Local hyperthermia enhances thrombosis in aneurysms containing platinum coils

Abstract

Despite recent technical advances in embolization of cerebral aneurysms with platinum coils, some aneurysms eventually resulted in incomplete packing with remnant neck or dome filling. Such a situation with a remaining inflow zone may pose a risk of rupture and subsequent regrowth. Metals characteristically generate heat under high-frequency alternating magnetic fields (AMF). We used this property to induce local hyperthermia and promote thrombogenesis in incompletely packed aneurysms. Glass model aneurysms packed with coils were subjected to AMF to investigate the correlation between weight of platinum and temperature elevation and the correlation between flow rates of water through the model and temperature elevation. Next, activated coagulation time (ACT) of blood obtained from dogs was studied at various temperatures. Finally, side-wall aneurysms created in the canine carotid artery using a venous patch were packed with platinum coils. Change in temperature and angiographic changes were investigated after AMF application. In the glass model, the weight of platinum was correlated with elevation of temperature, and a negative logarithmic correlation was evident between flow rate and elevation of temperature. Elevation of blood sample temperature tended to shorten ACT. In canine carotid aneurysms, elevation of intra-aneurysmal temperature was confirmed and sufficient elevation of temperature was found to promote angiographically evident thrombogenesis of the remnant space after AMF application. Local hyperthermia may be useful in completing luminal obliteration of aneurysms after coil embolization. It may particularly useful for ruptured aneurysms to prevent the early rerupture.

Figure 1

Side-wall aneurysm created using a venous patch in the carotid artery of a dog. A microtube was inserted into this aneurysm, through the tube, an optical fiber probe was placed in the aneurysm to measure temperature.

Figure 2

Correlation between weight of platinum and elevation of temperature in a glass model aneurysm. Circulation flow rate was 180 ml/min, and exposure to magnetic fields was for 10 min.

Figure 3

Correlation between flow rate and elevation of temperature in glass models. Closed circles, squares, triangles, open circles indicate data for weights of platinum of 0.880 g, 0.440 g, 0.240 g, 0.055 g, respectively.

Figure 4

Correlation between blood temperature in vitro and activated coagulation time (ACT).

Figure 5

Correlation between weight of platinum and elevation of temperature in canine carotid aneurysms. Exposure to magnetic fields was for 10 min. Temperature of surrounding tissue was measured simultaneously. Open circles indicate temperature of canine carotid aneurysms, closed circles indicate temperature of surrounding tissue.

Figure 6

Angiograms of experimental aneurysm 9. A) Before exposure to magnetic field. Contrast medium enters the aneurysm (arrow). B) Immediately after exposure. Contrast medium does not enter into the aneurysm (arrow), suggesting promotion of thrombogenesis.

Figure 7

Angiograms of experimental aneurysm 3. A) Before exposure to magnetic field. The aneurysm was partially occluded. B) Immediately after exposure, showing no further change.

Figure 8

Difference in elevation of temperature between aneurysms with successful thrombogenesis and failure despite magnetic field exposure. Elevation of temperature in the effective group (4.53 ± 0.46°C) was significantly higher (*p<0.05) than in the group with failure (2.00±1.25°C).