New balloon-thermography catheter for in vivo temperature measurements in human coronary atherosclerotic plaques: a novel approach for thermography?

Skin temperature maps as a measure of carotid artery stenosis

In this study, the effect of carotid artery stenosis on the neck skin temperature maps was investigated. With the presence of stenosis, alterations in the carotid artery hemodynamics bring about changes in the heat transfer to the surrounding tissue. This is expected to be captured in the resulting temperature map over the external neck skin surface; possibly it correlates to the presence of stenosis. A total of twenty carotid artery samples, from ten patients with both sides normal (0% stenosis), stenosis (>50%) on one side, and stenosis (>50%) on both sides, were studied. Duplex Ultrasound and infrared (IR) thermography examinations were performed. A computational study, on an ideal 3-dimensional (3D) carotid artery and jugular vein model encapsulated with a solid neck tissue phantom resembling the human neck, was carried out. Incorporating the patient-specific geometrical (depth of artery and stenosis) and flow (peak systolic and end diastolic inlet velocity) boundary conditions, conjugate bio-heat transfer was studied using a finite volume numerical scheme. Simulation results and in-vivo thermal maps show that the average temperature on the external neck skin surface is significantly higher for normal patients (32.82 ± 0.53 °C versus 32.00 ± 0.37 °C, p < 0.001). Furthermore, the thermal region of interests (TROIs) were extracted from the in-vivo thermal images, which both qualitatively and quantitatively distinguish the normal and diseased cases. This study suggests the potential of thermal feature-based screening of patients with carotid artery stenosis.

Microwave radiometry: a new non-invasive method for the detection of vulnerable plaque

Atherosclerosis and its consequences are the most rapidly growing vascular pathology, with myocardial infarction and ischemic cerebrovascular accident to remain a major cause of premature morbidity and death. In order to detect the morphological and functional characteristics of the vulnerable plaques, new imaging modalities have been developed. Intravascular thermography (IVT) is an invasive method, which provides information on the identification of the high-risk atheromatic plaques in coronary arteries. However, the invasive character of IVT excludes the method from primary prevention. Microwave radiometry (MR) is a new non-invasive method, which detects with high accuracy relative changes of temperature in human tissues whereas this thermal heterogeneity is indicative of inflammatory atherosclerotic plaque. Both experimental and clinical studies have proved the effectiveness of MR in detecting vulnerable plaque whereas recent studies have also revealed its association with plaque neoangiogenesis as assessed by contrast enhanced carotid ultrasound (CEUS).

Detection of the vulnerable coronary atheromatous plaque. Where are we now?

Atherosclerosis is a progressive process with potentially devastating consequences and has been identified as the leading cause of morbidity and mortality, especially in the industrial countries. The underlying mechanisms include endothelial dysfunction, lipid accumulation and enhanced inflammatory involvement resulting in plaque disruption or plaque erosion and subsequent thrombosis. However, it has been made evident, that the majority of rupture prone plaques that produce acute coronary syndromes are not severely stenotic. Conversely, lipid-rich plaques with thin fibrous cap, heavily infiltrated by inflammatory cells have been shown to predispose to rupture and thrombosis, independently of the degree of stenosis. Therefore, given the importance of plaque composition, a continuously growing interest in the development and improvement of diagnostic modalities will promptly and most importantly, accurately detect and characterize the high-risk atheromatous plaque. Use of these techniques may help risk stratification and allow the selection of the most appropriate therapeutic approach.

Numerical analysis of the cooling effect of blood over inflamed atherosclerotic plaque

Atherosclerotic plaques with high likelihood of rupture often show local temperature increase with respect to the surrounding arterial wall temperature. In this work, atherosclerotic plaque temperature was numerically determined during the different levels of blood flow reduction produced by the introduction of catheters at the vessel lumen. The temperature was calculated by solving the energy equation and the Navier-Stokes equations in 2D idealized arterial models. Arterial wall temperature depends on three basic factors: metabolic activity of the inflammatory cells embedded in the plaque, heat convection due to luminal blood flow, and heat conduction through the arterial wall and plaque. The calculations performed serve to simulate transient blood flow reduction produced by the presence of thermography catheters used to measure arterial wall temperature. The calculations estimate the spatial and temporal alterations in the cooling effect of blood flow and plaque temperature during the measurement process. The mathematical model developed provides a tool for analyzing the contribution of factors known to affect heat transfer at the plaque surface. Blood flow reduction leads to a nonuniform temperature increase ranging from 0.1 to 0.25 degrees Celsius in the plaque/lumen interface of the arterial geometries considered in this study. The temperature variation as well as the Nusselt number calculated along the plaque surface strongly depended on the arterial geometry and distribution of inflammatory cells. The calculations indicate that the minimum required time to obtain a steady temperature profile after arterial occlusion is 6 s. It was seen that in arteries with geometries involving bends, the temperature profiles appear asymmetrical and lean toward the downstream edge of the plaque.

