Intraoperative Dopplerography and angioscopy in carotid endarterectomy

Svistov D.V., Sherbuk Yu.A., Kandyba D.V.

Department of Neurosurgery, Military-Medical Academy, St.Petersburg, Russia

INTRODUCTION

Nowadays the problem of diagnosis and prevention of cerebrovascular diseases becomes more and more important. The stroke rate is 360-526 cases/yr per 100 000 men and it varies from 12:100 000 (females aged 30-49) up to 809:100 000 (males aged 70-74). Stroke occupies the first place among the causes of persistent invalidism. As for the USA, annual expenditures on treatment and indemnity for disability due to stroke exceed 30 000 000 000 $. Mortality during the first after-stroke year is equal to 35-38% and on the whole disorders of cerebral circulation are the cause of one forth of all fatal outcomes [2].

Only 10-20% of survivors after an acute stage of the disease restore their working ability, the rest become disabled [3]. More than half a million strokes is registered in the USA annually; 20-30% of them are conditioned by lesions of the internal carotid artery (ICA) [16] and the portion of asymptomatic stenosis is 2-5% [11]. The annual rate of ischemic stroke in symptomatic stenosis of ICA with involvement of more than 70% of its diameter and asymptomatic lesions is 3-5.7% and 5.5% respectively.

Carotid endarterectomy (CE) is the most important means of secondary prevention of ischemic stroke. The limiting factor of its preventive effect is a rather high level of perioperative cerebrovascular complications equal to 1.6-24%. Intraoperative complications make up 60% and 40% of them develop in pre- and postoperative periods. Ischemic disorders, including cerebral embolism (54%), circulatory ischemia in compression of the common carotid artery (CCA) and postoperative thrombosis (17%), are most frequent. Hyperemic hyperperfused lesions account for 29% of all complications [4].

T.M. Sundt et al. [15] summarized the results of 3111 CE. Severe neurologic disorders and fatal outcomes were watched in 1.8% of patients; as for postoperative stenosis it took place in 1 % of cases. According to W.S. Moore et al. [10], postoperative mortality in asymptomatic stenosis is 3.8%; its rate in stenosis with clinical manifestations is about 6%. The analysis of the results of 291 CE carried out by J.H. Wong et al. [18] is indicative of a greater number of complications: postoperative strokes and fatal outcomes were observed in 4.8-13% of cases depending on age and presence of associated pathology. Discussing various complications of CE Ch.P. Worlow et al. [1] mentioned those due to technical errors made during interventions: acute occlusion, thrombosis, embolism from an operation area, the carotid artery stratification conditioned first of all by drooping of intima and a poor-quality vascular suture.

Constant striving for reduction of the risk of CE resulted in development of numerous methods of monitoring for adequate protection of the brain. As a rule, they are based on estimation either of a vascular bed state (measuring occlusion pressure, residual blood flow, intraoperative dopplerography or scanning, angiography) or of the brain function (EEG/EVP monitoring). Taking into account specificity of an intervention, i.e. artery disobliteration, one cannot but agree that the most informative methods of intraoperative diagnosis are those used by a surgeon just in the operative field. The number of diagnostic methods is not very large and, thus, any experience of their application is of great interest.

The goal of the present research is studying possible ways of intraoperative assessment of CE and its quality by combined use of carotid video angioscopy and contact dopplerography.

MATHERIALS AND METHODS

The results of complex examination and surgical treatment of 19 patients with carotid artery stenoses operated in the Clinic of Neurosurgery of the Military-Medical Academy in 1995-2000 were analyzed.

