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ORIGINAL ARTICLE
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A prospective interventional study to assess the advantage of premedication with sublingual nitroglycerin in evaluation of peripheral vascular disease with computed tomography peripheral angiography


1 Department of Radiodiagnosis, Army Hospital (Research and Referral), New Delhi, India
2 Department of Cardiology, Army Hospital (Research and Referral), New Delhi, India

Date of Submission21-Sep-2020
Date of Decision22-Dec-2020
Date of Acceptance11-Apr-2021

Correspondence Address:
B Dhanalakshmi,
Department of Radiodiagnosis, Army Hospital (Research and Referral), New Delhi - 110 010
India
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/mjdrdypu.mjdrdypu_527_20

  Abstract 


Objectives: The objectives of this study were to investigate the influence of sublingual nitroglycerin (NTG) administration on peripheral vessel diameter, the number of evaluable segments, image quality, and adverse effects in patients with peripheral vascular disease (PVD) undergoing multidetector computed tomography (MDCT) angiography. Methods: A prospective randomized comparative interventional study was conducted on 48 inpatients with clinical diagnosis of PVD. The study patients were divided into two groups: one which was premedicated with 5 mg of sublingual NTG (NTG group) and the other without the use of NTG. MDCT images were recorded after 5 min of drug administration. The 10 segments of upper-limb vessels and 15 segments of lower-limb vessels were evaluated for diameter (mm), intraluminal contrast opacification (Hounsfield unit), collaterals, and stenosis (%). The data were entered in MS Excel and analyzed using SPSS. P < 0.05 was considered statistically significant. Results: The NTG group showed a statistically significant increase in diameter of radial artery (P = 0.01), common femoral artery, and all arterial segments of lower limb (P<0.05). The intraluminal contrast attenuation was higher in all segments (P < 0.05) in lower limbs. Good and continuous visualization of collateral vessels in segments with > 50% stenosis or occlusion was seen in the NTG group than the non-NTG group (P < 0.05). Conclusion: Sublingual NTG administration results in significant peripheral vessel dilatation, thus improving number of evaluable distal branches and collaterals with minimal side effects requiring no medical intervention. It helps increase the MDCT diagnostic accuracy and select appropriate treatment protocol.

Keywords: Collaterals, nitroglycerin, vascular diseases



How to cite this URL:
Dhanalakshmi B, Shijith K P, Sharma P. A prospective interventional study to assess the advantage of premedication with sublingual nitroglycerin in evaluation of peripheral vascular disease with computed tomography peripheral angiography. Med J DY Patil Vidyapeeth [Epub ahead of print] [cited 2021 Dec 6]. Available from: https://www.mjdrdypv.org/preprintarticle.asp?id=330699




  Introduction Top


Peripheral vascular disease (PVD) is one of the major causes of morbidity and mortality globally, causing significant burdens on health-care systems.[1],[2] They result from circulatory system dysfunction caused by damage, occlusion, and/or inflammation of arteries and/or veins.[3] It encompasses peripheral arterial disease (PAD), chronic venous insufficiency and deep vein thrombosis (DVT). They may be seen in the upper extremities but are most prevalent in the lower extremities.[1]

Early diagnosis and management of PVD is crucial to address the high rates of mortality and morbidity, however, 50% of them are asymptomatic and thus do not seek medical attention. Establishing effective diagnostic tools to determine vascular competence is essential particularly for asymptomatic PVD patients who have the same risk of morbidity and mortality as those with more obvious symptoms.[1] Four primary established invasive methods for evaluation of PVD are angiography, venography, ambulatory venous pressure, and intravascular ultrasound.[4]

Among them, computed tomography (CT) angiography plays a vital role in evaluation of PVD.[5],[6],[7] Multidetector CT (MDCT) images have good spatial and temporal resolutions. However, there is always a challenge in evaluation of distal vessels and collaterals since there is intrinsic vascular resistance in patients with PVD and narrow caliber of distal vessels with slow blood flow. Fast acquisition of multidetector CT with underlying PVD causing slow flow of blood beyond knee or elbow joints adds the difficulty in evaluation of arterial lumen. Thus, the patient undergoes caudal to cranial run after angiographic phase to visualize the distal vessels which may get filled up slowly, even though there will not be any change in arterial diameter in rerun phase.[8],[9] This causes difficulty in analyzing the distal segments, thus affecting the diagnostic accuracy of this tool.[10] Thus, exploring the factors which may increase the vessel caliber without affecting image quality is worthwhile and has the potential to improve the diagnostic accuracy of MDCT.[11],[12]

Sublingual nitroglycerin (NTG) has been proven to have vasodilation on arteries. Its vasodilation effect on the coronary arteries and secondary branches has been shown in various studies[13],[14] where it was concluded that the use of NTG can upgrade the results of MDCT in evaluation of coronary artery disease. Peedikayil et al.,[15] and Maruhashi et al.,[16] found that NTG-mediated dilation can better predict vascular disease risks than flow-mediated vasodilation. Hence, it is hypothesized that premedication with sublingual 5 mg NTG 5 min prior to the helical CT may improve the visualization of peripheral arteries, collaterals, and even digital arteries without the need of caudal to cranial CT rerun and radiation side effects.

