|Year : 2019 | Volume
| Issue : 2 | Page : 110-114
Development of cardiac risk assessment model for vascular surgery patients based on single-center experience
Vivek Kumar Singh1, Sudhir Rai2, Vembu Anand2
1 Department of Vascular Surgery, INHS Asvini, Mumbai, Maharashtra, India
2 Department of Vascular Surgery, Army Hospital R and R, New Delhi, India
|Date of Web Publication||6-Jun-2019|
Dr. Vivek Kumar Singh
Department of Vascular Surgery, INHS Asvini, Mumbai, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: Existing methodologies and risk stratification indices from western countries for predicting perioperative cardiac complications in vascular surgery patient lack sufficient predictive value and therefore cannot be recommended for risk stratification. There are no Indian studies for preoperative cardiac risk scores for patients who undergo vascular and endovascular procedures. The aim of this study is: (a) to test the usefulness of Detsky's cardiac index in an independent series of patients who underwent peripheral arterial vascular procedures and (b) to develop cardiac risk assessment model. Materials and Methods: We studied 103 patients at single-center who underwent cardiac risk stratification before undergoing vascular interventions. It was a prospective cohort study for 2 years. The Detsky's cardiac risk index was calculated for each patient to predict perioperative cardiac risk in patients undergoing vascular interventions. Sensitivity, specificity, positive and negative predictive values were calculated. To determine the accuracy of stratification for Detsky's index, the area under the receiver-operating characteristic curves was also calculated. Results: Eighteen patients (17.4%) had cardiac complications. The Detsky's index was found to be a satisfactory predictor of postoperative cardiac events (P < 0.001). There were a total of 10 mortalities (9.7%) with the Detsky's model, having positive predictive value of 73.3% and specificity of 94.1%. Discussion: The overall sensitivity, specificity, positive predictive value, negative predictive value of the Detsky's risk index in the prediction of cardiac events was 31.4%, 94.1%, 73.3%, 72.7% respectively. In our study, the area under ROC for Detsky class was 0.76 versus 0.75 and superior to C statistic. One important inference from the study was that 77.6% patients were smoker in the study group which emphasize direct relation of peripheral vascular disease with smoking. Conclusion: The study concluded that patients with good surgical risk and profile undergoing minor vascular procedures can be operated without further testing. For other patients, the next step would be to incorporate the Detsky index. A Detsky score of 20 or more is comparable to a major clinical predictor in the ACC/AHA15 scheme.
Keywords: ACC/AHA guidelines, cardiac risk index, major adverse cardiac events
|How to cite this article:|
Singh VK, Rai S, Anand V. Development of cardiac risk assessment model for vascular surgery patients based on single-center experience. Indian J Vasc Endovasc Surg 2019;6:110-4
|How to cite this URL:|
Singh VK, Rai S, Anand V. Development of cardiac risk assessment model for vascular surgery patients based on single-center experience. Indian J Vasc Endovasc Surg [serial online] 2019 [cited 2019 Jun 25];6:110-4. Available from: http://www.indjvascsurg.org/text.asp?2019/6/2/110/259655
| Introduction|| |
Vascular surgery patients undergoing noncardiac procedures have high risk for major cardiac events and leading cause of death. Approximately 40 million surgical procedures performed annually in Europe have postoperative myocardial infarction (MI) rate of 1% (400,000) and a cardiovascular mortality rate of 0.3% (133,000). The noncardiac surgeries have incidence of 6.2% for cardiac events.
Hertzer et al. published reports of 1000 patients in 1984 in a landmark study. These patients underwent noncardiac vascular surgery. It was observed that 61% of the patients had at least one coronary artery with a stenosis of 50% or more. US studies have shown similar data, with 1 million of the 27 million patients undergoing surgery in the US per year having cardiac complications.
The high prevalence of coronary artery disease (CAD) in vascular surgical patients is a major risk factor for perioperative cardiac events. There are guidelines which emphasize the need for an accurate clinical assessment, identifying the clinical markers of increased perioperative cardiovascular risk, suggesting the use of cardiac risk indices. Additional examinations or procedures, such as exercise or pharmacological stress tests, ambulatory electrocardiographic control, and coronary angioplasty, have failed to show a substantial effect in reducing perioperative cardiac morbidity, and therefore, cardiac risk indices have been recommended only for select patients., Ninety percent vascular surgery patients do not benefit by these tests, and therefore, critical assessment of cardiac risk index is essential. There are no Indian studies for preoperative cardiac risk scores for patients who undergo vascular interventions. Therefore, a study was done at a tertiary hospital with an aim to risk stratify patients according to cardiac risk index to predict cardiac events.
