Enhanced Coronary Flow Velocity During Intra-Aortic Balloon Pumping Assessed by Transthoracic Doppler Echocardiography

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1 Journal of the American College of Cardiology Vol. 43, No. 3, by the American College of Cardiology Foundation ISSN /04/$30.00 Published by Elsevier Inc. doi: /j.jacc During Intra-Aortic Balloon Pumping Assessed by Transthoracic Doppler Echocardiography Masaaki Takeuchi, MD,* Yuichi Nohtomi, MD, Hidetoshi Yoshitani, MD,* Chinami Miyazaki, MD,* Kazuo Sakamoto, MD,* Junichi Yoshikawa, MD Osaka and Fukuoka, Japan OBJECTIVES BACKGROUND METHODS RESULTS CONCLUSIONS The study was done to determine potential utility of measuring coronary flow velocity (CFV) by transthoracic Doppler echocardiography (TTDE) during intra-aortic balloon pumping (IABP). Use of IABP has been shown to increase CFV assessed by an invasive technique. The CFV in the left anterior descending coronary artery (LAD) can be measured by TTDE. Coronary flow velocity in the distal LAD by TTDE was measured in 40 critically ill patients requiring IABP. All patients received emergency coronary angiography. Both CFV and pressure data were obtained during 1:2 balloon pumping. Adequate diastolic CFV recording was obtained in all patients. The IABP decreased systolic pressure and increased diastolic pressure. Average peak diastolic flow velocity and diastolic velocity time integral was cm/s and cm with non-augmented beat. These values were increased significantly (61 38%, 59 35%, p 0.001) with augmented beat. Significant correlation was noted between % diastolic pressure augmentation and % increase in diastolic CFV (r 0.62 to 0.69, p 0.001). There was no significant difference in flow enhancement during IABP, irrespective to the proximal LAD stenosis severity (severe stenosis: 73 70%; intermediate stenosis: 61 29%; no significant stenosis: 58 29%; p NS, analysis of variance). By continuous recording of CFV, the optimal timing of balloon control could be adjusted to maximize flow velocity during augmentation. Use of TTDE can be employed in monitoring CFV augmentation during IABP. The IABP produced significant distal flow enhancement even in patients with critical proximal stenosis. This totally noninvasive approach may help to optimize the benefits of IABP for coronary flow augmentation. (J Am Coll Cardiol 2004;43:368 76) 2004 by the American College of Cardiology Foundation Although intra-aortic balloon pumping (IABP) has beneficial effect on cardiac afterload, controversy exists about its ability to increase coronary blood flow in patients with reperfused acute myocardial infarction (MI) or in those who have significant coronary stenosis (1 6). Previous studies using Doppler-tipped angioplasty guide wire demonstrated lack of significant flow improvement beyond most critical stenosis with IABP, and IABP mediated significant flow enhancement after amelioration of severe coronary obstructions in patients after successful coronary angioplasty (3). However, this method is applicable only in the cardiac catheterization laboratory, and the advancement of the Doppler guide wire beyond severe stenosis could impede coronary blood flow and adversely affect distal flow measurement. Several recent studies have reported that coronary flow velocity (CFV) in the distal part of the left anterior descending coronary artery (LAD) can be successfully measured by transthoracic Doppler echocardiography (TTDE), and measurements of coronary flow velocity reserve have been useful for detecting functionally significant LAD From the *Department of Internal Medicine, Tane General Hospital, Osaka, Japan; Department of Cardiology, Iizuka Hospital, Fukuoka, Japan; and Department of Internal Medicine and Cardiology, Graduate School of Medicine, Osaka City University, Osaka, Japan. Manuscript received May 7, 2003; revised manuscript received August 6, 2003, accepted August 26, stenosis (7 10). This totally noninvasive approach could also be useful for the continuous assessment of CFV during IABP. We hypothesized that CFV in the distal part of the LAD