Thus, we conducted this study to evaluate the effect of systematic sublingual use of NTG prior to imaging using the 256 slice MDCT (iCT Philips) on image quality and vessel analysis of the patients with PVDs. The primary objective of the study was to compare the vessel diameter with and without the use of NTG.


  Methods Top


A prospective randomized interventional comparative study was conducted in the department radiodiagnosis at a tertiary care center in New Delhi from December 2019 till February 2020. The study was approved by the institutional ethical committee (IEC/42/2020), and all expenses related to the use of MDCT were borne by the hospital.

The study included inpatients (age: 45–65 years, both genders) with clinical diagnosis of PVD. Any suspected case of atherosclerosis during the study period was undertaken for color Doppler Ultrasound (USG) to determine venous insufficiency and making a diagnosis. PAD was defined as the presence of stenosis of 50% or higher in any lower extremity artery between common iliac and Femoropopliteal (FPL) regions.[17] The patients with hypotension (systolic blood pressure <90 mmHg), profound bradycardia (heart rate <50/min), acute limb ischemia, pregnancy, deranged renal function, and allergy to contrast or nitrates were excluded from the study.

The sample size calculation was done based on the study of Ochi et al.,[18] who observed that the diameter of blood vessels (mm) with the use of NTG was 5.43 ± 0.71 in smokers and 4.84 ± 0.67 in controls. Taking these values as reference, the minimum required sample size with 80% power of study and 5% level of significance is 22 patients in each study group. To reduce margin of error, total sample size taken was 48 (24 patients per group).

After obtaining written informed consent from all the selected patients, the demographic and clinical information were noted on a separate case sheet for every individual. The study patients were randomized into two groups:

  • Group NTG (n = 24): The patients were premedicated with 5 mg of sublingual NTG, and after 5 min of drug administration, saline mouthwash was done keeping the patient in the gantry supine to avoid further absorption of drug and precipitation of postural hypotension. The rationale of the dose was that 0.5 mg tablet is the minimal dose available, and we assessed the peak action and not the effect of the entire drug. Hemodynamic parameters were recorded pre- and poststudy. After 20–30 min of observation, patients were shifted to ward
  • Group non-NTG (n = 24): The patients were not premedicated with NTG. It served as the control group.


The randomization was done by sealed envelope system. In this, we prepared sealed opaque envelopes. Once a patient consented to enter a trial, an envelope was opened, and the patient was then offered the allocated treatment regimen.

Both the patient groups underwent CT angiogram using the 256 slice MDCT (iCT Philips) with bolus tracking technique. A trigger threshold of 120 Hounsfield unit (HU) was kept keeping ROI from infrarenal aorta for lower limbs and arch of aorta for upper limbs. The nonionic iodinated contrast (Iohexol, Omnipaque 350) was injected using dual-head pressure injector in the dose of 1.5 ml/kg body weight at the rate of 4 ml/s followed by 1 ml/kg body weight saline chase at the rate of 4 ml/s. Parameters of the CT scan were: rotation time 0.5 sec with a distance covered of 15 mm/rotation, pitch 0.8, voltage of 120 kVp and current of 250 mAs. Automated triggering and exposure control were employed. CT spatial resolution was 0.6 mm × 0.6 mm × 2.0 mm. The table speed was 30 mm/s.

The evaluation of both the limbs was done. The upper-limb vessels were divided into 10 segments and lower-limb vessels were divided into 15 segments for separate analyses of each. Each segment was evaluated for diameter (mm), intraluminal contrast opacification (HU), collaterals, and stenosis (%). The data pertaining to the variables were compared among the cases and the controls.

The patients which showed severe obliteration of the peripheral vessels underwent digital subtraction angiography for confirmation.

Statistical analysis

The data were entered in MS Excel spreadsheet, and analysis was done using the Statistical Package for the Social Sciences (SPSS), IBM manufacturer, Chicago, USA, version 21.0. Categorical variables were presented in number and percentage (%) and continuous variables were presented as mean ± standard deviation. Quantitative variables were compared using unpaired t-test between the two groups. Qualitative variables were compared using Fisher's exact test and Chi-square test. P < 0.05 was considered statistically significant.


