| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
(Circulation. 2000;101:2026.)
© 2000 American Heart Association, Inc.
Brief Rapid Communications |
Noninvasive, Transthoracic, Low-Frequency Ultrasound Augments Thrombolysis in a Canine Model of Acute Myocardial Infarction
From the Division of Cardiology, Department of Medicine, Cedars-Sinai Medical Center, Los Angeles, Calif.
Correspondence to Robert J. Siegel, MD, Division of Cardiology, Room 5335, Cedars-Sinai Medical Center, 8700 Beverly Boulevard, Los Angeles, CA 90048. E-mail siegel{at}cshs.org
 |
Abstract |
|---|
 Top Abstract IntroductionMethodsResultsDiscussionReferences |
|---|
Background—Limitations of coronary thrombolysis include the time to reperfusion, patency rate, and bleeding. We evaluated the use of noninvasive transcutaneous ultrasound to augment coronary thrombolysis.
Methods and Results—In 24 dogs, a thrombotic occlusion of the
left anterior descending coronary artery was induced and
documented by 12-lead ECG and coronary angiography. After 
60
minutes of occlusion, tissue-type plasminogen
activator (t-PA; 1.42 mg/kg) was given
intravenously over 90 minutes. A total of 12 of the 24 dogs
had concomitant transcutaneous application of low-frequency ultrasound
(27 kHz) over the chest. At 90 minutes, the mean TIMI grade flow in the
t-PA alone group was 0.92±1.4 compared with 2.42±1.9 in the t-PA plus
ultrasound group (P=0.006). TIMI 2 to 3 flow was
present in 4 of 12 cases receiving t-PA alone compared with 10 of
12 cases receiving t-PA plus ultrasound (P=0.003). At
180 minutes, mean TIMI grade flow was 0.75±1.4 in the t-PA alone group
versus 2.58±0.9 in the t-PA plus ultrasound group
(P=0.001). Pathological examination confirmed the
angiographic patency rate and did not reveal injury secondary to
ultrasound in the skin, soft tissues, heart, or lungs.
Conclusions—In vivo, the noninvasive transthoracic application of low-frequency ultrasound (1) greatly augments the efficacy of t-PA–mediated thrombolysis, (2) seems safe, and (3) has substantial potential as a noninvasive adjunct to improve coronary patency without increasing the risk of bleeding.
Key Words: thrombolysis • myocardial infarction • ultrasonics • fibrinolysis
|
Introduction |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Coronary thrombolysis reduces mortality and preserves ventricular function, but it results in angiographic TIMI 3 flow in only 40% to 60% of patients. The procedure is further complicated by major bleeding in 5% of patients and by hemorrhagic stroke in 0.8% to 1.8% of patients.1 Consequently, an enhancement of thrombolysis without promoting bleeding is desirable. We evaluated the augmentation of coronary thrombolysis with intravenous tissue-type plasminogen activator (t-PA) and noninvasive, transthoracic, low-frequency (27 kHz) ultrasound.
|
Methods |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Transcutaneous Ultrasound Device
The ultrasound device consisted of a generator/amplifier and a controller, which provided 33 W to a titanium, transcutaneous transducer (Cybersonics Inc). The transducer was coupled to a cooling system that maintained a temperature
98°F. The continuous
mode, 27-kHz transducer provided 0.9 W/cm2
at its surface. This study was performed in accordance with the Guide for the Care and Use of Laboratory Animals of the US National Institutes of Health and approved by the Institutional Animal Care and Use Committee of Cedars-Sinai Medical Center.
In Vivo Induction of Canine Thrombotic Coronary
Occlusion
Dogs (20 to 30 kg) were anesthetized with thiopental;
anesthesia was maintained by enflurane inhalation.
Thrombotic coronary occlusions were induced in the midportion
of the left anterior descending coronary artery (LAD) by
electrical injury, as has been described previously.2 When
the ECG showed ST elevation 2 mm in 2 contiguous leads,
angiography was performed.
Coronary Thrombolysis Protocol
After LAD occlusion lasting 60 minutes, heparin (1000 U) was
given. Dogs were randomized to receive either t-PA alone (n=12) or
combined t-PA and transcutaneous 27-kHz ultrasound (n=12). The t-PA
infusion (1.42 mg/kg) was given over 90 minutes. After TIMI 2 to 3 flow
was obtained, heparin (1000 U) was given subcutaneously.
