The impact of the electrocardiogram (ECG) on clinical care is wide ranging and significant. The ECG is a primary tool for evaluating the unstable patient and a useful tool in the assessment of the stable patient. The ECG aids in clinical decision making for patients experiencing primary cardiac pathology. This includes conduction disturbances, acute coronary syndrome (ACS), and also such non‐cardiac pathology as pulmonary embolism (PE), metabolic disarray, and poisoning or overdose. The use of the ECG is widespread and requires every clinician to work toward competence in the efficient and accurate use and evaluation of the ECG.

Management of the Patient with Dysrhythmia

From its inception, rudimentary ECGs have been used to diagnose and treat rhythm disturbances. There are now well‐established treatment algorithms for both prehospital and in hospital treatment of life‐threatening cardiac dysrhythmias, and the ECG findings are paramount in these algorithms. The rapid diagnosis and management of life‐threatening dysrhythmias is often based on the interpretation of the single‐lead ECG (also called a rhythm strip).

A significant impact of the ECG and an area of continued research is in the treatment of sudden cardiac death. Symptomatic dysrhythmias may occur both outside the hospital and in patients who are under inpatient care. Sudden cardiac death is a commonly encountered extreme example of symptomatic dysrhythmia in which the ECG plays a pivotal role in assessment and management. Non‐cardiac arrest rhythms are also frequently identified, especially in hospitalized patients. These rhythm possibilities range from bradycardia to tachycardia, with and without conduction block. Clearly, the single‐lead ECG enables the clinician to diagnose the rhythm and initiate the most appropriate care based on the ECG information as well as the patient’s clinical situation.

Management of the Patient with Acute Coronary Syndrome

Beyond the recognition and treatment of cardiac rhythm disturbances, the ECG has impacted the care of patients with ACS with both the single‐ and the 12‐lead ECG. The 12‐lead ECG (as opposed to laboratory evaluation with a cardiac enzyme assay such as troponin) is the primary tool for identifying patients with ST segment elevation myocardial infarction (STEMI). In STEMI, the ECG rapidly identifies patients who are in emergent need of revascularization. The ECG is used in both the prehospital and in hospital environments to detect STEMI and has been shown to favorably impact the time to revascularization. Also, when used in the out of hospital setting, including clinics, urgent cares and Emergency Medical Services (EMS), the ECG may detect ischemic changes that resolve before the patient arrives at the emergency department and provides a valuable snapshot of an ischemic event. The benefits of out of hospital ECG are realized with little increase in time to transport, even in the emergency setting. Furthermore, many EMS systems have the capability to transmit the 12‐lead ECG for “real‐time” interpretation by a physician. This allows for rapid consultation with an EP and/or cardiologist who can make transport and treatment decisions including planning for reperfusion strategies even before the patient arrives to the hospital.

The interpretation of the 12‐lead ECG, however, is a skill that requires advanced training and practice in order to assure proficiency. Inaccurate interpretation of the ECG has been shown to impact the care of patients with ACS. In particular, clinicians must be particularly aware of ominous changes of the ST segment and the T wave. Inaccurate interpretation of the ECG, including the lack of recognition of ST segment and T wave abnormalities can have grave consequences for the patients and potentially expose them to inappropriate and dangerous therapies. A significant limitation of the 12‐lead ECG in the evaluation of the ACS patient is that it has rather poor sensitivity (i.e. often falsely negative) for the diagnosis of myocardial infarction. The ECG initially suggests acute infarction in only 50% of patients ultimately found to have an acute myocardial infarction.

Single‐lead ECG monitoring is also of significant importance in the ACS patient – not aimed at the detection of ST segment and T wave abnormalities associated with ACS but rather for the detection of complicating rhythm disturbances, such as sinus bradycardia, complete heart block, and ventricular fibrillation.