The ISAT trial: endovascular coiling superior to neurosurgical clipping in selected patients with aneurysmal subarachnoid hemorrhage [Classics Series]

This study summary is an excerpt from the book 2 Minute Medicine’s The Classics in Medicine: Summaries of the Landmark Trials

1. In patients with aneurysmal subarachnoid hemorrhage (SAH), endovascular coiling demonstrated significantly better survival compared to neurosurgical clipping.

2. Patients with ruptured posterior and middle cerebral artery were underrepresented in the cohort due to expert consensus for preferential endovascular coiling and neurosurgical clipping, respectively.

Original Date of Publication: October 2002

Study Rundown: Ruptured intracranial aneurysms are the most common cause of spontaneous SAH and are associated with significant morbidity and mortality. Historically, management options have included open neurosurgical clipping and endovascular therapy with detachable coiling. Choice of treatment was previously based on a combination of clinical judgement and the availability of technical expertise in endovascular therapy at referral centers. The purpose of the landmark International Subarachnoid Aneurysm Trial (ISAT) was to compare the safety and efficacy of endovascular coiling to neurosurgical clipping in patients deemed suitable for either treatment.

The ISAT trial randomized over 2000 patients with aneurysmal SAH to either neurosurgical clipping or endovascular coiling. At the conclusion of the trial, endovascular coiling demonstrated a 23% relative risk and 7% absolute risk reduction in significant disability or death compared to surgical clipping. The results of the ISAT trial thus favored endovascular clipping over surgical clipping in the treatment of ruptured intracranial aneurysm. However, extrapolation of these findings to all patients and aneurysm types was limited by the narrow scope of the ISAT population. During the enrollment phase of the trial, 80% of patients screened were excluded for not meeting the requirement for their aneurysm to be judged as equally amenable to neurosurgical or endovascular therapy. Over 80% of the included patients had aneurysms in the anterior cerebral or internal carotid artery. Posterior circulation and middle cerebral artery aneurysms were underrepresented due to expert consensus for preferential endovascular coiling and neurosurgical clipping, respectively; thus the results of ISAT were not applicable to these patient populations.

Click to read the study in the Lancet

In-Depth [randomized controlled trial]: The ISAT trial was an open-labeled, multicenter randomized controlled trial that compared the efficacy and safety of endovascular coiling to neurosurgical clipping in patients with SAH secondary to a ruptured intracranial aneurysm. Patients were screened in all participating centers if they had imaging-confirmed SAH and intracranial aneurysm. Patients were evaluated by both a neurosurgeon and an interventional radiologist and were included if the target lesion was felt to equally amenable to either endovascular coiling or neurosurgical clipping. The primary end-point was overall disability or survival at 2 months and 1 year, as measured by the modified Rankin scale. Secondary outcomes included rates of hospital admission or episodes of re-bleeding. The trial was stopped after the planned interim analysis at 1 year. Overall, 2143 patients out of 9559 screened met the inclusion/exclusion criteria and were randomized. There were no significant differences in baseline characteristics between the group randomized to endovascular treatment (n = 1073) and neurosurgery (n = 1070). However, 83% of patients had aneurysms in the anterior cerebral or internal carotid arteries. Patients with posterior circulation and middle cerebral artery aneurysms represented only 2.7% and 14.1% of patients, respectively. At the conclusion of the trial, patients randomized to endovascular coiling demonstrated significantly lower rates of disability or death at 1 year compared to surgical clipping (23.7% versus 30.6%; p = 0.019). Patients in the endovascular group had a relative- and absolute risk reduction of disability or death of 22.6% (95%CI 8.9% to 34.2%) and 6.9% (2.5% to 11.3%), respectively. The risk of re-bleeding after 1 year was 2 per 1276 patients in the endovascular group and 0 per 1081 patients in the neurosurgery group.

Molyneux A. International Subarachnoid Aneurysm Trial (ISAT) of neurosurgical clipping versus endovascular coiling in 2143 patients with ruptured intracranial aneurysms: a randomised trial. The Lancet. 2002 Oct 26;360(9342):1267–74.

©2022 2 Minute Medicine, Inc. All rights reserved. No works may be reproduced without expressed written consent from 2 Minute Medicine, Inc. Inquire about licensing here. No article should be construed as medical advice and is not intended as such by the authors or by 2 Minute Medicine, Inc