The ECG in Prehospital Emergency Care

William J. Brady, Korin B. Hudson, Robin Naples, Amita Sudhir, Steven H. Mitchell, Robert C. Reiser, Jeffrey D. Ferguson, William J. Brady, Korin Hudson, Robin Naples, Amita Sudhir, Steven Mitchell, Robert P. Reiser, Jeffrey Ferguson

• Publisher: Wiley-Blackwell
• Year: 2012
• ISBN:
  9781118473733
• Edition: 1
• Topic: Medicine
• Subtopic: Emergency Medicine & Critical Care

Now that state of the art equipment can be carried in ambulances, prehospital emergency staff are able toperform an ECGsoon afterarrivalon scene, enabling the EMS provider to gather important diagnostic information that can not only guide prehospital therapy but also direct hospital-based treatment.

This book exclusively addresses ECGs for prehospital emergencies, ranging from basic rhythm diagnosis to critical care applications of the electrocardiogram and advanced 12-lead ECG interpretation in the ACS patient. It provides self testing traces covering all these conditions seen in prehospital and hospital- based environments. It includes 200 randomly presented cases mirroring real life situations, with the answers set out separately together with additional invaluable information.

Written by highly experienced emergency physicians with EMS qualifications and experience, this textis an ideal learning tool for trainees and fully qualified staff alike, including ground EMS advanced life support providers, aeromedical staff, and inter-facility critical care transport personnel.

Section 1

The ECG in Prehospital Patient Care

Chapter 1

Clinical Applications of the Electrocardiogram (ECG)

Robert C. Schutt¹, William J. Brady², and Steven H. Mitchell³

¹Department of Medicine, University of Virginia School of Medicine, Charlottesville, USA

²Departments of Emergency Medicine and Medicine, University of Virginia School of Medicine, Charlottesville, USA

³Emergency Services, Harborview Medical Center, University of Washington School of Medicine, Seattle, USA

The electrocardiogram (ECG) has become a mainstay of medical care since Einthoven first introduced the concept of electrical imaging of the heart in 1903. He named the five electrical deflections of an “electrical heart beat” with the now well-known descriptors—P, Q, R, S, and T (Figure 1.1). Accurate interpretation of the ECG has become a necessary skill for every clinician who cares for acutely ill patients. The ECG is a non-invasive, inexpensive, easily performed test that allows a clinician to view the electrical activity in the heart. The ECG provides information not only about a patient's heart rhythm, but also about both cardiac (e.g., acute coronary syndrome [ACS] or myopericarditis) and non-cardiac conditions (e.g., electrolyte disorders, toxic ingestions, and pulmonary embolism).

Figure 1.1 The PQRST complex—a single “electrical heart beat.”

Electrocardiogram Evaluation of Rhythm Disturbances

The rapid and accurate detection of ventricular fibrillation leading to sudden cardiac death has led to the development of prehospital emergency medical service (EMS) systems worldwide since the late 1960s. The use of ECG monitoring has grown from this early important step to become a mainstay of patient evaluation, not only for cardiac arrest but also for many other conditions. The ECG is the primary tool for evaluating the underlying rhythm of the heart. The ability to evaluate the heart rhythm is critical as cardiac dysrhythmias often are symptomatic and require immediate treatment. However, even if the dysrhythmia is not symptomatic, treatment may still be required to prevent future complications. Atrial fibrillation is a good example of a cardiac dysrhythmia easily identified on ECG, where symptoms may be completely absent or may be severe requiring immediate intervention. Depending on the rate (either fast or slow), the patient's symptoms may range from a benign fluttering in the chest to more serious symptoms of fatigue, chest pain, or syncope. Figure 1.2 is an example of atrial fibrillation with rapid ventricular response. A patient who experiences heart block may be symptom free or at risk for syncope or cardiac arrest with a high-degree atrioventricular (AV) block, as seen in Figure 1.3. Even when a patient is stable and without active symptoms, the ECG may provide clues that a patient is at risk for a potentially malignant rhythm. The patient depicted in Figure 1.4 is an example of long QT syndrome complicated by malignant ventricular dysrhythmia. The recognition of a prolonged QT interval is critical as patients with this electrocardiographic finding are at higher risk for dysrhythmia and sudden cardiac death (Figure 1.4).

Figure 1.2 Atrial fibrillation with rapid ventricular response; note the “irregularly irregular” rhythm.

Figure 1.3 Third-degree AV block demonstrating no relationship between P wave (small arrow) and QRS complex (large arrow). This ECG nicely demonstrates the intrinsic ventricular rate of 20–40 beats per minute and sinus rate of 60–80 beats per minute.

Figure 1.4 Brief episode of torsades de pointes in a patient with a QTc interval of 579 ms.

One of the most important parts of prehospital medicine is the recognition and treatment of life-threatening dysrhythmias. For prehospital rhythm interpretation, the use of the ECG in a single- or multilead analysis mode is the most appropriate. For strict rhythm only analysis, the 12-lead ECG offers little additional information.

