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Hoja de Repaso del Examen NHA EKG Technician (CET) (2026)
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Rhythm Identification and Interpretation
35% del examen- PR interval: 0.12 to 0.20 second
- Three to five small boxes. Longer than 0.20 second and constant is first-degree AV block; shorter than 0.12 second suggests a junctional origin.
- QRS duration: less than 0.12 second
- Under three small boxes. A QRS of 0.12 second or more means the impulse did not travel the normal fast pathway, pointing to a bundle branch block or a ventricular origin.
- QT interval: generally under about 0.44 second at normal rates
- A useful bedside check is that the QT should be less than half the R-R interval. A prolonged QT raises the risk of dangerous ventricular rhythms.
- One small box = 0.04 second, one large box = 0.20 second
- True only at the standard paper speed of 25 mm/sec. At 50 mm/sec each small box becomes 0.02 second, which is why any speed change must be documented on the tracing.
- Regularity is measured R to R
- March the R-R intervals across the strip with calipers or the edge of a paper. Do the same P to P to measure the atrial rhythm separately, which is how AV blocks are unmasked.
- 300 method
- 300 divided by the number of large boxes between R waves. Memorize the sequence 300, 150, 100, 75, 60, 50 for one through six large boxes.
- 1500 method
- 1500 divided by the number of small boxes between R waves. Most accurate, but it requires a regular rhythm and careful counting.
- Six-second method
- Count QRS complexes in six seconds and multiply by 10. Required for irregular rhythms because the box methods assume every R-R interval is identical.
- Report both rates when they differ
- In atrial flutter or third-degree block the atrial and ventricular rates are not the same, so a single number would misrepresent the strip.
- Normal sinus rhythm
- Rate 60 to 100, regular, one upright P wave before every QRS, PR 0.12 to 0.20 second, QRS under 0.12 second.
- Sinus bradycardia / sinus tachycardia
- All normal sinus criteria except the rate: under 60 is bradycardia, over 100 is tachycardia. Sinus tachycardia is usually a response to fever, pain, exercise, anxiety, blood loss, or dehydration.
- Sinus arrhythmia
- All sinus criteria met except regularity; the R-R shortens with inspiration and lengthens with expiration. Common and benign in children and young adults.
- Atrial fibrillation / atrial flutter
- Fibrillation is irregularly irregular with no identifiable P waves and a chaotic baseline; flutter shows uniform sawtooth waves at about 250 to 350 per minute with conduction ratios such as 2:1, 3:1, or 4:1. Both keep a narrow QRS.
- Junctional rhythms
- Junctional escape 40 to 60, accelerated junctional 60 to 100, junctional tachycardia over 100. P wave inverted, absent, or following the QRS; PR under 0.12 second when visible; QRS narrow.
- Ventricular rhythms
- Idioventricular 20 to 40, accelerated idioventricular 40 to 100, ventricular tachycardia over 100 as three or more consecutive wide beats. No related P waves, QRS 0.12 second or greater. Ventricular fibrillation has no measurable rate, rhythm, P wave, or QRS at all.
- First-degree AV block
- Every P wave conducts, but the PR interval is constant and longer than 0.20 second. Nothing is dropped.
- Second-degree, Mobitz I (Wenckebach)
- The PR interval lengthens progressively until one P wave is not conducted and a QRS is dropped, then the cycle repeats. The ventricular rhythm is irregular in a repeating pattern.
- Second-degree, Mobitz II
- Conducted beats have a constant PR interval, but QRS complexes are dropped without warning. More dangerous than Mobitz I because it can progress to complete block.
- Third-degree (complete) AV block
- No impulses cross the AV node. P-P is regular, R-R is regular, and the PR interval constantly changes because the atria and ventricles are completely dissociated. The escape rate is 40 to 60 if junctional and 20 to 40 if ventricular.
- R-on-T is the dangerous PVC
- A PVC landing on the preceding T wave falls in the vulnerable period of repolarization and can trigger ventricular tachycardia or fibrillation. Report it promptly.
