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Interpreting the electrocardiogram (ECG) is a key step in determining the heart's electrical axis.  The cardiac axis is the sum of all depolarization vectors of the heart, and vector analysis determines the direction of the net flow of current through the heart. Adequate knowledge and appropriate application of vector analysis are important for all clinicians because defining the electrical axis can provide insight into underlying disease states and help steer the differential diagnosis towards or away from certain diagnoses. This activity describes what makes up the electrical axis and the ventricular (QRS) axis classifications and reviews various approaches to determining the electrical axis and causes of axis deviation, empowering healthcare professionals with the necessary knowledge and tools to improve patient care when interpreting the ECG and employing vector analysis in various disease states. Additionally, the activity highlights the role of the healthcare team in correctly analyzing the ECG to provide optimal patient care. Objectives: Identify the key components of electrical axis deviation on an electrocardiogram. Differentiate between right-axis deviation and left-axis deviation based on electrocardiogram patterns. Apply knowledge of vector analysis to interpret electrocardiograms and determine the electrical axis. Communicate findings and collaborate with other interprofessional team members in managing axis deviation cases. Access free multiple choice questions on this topic.

One of the key steps in interpreting an electrocardiogram (ECG) is determining the heart's electrical axis or the sum of all depolarization vectors of the heart. The cardiac vector suggests the direction of the net flow of current through the heart.[1] Determining the electrical axis can provide insight into underlying disease states and help steer the differential diagnosis towards or away from certain diagnoses. Axis determination is also important to correctly identify certain life-threatening arrhythmias that have implications for definitive management strategy. A vector is illustrated using an arrow, with the arrowhead pointing towards the net direction of the current flow. The length of the arrow is proportional to the voltage. A normal cardiac vector typically runs from the base of the heart to the apex. Cardiac depolarization occurs from the endocardium to the epicardium; however, some current may also travel through the walls of the cardiac chambers to the epicardium. The sum of all vectors/potentials that run from the base to the apex at an instant is also called an instantaneous mean vector. Vector analysis is the basic concept of analyzing ECG. Adequate knowledge and application of vector analysis are important for all clinicians. Axis and vector are used interchangeably throughout this topic.

Determining the electrical axis on an electrocardiogram can narrow the differential diagnoses and lead to an efficient diagnostic approach, helping to decrease the time needed to arrive at the correct diagnosis and improve patient outcomes. An interprofessional team of clinicians, nurses, and technicians trained in interpreting an ECG is necessary to achieve this goal. An emergency department nurse trained in the potential implications of axis deviation can help clinicians provide prompt and prudent diagnostic and therapeutic care for the patient. A cardiac specialty-trained nurse can assist clinicians in monitoring patients with acute cardiac pathology to help treat potential complications. A nurse well-versed in interpreting an ECG, especially in determining the electrical axis and its significance, should communicate the findings to the clinicians. In doing so, a collaborative interprofessional team of healthcare providers can improve patient care and outcomes.