would be increased by IABP even in patients with critical proximal stenosis. Thus, the purpose of this study was to evaluate 1) noninvasive assessment of coronary hemodynamics using TTDE during IABP; and 2) whether this method can be utilized to adjust the timing of balloon control in critically ill patients. METHODS The study group comprised 40 patients who had placement of an IABP for typical clinical indications. Written informed consent for the placement of IABP and emergency coronary angiography was obtained from the patient, or family, or both before the study. The protocol was approved by the hospital s ethics committee. Coronary angiography was performed in a routine fashion either after or before insertion of the IABP using the femoral approach with standard Judkins diagnostic catheters. Coronary angioplasty (balloon angioplasty, stent deployment) or thrombolytic therapy was performed when clinically indicated. After completion of the necessary in-

2 JACC Vol. 43, No. 3, 2004 February 4, 2004: Takeuchi et al. 369 Abbreviations and Acronyms APDV time-averaged peak diastolic velocity APSV time-averaged peak systolic velocity BP blood pressure CFV coronary flow velocity DFVI diastolic flow velocity integral IABP intra-aortic balloon pumping LAD left anterior descending coronary artery MI myocardial infarction QCA quantitative coronary angiography SFVI systolic flow velocity integral TIMI Thrombolysis In Myocardial Infarction TTDE transthoracic Doppler echocardiography terventions, patients were transferred to the coronary care unit. Coronary flow velocity recordings. All data were obtained during 1:2 IABP in the coronary care unit. The intra-aortic balloon inflation was begun at the aortic dicrotic notch, and deflation was set on the R wave with manual inflation and deflation adjustments. The TTDE was performed with a commercially available ultrasound machine (SONOS 5500, Philips Medical Systems, Andover, Massachusetts) with a broadband high-frequency (5 to 12 MHz) transducer (S12). Color Doppler detection of LAD flow was obtained as previously described (11,12). Briefly, the left ventricle was imaged in the low parasternal long axis cross section, and then the ultrasound beam was inclined laterally. Next, coronary blood flow in the distal portion of the LAD was identified as a color-filled tubular structure in the anterior interventricular sulcus under the guidance of Doppler color flow mapping. The long-axis sections were carefully adjusted to minimize the angle between the Doppler beam and the LAD flow. With a sample volume positioned on the color signal in the LAD in diastole, pulsed Doppler signal tracings of flow velocity in the LAD were recorded. Angle correction was performed if the angle between ultrasound beam and coronary flow direction was 20. The aortic blood pressure (BP) was simultaneously measured for the lumen of the intra-aortic balloon pump through fluid-filled tubing using standard pressure transducers. Coronary flow velocity measurements. Phasic coronary flow velocity signals were recorded at 50- and 100-mm/s speed, and measurements were made off-line by use of the built-in calculation package of the ultrasound unit (Fig. 1). Figure 1. Coronary flow velocity and pressure recordings demonstrating the effects of intra-aortic balloon pumping. (A) Left panel shows phasic coronary flow velocity during 1:2 balloon pumping in a patient with congestive heart failure and high-risk coronary angioplasty (two-vessel disease). First and third coronary flow velocity (CFV) is with augmented beat, and second and fourth CFV is with non-augmented beat. Diastolic CFV is augmented with balloon pumping. Right panel shows aortic pressure. The diastolic pressure before the balloon pumping is shown at D1. The augmented diastolic pressure was labeled S2. (B) Coronary flow velocity and aortic pressure in a patient with recent anterior MI and left main coronary stenosis plus two-vessel disease. First and third CFV is with augmented beat, and second and fourth CFV is with non-augmented beat. Again, diastolic CFV is enhanced with augmented beat.

