How to Do an EKG on a Patient: A Step-by-Step Procedure

Recording a 12-lead electrocardiogram (commonly called an EKG or ECG) is one of the most frequently performed clinical procedures, yet small errors in preparation and electrode placement can distort the tracing enough to mimic or mask serious heart conditions. The process itself takes only a few minutes once you know the steps, but the quality of the recording depends almost entirely on how carefully you prepare the patient’s skin, position the electrodes, and manage common sources of interference. What follows is the full procedure from patient encounter to finished tracing, along with the practical pitfalls that textbooks tend to gloss over.

Gather Your Equipment First

Before approaching the patient, have everything within arm’s reach. You will need the EKG machine itself (with a charged battery or plugged-in power cable), a full set of ten electrodes (four limb, six precordial), fresh adhesive electrode pads (sometimes called “stickers” or pre-gelled electrodes), alcohol prep pads or skin-prep wipes, a disposable razor, dry gauze or a towel, and a privacy sheet or gown. If your facility uses reusable suction-cup chest electrodes rather than disposable adhesive pads, you will also need conductive gel.

Modern machines have shrunk dramatically from the early days of electrocardiography. The original string galvanometer that Willem Einthoven developed required about five operators and weighed roughly 300 kilograms; today’s portable units weigh around one kilogram and are operated by a single person.¹ Despite that miniaturization, the underlying principle is the same: electrodes on the skin detect tiny electrical signals generated by the heart, and the machine amplifies and prints them as the familiar waveform.

Position and Prepare the Patient

Ask the patient to lie flat on their back (supine) with their arms relaxed at their sides. This position matters more than people realize. When patients are recorded in a prone or semi-reclined position, the distance between the heart and the chest electrodes changes, and muscle and bone can attenuate the signal.² If the patient cannot lie flat, note the position on the tracing so whoever reads it knows the context.

Explain the procedure briefly. Most patients have had an EKG before and know it is painless, but first-timers sometimes worry about being “shocked.” Let them know the machine only reads electrical activity and does not deliver any current. A calm patient produces a cleaner tracing because anxiety increases muscle tension and heart rate, both of which can introduce noise into the recording. Expose the chest, wrists, and ankles. Provide a drape or sheet for privacy, especially for female patients, and only uncover the areas you are actively working on.

Prepare the Skin

Good skin contact is the single biggest factor in getting a clean, readable EKG. The goal is to lower the electrical impedance at each electrode site so the heart’s tiny voltage signal passes through clearly. Three things raise impedance: body hair, oily or dead skin cells, and dry skin.

Hair: If the electrode site has dense hair, shave a small patch just large enough for the electrode pad. Hair lifts the electrode off the skin and creates air gaps that degrade the signal.
Oils and dead skin: Wipe each electrode site briskly with an alcohol prep pad or abrasive skin-prep pad. The slight friction removes the outer layer of dead cells and surface oils. Let the alcohol dry for a few seconds before applying the electrode; wet alcohol can actually increase impedance.
Dry skin: In patients with very dry skin, impedance can be high enough to reduce signal quality noticeably. Research on electrode materials has shown that even the type of metal in the electrode affects the signal in dry-skinned individuals, with some materials coupling the signal better than others.³ In practice, the fix is thorough skin prep: a bit of extra rubbing with the prep pad, and ensuring the electrode gel makes full contact.

Skip lotions or moisturizers as a substitute for proper prep. They can form a film between the gel and the skin that actually worsens contact. Stick with alcohol and mild abrasion.

Place the Limb Leads

The four limb electrodes are color-coded and labeled by the body part they go on. Different countries use different color schemes (the American system uses white, black, red, and green; the international IEC system uses red, yellow, green, and black), so always check the label printed on each lead wire rather than relying on color alone.

RA (Right Arm): Place on the inner right wrist or the right forearm, avoiding bony prominences.
LA (Left Arm): Place on the inner left wrist or the left forearm, in a corresponding position.
RL (Right Leg): Place on the right ankle or lower right leg, above the ankle bone. This electrode serves as the ground reference and does not contribute to the tracing itself.
LL (Left Leg): Place on the left ankle or lower left leg, again above the ankle bone.

