1 ECG Monitoring Fundamentals
Learn how ECG electrodes create different electrical views, how to select and position monitoring equipment, what major waveform components represent, and how to respond to artifact or an abnormal monitor display.
Standard 12-lead electrode placement
A uses 10 electrodes to produce 12 leads, which are different electrical views. The number of leads does not indicate the number of electrodes.
Place the chest electrodes at these landmarks:
V1: fourth intercostal space at the right sternal border.
V2: fourth intercostal space at the left sternal border.
V4: fifth intercostal space at the left midclavicular line.
V3: midway between V2 and V4. Identify V4 before placing V3.
V5: left anterior axillary line, level with V4.
V6: left midaxillary line, level with V4 and V5.
Keep V4, V5, and V6 on the same horizontal level. Correct landmarks matter because misplaced electrodes can change the tracing and mislead interpretation. Do not move chest electrodes simply to avoid breast tissue; place them on the chest wall at the correct anatomical landmarks, following local protocol.
and ambulatory monitoring
is continuous bedside monitoring. Torso placement of limb electrodes can support movement and reduce motion-related , but it is a monitoring configuration—not a substitute for a diagnostic 12-lead ECG with standard electrode positions. When a diagnostic 12-lead is needed, use standard placement and facility procedure.
For intermittent palpitations that are not occurring during a clinic visit, an is often a better general match when symptoms may occur over a longer period. A records continuously over a shorter, defined period. The appropriate device and duration depend on how often symptoms occur and the clinician’s plan. Follow instructions for recording symptoms and returning or transmitting monitor data.
What ECG waveform components represent
The ECG records electrical activity, not the mechanical contraction itself. Its common components represent:
: atrial depolarization.
: ventricular depolarization. The ventricles contract shortly after this electrical activation.
: ventricular repolarization.
: the time from the start of atrial depolarization to the start of ventricular depolarization, including conduction through the AV node.
Recognizing and improving signal quality
can distort a waveform or resemble an abnormal rhythm. A slowly drifting baseline while the patient breathes may result from respiration or movement. Rapid, irregular noise may result from skeletal-muscle activity such as shivering or tremor.
Other common causes include loose or dried electrodes, poor skin contact, cable problems, and electrical interference. To improve a noisy signal, reattach or replace a partly detached electrode, prepare the skin and apply the electrode to clean, dry skin, and reduce movement or cable tugging where possible. Also check that cables and connections are secure and that each electrode is in its intended location. Follow device instructions and facility policy for skin preparation and electrode replacement.
Responding to an abnormal monitor display
Assess the patient immediately when a monitor displays a sudden chaotic rhythm, even if the patient appears alert and is speaking. Check responsiveness and pulse while also checking the monitor and electrode connections. A reassuring appearance does not by itself rule out a serious rhythm.
If the patient is stable and is suspected, correct the signal problem and obtain a clean tracing according to protocol. If the patient is unresponsive or pulseless, activate the emergency response and follow resuscitation protocol. Do not delay emergency care when the patient is unstable.