Correlation of systemic inflammation with local inflammatory activity in non-culprit lesions: Beneficial effect of statins

BACKGROUND

In patients with acute coronary syndromes (ACS) increased systemic and local inflammatory activation in culprit lesions is observed. It is unknown, however, whether systemic inflammation is correlated with non-culprit lesion inflammatory activation. Moreover, the effect of statins on non-culprit lesion inflammation has not been extensively investigated. The aim of the present study was to investigate in non-culprit lesions 1) the correlation between plaque temperature measurements with the levels of C-reactive protein (CRP) and 2) whether statin administration is associated with reduced heat production.

METHODS

We included 71 patients with ACS or stable angina (SA) undergoing percutaneous coronary intervention in culprit lesions, having an intermediate non-culprit lesion. Forty patients were treated with statin and 31 patients were not treated. Systemic inflammatory status was assessed by CRP, and local inflammatory activation by measuring the temperature difference of non-culprit lesion (deltaT), assigned as the difference between the maximal temperature of the atherosclerotic plaque from the proximal vessel wall temperature.

RESULTS

Mean deltaT was 0.08+/-0.07 degrees C. Patients with ACS had higher deltaT compared to patients with SA (ACS: 0.10+/-0.07 degrees C vs SA: 0.05+/-0.06, p<0.01). deltaT was less in patients treated with statin in both groups (ACS: 0.07+/-0.04 degrees C vs 0.13+/-0.08 degrees C p=0.009; SA: 0.04+/-0.05 degrees C vs 0.09+/-0.07 degrees C, p=0.04). CRP was higher in patients with ACS compared to SA (1.18+/-1.12 vs 0.47+/-0.37 mg/dL, p=0.001). There was a positive correlation of deltaT and CRP values (R=0.46, p<0.001).

CONCLUSIONS

Local inflammatory activation in non-culprit lesions is correlated with systemic inflammation. Moreover, statins have a beneficial effect on non-culprit lesion heat production.

Correlation between morphologic characteristics and local temperature differences in culprit lesions of patients with symptomatic coronary artery disease

OBJECTIVES

The purpose of this study was to investigate the possible correlation between morphologic and functional characteristics of culprit lesions (CL) in patients with acute coronary syndromes (ACS) and chronic stable angina (CSA).

BACKGROUND

Intravascular ultrasound (IVUS) provides morphologic assessment and intracoronary thermography (ICT) evaluates the local inflammatory activation of CL.

METHODS

Eighty-one consecutive patients, 48 with ACS and 33 with CSA, were enrolled. Ratio of lesion to reference external elastic membrane area, indicated by IVUS, was defined as positive remodeling index (pRi) (> or =1) or negative remodeling index (nRi) (<1). We also investigated the existence of ruptured plaque (rp) in the CL. By ICT temperature difference (DeltaT) between the CL and the proximal vessel wall was measured.

RESULTS

Patients with ACS had greater remodeling index than patients with CSA (1.15 +/- 0.18 vs. 0.90 +/- 0.12; p < 0.01), as well as increased DeltaT (0.08 +/- 0.03 degrees C vs. 0.04 +/- 0.02 degrees C; p < 0.01). Patients with pRi had higher DeltaT than patients with nRi (0.07 +/- 0.03 degrees C vs. 0.04 +/- 0.02 degrees C; p < 0.001). In patients with nRi there was no difference in DeltaT between ACS and CSA (p = 0.22). Patients with rp had increased DeltaT compared with patients without rp (0.09 +/- 0.03 degrees C vs. 0.05 +/- 0.02 degrees C; p < 0.01). Multivariate analysis showed that DeltaT was independently correlated with the presence of rp, pRi, and ACS.

CONCLUSIONS

The present study showed that culprit lesions with plaque rupture and positive arterial remodeling have increased thermal heterogeneity, although in certain patients a discrepancy between morphogic and functional characteristics was observed. A combination of morphologic and functional examination may offer additional diagnostic and prognostic information.

Intracoronary thermography: does it help us in clinical decision making?