For a standard resting EKG, the electrodes go on the distal limbs, meaning the actual wrists and ankles. During exercise stress testing, a modified system (called the Mason-Likar configuration) moves the limb electrodes onto the torso for practical reasons, since arms and legs are moving. But this torso placement is not interchangeable with the standard positions. Moving the limb electrodes onto the torso shifts the electrical axis of the QRS complex to the right, reduces R-wave amplitude in leads I and aVL, and increases it in the inferior leads (II, III, aVF).⁴ The differences are large enough that a torso-placed EKG should never be directly compared to a standard limb-placed one as if they were equivalent.

A study in children reinforced this point, finding that torso electrode placement systematically shifted the QRS and P-wave axes rightward and distorted precordial wave amplitudes compared to standard distal limb placement. The measurement error was more pronounced in shorter participants.⁵ If you do use torso placement for any reason (an amputee, a restless patient), label it clearly on the printed tracing.

Place the Precordial (Chest) Leads

The six chest electrodes (V1 through V6) require precise anatomical placement. This is where most placement errors happen, particularly in women, in obese patients, and in people with unusual chest anatomy. Take your time here.

V1: Fourth intercostal space, right sternal border. Find the sternal angle (the slight ridge where the manubrium meets the body of the sternum, roughly at the level of the second rib). Count down two intercostal spaces from there. Place the electrode just to the right of the sternum.
V2: Fourth intercostal space, left sternal border. Directly across from V1 on the left side of the sternum.
V3: Midway between V2 and V4. Place V4 first, then split the difference.
V4: Fifth intercostal space, midclavicular line. The midclavicular line runs straight down from the midpoint of the collarbone. This is the most important landmark: V4 anchors the rest of the precordial leads.
V5: Same horizontal level as V4, on the anterior axillary line (the front crease of the armpit).
V6: Same horizontal level as V4, on the midaxillary line (the middle of the armpit).

A common mistake is placing V5 and V6 too high, following the curve of the rib instead of staying on the same horizontal plane as V4. Another frequent error is placing V1 and V2 in the wrong intercostal space, usually one space too high. This makes the R-wave progression across the chest leads look abnormal and can mimic or obscure pathology. In women with large breasts, the standard practice is to place V4 through V6 under the breast rather than on top of it, because breast tissue increases the distance between the electrode and the heart and dampens the signal.

Connect the Leads and Run the Tracing

Once all ten electrodes are on the patient, connect each lead wire to its corresponding electrode. Many modern adhesive pads snap directly onto the lead wire; older systems use clips or suction cups. Make sure every connection is firm and that no lead wire is pulling on an electrode (this creates artifact). Arrange the wires so they are not tangled or draped across the patient’s body in a way that creates tension.

On the machine, enter the patient’s identifying information: name, date of birth, medical record number, date, and time. Some machines auto-populate this from a barcode scan. Then press the record or acquire button. Most machines will acquire about ten seconds of data across all twelve leads simultaneously. Ask the patient to lie still, relax their muscles, and breathe normally. They do not need to hold their breath, but they should avoid talking or shifting position during those ten seconds.

Once the machine finishes acquiring, review the tracing on the screen (or printed page) before disconnecting the patient. Check that all twelve leads have a clear signal with identifiable P waves, QRS complexes, and T waves. If any lead looks flat, excessively noisy, or has a wandering baseline, troubleshoot before repeating the recording. Disconnecting the patient and then discovering you need to redo the EKG wastes time and annoys everyone.

Recognizing and Fixing Common Artifacts

Three types of noise show up repeatedly on EKG tracings, and each has a distinct look and a specific fix.

Baseline wander appears as a slow, rolling drift of the entire tracing up and down. It is usually caused by patient movement, breathing, or poor electrode contact. Powerline interference (also called 50 Hz or 60 Hz artifact, depending on your country’s electrical grid) appears as a fine, regular fuzz overlaid on the tracing. It comes from nearby electrical equipment, power cords running close to lead wires, or poor grounding.⁶ Muscle artifact (also called somatic tremor) looks like a chaotic, irregular jitter and comes from shivering, anxiety, Parkinson’s tremor, or the patient simply tensing their muscles.