| Material and Methods|| |
This is an observational, prospective, longitudinal, controlled cohort study, which assessed 103 patients at a single center from February 2013 to June 2015. Patient data on demographics, lifestyle, comorbidity, and other variables were obtained as shown in [Table 1], [Table 2], [Table 3], [Table 4]. Comorbidities studied included CAD, congestive heart failure, hypertension, peripheral vascular disease (revascularization/amputation for peripheral vascular disease and rest pain in lower extremity), sepsis, neurological event, or disease. Patient distribution who were at higher risk for peri-operative cardiac events was also studied as shown in [Table 5]. All patients underwent cardiology evaluation and their distribution is shown in [Table 6].
|Table 5: Distribution of patients at higher risk for peri-operative cardiac events|
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The study variables also included type of surgery, incidence and type of complications, risk stratification according to the Detsky's cardiac risk index, as shown in [Table 7] and [Table 8] and relationship between the risk and the complications, sensitivity, specificity, positive and negative predictive values of the cardiac risk index. In Detsky's risk index, patient based on scores were classified into Class I, II, and III with perioperative of low, intermediate, and high risk.
Primary study endpoints were the major adverse cardiac event (acute coronary syndrome, nonfatal MI or cardiac death). Secondary endpoints were congestive heart failure, ventricular fibrillation, supraventricular arrhythmias; ventricular arrhythmias; arterial hypotension or hypertension.
The categorical variables were expressed according to their frequencies (number and percentage) and analyzed using the Chi-square test. To determine the accuracy of stratification for Detsky's index, the area under the receiver-operating characteristic (ROC) curves was also calculated.
| Results|| |
The age of study population ranged from 32 to 81 years consisting of 90 men and 13 women. There were 56 patients with critical limb ischemia and 16 had aneurysmal disease, both thoracic and abdominal. Five patients had carotid artery disease. Patients with occlusive disease had disabling claudication or rest pain.
The left ventricular ejection fraction (LVEF) ranged from 25% to 60%. Eighty-four patients had LVEFs of >50%, and 14 had LVEFs of 50% or less with postoperative cardiac complications in six patients (42.8%). Sixty-seven had healthy myocardial wall motion, and 14 showed wall motion abnormalities out of which five had perioperative cardiac complications (35.7%).
Seventeen out of 18 postoperative cardiac complications occurred in patients above 40 years and the mean risk of cardiac complication or cardiac death was 7.6%. Acute MI occurred in 0.02% while cardiac death in 7.7%. Eighty patients were smokers who had peripheral arterial disease (77.6% of the study population). There were 3 females in the study group of which 1 was a chronic smoker. All 3 female patients were suffering from ischemic heart disease. High altitude-induced thrombosis was present in 6 patients (5% of study population).
The patients were classified according to Detsky's cardiac risk index into Class I (n = 88, low risk), Class II (n = 12, moderate risk), Class III (n = 3, high risk) as shown in [Figure 1]. Twenty-one patients underwent aortic, 47 patients underwent peripheral arterial surgeries, and 32 patients underwent endovascular procedures. Twenty-six patients had to undergo emergency surgery as a limb/life-saving procedure. There were six mortality in the emergency group (23% mortality in the emergency group) while 77 patients underwent elective procedures with three mortality in the group (3.8% mortality in the elective group). Ten patients had surgical complication postoperatively, but nil mortality occurred due to these complications.
|Figure 1: Distribution of patients as per Detsky's cardiac risk index: (1) Class I (blue) (2) Class II (green) (3) Class III (red)|
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Eighty-two percent of patients did not have any complications. However, there was 8% mortality. The various major/minor cardiac events and their distributions are shown in [Figure 2].
|Figure 2: Percentage distribution of patients developing cardiac events. (1) GrAy 82% (nil complications); (2) pink 1% (pulmonary edema); (3) light blue 1% (myocardial infarction) (4) orange 2% (hypotension); (5) sky blue 1% (hypertension); (6) purple 8% (cardiac arrest); (7) light green 1% (angina); (8) red 3% (acute coronary events); (9) blue 1% (accelerated hypertension)|
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Cardiac death or nonfatal MI averaged 2.9% in Detsky's class in high-risk group, 3.8% in intermediate-risk group, and 3.8% in low-risk group.