  Results Top


Among the 50 patients of PVD who were admitted during the study period, 2 were allergic to contrast and were thus excluded. The study was done on 48 patients (14 females and 34 males), with a mean age of 55.5 years [Table 1].
Table 1: Comparison of arterial diameter of upper-limb segment between nitrate and nonnitrate

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The most frequent symptom in lower-limb studies was intermittent claudication in 50% of patients, pain in 40%, and weakness in 25% of patients. The most frequent diagnosis among them was atherosclerosis. Upper-limb studies were commonly referred for differential pulse status (62.5% of patients) with a diagnosis of Takayasu's arteritis seen in 3/8 patients (37.5%). Diabetes (50%) and history of smoking (40%) were the most common risk factors. The baseline characteristics such as age, gender, symptoms and comorbidities were comparable among the cases and controls (P > 0.05), as shown in [Table 1].

Upper-limb studies were done in 8 patients (4 females and 4 males) and lower-limb studies were done in 40 patients (10 females and 30 males).

Per segment mean diameter of arteries was greater in the NTG group for all the arteries, however, the difference was statistically significant for common femoral artery and all segments beyond up to the toe in the lower limb (P < 0.05) and radial artery only in the upper limb (P = 0.01) [Table 2] and [Table 3]. The intraluminal contrast attenuation was higher in all segments (P < 0.05) in lower limbs, with not much difference in attenuation in upper-limb vessels.
Table 2: Comparison of arterial diameter of upper-limb segment between nitrate and nonnitrate

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Table 3: Comparison of arterial diameter of lower-limb vessels between nitrate and nonnitrate

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Good and continuous visualization of collateral vessels in segments with >50% stenosis or occlusion was seen more in the NTG group than the non-NTG group (P = 0.01). There was a significant improvement in the visualization of >50% stenosed vessels in the tibioperoneal region, and the number of nonanalyzable distal segments was higher in the non-NTG group [Table 4].
Table 4: Subjective assessment of lower-limb vasculature

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There were better signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) observed in the NTG premedicated group for distal vessels and collaterals. The representative images of arterial segments of the lower limb on MDCT with and without NTG are shown in [Figure 1] and [Figure 2].
Figure 1: Computed tomography angiography of the lower-limb vessels after premedication with nitroglycerin (longitudinal section)

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Figure 2: Computed tomography angiography of the lower-limb vessels without premedication with nitroglycerin (longitudinal section)

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There was no demonstrated side effects in patients undergoing premedication. There was a reduction in diastolic blood pressure of 10 mmHg in 10 patients without symptoms which lasted for 20 min. There was no change in systolic blood pressure. There was no postural hypotension observed after 20 min of keen observation in gantry. The overall imaging quality assessment was equal in both the groups.


  Discussion Top


To our knowledge, this is the first study on the evaluation of PVD where we found that 0.5 mg of sublingual NTG increased vessel diameter, the number of assessable artery segments, and image quality of MDCT.

The clinical practical use of NTG stems from its precise mechanism to generate nitric oxide (NO), which initiates smooth muscle relaxation independent of endothelial function.[19] Simultaneously, it also reduces the likelihood of artery vasospasm.

We used the 0.5 mg sublingual tablet of NTG with a half-life of 5 min. It acts fast allowing immediate dilation and contrast flow under gravity, thus preventing the rerun of MDCT. Pepe et al.[20] observed a maximal vasodilator response between 4 and 5 min after NTG administration using magnetic resonance imaging for visualization of the coronary artery lumen. This shows that the optimal starting time for image acquisition is probably between 3 and 4 min after sublingual administration of NTG. However, some of the studies favor the use of sublingual spray as the preferred method of administration considering it as the most efficacious and with fewer side effects.[21],[22] This warrants future studies to compare the sublingual and spray mode of NTG for vessel evaluation.

Compared to controls, patients who used NTG showed a significant increase in the vessel diameter of the lower limb from the common femoral artery and all segments beyond (up to the toe) with P < 0.05. In the upper limb, only the radial artery showed a significant increase in the arterial diameter which may be due to the sample size of those undergoing upper arm interventions. The findings were in line with the studies on coronary vessels which demonstrated an overall increase in diameter with the use of NTG, ranging from 8% to 30%.[11],[12],[23],[24],[25],[26],[27] Similarly, Chong et al.[28] also found that NTG significantly dilates radial arteries and suggested its use in challenging radial artery punctures and cannulations. In another study, Ochi et al.[18] observed a significant improvement in the brachial artery diameter after 0.3 mg of sublingual NTG. The significance of the brachial artery dilatation has been explored further in a study which determined that brachial artery response and dilation subsequent to NTG may be used in risk stratification of cardiovascular events.[29]

The specific reason for more dilation of lower-limb vessels as compared to upper limb with NTG may be due to different muscles, vasculature, and resistance patterns of the blood vessels. The response of the vascular bed of the upper extremities in patients with PAD is more like that in hypertensive patients but of the lower extremities, it shows more dilation with decreased resistance.[23],[24],[25],[26],[27],[28],[29]

