1 Introduction to Evidence-Based Medicine

In response to the growing demands of more evidence-based medicine in the management of cerebrovascular disorders, the American Heart Association (AHA) in conjunction with the American Stroke Association (ASA) has published guidelines on various clinical topics. The purpose of these guidelines is to provide an up-to-date comprehensive set of recommendations for clinicians providing care for patients with cerebrovascular diseases. These guidelines are derived from review of the literature by independent evidence review committees or writing groups comprising topic experts. The AHA/ASA also provides updates of new evidence through focused updates and scientific statements. The clinical topics reviewed range from indications for performing intracranial endovascular neurointerventional procedures to management of acute ischemic stroke and management of aneurysmal subarachnoid hemorrhage. ^{1 , 2 , 3 , 4 , 5 , 6 , 7}

The recommendation classification system of the AHA/ASA guidelines is adapted from that of the American College of Cardiology (ACC)/AHA clinical practice guidelines developed by the Task Force. ⁸ The classification system (Fig. 1.1 and Fig. 1.2) comprise class of recommendation (COR) and level of evidence (LOE). COR is a statement concerning the strength of the recommendation and often serves as the primary guide for clinicians. The choice of COR is dependent upon the effect size or strength, and magnitude of benefit in relation to risk for clinical strategies, interventions, treatments, or diagnostic testing in patient care. The certainty or precision of information in support of the recommendation is described by the LOE, classified by the type and quality of the evidence.

Class I and III recommendations are considered strong recommendations, based on effect size or strength, and benefit-to-risk es/timates. An intervention is considered a Class I recommendation when its benefits greatly outweigh its risks (benefit >>> risk). The suggested phrases for writing recommendations for Class I recommendation include: should; is recommended; is indicated; and is useful/effective/benefi-cial. Comparative effectiveness phrases for Class I recommendation include: treatment/strategy A is recommended/ indicated in preference to treatment B; and treatment A should be chosen over treatment B. The list of suggested phrases to use when writing recommendations was developed in 2003 by the ACC/AHA Task Force on practice guidelines. It is written such that a recommendation, if separated or presented apart from the rest of the document, would still convey the full intent of the recommendation.

Class III recommendation is further classified into Class III: No Benefit and Class III: Harm. Class III: Harm is a strong recommendation in which the intervention is harmful to patients or incur excessive cost without benefit (benefit < risk). This is usually derived from one or more trials in which the outcomes for intervention were worse compared to that of the control. An intervention is considered a Class III: No Benefit recommendation when evidence suggests that it is no better than the control (benefit = risk). However, it must be noted that such a recommendation is not to be associated with weak evidence of expert opinion (LOE C-LD, C-EO, or C) as randomized trials or carefully conducted observational studies are often required to ascertain lack of benefit. ⁸ The suggested phrases for writing recommendations for Class III: Harm recommendation include: potentially harmful; causes harm; associated with excessive morbidity/mortality; and should not be performed/administered. The suggested phrases for writing recommendations for Class III: No Benefit recommendation include: is not recommended; is not indicated; should not be performed/administered; and is not useful/beneficial/effective.

Class Ila recommendations are considered intermediate strength recommendations and carry less benefit in comparison to Class I recommendations (benefit >> risk). Suitable phrases for writing recommendations for Class Ila recommendation include: is reasonable; can be useful/effective/ beneficial; and is probably recommended or indicated. Comparative effectiveness phrases for Class Ila recommendation include: treatment/strategy A is probably recommended/ indicated in preference to treatment B and it is reasonable to choose treatment A over treatment B. Class lib recommendations are considered to be the weakest among the recommendations and pertain to interventions associated with marginal benefit-to-risk ratios or uncertain outcome advantages (benefitsrisk). Hence, additional evidence or studies are necessary to clarify the benefits or risks of the intervention. Suitable phrases for writing recommendations for Class lib recommendation include: may/might be considered; may/might be reasonable; and usefulness/effectiveness is unknown/unclear/uncertain or not well established.

The precision and quality of the scientific evidence in support of the effect or strength of an intervention is rated by the LOE based upon the type, quantity, consistency, and quality of clinical trials and other relevant sources. The evidence in support of each recommendation is graded based on study type, which may comprise randomized, observational, prospective, or retrospective studies. In addition, the quality of evidence is assessed for potential bias, relevance, and fidelity. In the 2015 update to the COR and LOE classification system (Fig. 1.2), the Task Force has provided additional categories offering greater granularity via distinct categories for randomized and nonrandomized evidence to better define the level and quality of evidence using a graded approach to evidence assessment.

Level A comprises evaluation of multiple populations, with high-quality evidence from more than one randomized controlled trial (RCT), meta-analyses of high-quality RCTs, or one or more RCTs corroborated by high-quality registry studies. Level B comprises limited population evaluation, where data is derived from a single RCT or nonrandomized studies. In the updated 2015 COR and LOE classification system (Fig. 1.2), Level B is further categorized into Level B-R (Randomized) and Level B-NR (Nonrandomized). Level B-R comprises moderate-quality evidence from one or more RCTs or meta-analyses of moderate-quality RCTs. Level B-NR comprises moderate-quality evidence from one or more well-designed, well-executed nonrandomized studies, observational studies, registry studies, or meta-analyses of such studies.

Very limited population evaluation is designated Level C, comprising consensus opinion of experts, case studies, or standard of care. In the updated 2015 COR and LOE classification system (Fig. 1.2), Level C is further categorized into Level C-LD (Limited Data) and Level C-EO (Expert Opinion). Level C-LD comprises randomized or nonrandomized observational or registry studies with limitations of design or execution, meta-analyses of randomized or nonrandomized observational or registry studies with limitations of design or execution, or physiological or mechanistic studies in human subjects. Level C-EO comprises consensus of expert opinion based on clinical experience. It is important to note that a recommendation with LOE C does not imply that the recommendation is weak as many important clinical questions in guidelines do not lend themselves to clinical trials (e.g., due to ethical concerns). Therefore, there may be a very clear clinical consensus that a particular intervention is useful or effective, despite the lack of RCTs.

To lead rather than lag behind clinical practice remains the ongoing challenge for these guidelines, focused updates, and scientific statements. These guidelines strive to maintain rigorous processes and methodology, while at the same time respond to the continually expanding literature in a timely manner. Similarly, the contents and recommendations provided within this book reflect the most up-to-date evidence that was rigorously evaluated at the time of writing. The scope of this book includes recommendations regarding endovascular treatment of cerebrovascular diseases beyond the previous guidelines set forth by the AHA/ASA.

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Section I Hemorrhagic Stroke 8 Unruptured Cerebral Arteriovenous Malformations 10 Dural Arteriovenous Fistulas 16 Carotid Dissection 22 Intra-arterial Chemotherapy 30 Spinal Dural Arteriovenous Fistulas and Malformations

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