Both baseline wander and powerline interference can distort the tracing enough to lead to incorrect interpretation if they are not addressed.⁷ Modern EKG machines apply digital filters to reduce these automatically, but the filters can only do so much. The best approach is always to fix the source: re-prep a loose electrode, move a power cord away from the lead wires, warm the room if the patient is shivering, or give an anxious patient a moment to settle.

Catching Lead Reversals Before They Cause Harm

Lead reversal is one of the most dangerous EKG mistakes because the resulting tracing can closely mimic real cardiac pathology. The most common reversal, swapping the right-arm and left-arm electrodes, produces a distinctive pattern: the P wave and QRS complex in lead I become inverted, which looks like a non-sinus atrial rhythm and can mimic the appearance of a high anterolateral myocardial infarction. Most experienced clinicians spot that one quickly.⁸

Subtler reversals are harder to catch. Swapping the right-arm and left-leg electrodes can create what looks like an inferior-wall heart attack in a perfectly healthy person, along with an abnormal-looking rhythm. Swapping the right-arm and right-leg connections produces a pattern of unusually low voltage across all the limb leads that can be mistaken for pericardial effusion or other pathology. Precordial lead switches show up as an abnormal R-wave progression, sometimes suggesting anterior wall damage that is not there.

The best prevention is a consistent routine. Always attach electrodes in the same order, always double-check the labels on each lead wire, and always glance at the tracing before removing the patient from the machine. If lead I has an inverted P wave and QRS but the patient has a normal sinus rhythm on the monitor, suspect a limb-lead reversal before suspecting disease.

Performing EKGs on Children

The procedure for children follows the same general steps, but with some important differences. Pediatric EKG interpretation uses different normal values than adult interpretation because the heart’s electrical axis and chamber sizes change with age. From a technical standpoint, the biggest practical challenge is keeping the child still. Younger children may need distraction (a video on a phone, a parent holding their hand) rather than the instruction to “lie still and relax” that works for adults.

Electrode placement in children can be tricky because the chest is smaller. V1 and V2 are still placed at the fourth intercostal space, but in a small child, counting intercostal spaces accurately requires careful palpation. Some pediatric settings use torso-mounted limb electrodes as a matter of convenience, since reaching a squirming toddler’s ankles while managing chest leads is logistically challenging. However, as research has shown, the torso configuration in children shifts QRS and P-wave axes rightward, overestimates some precordial wave amplitudes, and underestimates others, with the distortion being worse in shorter children.⁵ Whenever possible, use standard distal limb placement, and clearly document any deviation.

Speed Matters in Chest Pain

In emergency settings, the EKG is not just a diagnostic test; it is a triage tool. For patients presenting with chest pain, getting the EKG done quickly can change outcomes. Guidelines generally call for a door-to-EKG time of ten minutes or less in patients with suspected acute coronary syndrome. Research has found that delays in EKG acquisition are associated with worse clinical outcomes specifically in patients who turn out to be having a ST-elevation myocardial infarction (STEMI), with one study reporting roughly a fourfold increase in the odds of adverse outcomes at 30 days when the EKG was delayed.⁹

This does not mean you should skip skin prep or rush electrode placement so badly that the tracing is unreadable. A fast but artifact-ridden EKG that has to be repeated wastes more time than doing it right the first time. The takeaway is that efficiency matters: have your equipment ready, know your landmarks, and develop a smooth workflow so you can get a high-quality tracing in under two minutes of hands-on time.

Cleaning Equipment Between Patients

EKG lead wires and cables are shared between patients all day long, and they can harbor bacteria if not cleaned properly. In intensive care settings, researchers have studied the microbial contamination of manually reprocessed EKG lead wires and found that standard cleaning and disinfection protocols, such as wiping down the leads with antibacterial disinfectant wipes and allowing a drying time of at least 30 minutes, are used to reduce transmission risk.¹⁰ Disposable electrode pads should never be reused. If your facility uses reusable suction-cup electrodes, clean them with an approved disinfectant between patients and inspect the rubber cups for cracks where bacteria can hide.

