Reperfusion therapy, within which we include thrombolytic therapy and percutaneous coronary intervention (PCI), which includes angioplasty and stent placement, is the greatest advance in the treatment of acute myocardial infarction (AMI) since the advent of defibrillation and the establishment of Cardiac Care Units (CCU’s). The decision to administer a thrombolytic agent or call an interventional cardiologist is a difficult decision that becomes more complex as new research increases our knowledge base and multiplies our options. Despite great technological advances in other diagnostic fields and therapeutic procedures, the 12-lead electrocardiogram (ECG) remains the basis for the diagnosis and timely reperfusion of ST elevation AMI (STEMI). Consequently, advances in the recognition of candidates who may benefit from reperfusion therapy have been made primarily through increased sophistication in ECG interpretation.

Immediate reperfusion therapy is indicated primarily for ST elevation, with two well-defined and thoroughly discussed exceptions: 1) anterior ST depression indicative of posterior AMI; and 2) hyperacute T-waves. Because immediate PCI may be indicated for some cases of unstable angina and non ST Elevation AMI (UA/NSTEMI), we include a more limited discussion of these entities and their ECG findings. The diagnosis and management of UA/NSTEMI that presents with a nondiagnostic ECG is beyond the scope of this book.

Studies have shown that many patients with AMI who are eligible for reperfusion therapy do not receive it. Moreover, of those who do receive it, the time to administration of thrombolytic therapy, or "door-to-needle time" (DTNT) is often delayed, jeopardizing myocardium and leading to greater morbidity and mortality. Lack of physician confidence in ECG diagnosis and in analysis of risks versus benefits of thrombolytic therapy has been shown to be a significant contributing factor in these delays. The focus of this book is therefore on ECG interpretation and how this may be used to accurately diagnose AMI and to facilitate appropriate and timely therapy. Although we discuss fundamental concepts and developments in the field of reperfusion therapy, and we include brief chapters on choice of reperfusion therapy, adjunctive therapy, and therapy of UA/NSTEMI, we leave therapeutic details to other sources. In this way, we hope to offer you maximal coverage of sophisticated ECG interpretation and minimal obsolescence of therapeutic data.

Increased sophistication of ECG interpretation means that it is no longer adequate to simply recognize a massive anterior AMI and admit the patient to the CCU. It is no longer acceptable to recognize ST segment elevation as the sole diagnostic criterion for AMI and for thrombolytic administration. Many patients have ST elevation without AMI, as a result of baseline electrocardiographic conditions such as early repolarization, left ventricular hypertrophy (LVH), left bundle branch block (LBBB), ventricular aneurysm, and pericarditis. How do we recognize the look-alikes, or pseudoinfarctions, so that we can, to the best of our abilities, avoid administering thrombolytics to a patient who is not having an AMI? In contrast, many patients with AMI have subtle, nondiagnostic, or atypical ECG’s, including borderline ST elevation, lateral AMI, posterior AMI, or AMI hidden in LVH or Bundle Branch Block. How can we identify them? Furthermore, how can we recognize those patients who are having an AMI but for whom thrombolytic therapy is dangerous, as in cases of myocardial rupture? How do we use data from the ECG to evaluate the risk/benefit ratio of the administration of thrombolytics, particularly in patients for whom there are relative contraindications? The key to accurate and timely answers lies in our ability to interpret the ECG, and especially the subtle ECG’s that are the primary focus of this manual.

Accurate ECG interpretation is dependent on factual knowledge and a familiarity with ECG morphology, or pattern recognition. The purpose of this book is to provide you with the tools to quickly and accurately recognize ECG morphologies and make appropriate therapeutic decisions. In Parts I through III, we provide guidelines for the recognition of various ECG morphologies of ischemia, infarction, and pseudoinfarction and we illustrate diagnostic criteria with numerous ECGs, often several different examples of a given condition. Throughout the book, we focus on the difficult ECG, with many examples of both subtle infarction and pseudoinfarction. We give a brief and pertinent case history for each ECG so that it may be interpreted in clinical context and we highlight the important clinical considerations for each case as it relates to the reperfusion decision. In Part IV, we discuss pseudoinfarction patterns; in Part V we cover other important issues in the ECG diagnosis of AMI, and in Part VI we briefly cover therapeutics, including reperfusion treatment options, adjunctive therapy, and UA/NSTEMI.

This manual is written as a reference for quick use in a critical clinical situation, as well as a reference for more detailed study. Most importantly, the book contains repetition of important points, not only for reinforcement, but also so that any one section contains at least the essential information needed to manage your patient, avoiding the need to frequently flip pages back and forth. Chapters are easy to find. Key points are listed at the beginning of each chapter. Indexing and cross-referencing are used throughout so that you may locate information topically. Common abbreviations are used and defined in "Abbreviations," with many less common terms defined in the Glossary. Citations in the text that are annotated in that chapter are cited in boldface. The second part of each chapter consists of cases and their corresponding ECG’s. Each ECG is coded with an "ECG Type" (see Chapter 2) which corresponds to the indication for reperfusion therapy. The manual is designed to stay open when laid on a surface, so that you may flip through and easily compare your ECG with those in the book. An annotated bibliography is written in smaller type at the end of most sections.

This manual is also designed for more leisurely and detailed study in order to master fundamentals and fine-tune ECG interpretation. We begin with cross-sectional and external MRI photos of the heart to illustrate the anatomy and reciprocity of ECG leads, so that you will be better able to understand and quickly interpret ECGs spatially and logically, rather than simply by rote memorization. We discuss key points in greater detail and with reference to relevant research in an annotated bibliography at the end of most sections, with the exception of some chapters that do not directly relate to the clinical interpretation of the ECG. Important clinical trials of thrombolytics are described in detail in the Appendix so that the role of the ECG can be better understood in the context of the development of reperfusion therapy.

Our purpose is to provide a conceptual framework for interpreting ECG’s in the context of the reperfusion decision. We offer little theoretical discussion or electrophysiologic explication and we assume that the reader has a clinician’s basic working understanding of electrocardiograms and terminology. We expect that expert electrocardiographers may find some points oversimplified, lacking discussion of exceptions and of electrophysiology, but our purpose is to keep discussion brief and focussed on essentials of ECG interpretation in the context of the reperfusion decision. For more detailed and theoretical considerations, we refer you to an excellent text (1).

Lastly, it must be remembered that the ECG, albeit powerful, is only a test, with false positives and false negatives, and must be interpreted in the clinical context (i.e., the pretest probability). ECG’s are variable from patient to patient and concepts must be adapted to individuals. ST segments may rise early in one patient with occluded coronary arteries and later in another patient with apparently identical pathology. ST segments usually decrease quickly in TIMI grade 3 early reperfusion, but not always and sometimes not at all; T-waves invert after AMI of all kinds, sometimes deeply, and sometimes not. Any one patient may not conform to the concepts presented and must be approached individually by a prepared mind.

This manual is for all clinicians who treat patients with acute chest pain, and thus may have to recognize and treat an AMI. Thus, this book is for emergency physicians, cardiologists, intensivists, hospitalists, internists, family practitioners, and physician assistants as well as residents and medical students. It is also meant for nurses in the Cardiac Care Unit or the Emergency Department. It will be useful for both study and on-the-job reference.

This book is really for all of our patients who may be suffering from AMI. We hope that it will improve their care.