The concept of the "vulnerable" plaque has recently emerged to explain how quiescent atherosclerotic lesions evolve to cause clinical events. The morphologic and immunologic determinants specific for the vulnerable plaque have been reported: a large lipid core (>or=40% plaque volume) composed of free cholesterol crystals, cholesterol esters, and oxidized lipids impregnated with tissue factor; a thin fibrous cap depleted of smooth muscle cells and collagen; an outward (positive) remodeling; inflammatory cell infiltration of fibrous cap and adventitia (mostly monocyte-macrophages, some activated T cells, and mast cells); and increased neovascularity. Despite the large amount of information regarding the morphological characteristics of remote lesions, we lack studies with functional assessment of non-culprit lesions. Coronary thermography is a technique for functional assessment of coronary atherosclerotic plaques. Several catheter designs have been proposed. There are catheters with thermistor(s) and wires with thermal sensors at the distal tip. All designs have several advantages and disadvantages. Despite the current limitations of coronary thermography, we gained important pathophysiological and clinical information regarding the vulnerability of atheromatic plaques. It has been documented both experimentally and clinically that increased heat generation is associated with increased macrophage concentration within the plaque. The correlation between local inflammatory involvement and local heat generation has also been observed with the peripheral inflammatory markers such as C-reactive protein. Whether systemic treatment, with agents such as statins or interventional techniques, such as drug-eluting stents, will have an impact on stabilizing vulnerable plaques need to be determined in future studies. In conclusion, although there are several techniques for evaluating morphologically atheromatic plaques, thermography is a promising method for the functional assessment of vulnerable plaque and has been introduced into clinical practice, with a good predictive value for clinical events in patients with increased temperature in the atherosclerotic plaque.

Elevated Plaque Temperature in Non-Culprit De Novo Atheromatous Lesions of Patients With Acute Coronary Syndromes

OBJECTIVES

We investigated whether there is increased temperature in non-culprit lesions, and the correlation of clinical syndrome with heat production of non-culprit lesions.

BACKGROUND

There is a controversy regarding whether there is widespread inflammation involving non-culprit lesions, or whether inflammatory involvement is limited to the culprit lesion. Coronary thermography assesses the local inflammatory involvement in atherosclerotic lesions.

METHODS

We included patients suffering from stable angina (SA) or acute coronary syndrome (ACS). All patients had two or more angiographically detectable lesions at different arteries. Culprit lesions should be identified in all patients. Patients with chronic total occlusions and multiple significant lesions at the culprit vessel were excluded. We measured at each non-culprit lesion the temperature difference (DeltaT) between the atherosclerotic plaque and the proximal vessel wall temperature.

RESULTS

The study population included 42 patients: 23 with SA, 19 with ACS. The DeltaT in non-culprit lesions was 0.08 +/- 0.07 degrees C. Patients with ACS had a higher temperature difference in non-culprit lesions compared with patients with SA (ACS 0.11 +/- 0.08 degrees C vs. SA 0.05 +/- 0.06 degrees C; p < 0.01). The mean value of DeltaT in non-culprit lesions was higher in the untreated group compared with the treated group with statins (0.11 +/- 0.10 degrees C vs. 0.06 +/- 0.05 degrees C; p = 0.05).

CONCLUSIONS

The results of this study show that heat is generated in non-culprit lesions. Moreover, in patients with ACS, temperature difference is increased compared with patients with stable angina.

In vivo temperature heterogeneity is associated with plaque regions of increased MMP-9 activity

AIMS

Plaque rupture has been associated with a high matrix metalloproteinase (MMP) activity. Recently, regional temperature variations have been observed in atherosclerotic plaques in vivo and ascribed to the presence of macrophages. As macrophages are a major source of MMPs, we examined whether regional temperature changes are related to local MMP activity and macrophage accumulation.

METHODS AND RESULTS

Plaques were experimentally induced in rabbit (n=11) aortas, and at the day of sacrifice, a pull-back was performed with a thermography catheter. Hot (n=10), cold (n=10), and reference (n=11) regions were dissected and analysed for smooth muscle cell (SMC), lipids (L), collagen (COL), and macrophage (MPhi) cell densities (%); a vulnerability index (VI) was calculated as VI=MPhi+L/(SMC+COL). In addition, accumulation and activity of MMP-2 and MMP-9 were determined with zymography. Ten hot regions were identified with an average temperature of 0.40+/-0.03 degrees C (P<0.05 vs. reference) and 10 cold regions with 0.07+/-0.03 degrees C (P<0.05 vs. hot). In the hot regions, a higher macrophage density (173%), less SMC density (77%), and a higher VI (100%) were identified. In addition, MMP-9 (673%) activity was increased. A detailed regression analysis revealed that MMP-9 predicted hot regions better than macrophage accumulation alone.

CONCLUSION

In vivo temperature measurements enable to detect plaques that contain more macrophages, less SMCs, and a higher MMP-9 activity.

Sternal Nourishment in Various Conditions of Vascularization

BACKGROUND

Early changes in sternal perfusion were studied after midline sternotomy and different methods of mammary artery (MA) harvesting.