Many facilities have moved toward single-use lead wire sets for high-risk patients (those in isolation for MRSA, VRE, or C. difficile). Even in non-isolation settings, wiping down the entire cable from connector to electrode clip after each patient is a basic infection-control step that is easy to skip when you are busy and easy to regret when an outbreak is traced back to shared equipment.

What the Machine’s Interpretation Gets Right and Wrong

Almost every modern EKG machine will print a computerized interpretation at the top of the tracing. These automated readings are useful as a starting point but should never be treated as a final diagnosis. A study comparing computerized EKG analysis to cardiologist interpretation for atrial fibrillation found that the machine had lower sensitivity (about 78% versus 87%) and lower positive predictive value (roughly 86% versus 98%) compared to a cardiologist reading the same tracings. Among the EKGs that the computer misclassified, about 41% of those errors went unrecognized by the clinical team, leading to delayed anticoagulation in some cases and inappropriate initiation of blood thinners in others.¹¹

Newer AI-powered applications aim to improve on traditional algorithms, and there is genuine promise in using them as decision-support tools, particularly in frontline settings where specialist access is limited. The idea is to assist with rapid triage and provide a standardized first-pass reading while keeping final clinical judgment with the human provider.¹² For the person performing the EKG, the practical lesson is straightforward: the machine’s printed interpretation is a suggestion, not a diagnosis. Flag any tracing that the machine reads as abnormal for prompt physician review, but also flag any tracing that looks abnormal to your eyes even if the machine calls it normal.

Situations That Call for Extra Leads

The standard 12-lead EKG does an excellent job of surveying most of the heart, but it has blind spots. The right ventricle and the posterior wall of the left ventricle are underrepresented in the standard configuration. When a clinician suspects a right ventricular infarction (often prompted by inferior ST elevation on the standard tracing), they may ask for a right-sided EKG. This involves moving V3 through V6 to mirror-image positions on the right side of the chest. The resulting leads are labeled V3R through V6R.

For suspected posterior infarction, three additional leads (V7, V8, and V9) are placed on the back, continuing around from V6 along the same horizontal plane. V7 goes at the posterior axillary line, V8 at the tip of the scapula, and V9 at the left paraspinal border. These extra leads are not part of the routine procedure, but knowing how to set them up when asked is a valuable skill, especially in emergency departments where ST-elevation patterns drive immediate treatment decisions.

In both cases, the skin-preparation and electrode-placement principles are identical to the standard procedure. The only difference is the anatomical location. Label the printout clearly (“right-sided leads” or “posterior leads”) so that the reading clinician knows exactly what they are looking at. A posterior lead tracing filed without a label looks bizarre and can cause real confusion.

When Patients Have Implanted Devices

Patients with pacemakers or implantable cardioverter-defibrillators (ICDs) can and should have EKGs performed normally. The procedure does not interfere with the device, and the device does not interfere with the procedure. What does change is the interpretation: pacemaker spikes (small vertical deflections before the paced beat) appear on the tracing, and the QRS morphology of paced beats looks different from native beats. Computerized interpretation algorithms struggle with paced rhythms; the atrial fibrillation detection study noted above found that ventricular pacing was one of the strongest predictors of computerized misclassification.¹¹

Place the electrodes in the standard positions. Do not avoid placing an electrode near the device generator (usually under the left collarbone) unless it physically interferes with electrode adhesion. If the generator creates a visible bump, place the nearby electrode as close to the standard position as possible and note the adjustment. The EKG machine reads electrical signals passively; it does not emit energy that could reprogram or trigger the implanted device.

Equipment Safety Standards

Portable EKG machines used in clinical and home healthcare settings are manufactured to meet international electrical safety standards (IEC 60601-1), which include requirements for mechanical robustness, insulation, and protection against electrical leakage.¹³ For the person performing the EKG, the practical implications are simple: use equipment that has been inspected and maintained according to your facility’s biomedical engineering schedule, do not use machines with frayed cords or cracked housings, and never attempt to open or repair the device yourself. If a machine gives you a shock or displays erratic behavior, take it out of service immediately and report it. These are not dramatic risks in well-maintained facilities, but they are worth mentioning because home-use and portable EKG devices are becoming more common, and not all of them undergo the same level of quality control as hospital-grade equipment.