3 370 Takeuchi et al. JACC Vol. 43, No. 3, 2004 February 4, 2004: The diastolic flow velocity integral (DFVI) was obtained by planimetry of the area under the diastolic velocity signal. The time-averaged peak diastolic flow velocity (APDV) was determined from the traced area of the diastolic flow velocity signal. Deceleration time of diastolic flow velocity was also measured. At least three augmented and three non-augmented beats with adequate quality of coronary flow velocity envelope were measured and averaged in each setting. In addition to the absolute values, coronary flow velocity variables were also reported as a percent of nonaugmented beat value calculated as [(CFV variables augmented CFV variables non-augmented)/cfv variables non-augmented] 100. In patients who could be recorded, adequate systolic CFV envelope, systolic flow velocity integral (SFVI), and time-averaged peak systolic flow velocity (APSV) were also measured with non-augmented beat and with augmented beat. Optimal timing of balloon control. The effect of balloon timing on CFV was examined in 13 patients with coronary artery disease (CAD). The optimal timing of balloon inflation was adjusted so that diastolic flow augmentation coincided with the upstroke of diastolic acceleration flow velocity. The optimal timing of balloon deflation was adjusted on the R wave of the electrocardiogram (ECG). After obtaining CFV with optimal timing of balloon control, the inflation timing was delayed in 11 patients, and the deflation timing was moved to a point earlier than the R wave in seven patients under the continuous recording of CFV. Pressure measurements. Aortic pressure was recorded at 25- and 50-mm/s paper speed. During IABP, the first lowest arterial pressure after the R wave was defined as non-augmented diastolic pressure (D1) (Fig. 1). The augmented diastolic pressure was labeled S2. The percent diastolic pressure augmentation was calculated as [(S2 D1)/D1] 100 as previously reported (2,3). Analysis of coronary angiography. Percent diameter stenosis in the LAD and left main coronary artery was quantitatively analyzed by Philips quantitative coronary angiography (QCA) DCI-ACA system or the Toshiba QCA system. Contrast flow through in the LAD was graded by standard Thrombolysis In Myocardial Infarction (TIMI) flow scale of 0 to 3 from the final coronary angiogram (13). Patients were classified according to the presence and severity of proximal LAD or left main coronary artery stenosis: severe stenosis ( 90%); intermediate stenosis (50% to 90%); and no significant stenosis ( 50%). Observer variability. Interobserver measurement variability was determined by independent measurement on the same CFV recording, and by measurement on the independent CFV recording in eight randomly selected patients. Intraobserver variability was determined by having one observer remeasure the spectral envelopes in eight patients one month apart. Interobserver and intraobserver variabilities were calculated as the SD of the differences between two measurements and expressed as a percent of the average value. Statistical analysis. Data are expressed as mean SD. Each patient served as his or her own control by using the non-augmented data as the baseline value. The difference of CFV and pressure data between non-augmented beats and augmented beats was evaluated by the paired Student t test. Comparisons of continuous variables among three groups were made by analysis of variance (ANOVA). Linear regression analysis was applied to estimate the relation between pressure data and percent diastolic CFV changes. Statistical differences were considered significant at a value of p RESULTS Study patients. Twenty-six patients had acute MIs, including 17 anterior, 5 inferior, and 4 lateral infarctions (Table 1). Three patients required IABP for high-risk coronary angioplasty, and four patients had unstable angina with multivessel disease. One patient had intractable ventricular fibrillations after recent MI. Six other patients had cardiogenic shock, due to acute myocarditis in two, dilated cardiomyopathy in two, and ischemic cardiomyopathy in two patients, respectively. Coronary artery disease was generally extensive, and eight patients had significant left main