METHODS

Our observations were made in the swine model after midline sternotomy. In group 1 (6 animals), after unilateral skeletonized MA harvesting, (99m)Tc particles were injected intravenously. In group 2 (7 animals), after unilateral mammary artery and vein harvesting (semiskeletonized technique), (99m)Tc particles were injected intravenously. In group 3 (5 animals), after skeletonized bilateral MA harvesting, 99mTc particles were injected into the intercostal musculature lateral to the sternal border. In groups 1 to 3, sternal samples were analyzed using gamma counting. In group 4 (6 animals), unilateral skeletonized MA harvesting was performed. In group 5 (5 animals), the MA was harvested unilaterally using the semiskeletonized technique. In groups 4 and 5, sternal blood flow was assessed using thermography. Data were collected in all groups for 5 hours postoperatively.

RESULTS

Both radioactive and thermographic flow measurements showed a statistically significant decrease in sternal blood flow on the side of harvested mammary vessels, regardless of harvesting technique. Radioactivity of the devascularized hemisterni on the side of intramuscular particle injection was substantially higher than in the contralateral half, confirming the role of diffusion in sternal nourishment. The distal sternal segments were least perfused by the MA.

CONCLUSIONS

There is an acute reduction of sternal perfusion during the early postoperative period, even if collaterals are preserved by skeletonized MA harvesting. Diffusion plays an important role in sternal nourishment, particularly of the xiphoid, and even more so after MA harvesting.

Detection of increased temperature of the culprit lesion after recent myocardial infarction: the favorable effect of statins

BACKGROUND

Increased thermal heterogeneity has been demonstrated in atherosclerotic plaques, with the higher temperature recorded in acute myocardial infarction (MI). Dietary or treatment interventions reduce heat production. The purpose of the present study was to investigate whether increased plaque temperature is maintained for a prolonged period after MI and the role of statin administration.

METHODS

We enrolled 55 patients, 29 with recent MI and 26 with chronic stable angina (CSA). Total cholesterol, C-reactive protein (CRP), interleukin-6 (IL-6) and soluble adhesion molecules were measured in the study population. All patients underwent coronary plaque temperature measurements. Temperature difference (DeltaT) was designated as the temperature of the culprit atherosclerotic plaque minus the temperature of the proximal healthy vessel wall.

RESULTS

Under treatment with statins were 19 patients with recent MI and 14 with CSA. In patients with recent MI DeltaT was 0.19 +/- 0.18 degrees C, while in patients with CSA was 0.10 +/- 0.08 degrees C (P = .03). Patients treated with statins had lower DeltaT compared to untreated patients (0.10 +/- 0.11 versus 0.20 +/- 0.18 degrees C, P = .01). Treated patients with recent MI had similar DeltaT compared to CSA patients treated with statins (0.13 +/- 0.13 versus 0.07 +/- .06 degrees C, P = .14), while untreated patients with recent MI had substantially increased DeltaT compared to untreated patients with CSA (0.28 +/- 0.22 versus 0.14 +/- 0.10 degrees C, P = .04). DeltaT was positively correlated with CRP (R = 0.50, P < .01), IL-6 (R = 0.58, P < .01), and intercellular adhesion molecule-1 (R = 0.40, P = .03) levels.

CONCLUSION

Increased plaque temperature is observed for an extended period after myocardial infarction, indicating that the inflammatory process is sustained after plaque rupture. Statins have a beneficial effect after MI on plaque temperature.

Vulnerable plaque: the challenge to identify and treat it

In order to understand, treat, and prevent acute coronary syndromes we need to improve our ability to identify the rupture-prone, vulnerable atherosclerotic coronary plaque. The diagnostic modalities that are currently available to clinical practice have not fulfilled this expectation, and newer diagnostic techniques based on the recently identified features of the vulnerable plaque are quite promising. Coronary angiography, intravascular ultrasound, and angioscopy have been used in the clinical arena of interventional cardiology with several limitations regarding the identification of the vulnerable plaque. Thermography, optical coherence tomography, elastography, Raman spectroscopy, and infrared spectroscopy are used in clinical trials and the results are encouraging. Ultrafast computed tomography and magnetic resonance imaging have the advantage of being noninvasive. With our progress in the identification of the rupture-prone vulnerable coronary plaque, we will be able to identify patients that are at high risk and will benefit from a more aggressive therapeutic approach.

Thermography of the cardiovascular system

The identification of vulnerable plaque is one of the primary goals in cardiology during the last years. Several techniques have been developed for the anatomic and functional assessment of atherosclerotic plaques. Thermography is a new method for the evaluation of the inflammatory process locally within the atherosclerotic plaque. Several animal and clinical studies demonstrated the value of thermography not only for the detection of inflamed atherosclerotic plaques, but its use in new fields like in the evaluation of inflammation in the coronary vascular bed and the cardiovascular system. This article reviews the developments and the clinical implications of thermography.