What is the difference between an ECG and an EKG?

There is no difference between an ECG and an EKG; both terms refer to the exact same electrocardiogram test that records the heart's electrical activity, with EKG being the German-influenced spelling.

Are ECG and EKG the same test?

Yes, an ECG and an EKG are identical tests, as both measure the same electrical signals from your heart using the same electrodes, wires, and monitoring equipment, differing only in spelling.

Which is better, an ECG or an EKG?

Neither is better because ECG and EKG are the same procedure, so the choice of spelling depends on regional preference, with EKG used more in American English and ECG in British English.

Does an ECG or EKG cost more?

An ECG and EKG cost exactly the same amount because they are the same test, with typical prices ranging from $50 to $200 depending on location, facility, and insurance coverage.

Is an ECG or EKG safer?

An ECG and EKG are equally safe, as both are non-invasive procedures that only record electrical activity and carry no radiation risk, making them safe for all patients.

Why do doctors use EKG instead of ECG?

Doctors use EKG instead of ECG to reduce confusion with an EEG, which measures brain activity, since the German spelling EKG clearly distinguishes the heart test from the brain test.

What is a common beginner mistake about ECG and EKG?

A common beginner mistake is assuming ECG and EKG are different tests, when they are actually the same electrocardiogram, and the only difference is the spelling used in different regions.

Can I use ECG and EKG interchangeably?

Yes, you can use ECG and EKG interchangeably because they describe the same diagnostic test, so healthcare providers will understand either term when you discuss your heart health.

When would a doctor order an EKG instead of an ECG?

A doctor would order an EKG instead of an ECG based on the hospital's spelling preference, since both terms refer to the same test used to diagnose arrhythmias, heart attacks, and other cardiac conditions.

Can I switch from an ECG to an EKG?

You can switch from an ECG to an EKG without any medical implications because they are the same test, so your doctor will simply use the alternate spelling in your medical records.

Difference Between

Difference Between Ecg and Ekg

Written byNex Virox Team

Editorial Team

Reviewed byVarshal Nirbhavane

Senior SEO & Organic Growth Professional · 5+ years

Published: August 26, 202618 min read

Quick answer

The main difference between Ecg and Ekg is that they are two spellings of the exact same medical test, with no clinical difference. Ecg is the abbreviation from the English term electrocardiogram, while Ekg is the version derived from the German Elektrokardiogramm.

Key takeaways

No clinical difference: ECG and EKG are identical tests, differing only by spelling and abbreviation.
Same procedure: Both record heart electrical activity using electrodes on the chest, arms, and legs.
Identical cost: ECG and EKG tests share equal pricing, duration, and diagnostic accuracy in medical practice.
Best-fit use: Choose either term when diagnosing arrhythmias, heart attacks, or chamber enlargement conditions.
Common mistake: Assuming EKG means a different test, when it simply represents the German spelling.