- Always check the patient before the monitor
- A patient who is alert, talking, or brushing teeth is not in ventricular fibrillation. Confirm any alarming rhythm at the bedside before acting on it or dismissing it.
- Confirm asystole in more than one lead
- A flat line in a single lead is more often a disconnected wire than true asystole. Verify in a second lead and at the bedside.
- Lethal rhythms requiring immediate response
- Ventricular fibrillation, pulseless ventricular tachycardia, and asystole produce no effective cardiac output. Call for help and activate the emergency response at once, then assist within the limits of your training.
- Report promptly, but not as an arrest
- New-onset atrial fibrillation, symptomatic bradycardia, Mobitz II, third-degree block, frequent or multifocal PVCs, and R-on-T beats all require prompt notification of the nurse or physician.
- A technician recognizes; a physician diagnoses
- Describe what you see and report it. Naming a rhythm on a strip for the chart is part of the job; telling a patient what it means medically is not.
EKG Acquisition, Lead Placement, and Troubleshooting
28% del examen- V1 and V2
- V1: fourth intercostal space, right sternal border. V2: fourth intercostal space, left sternal border.
- V3 and V4
- V4 is placed first, in the fifth intercostal space at the left midclavicular line. V3 then goes midway between V2 and V4.
- V5 and V6
- V5: left anterior axillary line, level with V4. V6: left midaxillary line, level with V4 and V5. Both are aligned horizontally, not by rib space.
- Limb electrodes
- Place on flat, fleshy, non-muscular areas of both arms and both lower legs, positioned symmetrically left to right. Avoid bony prominences and muscle bellies.
- Special placements
- For large breast tissue, place chest electrodes under the breast on the chest wall at the true landmark. For an amputated limb, move that electrode to the nearest torso site and mirror the opposite side. Document every deviation on the tracing.
- Color convention
- White on the right, smoke (black) over fire (red), clouds (white and black) over grass (green and red). Brown is the chest electrode in a 5-lead system.
- Torso placement is intentional
- Monitoring electrodes go on bone or flat torso surfaces to reduce muscle artifact, not on the limbs, and monitoring tracings are not used for diagnostic measurement.
- Lead II for rhythm
- Lead II runs roughly parallel to the heart's normal conduction axis, producing the most upright and visible P waves, which is why it is the default rhythm lead.
- Change electrodes at least daily
- Gel dries out over hours and is the leading cause of false alarms. Rotate sites slightly to protect the skin and document skin condition.
- Standard calibration: 10 mm/mV
- The standardization mark should measure exactly two large boxes tall. Verify it on every tracing before handing the strip off.
- Standard paper speed: 25 mm/sec
- This is what makes one small box equal 0.04 second. Always confirm it before measuring any interval.
- Half standardization (5 mm/mV)
- Use when complexes are so tall they overlap adjacent leads. Mark the tracing clearly, because amplitudes will read half their true value.
- Double paper speed (50 mm/sec)
- Use to spread out very fast rhythms. Each small box then represents 0.02 second, so intervals must be recalculated on the new scale.
- Never adjust settings to make a tracing look better
- Settings are changed for legibility, never to make a tracing resemble a previous one or to hide an abnormality.
- Clip, cleanse, dry, abrade
- Clip hair only where an electrode will sit; cleanse with alcohol and let it dry; gently abrade with dry gauze. Never apply electrodes to wet skin.
- Supine, arms at the sides, legs uncrossed
- Crossed legs and folded arms bridge electrodes and generate muscle artifact. Support the limbs on the bed so they can fully relax.
- Document any non-standard position
- Semi-Fowler, upright, or lateral positioning changes the tracing, so the position used must be written on the strip for the interpreting physician.
- Provide privacy and draping
- Expose only the area needed for placement, drape the patient, and explain each step before touching. This is both a professional and a practical requirement for cooperation.
- Discard dried or expired electrodes
- Dried conductive gel cannot be revived with water or alcohol. Open a fresh, in-date package.