The main radiation methods used for diagnosis of occluding lesions of carotid arteries included ultrasonic dopplerography (19 cases), duplex scanning (15 cases), spiral CT angiography (16 cases), digital subtraction angiography (19 cases). The most frequent localization of an atherosclerotic lesion was a posterior surface of the carotid artery (36.3%). Lesions with lateral (23.8%), anterior (21.5%) and medial (18.4%) localization were observed less frequently. Stenosing atherosclerotic plaques were located along the whole circumference of the vessel in 32% of cases; one forth - three forths and less than one forth of the circumference were involved in 38.5% and 29.5% of patients respectively. The majority of lesions was watched in the opening of ICA (56.5%) and bifurcation of CCA (26.9%). Atherosclerotic changes in other segments of CCA, external carotid artery (ECA) and ICA were diagnosed only in 12.1% of cases. Bilateral and unilateral atherosclerotic lesions of carotid arteries were observed in 10 (52.6%) and 9 (47.4%) patients respectively. Scantiness of symptoms was typical of 2 cases (10,5%) only. Histories of the rest patients were indicative of episodes of infarction and transient disorders of blood circulation in carotid basins. Distribution of patients according to risk factors of postoperative cerebrovascular complications is given in table 1. The mean specific value of the prognosticated risk of complications [15] was equal to 5.3%.

Table 1

Distribution of Operated Patients According to Risk Factors of Postoperative Cerebrovascular Complications

Risk Factors

Presence (+) or Absence (-)

of a Risk Factor

Number of Cases

Neurologic

+

17

-

2

General somatic

+

13

-

6

Angiographic

+

10

-

9

 

Mean Value of a Risk of

Complications [15]

Number of Cases

% of Observations

< 1%

1

5.3

1.8%

2

10.5

4.0%

9

47.4

> 8.5%

7

36.8

 

There were 20 interventions (it was performed on both sides in 1 patient). Conventional CE with plasty of an arteriotomic incision by autovein (15) or PTFE (Gore-Tex) (5) was made in all cases. Intraoperative transcranial monitoring of blood flow velocity (BFV) in the ipsilateral middle cerebral artery (MCA) was carried out with a probe of 2 MHz fixed in projection of a temporal window with the help of the MARC500 helmet.

Intraoperative contact dopplerography was ensured by use of 4 CW/PW, 8 CW/PW, 16 PW, 20PW MHz ultrasonic probes of such devices as Pioneer 2020/4040 (EME-NICOLET), MDX-2+(DWL), Angiodin (BIOSS). Probes were sterilized in the C4 solution just before use. They were applied at an angle of 45o with mandatory conformity between pre- and post-manipulation positioning. Registration was carried out in CCA, the opening and distal segment of ICA and the opening of ECA. Maximum and average systolic BFV, average maximum BFV (the envelope), pulse index, stenosis index were registered before and after endarterectomy (before arteriotomy and after blood flow restoration). Portable sensors of 16-20 MHz were extremely handy and their only drawback was a limited control range and a small scale of peak velocity measurements. The shortcoming of low-frequency modes (4-8 MHz), which ensured an unlimited range of measuring peak velocities, was absence of adapted miniature sensors; sometimes it did not allow to preserve the optimum angle of insonation.

Intraoperative video angioscopy was carried out during CE in 6 patients. The Concept rigid endoscope (Switzerland) with a diameter of 4 mm and an angular view of 30o was used. Endoscopic manipulations on vessels were accompanied by continuous infusion of saline (1 unit of heparin per 1 ml) administered via a microirrigator which was attached to the endoscope. Irrigation fluid was injected into the vessel’s lumen under pressure and with the help of a system for intravenous infusion. It resulted in dilation of the artery up to its normal size. A microscopic video camera attached to the endoscope eyepiece allowed to transmit an image to a video monitor. Thus, a surgeon and his assistants examined an operative field with five-tenfold magnification. Results were estimated with taking into account the whole complex of control studies, i.e. neurologic, ultrasonic and angiographic examinations (duplex scanning, spiral CT angiography or digital subtraction angiography).

RESULTS

There were no cerebrovascular complications when the algorithm of intraoperative diagnosis worked out by us was used. It is a rather important fact against a background of the expected high level of complications. Adequate patency of ICA was achieved in all cases. We did not observe residual stenosis with involvement of more than 30% of vessels’ diameter. Intraoperative diagnosis and elimination of some technical defects made it possible to obtain satisfactory final results of treatment.

Intraoperative dopplerography and the previous experience of diagnosis of occluding lesions of carotid arteries at the stage of preoperative examination made it possible to work out criteria of residual stenosis and acute thrombosis or ICA obstruction demanding revision:

Registration of blood flow indices is to be carried out in some minutes after restoration of circulation. It is necessary for correction of transient hyperemia which usually appears after removal of forceps from CCA. An example of restoration of normal blood flow in proximal segments (ICA) after disobliteration is given in Fig.1.