Table of Contents18 sections

Difference Between Ecg and Ekg: Comparison Table

Aspect	Ecg	Ekg
Definition	Electrocardiogram records the heart's electrical activity over time.	Electrokardiogram is the German-derived spelling of the same test.
Purpose	Detects arrhythmias, ischemia, and chamber enlargement by measuring electrical signals.	Identifies identical cardiac conditions using the same electrical tracing method.
Core Mechanism	Measures voltage changes between electrodes placed on the skin.	Uses the same electrode placement to capture the heart's depolarization wave.
Origin	Derived from the Greek word "kardia" meaning heart.	Derived from the German word "kardio" meaning heart.
Waveform	Displays P wave, QRS complex, and T wave on graph paper.	Shows identical P, QRS, and T wave deflections on the tracing.
Lead System	Standard 12-lead configuration uses 10 electrodes on the chest and limbs.	Uses the same 12-lead setup with 10 electrodes in identical positions.
Signal Type	Captures electrical impulses measured in millivolts from the heart.	Records the same millivolt-level electrical signals from the myocardium.
Graph Speed	Paper runs at 25 millimeters per second for standard tracings.	Runs at the same 25 millimeters per second speed for comparison.
Voltage Scale	Standard calibration sets 10 millimeters equal to 1 millivolt.	Uses identical calibration of 10 millimeters per millivolt.
Test Duration	Resting recording typically lasts 10 seconds for a full rhythm strip.	Resting recording also captures 10 seconds of continuous heart activity.
Interpretation	Read by cardiologists who analyze intervals, axes, and wave morphology.	Interpreted by the same cardiology standards for intervals and axes.
Clinical Use	Used in emergency rooms to rule out myocardial infarction quickly.	Used in the same emergency settings for rapid chest pain evaluation.
Diagnostic Scope	Detects conduction blocks, atrial fibrillation, and ventricular hypertrophy.	Detects the same conduction blocks and rhythm disturbances.
Electrode Count	Ten adhesive electrodes placed on specific anatomical landmarks.	Ten electrodes placed on identical anatomical chest and limb points.
Artifact Handling	Filters muscle tremor and baseline wander using signal processing.	Applies the same filtering algorithms to reduce motion artifacts.
Portability	Available in handheld devices for point-of-care testing.	Available in the same portable monitor formats for bedside use.
Cost	Resting ECG typically costs between $50 and $200 without insurance.	EKG pricing is identical since it is the same procedure billed equally.
Speed	Results available within minutes after electrode placement.	Results available in the same minutes after the tracing is captured.
Accuracy	Correctly identifies ST-elevation myocardial infarction with high sensitivity.	Offers identical diagnostic accuracy because the test is the same.
Durability	Machine components last years with routine calibration checks.	Same durable hardware design with similar lifespan expectations.
Scalability	Integrates into hospital networks for remote telemetry monitoring.	Integrates into the same telemetry systems for continuous surveillance.
Maintenance	Requires periodic electrode replacement and printer paper refills.	Requires identical consumable replacements and routine servicing.
Safety	Non-invasive procedure with no radiation exposure and minimal risk.	Carries the same non-invasive safety profile with zero radiation.
Compatibility	Works with standard electronic health record systems for storage.	Compatible with the same EHR platforms for seamless data transfer.
Availability	Offered in virtually all hospitals, clinics, and urgent care centers.	Offered in the same facilities under the alternative spelling.
Example Use	Pre-operative screening for patients over 50 undergoing surgery.	Pre-operative screening for the same age group before procedures.
Typical Users	Cardiologists, emergency physicians, and primary care providers.	Same physician groups including internists and hospitalists.
Limitation	Cannot detect intermittent arrhythmias that occur outside the recording window.	Shares the same limitation of missing transient events between tracings.
Best-Fit Scenario	Ideal for evaluating syncope, palpitations, or routine annual physicals.	Best for the same symptom evaluation and routine cardiac screening.

What Is Ecg?

Ecg is an abbreviation for electrocardiogram, a medical test that records the heart's electrical activity. It detects rhythm abnormalities, ischemia, and chamber enlargement. The test exists to help clinicians diagnose cardiac conditions quickly, non-invasively, and at the point of care.

Definition of Ecg

An Ecg is a graphical representation of the heart's electrical depolarization and repolarization cycles, captured via surface electrodes placed on the skin. It measures voltage changes over time across specific leads, producing waveforms labeled P, QRS, and T that reflect atrial and ventricular activity.

Key Characteristics of Ecg

Characteristic	What It Means in Practice
Non-invasive	Uses skin electrodes only; no needles, no radiation, and no patient preparation required.
Rapid acquisition	A standard 12-lead Ecg captures data in under 10 seconds at the bedside.
Electrical signal	Measures voltage changes, not mechanical pumping; it cannot show ejection fraction directly.
Waveform components	P wave, QRS complex, and T wave each correspond to specific cardiac electrical phases.
Lead system	Standard 12-lead uses 10 electrodes to view the heart from 12 different angles.
Real-time output	Displays live rhythm on a monitor, enabling immediate arrhythmia detection during procedures.
Diagnostic scope	Detects ischemia, infarction, hypertrophy, conduction blocks, and electrolyte disturbances.
Interpretation skill	Requires trained clinicians to read subtle ST-segment and T-wave changes accurately.
Time-sensitive	Captures only the moment of recording; transient arrhythmias may be missed entirely.
Universal standard	Uses standardized paper speed of 25 mm/s and calibration of 10 mm/mV globally.