coronary stenosis. Final coronary angiography showed severe proximal LAD or left main stenosis ( 90%) in seven patients, intermediate stenosis (50% to 90%) in 11, and no significant stenosis ( 50%) in 22 patients, respectively. Seven patients had received emergency or elective coronary bypass surgery after the coronary angiography. Four patients died of intractable congestive heart failure and hypotension. In 17 patients with acute anterior infarction, percutaneous coronary intervention had been performed in 14 patients (primary coronary angioplasty in 13 and thrombolytic therapy in 1), and the other three patients did not receive coronary intervention owing to significant left main coronary stenosis. Final angiography showed TIMI-2 LAD flow in nine patients and TIMI-3 LAD flow in eight patients. Systemic hemodynamics. All patients had sinus rhythm with a mean heart rate of beats/min (range 58 to 124 beats/min) during acquisition of data. Seven patients had baseline systolic BP 90 mm Hg. Intra-aortic balloon pumping decreased systolic BP from mm Hg with non-augmented beat to mm Hg with augmented beat (p 0.001). Diastolic BP (61 13 mm Hg) was augmented to mm Hg (p 0.001), an average increase of % (range 38% to 440%). Coronary flow velocity. Adequate quality of diastolic coronary flow velocity envelope was obtained in all patients (Table 2). The mean value of diastolic deceleration time was ms (range 69 to 2,430 ms). The APDV with non-augmented beat was cm/s, and IABP significantly increased APDV to cm/s (% increase: 61 38%, p 0.001). The DFVI during balloon

4 JACC Vol. 43, No. 3, 2004 February 4, 2004: Takeuchi et al. 371 Table 1. Clinical and Angiographic Data Final CAG Patient No. Age/Gender Diagnosis Initial CAG PCI LAD LMCA 1 67/M Myocarditis, cardiogenic shock Normal No /M AMI (anterior) 1VD PTCA (stent, #6,7) /M AMI (anterior) 1VD PTCA (stent, #6) /M AMI (anterior), cardiogenic shock 1VD PTCA (stent, #6) /M AMI (anterior) 2VD PTCA (POBA, #6) /M AMI (lateral), cardiogenic shock 2VD, LMTD PTCA (stent, #5,11) /M AMI (anterior) 1VD, LMTD PTCR /F RMI (anterior), high-risk PTCA 3VD PTCA (unsuccessful) * 9 58/M AMI (anterior) 1VD PTCA (stent, #6) /M AMI (anterior) 3VD, LMTD No /F UAP LMTD No /M AMI (anterior) 1VD PTCA (stent, #6) /M AMI (anterior), cardiogenic shock 1VD PTCA (stent, #7) /M AMI (anterior) 1VD PTCA (stent, #6) /F Myocarditis, cardiogenic shock Normal No /M AMI (anterior) 1VD PTCA (stent, #6) /F AMI (lateral), cardiogenic shock 2VD PTCA (stent, #11) /M AMI (anterior) 3VD, LMTD No /M AMI (anterior) 1VD PTCA (stent, #6) /F AMI (anterior) 2VD, LMTD No /M ICM, cardiogenic shock 3VD No /F AMI (anterior) 3VD PTCA (stent, #7) /M DCM, cardiogenic shock Normal No /M AMI (lateral) 3VD PTCA (stent, #11) /M AMI (inferior) 3VD PTCA (stent, #2) /F AMI (lateral) 3VD PTCA (stent, #11) /M AMI (inferior) 1VD PTCA (stent, #2) /M ICM, high-risk PTCA 3VD PTCA (stent, #1,7,11) /F AMI (inferior), cardiogenic shock 3VD PTCA (stent, #1) /M UAP 2VD PTCA (stent, #6) /F UAP 3VD No /M AMI (inferior), no reflow after PCI 1VD PTCA (stent, #3) /F DCM, cardiogenic shock Normal No /M OMI (anterior), UAP 3VD PTCA (stent, #1) /M AMI (anterior) 1VD PTCA (stent, #7) /M ICM, cardiogenic shock 1VD, LMTD No /M OMI (lateral), high risk PTCA 2VD PTCA (stent, #3,4) /M AMI (inferior), Vf, shock 2VD PTCA (stent, #2) /F RMI (anterior), Vf, shock 2VD, LMTD PTCA (stent, #5) /M AMI (anterior) 2VD PTCA (stent, #7) *Good intracoronary collateral (septal to septal). # Number of coronary artery segments by American Heart Association classification. AMI acute myocardial infarction; CAG coronary angiography; DCM dilated cardiomyopathy; F female; ICM ischemic cardiomyopathy; LAD left anterior descending coronary artery; LMCA left main coronary artery; LMTD left main coronary disease; M male; OMI old myocardial infarction; PCI percutaneous coronary intervention; POBA balloon angioplasty; PTCA coronary angioplasty; PTCR coronary thrombolysis; RMI recent myocardial infarction; TIMI Thrombolysis In Myocardial Infarction flow scale; UAP unstable angina, Vf ventricular fibrillation; VD vessel disease. TIMI pumping was also increased 59 35% over DFVI with non-augmented beat (from cm to cm, p 0.001). Although there was no significant correlation