Another interesting finding was that NTG causes major effects on the distal small luminal vessels rather than large diameter vessels. Similar results were seen in the study by Klass et al.[25] who showed that the relative vessel diameter increase is larger in distal segments compared to proximal segments. Okada et al.[27] and Sato et al.[26] confirmed this observation for dilation of the peripheral segments. The reason that NTG dilates the narrowed arterial segments (by atherosclerotic process) more than the normal unaffected ones is (1) the increased scope of dilation and (2) Nitric-oxide mediated effect on the arterial media layer.[30]

The greater visualization of the narrowed or stenosed distal vessels as seen in the index study becomes significant from the treatment point of view. The management of the PVD falls into lifestyle, medical, and surgical therapies. Surgical therapies include stents, arterectomies, angioplasty, and bypass surgery. Among them, bypass surgery is the most invasive which is used for restoring blood flow in cases with large stenosed portion of the vessels.[31] NTG vasodilation may help us know if partial or whole of the segment is stenosed. In cases with partial blockage, stents and angioplasty may be a convenient method.

Among the segments with >50% stenosis or occlusion, a significant improvement in the visualization of collateral vessels was seen in the NTG group (80.39% segments [41/51] in the NTG group vs. 58.44% [45/77] segments in the non-NTG group, P = 0.01). Literature quotes sensitivity (Sn) and specificity (Sp) for evaluation of vessels with ≥50% stenosis degree. Chun et al.[32] reported a Sn and Sp of 97% and 84.6% for NTG as compared to 90.0% and 70.0%, respectively, for the control group. It was noted that diagnostic accuracies for proximal, mid, and distal segments were all higher in the patients who received sublingual NTG. Overall Sn and Sp for segment-based evaluation were 83% and 97.8% for the NTG group compared to 63.6% and 94.8%, respectively, for the control group. Kang et al.[24] showed that the diagnostic accuracy for finding any atherosclerosis was higher in the NTG group as compared to the control group (85.8% vs. 80.1%).

A better SNR and CNR were also observed in the NTG premedicated group for distal vessels and collaterals. The findings were in line with three studies which found that the administration of sublingual NTG resulted in significantly better subjective image quality, especially for the posterior descending artery.[12],[25],[33] In contrast, Decramer et al.[11] and Okada et al.[27] did not observe an effect of NTG on objective measures such as SNR and CNR.

The side effect profile of NTG remains mild. Tachycardia was noted in five patients in our study at 4 min after the NTG administration, but it did not require any intervention. Other studies have also observed significant changes in heart rate.[26],[27] Among other hemodynamic disturbances, Okada et al.[27] observed a notable decrease in systolic (10.6%) and diastolic (9.1%) blood pressure. However, few studies observed no significant changes in blood pressure and/or heart rate.[11],[32],[34] Other side effects may include mild headache or dizziness (due to NTG-induced hypotension) which may be alleviated without medical intervention.[11],[12],[26],[32] It must be stressed here that patients with diminished cardiac output/severe hypotension, increased intracranial pressure, or patients using phosphodiesterase inhibitors may have serious side effects and thus such patients may be avoided for using NTG.[21],[35]

A point of concern as stated among studies done on coronaries is that the administration of NTG could result in overestimation of the stenosis degree[36] because the vascular reactivity of the disease segments to NTG falls. However, this phenomenon was not seen in the peripheral vessels of the limbs in the index study. However, future research is needed to determine the exact mechanism behind it.

Apart from the use of NTG in assisting MDCT for diagnosing PVD, a variety of other noninvasive diagnostic methods such as plethysmography, Doppler ultrasound, and blood pressure methods (Ankle Brachial Index, Segmental blood pressure measurement, and Toe Brachial Index) have been developed.[37],[38] However, each method has limitations, which continue to motivate the development of new diagnostic and clinically applied methods, the latest being pulse wave velocity, vascular optical tomographic imaging, and polymer-based sensors. However, their validity and routine clinical use needs further evaluation and thus NTG may be a useful method to enhance the current clinical MDCT image analysis for the management of PVD.

Limitations of the study

First, we did not follow the patients for surgery and the outcomes. Second, NTG may not be used in patients with diminished cardiac output/severe hypotension, increased intracranial pressure, or patients using phosphodiesterase inhibitors. Finally, although there were more males in the study, subgroup analysis on the basis of gender was not done as the study sample was not powered for that.


  Conclusion Top


Sublingual NTG administration results in significant peripheral vessel dilatation, thus improving number of evaluable distal branches and collaterals with minimal side effects requiring no medical intervention. It helps increase the MDCT diagnostic accuracy and select appropriate treatment protocol.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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