probe with 3 MHz offset doppler (Diasonics, Bedford, UK). The two transducer positions used were lateral to the upper sternal margin just below the clavicle, and above the clavicle with the ultrasound beam angled downwards and forwards. For intracoronary doppler studies we used a monorail 20 MHz catheter tip transducer (Schneider, Beulach, Switzerland) during routine coronary angiography. Preoperative coronary arteriograms were recorded on 35 mm cine-film and reported according to the Green Lane (Auckland) semi-quantitative analysis scheme,4 which assigns a "myocardial score" for the distribution of individual vessels as well as incorporating an assessment of the degree of stenosis. From the original reports of -the preoperative arteriograms we aggregated myocardial scores for all vessels supplied by the IMA graft downstream of the principal native vessel stenosis: for example, a sequential graft to the left anterior descending and two diagonal coronary arteries would aggregate the myocardial scores of all these vessels. The myocardial score was modified to take account of competing native coronary flow by multiplying the score by 1 in the case of total proximal occlusion, by 05 if proximal occlusion was by a single stenosis of or below 70% normal vessel diameter, and by 0-75 if the proximal stenosis showed more than 70% occlusion but was not complete. This "run-off" score was compared with measured IMA graft flow. Statistical comparisons were made with the Mann Whitney test, Wilcoxon’s test for paired observations, and Spearman’s correlation coefficient. Results are presented as median (range) for flow data, and as mean (standard deviation) for vessel diameter and flow per beat, for which data distribution was close to a normal distribution.
ADDRESSES: Departments of Cardiology (Prof D. P de Bono, MD, N. J. Samani, MRCP), Surgery (T. J. Spyt, FRCS), and Medical Physics (T. Hartshorne, A. J. Thrush, MSc, D. H. Evans, PhD), University of Leicester, Leicester, UK. Correspondence to Prof David de Bono, Clinical Sciences Wing, Glenfield General Hospital, Leicester LE3 9QP, UK.
380
Results Flow in the non-grafted IMA was detected in all 19 who had a unilateral IMA graft. The doppler sonogram (which represents instantaneous axial blood-flow velocities, calculated from doppler frequency shift, plotted against time) from this vessel (fig 1) resembles that of other medium-sized systemic arteries such as the external carotid artery. Flow in the proximal part of an IMA grafted to a left anterior descending coronary artery was identified in 16 of 26 patients (61%) who had had this procedure; a characteristic grafted-IMA doppler sonogram is shown in fig 2. The main difference between ungrafted and grafted IMA sonograms is that the grafted IMAs show substantial forward flow during diastole. Integration of the velocity derived from the intensityweighted mean doppler-shift frequency with respect to time allows the proportion of total flow that occurs in systole and diastole to be calculated independently of any measurement of vessel diameter, provided this size remains approximately the same in systole and diastole. For ungrafted right IMAs most flow occurred during systole (median 72% [range 57-83%]). With grafted left IMAs the proportion was reversed; the median systolic proportion of flow was only Grafted right IMAs showed a 34% (22-43%; p