between baseline systolic BP and percent increase in APDV (r 0.11, p NS) or percent increase in DFVI (r 0.12, p NS), significant correlation was noted between percent diastolic pressure augmentation and percent increase in APDV (r 0.69, p 0.001); and that in DFVI (r 0.62, p 0.001). Adequate quality of systolic coronary flow velocity envelope was obtained in 26 of 40 patients. There was no significant difference of APSV ( cm/s vs cm/s) and SFVI ( cm vs cm) between non-augmented beat and augmented beat. The effect of proximal coronary stenosis on diastolic CFV augmentation during IABP is shown in Figure 2. There was no significant difference of percent increase in diastolic CFV among three groups (p NS, ANOVA). The same results were obtained even if we excluded four patients with normal coronary arteries. In 17 patients with acute anterior MI, rapid deceleration of diastolic flow velocity (diastolic deceleration time 600 ms) and early systolic retrograde flow, which were suggestive of the presence of no-reflow phenomenon (13 16), was observed in 12 and 9 patients, respectively. Intra-aortic balloon pumping increased APDV from cm/s to cm/s (p 0.001) and DFVI from

5 372 Takeuchi et al. JACC Vol. 43, No. 3, 2004 February 4, 2004: Table 2. Coronary Flow Velocity Data Patient SRF DcT APDV (cm/s) DFVI (cm) Base IABP % Base IABP % 1 Yes 1, Yes Yes Yes No No Yes No 1, No No No 2, Yes Yes Yes No Yes No 1, No 1, No No No 1, No No 1, No No No No No No No 1, No 1, No No No No No No No 1, No No Mean SD APDV time-averaged peak diastolic velocity; Base nonaugmented beat; DcT deceleration time of diastolic coronary flow velocity; DFVI diastolic flow velocity integral; IABP augmented beat; SRF systolic retrograde flow; % percent increase. cm to cm (p 0.005) in 12 patients with diastolic deceleration time 600 ms, and from cm/s to cm/s (p 0.001) and cm to cm (p 0.05), respectively, in 9 patients with early systolic retrograde flow. There was no significant difference of percent increase in APDV (52 29% vs %) and DFVI (55 33% vs %) between patients with rapid diastolic deceleration time and those without. No difference of percent increase in APDV (49 32% vs %) and that in DFVI (52 38% vs %) was noted between patients with systolic retrograde flow and those without. There was no significant difference of APSV ( cm/s vs cm/s) and SFVI ( cm vs cm) between non-augmented beat and augmented beat in nine patients with systolic retrograde flow. Effect of balloon timing on CFV. Optimal balloon inflation was achieved to adjust diastolic flow augmentation to coincide with upstroke of diastolic acceleration flow (Fig. 3B, arrow). Delayed balloon inflation significantly decreased APDV ( cm/s vs cm/s, p 0.001) and DFVI ( cm vs cm, p 0.001) (Fig. 4). Although D1 did not change ( mm Hg vs mm Hg), S2 also significantly decreased ( mm Hg vs mm Hg, p 0.05).

6 JACC Vol. 43, No. 3, 2004 February 4, 2004: Takeuchi et al. 373 Figure 2. Effect of balloon pumping on coronary flow velocity among three groups according to the severity of proximal stenosis. APDV time-averaged peak diastolic velocity (cm/s); DFVI diastolic flow velocity integral (cm); IABP% percent increase intra-aortic balloon pumping. Shaded bars no significant stenosis; black bars intermediate stenosis; open bars severe stenosis. Early balloon deflation also significantly decreased APDV ( cm/s vs cm/s, p 0.05) and DFVI ( cm vs cm, p 0.05). However, there was no difference of D1 ( mm Hg vs mm Hg, p NS) and S2 ( mm Hg vs mm Hg, p 0.1). Observer variabilities. Interobserver variability by independent measurement on the same recording and the Figure 3. Adjustment of balloon timing during coronary flow velocity recording. Coronary flow velocity during 1:2 balloon pumping in a patient with high-risk percutaneous transluminal coronary angioplasty. Upper panel shows coronary flow velocity and lower panel shows aortic blood pressure. (A) Delayed inflation; there is a notch between diastolic deceleration flow and augmentation flow (arrow). (B) Optimal timing of balloon control; diastolic flow augmentation coincides with the upstroke of diastolic acceleration flow velocity (arrow). (C) Early deflation; flow velocity is terminated early before the R- wave on electrocardiogram (arrows).

