CRAT flashcards

31 cards. Read the term and the definition here. The deck at the top of this page is optional.

Normal PR interval

The PR interval measures from the start of the P wave to the start of the QRS and normally lasts 0.12 to 0.20 seconds, or three to five small boxes on standard paper.

Regularity assessment rule

Compare consecutive R-R intervals; a variation greater than 0.12 seconds, about three small boxes, defines an irregular rhythm and prompts a search for atrial fibrillation, ectopy, or block.

Wide QRS definition

A QRS complex of 0.12 seconds or more, equal to three small boxes, is wide and indicates ventricular origin, bundle branch block, pre-excitation, or a paced rhythm.

Third-degree AV block

Complete AV block shows no consistent PR relationship; P waves and QRS complexes march independently, and the escape rhythm may be junctional or ventricular depending on the block level.

Wenckebach pattern

Second-degree AV block type I shows progressive PR lengthening over successive beats until one P wave fails to conduct, usually followed by a shorter PR after the dropped beat.

Atrial fibrillation features

Atrial fibrillation produces an irregularly irregular ventricular response with no distinct P waves; the baseline shows fibrillatory waves instead of organized atrial activity.

Ventricular tachycardia red flags

AV dissociation, fusion beats, capture beats, extreme axis, and precordial concordance all favor ventricular tachycardia over supraventricular tachycardia with aberrancy in a wide-complex rhythm.

Sinus rhythm criteria

Sinus rhythm requires a rate of 60 to 100 bpm, regular R-R intervals, an upright P wave in lead II before every QRS, and a normal PR interval and QRS duration.

Standard ECG calibration

At 25 mm/s and 10 mm/mV, one small box represents 0.04 seconds and 0.1 mV, while one large box represents 0.20 seconds and 0.5 mV.

V1 and V2 placement

V1 sits at the fourth intercostal space on the right sternal border and V2 at the fourth intercostal space on the left sternal border, both in the same horizontal plane.

Significant ST elevation

ST elevation measured at the J point is significant when 1 mm or more in two contiguous limb leads or 2 mm or more in two contiguous precordial leads, with sex-specific V2-V3 thresholds.

Contiguous inferior leads

Leads II, III, and aVF view the inferior wall; ST changes in two of these three leads indicate an inferior injury pattern, often from right coronary artery occlusion.

Bazett QTc formula

The corrected QT equals the measured QT divided by the square root of the R-R interval in seconds; normal values are under 0.44 seconds in men and 0.46 seconds in women.

Sokolow-Lyon LVH criteria

Left ventricular hypertrophy is suggested when the S wave in V1 plus the R wave in V5 or V6 totals 35 mm or more, though voltage criteria are less reliable in young patients.

Axis quadrant method

A positive QRS in leads I and aVF indicates normal axis; positive I with negative aVF is left axis; negative I with positive aVF is right axis; both negative is extreme axis.

Hyperkalemia ECG changes

Hyperkalemia produces tall peaked T waves, PR prolongation, loss of P waves, and QRS widening that can progress to a sine wave pattern and cardiac arrest.

Reciprocal ST depression

ST depression in leads opposite an injury site, such as inferior depression with a high lateral infarct, supports the diagnosis of acute transmural ischemia rather than a benign change.

Intrinsic pacemaker rates

The SA node fires at 60 to 100 bpm, the AV junction at 40 to 60 bpm, and ventricular Purkinje fibers at 20 to 40 bpm, providing progressively slower backup rhythms.

AV nodal delay

The AV node slows conduction by roughly 0.1 seconds, allowing atrial contraction to complete ventricular filling before the ventricles depolarize and contract.

Cardiac output formula

Cardiac output equals heart rate multiplied by stroke volume; a normal resting value is about 4 to 8 liters per minute, with stroke volume around 60 to 100 mL.

Frank-Starling relationship

Increasing preload stretches ventricular fibers and increases stroke volume up to a physiologic limit, beyond which excessive stretch reduces contractile efficiency and cardiac output.

Right coronary artery supply

The right coronary artery supplies the SA node in about 60 percent of people and the AV node in about 85 to 90 percent, which is why inferior infarcts often cause bradyarrhythmias.

Left ventricular wall thickness

The left ventricle has a thicker myocardium than the right because it pumps against systemic pressures near 120 mmHg while the right ventricle faces pulmonary pressures near 25 mmHg.

Atrial contribution to filling

Atrial systole contributes roughly 20 percent of ventricular filling at rest, a contribution that becomes more important when ventricular compliance is reduced or the rate is fast.

Vagal effect on conduction

Parasympathetic stimulation through the vagus nerve slows SA node firing and AV nodal conduction via muscarinic receptors, lowering heart rate and prolonging the PR interval.

Adult defibrillation energy

For ventricular fibrillation or pulseless ventricular tachycardia, biphasic shocks use 120 to 200 J and monophasic shocks use 360 J, with compressions resumed immediately after delivery.

Synchronized cardioversion purpose

Synchronized cardioversion times the shock to the R wave to avoid delivering energy during the T wave, which could provoke ventricular fibrillation in a patient with a pulse.

Adenosine dosing for SVT

Adenosine is given as a 6 mg rapid IV push with a saline flush, followed by 12 mg if the rhythm persists; its half-life is under 10 seconds.

Atropine for bradycardia

Symptomatic bradycardia is treated with atropine 1 mg IV every 3 to 5 minutes to a maximum of 3 mg, with transcutaneous pacing used if atropine fails.

High-quality CPR parameters

Compressions are delivered at 100 to 120 per minute to a depth of at least 5 cm but no more than 6 cm, with full recoil and interruptions kept under 10 seconds.

Pulse oximetry limitations

SpO2 readings become unreliable with poor peripheral perfusion, motion artifact, nail polish, or severe anemia, so values must be correlated with rhythm and clinical status.