Common Examples of Ecg

12-lead resting Ecg – the standard diagnostic tool for chest pain evaluation in emergency departments.
Holter monitor – a portable continuous Ecg worn for 24 to 48 hours to catch intermittent arrhythmias.
Event recorder – a patient-activated Ecg device that logs rhythm only when symptoms occur.
Exercise stress Ecg – records cardiac electrical activity while the patient walks on a treadmill to unmask ischemia.
Telemetry monitoring – continuous Ecg surveillance on hospital wards for unstable cardiac patients.
Preoperative Ecg – routine baseline screening before surgery to detect silent cardiac disease.
Implantable loop recorder – a subcutaneous Ecg device that monitors rhythm for up to three years.
Fetal Ecg – monitors the unborn baby's heart rate during labor to assess distress.
Signal-averaged Ecg – detects late ventricular potentials that predict risk for dangerous arrhythmias.
Ambulatory patch monitor – a single-lead Ecg patch worn on the chest for up to 14 days.

Advantages and Limitations of Ecg

Advantages	Limitations
Provides immediate results at bedside, enabling rapid triage for acute coronary syndromes.	Cannot detect coronary artery blockages that do not yet affect electrical activity.
Costs a fraction of imaging tests and requires no specialized facility or technician.	Misses transient arrhythmias that occur between recordings, leading to false reassurance.
Detects silent myocardial infarctions that patients never felt or reported clinically.	Offers no information about mechanical pump function or actual cardiac output.
Guides life-saving decisions like thrombolysis administration within minutes of arrival.	Poor sensitivity for right ventricular infarction, often requiring additional right-sided leads.
Non-invasive and repeatable, making it safe for serial monitoring during treatment.	Skin preparation errors or electrode misplacement produce artifacts that mimic serious pathology.
Identifies electrolyte imbalances like hyperkalemia through characteristic T-wave changes.	Cannot predict future arrhythmic events in patients with structurally normal hearts.
Universal interpretation criteria allow consistent communication across global healthcare teams.	Overreads of benign variants lead to unnecessary anxiety, testing, and hospital admissions.
Portable devices enable prehospital diagnosis by paramedics in ambulances.	Fails to detect microvascular disease, which requires angiography or perfusion imaging.
Baseline Ecg provides a comparison point for future tracings after interventions.	Artifact from patient movement, tremor, or poor electrode contact degrades diagnostic quality.
Helps monitor drug effects on cardiac conduction, such as QT prolongation from medications.	Single Ecg cannot assess dynamic changes; serial tracings are often mandatory for accuracy.

What Is Ekg?

Ekg is the electrocardiogram, a test that records the heart's electrical activity. It uses electrodes on the skin to trace the heartbeat's rhythm and timing. It exists to detect abnormal rhythms, damage, and poor blood flow quickly and painlessly.

Definition of Ekg

An Ekg is a graphical representation of the heart's electrical depolarization and repolarization cycles, captured via surface electrodes and displayed as P, QRS, and T waves. It measures conduction intervals and heart rate. Clinicians interpret these waveforms to diagnose cardiac arrhythmias and ischemic changes.

Key Characteristics of Ekg

Characteristic	What It Means in Practice
Non-invasive procedure	No needles or incisions are required, so patients experience no pain during the test.
Rapid acquisition	Standard 12-lead capture takes under five minutes, enabling fast triage in emergencies.
Surface electrode placement	Ten sticky patches on the chest and limbs detect the heart's electrical signals from outside.
Waveform output	Produces P, QRS, and T waves that represent atrial and ventricular electrical events.
Rhythm analysis	Reveals regular or irregular heartbeats, including atrial fibrillation and premature beats.
Conduction timing	Measures PR, QRS, and QT intervals to expose blockages in electrical pathways.
Ischemia detection	ST-segment changes can indicate reduced oxygen supply to the heart muscle.
Portable equipment	Handheld devices allow bedside, ambulance, and home monitoring without a fixed lab.
Serial comparison	Repeated tracings track changes over time, such as evolving heart attacks or drug effects.
Immediate interpretation	Results are available instantly, allowing doctors to act on critical findings within minutes.