- Wandering baseline
- Slow up-and-down drift. Reapply fresh electrodes to clean dry skin, secure the cables so they are not pulling, and coach normal quiet breathing.
- Somatic tremor
- Irregular jagged spikes. Warm the patient, support the arms and legs, reduce anxiety with explanation, and move limb electrodes closer to the torso only if necessary and documented.
- Sixty-cycle AC interference
- Uniform fuzzy band at 60 hertz. Unplug or move nearby electrical equipment, separate the patient cable from power cords, verify the ground electrode, and keep the patient from touching metal bed rails.
- Artifact in one lead only
- Suspect that lead's electrode or wire. Replace the electrode and reseat the connector rather than restarting the whole setup.
- Suspect lead reversal when a tracing is clean but wrong
- Inverted P, QRS, and T in lead I with normal chest leads indicates right arm and left arm reversal. Correct the electrodes and repeat the tracing rather than sending it as is.
- Remove damaged equipment from service
- A frayed cable with exposed conductor is both an artifact source and an electrical hazard. Tag it and take it out of use.
Safety, Communication, and Professional Responsibilities
19% del examen- Two identifiers, patient-stated
- Have the patient state name and date of birth and verify against the armband and the order. Do not simply call a name and accept whoever answers.· The Joint Commission National Patient Safety Goal 01.01.01
- Explain before you touch
- Describe the procedure in everyday language, tell the patient the test is painless and delivers no current, and answer questions within your scope.
- Honor refusal
- Stop, notify the nurse or ordering provider, and document the refusal. Proceeding without consent can constitute battery, and a family member cannot consent for a competent adult.
- Use interpreters, not family, for language barriers
- A qualified interpreter protects accuracy and privacy; relying on a relative risks both.
- Minimum necessary access
- Look only at the information required for your assigned duties. Browsing a coworker's, neighbor's, or celebrity's chart is a reportable violation regardless of motive.· HIPAA
- No clinical talk in public areas
- Elevators, hallways, cafeterias, and waiting rooms are not private. Overheard discussion is an improper disclosure even without the patient's last name.· HIPAA
- Results go to the provider
- Do not release a tracing or its meaning to the patient, a spouse, or another visitor. Refer results questions to the physician and tell the nurse the question was asked.
- Secure the record
- Do not leave tracings on counters, do not share login credentials, log out of workstations, and dispose of any printed identifiers in secure shredding.· HIPAA
- Hand hygiene at every transition
- Before and after patient contact, after glove removal, and after handling equipment. Gloves are not a substitute for clean hands.· CDC Guideline for Hand Hygiene in Health-Care Settings
- Standard precautions apply to everyone
- Treat all blood and other potentially infectious material as infectious regardless of the patient's known diagnosis.· OSHA 29 CFR 1910.1030
- Report exposure incidents immediately
- Wash the area at once, notify the supervisor without delay, and follow the facility's confidential post-exposure evaluation protocol.· OSHA 29 CFR 1910.1030
- Disinfect and inspect between patients
- Wipe machine surfaces and cables with an approved disinfectant, uncoil wires gently rather than wrapping them tightly, and never immerse a patient cable.
- Follow isolation precautions
- Observe contact, droplet, or airborne precautions posted for the room, and disinfect any equipment that leaves an isolation room.
- Do not interpret for the patient
- Explain that the physician reads the tracing and will discuss the results, and pass the patient's question along to the nurse.
- Lethal rhythms: patient first, help second
- For ventricular fibrillation, pulseless ventricular tachycardia, or asystole, verify the patient, call for help and activate the emergency response, and begin CPR according to your training. Do not finish the test or chart first.
- Report critical findings immediately
- New ST elevation, ventricular tachycardia, third-degree block, symptomatic bradycardia, or a patient with chest pain requires the nurse or physician now, and the patient stays in the department.
- Label every tracing completely
- Name and identifier, date, exact time, technician identification, and any deviation from standard technique or settings.
- Correct errors, never erase them
- Draw a single line through the error so it stays readable, write the correct entry, and initial and date the correction. Never use correction fluid or destroy a record.
