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Interact CardioVasc Thorac Surg 2007;6:451-455. doi:10.1510/icvts.2007.156273 © 2007 European Association of Cardio-Thoracic Surgery
An objective method for grading of distal disease in the grafted coronary arteriesDivision of Cardiothoracic Surgery, King Khalid University Hospital, Riyadh, Saudi Arabia Received 16 March 2007; received in revised form 10 April 2007; accepted 4 May 2007
The impact of diffuseness of coronary artery disease on the outcome of coronary bypass grafting remains unclear due to the absence of an objective grading system for diffuseness. This study proposes a system and validates it by transit time flow measurements. All patients operated upon by the author from July 2004 to August 2006 were enrolled in the study. The patients who had procedures other than isolated coronary bypass grafting were excluded. This resulted in a set of 186 (151 male and 35 female) patients with a mean age of 59.55 years. Those vessels which had endarterectomies, on-lay patches, multiple/sequential grafts to a single artery were removed from analysis. The diffuseness of distal disease was graded from 0 to 3 on the basis of (i) the size of vessel and (ii) the number as well as significance of atheromatous lesions distal to the graft. The correlation analysis showed a moderate positive correlation between pulsitility index and grade of diffuseness and a moderate negative correlation between graft flow and grade of diffuseness (P<0.0001). This study shows that the proposed method of grading provides an objective and reliable system for the assessment of severity of distal disease in the grafted coronary arteries.
Key Words: Diffuse coronary artery disease; Transit time flow; Coronary bypass surgery
In the current era of aggressive coronary interventions, a growing percentage of patients with diffuse disease are sent for coronary bypass surgery. There is no system of grading for the diffuseness of coronary artery disease. It is customary amongst the cardiac surgeons to describe the severity of disease distal to a graft in entirely subjective and unreliable terms of mild, moderate and severe. Therefore, it is desirable to develop an objective system of grading the diffuseness of coronary artery disease so that one could study the impact of diffuseness on the patency of grafts.
2.1. Study design and patient profile This is a prospective observational study of patients operated upon by the author for coronary bypass surgery from July 2004 to August 2006. The information was entered in our electronic database (Cascade Databases, Lahore). Exclusion criteria were defined as follows:
Application of criteria (a) resulted in a set of 186 patients who had a total of 553 grafts. These included 151 (81.2%) male and 35 (18.8%) female patients. The mean age was 59.55 years with a standard deviation (S.D.) of 10.76 years. There were 74 (66.7%) diabetic and 15 (10.8%) actively smoking patients. Uncontrolled hypertension (systolic blood pressure >140 mmHg and/or diastolic blood pressure >90 mmHg) was present in 11 (5.9%) patients while 104 (55.9%) patients were taking antihypertensive treatment to achieve normal blood pressure. Family history of ischemic heart disease was present in 31 (16.7%) patients. Hypercholesterolemia (serum cholesterol >5.2 µmol/l) was found in 29 (15.6%) patients, while 80 (43.0%) patients were taking statins and had normal cholesterol level. Sixty-four (68.9%) patients had class II–III angina and 24 (12.5%) had class IV angina. Three-vessel disease was present in 159 (74%) patients. Twenty-five (13.4%) patients had more than 70% stenosis of the left main coronary artery. The mean left ventricular ejection fraction was 45.46% (S.D. 10.77%). Conventional coronary artery bypass grafting (ConCAB) was done in 107 (57.5%) patients. The ConCAB was conducted by using an aortic cross clamp, cold antegrade intermittent blood cardioplegia and systemic hypothermia to 32°C. Off-pump coronary bypass (OPCAB) was performed for 50 (26.9%) patients and on-pump beating-heart coronary artery bypass (OBCAB) was performed for 29 (15.6%) patients. The mean number of bypass grafts was 3.05 (S.D.=1.09). All patients received detailed counselling about the technical details of the operations and the study for making informed consent. The study was conducted by observing the code of confidentiality for medical practice given by the National Health Services of the UK (www.dh.gov.uk) and principles mentioned in the Helsinki convention (http://onlineethics.org/reseth/helsinki.html). 2.2. Grading and validation of distal disease After application of exclusion criteria (b) to (e) only 468 grafts were found suitable for study. These included 167 grafts to the left anterior descending coronary artery (117 arterial and 50 vein grafts), 59 grafts to the diagonal, 133 grafts to the obtuse marginal, 55 grafts to the right coronary and 54 grafts to the posterior descending/postero-lateral coronary arteries.Table 1 shows that the grading of diffuseness was done on the basis of (i) the size of vessel and (ii) the number as well as significance of atheromatous lesions distal to the graft. The size of the grafted arteries was measured by passing metallic probes of diameters ranging from 1 mm to 2 mm. After completion of anastomses the grafts were tested with a transit time flow (TTF) meter. It was made sure that all grafts were tested in similar hemodynamic conditions (mean arterial pressure 70–85 mmHg, heart rate 65–80/min and pulmonary artery wedge pressure 5–12 mmHg and hemoglobin of 7–9 g/dl). In cases of unexplained abnormal flow or pulsitility index, the technical reasons were excluded by revising doubtful anastomosis. Such grafts were, however, removed from the study.
2.3. Statistical analysis Three different coefficients of correlation were calculated i.e. Spearman's Rho, Kendal's Tau-b and Pearson's. The commonly used Pearson's coefficient is less appropriate because of two reasons:
The statistical analysis was done using SPSS (SPSS 10 for Windows, SPSS Inc, Chicago, IL).