Common Examples of Ekg

12-lead resting Ekg – the standard diagnostic tracing used in clinics and hospitals to assess baseline heart function.
Holter monitor – a portable device worn for 24-48 hours to catch intermittent arrhythmias during daily activity.
Event recorder – a patient-activated device used for weeks to capture rare symptoms like palpitations or fainting.
Exercise stress test Ekg – records the heart during treadmill exertion to reveal exercise-induced ischemia or rhythm problems.
Preoperative screening Ekg – routine check before surgery to identify undiagnosed heart conditions that raise anesthesia risk.
Emergency department Ekg – rapid triage tool for chest pain to quickly identify ST-elevation myocardial infarction.
Smartwatch single-lead Ekg – consumer wearable that records a single rhythm strip to screen for atrial fibrillation.
Ambulance 12-lead Ekg – performed en route to hospital so the receiving team can prepare for immediate intervention.
Pediatric congenital Ekg – used in children to evaluate structural defects and inherited rhythm disorders like long QT syndrome.
Intraoperative Ekg monitoring – continuous tracing during surgery to detect ischemia or arrhythmias under anesthesia.

Advantages and Limitations of Ekg

Advantages	Limitations
Delivers results in minutes, enabling immediate clinical decisions in urgent cardiac situations.	Cannot reliably diagnose structural problems like valve defects or heart chamber enlargement.
Completely painless and safe, with no radiation exposure or contrast agents required.	A normal resting Ekg misses transient arrhythmias that occur only during specific activities.
Widely available in clinics, ambulances, and remote settings due to low equipment cost.	Skin preparation errors, patient movement, or electrode misplacement can produce misleading artifacts.
Provides a permanent, reproducible record that allows comparison across different visits.	Interpretation is subjective, and two cardiologists may disagree on borderline ST-segment changes.
Detects silent ischemia in patients who experience no chest pain or other warning symptoms.	Cannot measure cardiac output, blood pressure, or the heart's actual pumping efficiency.
Reveals conduction blocks and pacemaker function with precise interval measurements.	Misses coronary artery blockages that do not yet affect resting electrical activity.
Inexpensive enough for routine screening in large populations and annual physical exams.	Fails to capture heart rhythm during sleep or exercise unless paired with a wearable monitor.
Guides immediate treatment decisions like thrombolysis or catheterization in heart attack cases.	Cannot distinguish between different causes of identical waveforms, such as drug effects versus electrolyte imbalance.
Safe for repeated use in pregnancy, pediatrics, and patients with pacemakers or implants.	Poor sensitivity for detecting past heart attacks that have healed and no longer show active changes.
Works effectively in emergency triage to prioritize patients who need urgent cardiac care.	Single-lead consumer devices capture limited data and frequently produce false positives that cause anxiety.

Similarities Between Ecg and Ekg

Shared Aspect	How Ecg and Ekg Are Alike
Core Purpose	Both Ecg and Ekg record the heart's electrical activity to identify cardiac abnormalities.
Medical Meaning	Ecg and Ekg are identical tests; both terms describe the exact same procedure.
Word Origin	Ecg and Ekg derive from the same Greek word kardia, meaning heart.
Primary Output	Both Ecg and Ekg produce a graph tracing the heart's electrical impulses over time.
Test Duration	Ecg and Ekg both take roughly five to ten minutes to complete in a clinical setting.
Patient Position	Patients lie flat and still for both Ecg and Ekg to ensure accurate readings.
Electrode Count	Both Ecg and Ekg typically use ten electrodes placed on the chest and limbs.
Skin Preparation	Technicians clean the skin before applying electrodes for both Ecg and Ekg.
Pain Level	Both Ecg and Ekg are painless, non-invasive procedures with no needles involved.
Risk Profile	Ecg and Ekg carry virtually no risk of complications or side effects for patients.
Test Speed	Both Ecg and Ekg capture heart activity within a few seconds of recording.
Reading Format	Ecg and Ekg both display results on paper or a digital screen for review.
Wave Components	Both Ecg and Ekg show P waves, QRS complexes, and T waves in the trace.
Heart Rate Data	Ecg and Ekg both calculate the heart rate in beats per minute.
Rhythm Analysis	Both Ecg and Ekg evaluate whether the heart rhythm is regular or irregular.
Arrhythmia Detection	Ecg and Ekg both help doctors spot abnormal heart rhythms like atrial fibrillation.
Ischemia Signs	Both Ecg and Ekg reveal indicators of reduced blood flow to the heart muscle.
Heart Attack Clues	Ecg and Ekg both assist in diagnosing heart attacks by showing ST-segment changes.
Electrolyte Effects	Both Ecg and Ekg reflect imbalances in potassium, calcium, and magnesium levels.
Ordering Physician	Both Ecg and Ekg are ordered by doctors when cardiac evaluation is necessary.
Performing Staff	Ecg and Ekg are both administered by trained technicians, nurses, or physicians.
Reading Expert	Both Ecg and Ekg are interpreted by cardiologists or specially trained clinicians.
Clinical Setting	Ecg and Ekg both occur in hospitals, clinics, emergency rooms, and ambulances.
Baseline Use	Both Ecg and Ekg serve as a baseline before surgery or other medical procedures.
Routine Screening	Ecg and Ekg both function as part of routine physical examinations for many adults.
Monitoring Role	Both Ecg and Ekg track heart health in patients with known cardiac conditions.
Equipment Type	Ecg and Ekg both rely on an electrocardiograph machine with attached leads.
Standard Protocol	Both Ecg and Ekg follow the same standardized 12-lead placement procedure.
Insurance Coverage	Ecg and Ekg are both typically covered by health insurance as standard diagnostics.
Result Speed	Both Ecg and Ekg provide immediate results that doctors can review right away.