According to dopplerographic findings revision of an arteriotomic incision was necessary in 4 cases (25%). Its causes were acute obstruction of ICA due to detachment of intima flap in a distal segment (1), mechanic stenosis of ICA in the area of a patch angle (2), stenosis of the ECA opening in the area of a vascular suture (1). Elimination of these defects resulted in adequate restoration of blood flow. It is worth mentioning that transcranial monitoring of BFV in the ipsilateral MCA revealed impaired patency of ICA only in one observation (6.3%) when there was residual blood flow in MCA after removal of forceps from CCA. At the same time there was no correlation between such a "classical" criterion of anastomosis quality as the artery pulsation and blood flow parameters. As for the case under discussion pulsation of vessels in a wound was perfect and even excessive.

Thus, intraoperative dopplerography can be regarded as an adequate means of quality control in reconstructive operations for stenosing lesions of carotid arteries. An essential limitation of Doppler diagnosis lies in the following: detection of impaired patency of a major vessel necessitates hermetic sealing of the artery and restoration of blood flow in it. This demands much time and a patient is subject to a certain risk of complications when even partially reduced blood flow is restored under conditions of embologenic vascular lesions (thrombosis/intima stratification). There is no doubt that technical defects which can lead to insufficient patency of the vessel should be detected before hermetic sealing of an artery. Visual examination of a wound with the help of magnifying optics seems to be quite natural, but it is impossible to examine a distal angle of an arteriotomic incision after placing sutures along a patch’s semi-perimeter. However, it is that very angle which is of crucial importance from the point of view of subsequent possible narrowing of ICA or obstruction due to stratification of its wall.

Intraoperative video angioscopy was used with the purpose of visual control of the vessel state in a plasty zone. Examination was carried out during a period ranging from arteriotomy up to incision sewing. The way of endoscope introduction into a lumen is illustrated in Fig. 2.

The first stage (a period just after arteriotomy of ICA) consisted in endoscope introduction into the vessel lumen washed with saline and visual assessment of morphologic peculiarities of an atherosclerotic plaque, its spread, presence of ulcerations and craters as well as plaque sequesters and thrombi (Fig. 3).

The second stage (a period after removal of an atherosclerotic plaque and fixing intima scraps in a distal segment of ICA with transwall sutures) was characterized by use of carotid angiovideoendoscopy for estimating efficacy of removal of an atherosclerotic plaque as well as fixing intima scraps in a distal segment of ICA. Bleeding from vasa vasorum of a smooth glittering wall of ICA was detected in a flow of fluid and its gaping lumen was visualized (Fig. 4).

The third stage of angiovideoendoscopy was connected with a period of plasty of a vascular wall. All manipulations were ceased before final stitching of an arteriotomic incision of 7-8 mm sufficient for introduction of a tip of the endoscope with an irrigator. A wound surface, patch and every three ends of a zone of CCA bifurcation were examined. Irrigation fluid widened vascular walls up to the normal size and residues of intima were floating slowly in an operative field (Fig. 5). Detected large fragments of intima were removed with the help of small forceps introduced through an arteriotomic hole. At the beginning this procedure demanded extraction of the endoscope with subsequent blind removal of intima fragments with forceps. Later on, when enough experience was gained, it was done under endoscopic control and offered no difficulty. Then some repeated video angiographic examinations were carried out. If some serious defects were detected (considerable detachment and floating intima, thrombus, hematoma under intima stratifying arterial walls, marked narrowing of the internal vascular lumen), sutures on a vascular wall were removed and defects were eliminated in direct view of a wound. In case of satisfactory quality of performed CE a standard method was used for wound closure.

Use of intraoperative video angioscopy allowed to reveal thin strips of the artery tunica media which looked like fur hair and floated in irrigation solution. They were extremely small and, as a rule, their removal was impossible. We did not watch any complications caused by microscopic strips of tunica media which had not been removed the artery lumen. This phenomenon was absent when the vascular wall was examined in a “dry field”. The wall was smooth and glittering. Thus, angioscopy with magnification in a flow allows to detect specific states of the vascular wall in a zone of intervention which have not been diagnosed before.