Sensitivity, specificity, and positive and negative predictive values were calculated according to Fletcher et al. The overall sensitivity, specificity, positive predictive value, and negative predictive value of the Detsky's risk index in the prediction of cardiac events were 31.4%, 94.1%, 73.3%, and 72.7% respectively as shown in [Table 9]. In our study, the area under ROC for Detsky's class was 0.76 versus 0.75 and superior to C statistic.
|Table 9: Data analysis of cardiac events as per Detsky's cardiac risk index|
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| Discussion|| |
Two most commonly used cardiac risk index are revised cardiac risk index  and Detsky's cardiac risk index. As a protocol, we followed the Detsk's risk index to predict cardiac complications in perioperative period in patients operated at our center. In our study, cardiac death or nonfatal MI averaged 2.9% in Detsky's class in high risk group, 3.8% in intermediate risk, and 3.8% in low risk group. Detsky work was originally published in Journal of general internal medicine where authors prospectively studied 455 consecutive patients. Though the original index performed poorly in the validation data for patients undergoing major surgery, it still added predictive information to a statistically significant degree (P < 0.05). The modified index also added predictive information for patients undergoing both major and minor surgery, demonstrating an area under the ROC curve of 0.75 (95% confidence interval of 0.70–0.80). In our study, the area under ROC for Detsky's class (0.76 vs. 0.75) was superior to C statistic, calculated in the original study. Therefore, based on ROC curve too (as shown below), Detsky had higher predictive value when compared to other risk assessment models as shown in [Table 10].
Data analysis showed that Detsky's index performed well with high specificity (100%), positive predictive value (100%), and negative predictive values (84%) for high-risk patients.
Previous cardiac indices such as the one proposed by Goldman et al. used logistic regression models to create point-based risk score systems. We instead chose based on the predictive value for major/minor adverse postoperative cardiac event. The C statistic curve too had higher value under the curve for Detsky's. This approach allowed direct modeling and prediction of cardiac events, using the risk index to predict risk based on a point system.
One important inference from the study was that 77.6% of patients were smoker in the study group which emphasize direct relation of peripheral vascular disease with smoking. There was 23% mortality in emergency group as compared to 3.8% in elective group. Emergency group posed significant risk in terms of mortality because of lesser optimization of patients in view of major life- and limb-saving surgeries. These data suggest the importance of relevant cardiac risk assessment and optimization of patients before taken up for interventions.
The present study had some limitations. Though all patients were subjected to baseline echocardiography to risk stratify by cardiologist, patients with preoperative high risk were not routinely evaluated with further coronary angiography or stress myocardial perfusion imaging (MPI). Three patients were high-risk group, and none underwent stress MPI or coronary angiography. This dichotomy existed because few of the patients were taken up for emergency surgeries without further cardiac evaluation.
The study concluded that patients with good surgical risk and profile undergoing minor vascular procedures can be operated without further testing. For other patients, the next step would be to incorporate the Detsky's index. A Detsky's score of 20 or more is comparable to a major clinical predictor in the ACC/AHA  scheme, and it is an indication for further evaluation or treatment before surgery.
The categorical variables were expressed according to their frequencies (number and percentage) and analyzed using the Chi-square test. When the expected values were <5, the Fisher's exact test was used. The statistical significance value of P < 0.05 was adopted.
To determine and compare the accuracy of different systems of stratification for each index, the areas under the ROC curves were calculated. The ROC curves were plotted on a graph with the values of sensitivity in the ordinate axis, and the proportion of false positives (1-specificity) in the abscissa axis. With regard to the interpretation of the ROC curve, the greater the area under the curve, more accurate the cardiac risk index was considered. The areas were compared using a nonparametric method according to the technique by Hanley and McNeil 49 (expected sensitivity between 60% and 75%). In our study, the area under the ROC curve for Detsky's risk index was 0.76 with 95% confidence interval.
The overall sensitivity, specificity, positive predictive value, negative predictive value of the Detsky's risk index in the prediction of cardiac events was 31.4%, 94.1%, 73.3%, 72.7% respectively.
| Conclusion|| |
The study concluded that perioperative cardiac morbidity and mortality is an important factor in patients undergoing noncardiac vascular surgery. Therefore, cardiac risk assessment provides a framework for determining a patient's surgical risk and prognosis. The assessment of risk factors is essential for surgery, since in this context it is possible to plan the procedure, in terms of both the decision to perform surgery and the possibility of taking other measures to minimize the risk of cardiac complications. In high-risk patients, if the surgery is not an emergency, there is an opportunity to consider proper evaluation before the procedure or performing a lower risk intervention. Any interventional procedure should be undertaken with appropriate perioperative surveillance. Our study concludes with recommendation that Detsky's risk index and ACC/AHA guidelines for preoperative cardiac risk assessment should be included in the institutional protocol for peripheral vascular surgery.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]