Ecg or Ekg: Which Should You Choose?

Ecg and Ekg are the exact same test. The only difference is spelling, not technology, cost, or procedure. Your choice depends entirely on which term your doctor, hospital, or region uses, so simply follow their preference to avoid confusion.

When to Use Ecg

Choose Ecg when your medical records, clinic, or healthcare system uses this spelling. It is the standard in most of Europe, Asia, and Australia. Use it for international medical documentation, research papers, or communication with non-US providers to ensure clarity.

When to Use Ekg

Choose Ekg when your doctor, cardiologist, or US-based facility writes it this way. This spelling is common in North America to avoid confusion with other medical abbreviations. Use it for local appointments, US insurance forms, or when speaking with American healthcare staff to match their terminology.

Common Misconceptions About Ecg and Ekg

Common Myth	The Reality
An Ecg and an Ekg are two different medical tests.	An Ecg and an Ekg are the exact same test; the only difference is spelling, with Ekg being the German abbreviation.
An Ekg is a more advanced version of an Ecg.	An Ekg is not advanced; it records identical electrical heart activity using the same 12-lead procedure as an Ecg.
The Ecg measures blood pressure and heart rate.	An Ecg measures electrical impulses of the heart, not blood pressure; it can reveal rhythm but not pumping force.
An Ekg can predict a future heart attack with certainty.	An Ekg cannot predict future heart attacks; it only captures current electrical activity and may appear normal between episodes.
You need a referral to get an Ecg or Ekg test.	You do not need a referral for an Ecg; many clinics and pharmacies offer walk-in Ecg and Ekg testing without a doctor's order.
The Ecg is painful because it uses electric shocks.	An Ecg is painless and uses no shocks; it only detects the heart's own natural electrical signals through sticky electrodes.
An Ekg takes over an hour to complete.	An Ekg typically takes five to ten minutes, including electrode placement and the actual recording of heart activity.
Doctors always need an Ecg to diagnose any heart problem.	Doctors do not always need an Ecg; some conditions require echocardiograms or stress tests because an Ecg only shows electrical activity.
An Ekg is only for older adults or athletes.	An Ekg is for anyone with symptoms like palpitations or chest pain, regardless of age, fitness level, or athletic status.
You must fast before having an Ecg test.	You do not need to fast before an Ecg; normal eating and drinking do not significantly alter the electrical readings.
The Ecg and Ekg check different sides of the heart.	An Ecg checks all heart chambers equally; both Ecg and Ekg use the same electrode placements to view the whole heart.
An Ekg result is always abnormal if you feel symptoms.	An Ekg result can be normal even with symptoms; arrhythmias are often intermittent and may not occur during the short Ecg recording.
Smartwatches with Ecg features replace a medical Ecg.	A smartwatch Ecg is a screening tool, not a replacement; a 12-lead Ecg captures far more detail for clinical diagnosis.
An Ecg uses ultrasound waves to create images.	An Ecg uses electrodes to record electrical signals; ultrasound imaging of the heart is a separate test called an echocardiogram.
You cannot exercise before an Ecg appointment.	You can exercise before an Ecg, but vigorous activity may temporarily raise heart rate; resting for five minutes before is recommended.
The Ekg is a newer technology than the Ecg.	An Ekg is not newer; both terms describe the same century-old electrocardiography technology, with Ekg simply being the German spelling.
An Ecg can tell you if your arteries are blocked.	An Ecg cannot directly show blocked arteries; it may hint at damage during a heart attack, but angiography is the definitive test.
Results from an Ecg are available instantly to patients.	An Ecg tracing is printed instantly, but interpretation by a cardiologist for official results can take hours or days.
You should stop heart medications before an Ecg.	You should not stop heart medications before an Ecg unless your doctor instructs you; stopping can cause dangerous rhythm changes.
An Ekg is performed only in hospital emergency rooms.	An Ekg is performed in clinics, ambulances, doctor offices, and even at home with portable devices, not just in emergency rooms.
Pregnant women cannot safely have an Ecg test.	Pregnant women can safely have an Ecg; the test uses no radiation and poses no known risk to the fetus.
The Ecg records the heart's sound like a stethoscope.	An Ecg records electrical signals, not sounds; heart sounds are heard with a stethoscope or recorded by a phonocardiogram.
An Ekg requires shaving all chest hair completely.	An Ekg may require clipping small patches of chest hair for electrode contact, but full shaving is rarely necessary.
One Ecg reading is enough to rule out all heart disease.	One Ecg cannot rule out all heart disease; many conditions require serial Ecg tests, monitoring, or additional imaging for diagnosis.
An Ecg and an Ekg have different costs.	An Ecg and an Ekg have identical costs because they are the same procedure; price varies by facility, not by spelling.
You need to remove all jewelry for an Ecg test.	You do not need to remove jewelry for an Ecg; metal does not interfere with the electrical signal recording on the chest.
An Ekg can diagnose heart valve problems directly.	An Ekg cannot diagnose valve problems; valve issues require an echocardiogram, which uses ultrasound to visualize valve movement.
The Ecg requires you to hold your breath.	An Ecg does not require holding your breath; you breathe normally, though you may be asked to lie still and relax.
An abnormal Ecg always means you are having a heart attack.	An abnormal Ecg can indicate many things, including electrolyte imbalances or prior damage; it does not always mean an active heart attack.
Children never need an Ecg or Ekg test.	Children do need an Ecg for congenital heart conditions, murmurs, or palpitations; pediatric Ecg uses the same principles with smaller electrodes.