Electrocardiograhic Evaluation in the Setting of Acute Coronary Syndrome

The ECG is also an important tool in evaluating the patient with a suspected ACS. The 12-lead ECG can not only provide important information regarding the ACS diagnosis but also guides therapy and predicts risk, and can suggest alternative diagnoses. The use of the 12-lead ECG in “diagnostic mode” is the most appropriate electrocardiographic tool; the use of single-lead rhythm monitoring is not of value with regard to ACS detection—yet single-lead monitoring is of extreme importance in the detection of cardiac rhythms, which can complicate ACS events (Figure 1.5).

Figure 1.5 In rhythm mode, ECG monitoring devices attempt to reduce artifact, enabling a more accurate rhythm evaluation. This artifact dampening effect can lead to distortion of the ST segment, producing ST segment changes which are, in fact, not present in diagnostic (or 12-lead ECG) mode. Shown here is a lead II tracing in a patient in diagnostic mode (a) and non-diagnostic rhythm mode (b). Note the appearance of ST segment elevation in rhythm mode, which is not present in the diagnostic mode.

In patients with ST segment elevation myocardial infarction (STEMI), the ECG not only provides the specific diagnosis but is also the primary means for determining a patient's need for emergent reperfusion of the obstructed coronary artery; refer to Figure 1.6, which demonstrates an ECG of a patient with an inferior wall STEMI. It has been shown in numerous studies that the prehospital 12-lead ECG markedly reduces the time to hospital-based reperfusion (fibrinolysis and percutaneous coronary intervention) in patients with STEMI. In non-ST segment elevation myocardial infarction (NSTEMI) the ECG is also valuable. The ECG can display evidence of ongoing cardiac injury with T wave inversion or ST segment depression. The ECG can also help localize the obstructed coronary artery; for example, Wellens' Syndrome has a characteristic ECG pattern with changes to the T wave in the precordial leads, predominantly leads V2–V4, which can indicate a high-degree obstruction of the proximal left anterior descending coronary artery.

Figure 1.6 Acute inferior and lateral wall ST segment elevation myocardial infarction (STEMI).

Electrocardiograhic Evaluation in the Setting of Non–Acute Coronary Syndrome Pathology

The ECG is also a useful tool in the evaluation of non-coronary artery pathology that manifests with changes to the ECG. Refer to Table 1.1 for a list of selected diseases not related to coronary obstruction that may have significant abnormalities evident on the ECG. Pericarditis (inflammation of the pericardial sac) leads to a diffuse pattern of PR segment depression and ST segment elevation that can be differentiated from STEMI as the elevation is present in a pattern not anatomically related to a coronary artery distribution. At the same time, the diagnosis of pericarditis can be difficult, and the patient may present with chest pain and ST segment elevation, potentially leading to the incorrect diagnosis of STEMI. Pericardial effusion with ultimate cardiac tamponade is caused by fluid in the pericardium that can accumulate owing to a variety of causes including recent viral infection or cancer. On the ECG, this condition leads to sinus tachycardia and low QRS complex voltage. Electrical alternans is also seen in this setting and is characterized by beat-to-beat alterations in the QRS complex size, reflecting the swinging motion of the heart in the pericardial fluid.

Table 1.1 Selected examples of non-coronary pathology evaluated by ECG

Pericarditis Diffuse non-anatomical ST segment elevation without reciprocal changes Diffuse PR segment depression Isolated ST segment depression and PR elevation in aVR

Pericardial tamponade Electrical alternans Low QRS complex voltage Diffuse PR segment depression

Hypothermia Osborn “J” waves Bradycardias and AV blocks Prolongation/widening of PR interval, QRS complex, and QT interval Atrial fibrillation with slow ventricular response

Hyperkalemia Diffuse non-anatomical peaked T waves Widening of PR interval and QRS complex widths

CNS events Diffuse, deep T wave inversions Minor ST segment elevations in leads with T wave inversions

Overdose and intoxication Rhythm disturbances Widened QRS complex Prolonged QT interval

There are also a host of conditions that are not primarily related to the heart where the ECG may provide a clue to diagnosis. Pulmonary embolism can present with the classic “S1Q3T3” on the ECG (Figure 1.7). Osborn waves are positive deflections occurring at the junction between the QRS complex and the ST segment that are typically observed in patients suffering from hypothermia with a temperature of less than 32°F. Several electrolyte disturbances exhibit characteristic changes to the ECG. Hyperkalemia first results in peaked T waves most apparent in the precordial leads. If the condition is untreated, however, the ECG may progress to widening of the QRS complex and the eventual fusing of the QRS complex and the T wave, resulting in a sine wave configuration and ultimately cardiac arrest. Central nervous system (CNS) events such as intraparenchymal hemorrhage, ischemic stroke, and mass lesion may also present with changes in the ECG, largely involving the T wave with inversion and prolongation of the QT interval.

Figure 1.7 S1Q3T3 pattern in a young patient with bilateral pulmonary embolism. The S wave in lead I is indicated by the long arrow, the Q wave in lead III (medium arrow), and the inverted T wave in lead III (small arrow).

Chapte...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• List of Contributors
• Foreword
• Preface
• Section 1: The ECG in Prehospital Patient Care
• Section 2: Cardiac Rhythms and Cardiac Dysrhythmias
• Section 3: Acute Coronary Syndrome and the 12-Lead ECG
• Section 4: Special Populations, High-Risk Presentation Scenarios, and Advanced Electrocardiographic Techniques
• Section 5: Electrocardiographic Differential Diagnosis of Common ECG Presentations
• Index