Restoration of blood flow in a group of patients who underwent angioscopy had no peculiarities. Normal blood flow without any signs of impaired patency of ICA was typical of all cases. There were no postoperative complications as well. The risk of complications was reduced in comparison with virtual indices.

DISCUSSION

A direct therapeutic and preventive effect of CE is determined by a quality of reconstruction of an injured vascular segment and as a result its adequate urgent assessment during an operation acquires great importance. Some time ago postoperative angiography was the most widespread method confirming efficacy of deoccluding interventions. The 70s were marked by use of dynamic dopplerographic control but, in any case, it was carried out after hermetic closure of a wound and outside an operating room. It excluded the possibility of one-stage correction of detected defects.

Intraoperative angiography of CCA can be carried out after hermetic closure of an arteriotomic incision. Described methods are based on puncture administration of a contrast substance into CCA for making one film [6]. Angiographic changes demanding revision of a zone of vascular suture, especially an area of a patch’s distal angle, are watched in 2.5-5% of cases [12, 13] and it allows the authors to speak of considerable reduction of a risk of neurologic complications thanks to timely correction. It is evident that intraoperative angiography is an important educational means which makes it possible to detect technical errors with the purpose of improvement of surgical technique [13]. Shortcomings of angiography are conditioned by necessity of participation of radiological services, a risk of subintimal administration of a contrast substance. That is why Andersen et al. [5] recommend to use it only in such dubious cases as stitching of intima at a distal angle of an incision, visible external narrowing, etc. Today intraoperative angiography is applied by surgeons with good knowledge of the technique of examination, but it is not widely adopted. Thus, intraoperative angiography in CE has failed to be generally recognized as it is time-consuming, demands additional expenditures and well-trained personnel. Besides it presents certain danger due to its invasiveness and intra-arterial administration of contrast substances.

Informal use of dopplerography when probes are applied to all big branches in a zone of intervention is a rather effective means of assessing patency of vessels after endarterectomy. Zieler R.E. et al. [19] analyzed use of pulse dopplerography in 45 patients. This method turned out to be helpful in selecting patients who needed angiographic control. Intraoperative dopplerograpgy is capable of diagnosis of residual narrowing of ICA and ECA in 4.3-4.5% and 8.7-9% respectively [14, 19]. Today dopplerography is quite available, but unfortunately it is not a widely adopted method of control.

In 1977 J.B. Towne and V.M. Bernhard [17] started to use vascular endoscopy in operations on carotid arteries. They worked with rigid endoscopes usually applied in urology and found out some technical difficulties including a cumbersome character of the method and impossibility of carrying out endoscopic examination in each specific case.

J.T. Mehigan et al. [7-9] demonstrated advantages of intraoperative carotid video angioscopy in a series of works. Video endoscopic technique allowed to get a three-dimensional colour well-defined image for adequate estimation of CE quality. In case of technical defects the inner part of the vessel was achieved by means of open arteriotomy. It ensured possibility of carrying out repeated examinations after correcting manipulations with the help of a convenient and simple procedure. The authors did not watch any complications caused by carotid angioscopy and obtained information was a valuable educational material which could be stored easily for further use.

Our small experience of combined application of intraoperative dopplerography and video angioscopy is a convincing demonstration of adequacy and precision of this method in timely detection and correction of technical defects of endarterectomy. Intraoperative carotid video endoscopy minimizing direct defects of surgical intervention and being a quick-done, safe, easily reproducible, highly informative procedure as well as intraoperative contact dopplerography are an alternative to intra- and postoperative angiography in the majority of patients with stenosing and occluding lesions of carotid arteries.

Thus, our investigations show that use of endoscopes with a small diameter and contact dopplerography in reconstructive surgery of carotid arteries is rather prospective as it prevents early postoperative thrombosis in inadequate removal of an atherosclerotic plaque and intimthromboectomy, helps to verify presence of residual thrombi and to detect defects of vascular sutures whose timely elimination allows to avoid development of dangerous complications and provides optimum results of an operation.

 

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