CRAT key terms

A normal heart rhythm originating in the sinoatrial node, shown by upright P waves before each QRS complex in lead II at a rate of 60 to 100 beats per minute.

The heart's natural pacemaker, a small cluster of specialized cells in the upper right atrium that spontaneously generates electrical impulses and normally sets the rate of the heart.

The first deflection on an ECG tracing, representing electrical activation of the atria. It is normally upright in lead II and precedes each QRS complex in sinus rhythm.

The time from the start of atrial activation to the start of ventricular activation, measured from the beginning of the P wave to the beginning of the QRS complex and normally lasting 0.12 to 0.20 seconds.

The sharp deflection representing electrical activation of the ventricles. A normal complex is narrow, under 0.12 seconds, while widening suggests abnormal conduction through the ventricles.

The total time from the start of ventricular activation to the end of ventricular recovery, measured from the beginning of the QRS complex to the end of the T wave and corrected for heart rate.

The flat portion of the tracing between the end of the QRS complex and the start of the T wave, representing the plateau phase of ventricular recovery. Elevation or depression here can signal ischemia.

The junction where the QRS complex ends and the ST segment begins. It is the reference point used to judge whether the ST segment is elevated or depressed relative to the baseline.

The deflection following the QRS complex that reflects ventricular recovery, or repolarization. It is normally upright in most leads and can invert or peak with ischemia or electrolyte imbalance.

The ability of certain cardiac cells to generate electrical impulses on their own without outside stimulation. Pacemaker cells in the sinoatrial node have the highest natural rate.

A mechanism of abnormal rhythm in which an electrical impulse travels in a loop and re-excites tissue it has already passed. It underlies many tachycardias, including atrial flutter and some ventricular rhythms.

A brief interval after cardiac cells activate during which they cannot be stimulated again, protecting the heart from excessive rates and shaping where abnormal impulses can travel.

The volume of blood the heart pumps each minute, calculated as heart rate multiplied by stroke volume. Rhythm disturbances can reduce it by lowering either factor.

The amount of blood ejected from a ventricle with each contraction. It depends on how much the ventricle fills, how forcefully it contracts, and the resistance it pumps against.

The number of times the heart beats per minute. On a standard tracing it can be estimated by dividing 300 by the number of large boxes between QRS complexes.

A heart rate slower than normal, generally under 60 beats per minute in an adult. It may be a normal finding in athletes or may cause dizziness and low blood pressure.

A heart rate faster than normal, generally over 100 beats per minute in an adult. Sustained rapid rates can reduce filling time and lower cardiac output.

A rapid, irregular rhythm in which the atria quiver instead of contracting in an organized way. The tracing shows no distinct P waves and an irregularly irregular ventricular response.

An organized rapid atrial rhythm producing a characteristic sawtooth pattern of flutter waves instead of normal P waves, often with a regular ventricular response at a fixed conduction ratio.

A rhythm in which the spacing between QRS complexes varies unpredictably, with no repeating pattern. Atrial fibrillation is the classic cause.

A beat that occurs earlier than expected in the underlying rhythm, arising from an irritable focus in the atria or ventricles. It is usually followed by a pause before the next normal beat.

An early beat arising from the ventricles, seen as a wide, bizarre QRS complex without a preceding P wave. Frequent or multifocal forms may warn of more dangerous rhythms.

A rapid rhythm originating in the ventricles, usually with wide QRS complexes at a rate above 100 beats per minute. It may be stable or may deteriorate into a pulseless state.

Chaotic, disorganized electrical activity in the ventricles with no identifiable QRS complexes. The heart cannot pump effectively, and this rhythm is a cardiac arrest emergency requiring immediate defibrillation.

The absence of any electrical activity on the tracing, appearing as a flat line. It is a cardiac arrest rhythm that is not shockable and is treated with CPR and medications.

An organized electrical rhythm on the monitor that produces no detectable pulse or effective circulation. Treatment focuses on finding and correcting the underlying cause.

A delay or failure of electrical conduction between the atria and ventricles, graded from first to third degree. Higher degrees can slow the rate severely and require pacing.

A consistent prolongation of the PR interval beyond 0.20 seconds, with every P wave still followed by a QRS complex. It usually causes no symptoms and needs no treatment.

A relay station between the atria and ventricles that delays the electrical impulse briefly before passing it to the ventricles, allowing the atria to empty into the ventricles.

A short tract of conducting fibers that carries the electrical impulse from the atrioventricular node into the ventricles, where it splits into the right and left bundle branches.

Specialized conducting cells that spread the electrical impulse rapidly through the ventricular muscle walls, allowing the ventricles to contract together and pump efficiently.

A conduction delay in the right or left bundle branch that widens the QRS complex, usually beyond 0.12 seconds. It changes the shape of the tracing but does not always impair pumping.

A beat that arises from a lower pacemaker site when the normal pacemaker fails or pauses too long, protecting the heart from a prolonged pause. It often appears wide and late.

A premature beat that lands during the vulnerable recovery phase of the previous beat, shown by a QRS complex falling on the T wave. It can trigger dangerous ventricular rhythms.

A form of polymorphic ventricular tachycardia in which the QRS complexes twist around the baseline, associated with a prolonged QT interval. It can degenerate into ventricular fibrillation.

Delivery of an unsynchronized electrical shock across the chest to stop chaotic ventricular activity and allow a normal rhythm to resume. It is used for ventricular fibrillation and pulseless ventricular tachycardia.

Delivery of a shock synchronized to the QRS complex to convert an organized rapid rhythm back to normal. Synchronization avoids shocking during the vulnerable recovery phase.

Electrical or movement interference on the tracing that mimics or distorts real cardiac activity, such as patient shivering, loose electrodes, or nearby equipment. It must be recognized before treating a rhythm.

The correct positioning of monitoring electrodes on the body, which determines the shape and accuracy of the tracing. Poor placement produces distorted complexes and false alarms.