Application of Ultrasound
The ultrasound transducer was applied (12 cases) to the left
parasternal area. If TIMI 2 to 3 flow occurred, ultrasound was
discontinued. In 4 dogs in the t-PA plus ultrasound group and in 3 dogs
in the t-PA alone group, 120 minutes after the t-PA infusion was given,
ultrasound was applied to the right hemithorax for 30 minutes to assess
for ultrasound-induced lung damage.
Coronary Angiographic Protocol
Right anterior oblique, anteroposterior, and left anterior
oblique angiograms were made at baseline, after occlusion, and every 30
minutes until starting treatment. After beginning t-PA or t-PA plus
ultrasound treatment, ECGs and angiograms were done at 20, 40, 60, 90,
120, 150, and 180 minutes for monitoring thrombolysis.
Angiograms were analyzed by an independent angiographic core
laboratory that was blinded to treatment group
(Cardiovascular Core Analysis Laboratory,
Stanford University, Stanford, Calif).
Measurement of Ultrasound Power Output In Vivo
A hydrophone (Bruel and Kjaer, model 8103), amplifier (Nexus,
model 2692), and oscilloscope (Digital Hewlett Packard, model 54600B)
measured the intrathoracic delivery of ultrasound energy in vivo in 3
additional dogs. The hydrophone was placed on the anterior surface or,
alternatively, immediately beneath the posterior surface of the heart.
The 27-kHz ultrasound transducer was placed on the anterior chest wall.
The average peak intensity was 0.45 W/cm2 on the
anterior surface of the heart. The largest peak intensity on the
anterior surface was 0.58 W/cm2 and, on the
posterior aspect beneath the heart, it was 0.55
W/cm2.
Pathological Studies
Dogs were euthanized; their hearts were then excised and fixed
in formalin for 24 to 72 hours and cut transversely in 1-cm intervals
from apex to base. The LAD was sectioned at 2-mm intervals. Distal
arterial cross-sections were evaluated for embolization.
Representative sections from the proximal,
middle, and distal LAD, as well as from the skin, soft tissues,
heart, and lung were submitted for microscopic
examination.2
Statistical Analysis
Data were expressed as mean±SD. The unpaired Student’s
t test was used to compare the mean TIMI grade differences
between the 2 groups. Fisher’s exact, 2-tailed test was used to
compare the percentage of TIMI grade flow between the 2 groups.
P0.05 was considered statistically significant.
|
Results |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
Angiographic Results
The Table
shows the TIMI grade for
both groups after 20 and 90 minutes of t-PA infusion and after 90
minutes of observation. Ninety minutes after treatment in the t-PA
alone group (180 minutes), 3 cases had TIMI 3 flow (25%), and 9 cases
had TIMI 0 flow with persistent occlusion (75%). The group receiving
t-PA plus ultrasound had a greater frequency of reperfusion: 9 dogs had
TIMI 3 flow (75%), 2 had TIMI 2 flow (17%), and 1 had TIMI 0 flow
(8%; P=0.003). The mean TIMI flow grade for the t-PA group
alone was 0.75, compared with 2.58 for the dogs receiving t-PA plus
ultrasound (P<0.001). Figure 1 shows successful reperfusion of a LAD
thrombotic occlusion treated with the combination of t-PA plus
ultrasound, and the corresponding ECGs. During angiographic monitoring,
2 dogs in the t-PA alone group reoccluded (40%), whereas no dogs in
the t-PA plus ultrasound group had coronary reocclusion. No
dogs with TIMI 0 flow at 90 minutes improved their TIMI flow grade
after 180 minutes of observation. No arterial dissection,
disruption, or side branch occlusion secondary to ultrasound was
detected.
|
|
Pathological Studies
Angiographic findings were confirmed by histopathology (Figure 2). Eleven cases treated with t-PA plus
ultrasound had minimal (occupying <25% of lumen) thrombus or no
thrombus, and one case had an occlusive thrombus. No
ultrasound-mediated injury to the skin, soft tissue,
myocardium, coronary arteries, cardiac conduction
system, or lungs occurred. In the t-PA alone group, 9 dogs had
occlusive thrombi in the LAD, and 1 had distal embolization on
angiography, which was confirmed by pathologic examination. Distal
embolization was not detected in any dog receiving t-PA and
ultrasound.
|
|
Discussion |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
This is the first in vivo study to demonstrate that noninvasive ultrasound can be used to enhance coronary arterial thrombolysis. Twice as many dogs receiving adjunctive transthoracic ultrasound had TIMI 3 flow at 20 minutes compared with those receiving t-PA alone (8 versus 4 dogs). On the follow-up angiograms taken 90 minutes after completion of the t-PA infusion, a 3-fold greater incidence of TIMI 3 flow existed in the ultrasound group (9 versus 3 dogs; P=0.039). The low incidence of reperfusion with t-PA alone is consistent with the findings of Cercek et al,3 who found in a canine model that the concomitant use of full-dose heparin was necessary for effective clot lysis with t-PA. The low incidence of reocclusion in the ultrasound-treated group may reflect more complete thrombolysis and/or the absence of downstream embolization in this group. Gross and histopathologic studies confirmed the angiographic patency of vessels after treatment in each group.