Table 2 shows mean values of graft flows and pulsitility indices according to the type of coronary artery and severity of disease. It is clear that graft flows decreased with increase in the severity of distal disease and pulsitility indices increased as the severity of disease got worse (Fig. 1).
Table 3 shows correlation analysis. The correlation coefficients indicate a moderate co-relation between the classified grade and pulsitility index. Similarly, there is moderate correlation between graft flow and the grade of distal disease. The P-values for both correlations are <0.001 which makes them highly significant, meaning thereby that the probability of having zero/no correlation is almost unlikely. In simple words the groups created by the grading system are quite meaningful.
The practice of coronary bypass surgery has undergone significant changes due to aggressive use of coronary stents. The number of bypass procedures is reducing and the clinical profile of patients referred for surgery is getting worse [1, 2]. This has made coronary bypass surgery much more challenging. Bypass grafting of diffusely diseased vessels usually need innovative operations like on-lay patches, endarterectomies and more than one graft for one vessel. There is considerable evidence that medically treated patients with severe and diffuse coronary artery disease fare badly [3, 4]. Da Rocha et al. have shown that 2/3 of the patients who were not offered bypass surgery because of diffuse disease, either died or had non-fatal myocardial infarction within 12 months [3]. Many such patients are frequently denied coronary bypass surgery believing that CABG would have poor outcome in diffuse coronary disease. However, there is no clear evidence regarding the impact of diffuse coronary disease on mortality and morbidity. Johnson et al. showed that diffuse disease was a risk for mortality [5]. However, they labelled diffuse disease only in those patients who had endarterectomy. Defining endarterectomy as equivalent to diffuseness is flawed, as many patients with diffuse disease might have not undergone endarterectomy. At the same time endarterectomy has disadvantages of its own. The multivariate analysis by Wright et al. [6] showed that diffuseness of coronary artery was a risk factor for mortality. They also relied on subjective description of ‘diffuse coronary disease’ mentioned in the case notes of the patients. As a matter of fact, the diffuseness of disease is not included in any of the widely used risk scoring systems for the very simple reason that there is no objective definition of it. The methods of grading described in the past were not based on the surgeon's perspective of distal disease and concentrated mainly on the degree of proximal stenosis and the amount of myocardium in danger. Many cardiologists follow the Brandt et al. method to report on coronary angiograms which scores only the significant proximal stenosis with reference to the amount of myocardium supplied by the particular artery and does not consider the status of distal vessel [7]. Graham et al. have recognized this shortcoming and developed a score for diffuseness of disease on the basis of proximal stenosis, amount of myocardium under threat and state of distal disease [8]. Despite all its improvements on the previous methods it is still not objective because it describes the distal disease by the same undefined terms of mild, moderate and severe distal disease. Moreover, like all previous systems, it is also based entirely on the radiological interpretation of the disease. Many surgeons would agree with the author's observation that angiographic appearance is sometimes seriously misleading in diffuse disease. The article by Pidgeon et al. supports this observation and states that the disease in the vessel was found twice more commonly during operation than detected by reviewing the angiogram [9]. This is partly due to the fact that the angiograms provide only two-dimensional views. In addition to this, the appearance on the cine films depends a lot on the types of views recorded during angiography and the software used to display the films. There is also an unpredictable inter-observer variation while reading the angiograms [10]. Validation of any proposed grading system is another difficult task. The author has employed Transit Time Flow measurements to check the grades defined in the system. Transit time flow measurement has been in use for more than 10 years and has proved to be a very effective and reliable method of assessing flow in both arterial and vein grafts [11, 12]. The system developed by the author (Table 1) is based on two important factors:
The size of a healthy coronary artery depends on the body size, gender, segment of the coronary artery and anatomical dominance of circulation; and may vary from over 5 mm in the left main coronary artery to <1.0 mm in distal part of a small branch of main arteries [13]. There is evidence that coronary bypass surgery for small vessels has relatively poor outcome [14]. There could be concerns regarding the sizing of vessels by using malleable probe. It is emphasized that probing of vessels is done to measure their diameter and not to dilate them. In Table 1, the expression ‘allows the probe with resistance’ means that the vessel accommodated the probe while the operator could feel the vessel wall hugging the probe. Any resistance which requires force to forward the probe is an indication that the vessel is too small to accommodate the probe. The application of force is, therefore, not desired. Moreover, the author started the assessment of coronary lumen size with the smallest probe and gradually used the next larger size. Following these very basic principles the author has not witnessed any complications attributable to probing of coronaries. Another argument could be regarding the exclusion of those patients who required endarterectomies or on-lay patch arterioplasties. We have noticed that after successful completion of such procedures the flows and the pulsitility indices became as good as those vessels which had no disease. Inclusion of their data would have mitigated the statistics because, by definition, these vessels belong to the category of ‘severe’ distal disease. The strength of the study lies in the fact that all operations were done by one operator, which excludes any differences resulting from techniques of bypass grafting or the operation of transit time flow meter. Moreover, this is the first objective attempt to quantify the severity of disease. The grading system would definitely help surgeons to conduct their audits more effectively. It would also enable us to draw more accurate and enlightening conclusions regarding outcome of CABG in diffuse disease.
The grading system used in this study is practical, objective and reliable.
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Abstract
1. Introduction