7 374 Takeuchi et al. JACC Vol. 43, No. 3, 2004 February 4, 2004: Figure 4. Individual value of coronary flow velocity during adjustment of the timing of balloon control. Abbreviations as in Figure 2. independent recordings were 4.8% and 7.3%, respectively. Intraobserver variability for the measurements of CFV recordings was 3.0%. DISCUSSION This study demonstrates that the measurement of diastolic CFV in the distal part of the LAD by TTDE during IABP was highly feasible and that diastolic CFV was increased significantly with augmented diastolic pressure during IABP, even in patients with critical proximal stenosis. Diastolic CFV in the distal LAD was also augmented by IABP in patients with reperfused anterior MI and no-reflow phenomenon. These results directly support the potential for augmenting myocardial perfusion during balloon pumping. We also demonstrated that optimal balloon timing on coronary flow augmentation could be adjusted under the guidance of CFV recording by TTDE. Thus, TTDE is useful for non-invasive assessment of coronary hemodynamics during IABP. Previous studies. Controversy exists regarding the ability of IABP to increase coronary blood flow in patients who are critically ill or who have significant atherosclerotic coronary stenosis (1 4,6). Although previous studies demonstrated significantly augmented CFV in the proximal LAD by transesophageal echocardiography (6) or augmented CFV in the proximal coronary arteries by Doppler catheters (2), those studies did not address distal flow response in the presence of obstructive coronary narrowings. Subsequently, Kern et al. (3) used Doppler-tipped angioplasty guide wire for measuring CFV distal to the stenosis during IABP and demonstrated a limited distal flow velocity and a failure to increase flow beyond the most critical coronary stenosis. After relief of vessel occlusion or severe coronary stenosis by angioplasty, a 25% augmentation of distal mean CFV and a 35% increase in distal diastolic velocity integral was observed by IABP. However, the advancement of Doppler guide wire itself across the severe stenosis could impede distal coronary blood flow and adversely affect flow measurements. Current study. To our best knowledge, this is the first study to examine the effect of IABP on CFV in the distal LAD by TTDE. Adequate quality of diastolic CFV envelope in the distal LAD was obtained in all patients, and a 60% augmentation of distal CFV by balloon pumping was observed. In contrast to the results of previous studies. IABP produced significant distal flow enhancement even in patients with critical proximal LAD stenosis. Diastolic aortic pressure is a well-known determinant of coronary flow; thus, an increase in the diastolic pressure induced by IABP will have a significant impact on coronary flow augmentation (6). The significant correlation between percent diastolic pressure augmentation and percent increase in diastolic CFV in this study was in agreement with previous studies (2,6). Although we did not measure coronary pressure at the site of CFV recording, these findings suggest that autoregulation of CFV was lost or out of range in the critically ill, and the change in the CFV depends on the degree of distal perfusion pressure. Patients who experience no-reflow phenomenon after MI have an increased risk of poor left ventricular function and prognosis (17 19). The CFV pattern of no-reflow phenomenon in patients with reperfused acute MI is characterized

8 JACC Vol. 43, No. 3, 2004 February 4, 2004: Takeuchi et al. 375 by the appearance of systolic retrograde flow and rapid deceleration slope of diastolic flow by use of a Doppler guide wire (13 15). In patients with reperfused acute anterior MI, we demonstrated that the degree of diastolic CFV enhancement by IABP was comparable between patients with systolic retrograde flow/rapid deceleration slope and those without. There was no significant difference of systolic flow velocity between the non-augmented beat and the augmented beat in patients with systolic retrograde flow. These results suggest that in addition to pharmacologic interventions (20,21). IABP is an effective therapeutic strategy to enhance CFV in no-reflow phenomenon. This study also showed that the degree of the increase in CFV by IABP depends on the timing of balloon inflation and deflation, and TTDE allows adjusting the optimal timing of balloon control for maximal CFV enhancement. This is another advantage of noninvasive monitoring of CFV during balloon pumping. Study limitations. Flow velocity measurements do not provide an absolute value but are linearly related to changes in absolute flow when vessel area remains constant. Although we did not measure coronary vessel diameter, unchanged diameter during balloon pumping was reported in a previous study (3). Coronary flow velocity measurements were not performed before the interventional therapy but were performed after the patients were admitted to the coronary care unit. Thus, we cannot guarantee whether the same results would be obtained before coronary intervention in the cardiac catheterization laboratory. It was only in two-thirds of the study patients that an adequate quality systolic flow velocity envelope could be recorded, because of the movement of coronary vessels during cardiac cycle and wall motion artifact. However, diastolic flow is dominant in this part of the epicardial coronary artery. The finding that no significant change in systolic flow velocity between non-augmented beat and augmented beat was observed in this study, especially in patients with systolic retrograde flow, suggests that systolic flow velocity has only a small impact on coronary flow augmentation during IABP. Conclusions. Transthoracic Doppler echocardiography can be used in monitoring CFV augmentation during IABP. In contrast to previous invasive studies, IABP produced significant distal flow enhancement even in patients with critical proximal stenosis. This totally noninvasive approach may help to optimize the benefits of IABP for coronary flow augmentation. Reprint requests and correspondence: Dr. Masaaki Takeuchi, Department of Internal Medicine, Tane General Hospital, Sakaigawa, Nishi-ku, Osaka, Japan. masaaki_ takeuchi@hotmail.com. REFERENCES 1. Katz ES, Tunick PA, Kronzon I. 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