Data from this and previous studies using similar transcutaneous,
low-frequency ultrasound devices4 5 6 suggest that this
method is safe and without acute adverse effects. The absence of damage
is consistent with the use of peak intensity levels 0.6
W/cm2. This peak intensity is below the 1 to 2
W/cm2 value described by Suchkova et
al6 as being potentially hazardous.
Other authors have shown that low-frequency ultrasound accelerates enzymatic thrombolysis at intensities similar to those used in our study.6 7 8 9 Low-frequency ultrasound has excellent tissue penetration for effective clot lysis.4 5 6 Ultrasound enhancement of t-PA fibrinolysis occurs in the absence of heating and with minimal mechanical effect on the clot.6 7 8 This effect, which is not fibrinolytic-specific, occurs with t-PA, streptokinase, and urokinase. The multiple mechanisms for the ultrasound augmentation of fibrinolysis have been primarily elucidated by the laboratory run by Francis.6 7 8 9 One primary effect of ultrasound is an increase in the transport of the fibrinolytic enzyme into the clot.7 8 9 10 Ultrasound increases t-PA uptake and its depth of penetration into clots. Ultrasound exposure enhances fluid permeation through fibrin gels.10 Electron microscopy has shown that ultrasound exposure reversibly disaggregates fibrin fibers.9 Such changes are thought to promote an increase in fibrin binding sites for fibrinolytic agents.
Prior studies have shown the feasibility of using ultrasound to
facilitate thrombolysis in
vitro6 7 11 12 and in vivo.4 5 6 8 11 12 13 In
vivo studies have been primarily performed in thrombosed iliofemoral
arteries and have shown substantial enhancement of chemical
thrombolysis, namely, a 4-fold increase in
reperfusion.4 8 12 Initial studies using high-power
ultrasound outputs were complicated by thermal damage.8
Subsequent studies, however, have shown an elimination of tissue damage
while still achieving reperfusion rates that are greater than those
achieved with the thrombolytic agent
alone.4 5 8 In summary, the in vivo studies to date are
consistent with the vitro finding that ultrasound augments
chemical thrombolysis.4 6 8 11 12 13
Limitations
In this study, we used a prototype of a therapeutic ultrasound
device. In the one case in this study in which there was no
facilitation of t-PA–mediated coronary
thrombolysis, a subsequent evaluation of the ultrasound
unit by the manufacturer revealed that the device was not delivering
energy sufficient for clot lysis. Although this finding reflects a
current technological limitation, it also suggests that the lack of
augmentation of t-PA thrombolysis by ultrasound (1 of
12 cases) was due to mechanical failure. The development of an energy
feedback system is requisite before clinical application. Further,
chronic survival studies in animals are needed to assess the long-term
effects of ultrasound. Because neither aspirin nor other
antiplatelet agents were given in this study, future experiments
should be done to assess their interaction with ultrasound.
Conclusions
This study demonstrates that a nonpharmacological, noninvasive
approach is feasible to facilitate coronary
thrombolysis. We found that transcutaneous,
transthoracic, low-frequency ultrasound significantly
augments t-PA–mediated coronary thrombolysis
in a dog model of acute myocardial infarction. The theoretical
advantages of this approach include the following. (1) The efficacy of
the thrombolytic drug is enhanced. (2) The enhancement
of the thrombolytic effect is localized to the
ultrasound treatment area. (3) The addition of ultrasound does not
increase the risk of systemic bleeding. (4) No additional adverse
interactions seem to exist, such as those that may occur with
adjunctive pharmacotherapy for thrombolysis.
|
Acknowledgments |
|---|
The authors thank Dr Stuart Bunting and Genentech (South San Francisco, Calif) for providing the t-PA used in this study.
Received December 29, 1999; revision received March 8, 2000; accepted March 8, 2000.
|
References |
|---|
|
TopAbstractIntroductionMethodsResultsDiscussionReferences |
|---|
-
White HD, Von de Werf F. Thrombolysis
for acute myocardial infarction. Circulation.. 1998;97:1632–1646.
