Key Points
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Conventional electrophysiology cryoablation catheters do not cause significant damage to coronary vessels, although direct epicardial applications can potentially result in intimal hyperplasia.
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Coronary spasm can be caused by cryoapplication in the vicinity of the vessel and was reported clinically.
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Large surgical probes, applied directly to the artery, may result in significant damage of the vessel wall, leading to severe hyperplasia and potentially even to complete vessel occlusion chronically.
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No acute thrombosis or myocardial infarction has been observed or reported with direct cryoapplication to the artery, even with large, powerful surgical probes.
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Coronary sinus and superior vena cava remain patent after direct cryoapplication.
Cryoablation effects on the arteries are dependant on the extent and depth of cryolesion into arterial walls. In cases where conventional transvenous cryocatheters (−80°C) are placed adjacent to the artery, usually no major damage or occlusion of the artery could be found. Coronary spasm, however, was reported clinically with ablation of the typical flutter isthmus area ( Figure 6–1 ). No thrombosis of the arteries has been demonstrated, however, when −80°C freezing with conventional size catheters is applied next to the artery.
In an elegant work, Aoyama et al demonstrated that freezing applications with transvenous cryocatheter next to circumflex artery does not cause coronary stenosis ( Figure 6–2 ). Fast blood flow in the coronary artery stops penetration of cryolesion to deeper levels and protects intima from extensive freezing, or at least minimizes area of intima subjected to lethal temperatures. Because of the small area affected, arterial stenosis is an unlikely consequence; however, at least intimal hyperplasia was reported. Although this applies to currently available conventional transvenous catheters, more powerful cryoprobes, able to freeze coronary arteries transmurally, can cause significant damage to the artery.
Intimal hyperplasia is a primary and nonspecific vessel response to the injury and is frequently observed after cryoinjury to coronary arteries. Intimal hyperplasia can also develop in some cases where lesions have been applied epicardially, even with conventional EP catheters. More powerful surgical cryoprobes that produce larger and deeper lesions can overcome vessel blood flow and result in complete and temporary interruption of the blood flow.
We have evaluated effects of cryoablation on coronary arteries with liquid nitrogen–based cryoprobes in experimental settings. Lesions have been placed on left anterior descending (LAD) and diagonal branches. In cases of cryoablation of LAD arteries, typical electrocardiographic changes, reflecting acute injury, can be observed after freezing the LAD artery with immediate resolution of ischemia after thawing of cryolesion ( Figure 6–3 ).
In our experimental series, we subjected dog LAD or D1 to complete freezing for 2 minutes. We then observed the animals for up to 1 year. No acute occlusions or myocardial infarctions were observed in any animals. After 3 days, hypocellular media could be seen, with preserved elastic membrane and no visible endothelium ( Figure 6–4 ).