- Holter: diary and dryness
- Instruct the patient to record activities and symptoms with times, to keep the monitor and electrodes dry with no showering or swimming, and to avoid removing electrodes for any reason during the recording.
- Holter: normal routine
- The point of the study is to capture everyday events, so the patient should follow a usual routine rather than restricting activity.
- Telemetry: continuous observation
- Change electrodes at least daily, check the transmitter battery, and confirm the signal at the central station before leaving the room.
- Stress test prep
- As directed by the facility, the patient avoids food, caffeine, and tobacco before the test, wears comfortable two-piece clothing and supportive walking shoes, and reviews all medications with the provider, since drugs such as beta blockers blunt the heart rate response.
- Stress test termination
- Stop the test and notify the supervising provider immediately for chest pain, significant ST changes, dangerous arrhythmias, a falling blood pressure, severe shortness of breath, dizziness, or the patient's request to stop.
Cardiac Anatomy, Physiology, and Common Conditions
18% del examen- Right side to the lungs, left side to the body
- Pulmonary circulation is right heart to lungs and back; systemic circulation is left heart to body and back.
- Atrioventricular valves
- Tricuspid on the right, mitral (bicuspid) on the left. They close at the start of ventricular systole to prevent backflow into the atria.
- Semilunar valves
- Pulmonic guards the right ventricular outflow, aortic guards the left. They close at the end of systole to prevent backflow into the ventricles.
- Three layers of the heart wall
- Endocardium inside, myocardium in the middle doing the work, epicardium outside, all within the pericardial sac.
- Conduction pathway order
- SA node, then AV node, then bundle of His, then right and left bundle branches, then Purkinje fibers.
- SA node: 60 to 100 beats per minute
- The primary pacemaker, which is why normal sinus rhythm is defined by that rate range.
- AV junction: 40 to 60 beats per minute
- The backup pacemaker. A rhythm in this range with inverted, absent, or post-QRS P waves is a junctional escape rhythm.
- Purkinje fibers: 20 to 40 beats per minute
- The pacemaker of last resort. Because the impulse starts below the junction, the QRS is wide and no P waves precede it.
- The AV delay is protective
- It allows atrial contraction to complete before the ventricles fire, and it limits how many atrial impulses reach the ventricles in atrial flutter or fibrillation.
- Depolarization equals stimulus to contract
- Atrial depolarization produces the P wave; ventricular depolarization produces the QRS. Ventricular repolarization produces the T wave.
- Systole and diastole
- Systole is contraction and ejection with the AV valves closed. Diastole is relaxation and filling with the AV valves open.
- Cardiac output = heart rate x stroke volume
- Normally about 4 to 8 liters per minute. Stroke volume is the amount ejected by the left ventricle each beat.
- Coronary arteries fill during diastole
- The right and left coronary arteries branch from the base of the aorta and perfuse the myocardium mainly when it is relaxed, which is why very fast rates can provoke ischemia.
- Electrical activity does not guarantee a pulse
- Always assess the patient. A normal-looking rhythm on the monitor in an unresponsive patient is an emergency, not a reassuring finding.
- Angina versus infarction
- Angina is temporary, exertional, relieved by rest or nitroglycerin, and causes no permanent damage. Infarction is prolonged occlusion causing tissue death.
- ST elevation in related leads suggests acute injury
- Leads II, III, and aVF view the inferior wall; V1 through V4 view the anterior wall; I, aVL, V5, and V6 view the lateral wall. Report the finding to the provider immediately.
- Congestive heart failure
- Left-sided failure causes shortness of breath and orthopnea from pulmonary congestion; right-sided failure causes peripheral edema and jugular venous distention.
- Hypertension and hypertrophy
- Chronic pressure overload thickens the left ventricle, producing tall R waves in the left-sided leads and deep S waves in V1 and V2.
- Recognize, report, do not diagnose
- Describe the finding, notify the nurse or physician at once for anything urgent, and leave the interpretation and the conversation with the patient to the provider.
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