[Abstract/Free Full Text]
-
Steffen W, Fishbein MC, Luo H, et al. High
intensity, low frequency catheter-delivered ultrasound dissolution of
occlusive coronary artery thrombi: an in vitro and in vivo
study. J Am Coll Cardiol. 1994;24:1571–1579.[Abstract]
-
Cercek B, Lew A, Hod H, et al. Enhancement of
thrombolysis with tissue-type plasminogen
activator by pretreatment with heparin.
Circulation. 1986;74:583–587.
[Abstract/Free Full Text]
-
Luo H, Birnbaum Y, Fishbein MC, et al. Enhancement of
thrombolysis in vivo without skin and soft tissue
damage by transcutaneous ultrasound. Thromb Res. 1998;89:171–177.[Medline]
[Order article via Infotrieve]
-
Birnbaum Y, Luo H, Nagai T, et al.
Recanalization of thrombosed iliofemoral arteries
by transcutaneous ultrasound combined with intravenous
infusion of microbubbles. Circulation. 1998;97:130–134.
[Abstract/Free Full Text]
-
Suchkova V, Siddiqi FN, Carstensen EL, et al.
Enhancement of fibrinolysis with 40-kHz ultrasound.
Circulation. 1998;98:1030–1035.
[Abstract/Free Full Text]
-
Francis CW, Önundarson PT, Carstensen EL, et al.
Enhancement of fibrinolysis in vitro by ultrasound.
J Clin Invest. 1992;90:2063–2068.
-
Riggs PN, Francis CW, Bartos SR, et al. Ultrasound
enhancement of rabbit femoral artery thrombolysis.
Cardiovasc Surg. 1997;5:201–207.[Medline]
[Order article via Infotrieve]
-
Braaten J, Goss RA, Francis CW. Ultrasound reversibly
disaggregates fibrin fibers. Thromb Haemost. 1997;78:1063–1068.[Medline]
[Order article via Infotrieve]
-
Siddiqi FN, Blinc A, Braaten J, et al. Ultrasound
increases flow through fibrin gels. Thromb Haemost. 1995;73:495–498.[Medline]
[Order article via Infotrieve]
-
Lauer CG, Burge R, Tang DB, et al. Effect of ultrasound
on tissue-type plasminogen activator-induced
thrombolysis. Circulation. 1992;86:1257–1264.
[Abstract/Free Full Text]
-
Luo H, Nishioka T, Fishbein MC, et al. Transcutaneous
ultrasound augments lysis of arterial thrombi in vivo.
Circulation. 1996;94:775–778.
[Abstract/Free Full Text]
-
Luo H, Steffen W, Cercek B, et al. Enhancement of
thrombolysis by external ultrasound. Am
Heart J. 1993;125:1564–1569.[Medline]
[Order article via Infotrieve]
This article has been cited by other articles:
 |
|
 |
|
  K. Iida, H. Luo, K. Hagisawa, T. Akima, P. K. Shah, T. Z. Naqvi, and R. J. Siegel Noninvasive Low-Frequency Ultrasound Energy Causes Vasodilation in Humans J. Am. Coll. Cardiol., August 1, 2006; 48(3): 532 - 537. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Siegel, V. N. Suchkova, T. Miyamoto, H. Luo, R. B. Baggs, Y. Neuman, M. Horzewski, V. Suorsa, S. Kobal, T. Thompson, et al. Ultrasound energy improves myocardial perfusion in the presence of coronary occlusion J. Am. Coll. Cardiol., October 6, 2004; 44(7): 1454 - 1458. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. J. Siegel, H. Luo, Y. Birnbaum, M. C. Fishbein, and T. Miyamoto Reply J. Am. Coll. Cardiol., July 7, 2004; 44(1): 211 - 211. [Full Text] [PDF]
|
|
|
|
|
|
H. C. Herrmann Optimizing outcomes in ST-segment elevation myocardial infarction J. Am. Coll. Cardiol., October 15, 2003; 42(8): 1357 - 1359. [Full Text] [PDF]
|
|
|
|
 |
|
 M. Nedelmann, B. M. Eicke, E. G. Lierke, A. Heimann, O. Kempski, and H. C. Hopf Low-Frequency Ultrasound Induces Nonenzymatic Thrombolysis In Vitro J. Ultrasound Med., June 1, 2002; 21(6): 649 - 656. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. Z. Goldhaber Echocardiography in the Management of Pulmonary Embolism Ann Intern Med, May 7, 2002; 136(9): 691 - 700. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. W Francis and V. N Suchkova Ultrasound and thrombolysis Vascular Medicine, August 1, 2001; 6(3): 181 - 187. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||