Conclusion

Difference Between Ecg and Ekg is zero; both terms describe the identical electrocardiogram test. Choose Ecg when following American English conventions. Choose Ekg when following German or international spelling standards. Neither option changes the procedure, equipment, or results, so your choice depends purely on regional spelling preference.

FAQs on Difference Between Ecg and Ekg

What is the difference between an ECG and an EKG?: There is no difference between an ECG and an EKG; both terms refer to the exact same electrocardiogram test that records the heart's electrical activity, with EKG being the German-influenced spelling.
Are ECG and EKG the same test?: Yes, an ECG and an EKG are identical tests, as both measure the same electrical signals from your heart using the same electrodes, wires, and monitoring equipment, differing only in spelling.
Which is better, an ECG or an EKG?: Neither is better because ECG and EKG are the same procedure, so the choice of spelling depends on regional preference, with EKG used more in American English and ECG in British English.
Does an ECG or EKG cost more?: An ECG and EKG cost exactly the same amount because they are the same test, with typical prices ranging from $50 to $200 depending on location, facility, and insurance coverage.
Is an ECG or EKG safer?: An ECG and EKG are equally safe, as both are non-invasive procedures that only record electrical activity and carry no radiation risk, making them safe for all patients.
Why do doctors use EKG instead of ECG?: Doctors use EKG instead of ECG to reduce confusion with an EEG, which measures brain activity, since the German spelling EKG clearly distinguishes the heart test from the brain test.
What is a common beginner mistake about ECG and EKG?: A common beginner mistake is assuming ECG and EKG are different tests, when they are actually the same electrocardiogram, and the only difference is the spelling used in different regions.
Can I use ECG and EKG interchangeably?: Yes, you can use ECG and EKG interchangeably because they describe the same diagnostic test, so healthcare providers will understand either term when you discuss your heart health.
When would a doctor order an EKG instead of an ECG?: A doctor would order an EKG instead of an ECG based on the hospital's spelling preference, since both terms refer to the same test used to diagnose arrhythmias, heart attacks, and other cardiac conditions.
Can I switch from an ECG to an EKG?: You can switch from an ECG to an EKG without any medical implications because they are the same test, so your doctor will simply use the alternate spelling in your medical records.