CRAS key terms

The ability of a cardiac cell to spontaneously generate an electrical impulse without outside stimulation. Pacemaker cells in the sinoatrial node have the highest automaticity, so they normally set the heart rate.

A small cluster of specialized cells in the upper right atrium that normally starts each heartbeat. It fires faster than any other pacemaker tissue, making it the heart's primary natural pacemaker.

A structure at the junction of the atria and ventricles that delays electrical signals before passing them to the ventricles. This delay lets the atria finish emptying so the ventricles can fill before they contract.

A short tract of conducting fibers that carries impulses from the atrioventricular node into the ventricles. It divides into right and left bundle branches that spread activation across the ventricular muscle.

The brief time after a cardiac cell fires when it cannot be excited again, or can be excited only by a strong stimulus. It protects the heart from excessive firing and limits how fast tissue can conduct.

A circuit in which an impulse travels around a loop of tissue and re-excites the tissue it just passed. It requires slowed conduction and a unidirectional block, and it underlies many tachyarrhythmias.

An arrhythmia mechanism in which an impulse is started by an afterdepolarization, an abnormal rise in cell voltage that occurs during or just after repolarization. It is often linked to digitalis toxicity and long QT syndrome.

A heartbeat that starts from a focus outside the normal sinoatrial node. It appears early in the cycle and is named after its origin, such as a premature atrial or premature ventricular contraction.

The first deflection on an ECG, representing electrical activation of the atria. Its shape, size, and relationship to the QRS help identify the rhythm and whether the atria are firing normally.

The time from the start of atrial activation to the start of ventricular activation on the ECG, normally about 0.12 to 0.20 seconds. It reflects conduction through the atrioventricular node and His bundle.

The ECG waveform produced by ventricular depolarization, normally narrow because activation spreads quickly through the conduction system. A wide QRS suggests delayed or abnormal ventricular conduction.

The time from the start of ventricular depolarization to the end of ventricular repolarization on the ECG. It is corrected for heart rate, and a prolonged value raises the risk of dangerous ventricular arrhythmias.

A rhythm with no detectable electrical activity and no effective mechanical contraction. It appears as a flat line on the monitor and is treated with high-quality CPR and epinephrine, not defibrillation.

An organized rhythm on the monitor that does not produce a palpable pulse or effective blood flow. Treatment focuses on finding and correcting the underlying cause, such as hypovolemia or tension pneumothorax.

A portable device worn continuously, usually for 24 to 48 hours, that records every heartbeat during normal activity. It is used to catch intermittent arrhythmias that a brief office ECG would miss.

A small monitor worn for weeks that records only when the patient activates it or when an abnormal rhythm is detected. It is useful for symptoms that occur infrequently.

Recording the heart's electrical activity while the patient goes about daily life, using devices such as Holter monitors, event recorders, or patch monitors. It links symptoms to rhythms over time.

A procedure in which catheters inside the heart record electrical signals and deliver timed stimuli to test conduction and provoke arrhythmias. It maps the mechanism and guides treatment such as ablation.

Delivering precisely timed electrical impulses through a catheter to test how the heart responds. It can measure conduction times, check for inducible arrhythmias, and assess device or drug effects.

Using a catheter to deliver energy, usually radiofrequency or cryothermal, that destroys a small area of tissue causing an arrhythmia. It is used to cure or control many supraventricular and ventricular arrhythmias.

A medication given to prevent, slow, or stop abnormal heart rhythms. Drugs are grouped by their main electrical effect, and each class has distinct uses and adverse effects.

A broad-spectrum antiarrhythmic used for ventricular and atrial arrhythmias. It can affect the thyroid, lungs, liver, and eyes, so patients need periodic monitoring and education about warning symptoms.

A drug that blocks the effects of adrenaline on the heart, slowing the heart rate and reducing the force of contraction. It is used for many tachyarrhythmias and to protect patients with heart failure.

Medication that reduces the blood's ability to clot, lowering stroke risk in patients with atrial fibrillation. Choice of agent depends on kidney function, bleeding risk, and other factors.

A tool that estimates stroke risk in atrial fibrillation using factors such as heart failure, hypertension, age, diabetes, and prior stroke. A higher score supports the use of anticoagulation.

An implanted device that delivers small electrical pulses to the heart when the natural rate is too slow or conduction fails. It can pace the atrium, the ventricle, or both.

An implanted device that monitors the heart and delivers a shock or rapid pacing to stop dangerous ventricular arrhythmias. It may also pace the heart like a standard pacemaker.

The response of heart muscle to a pacing pulse, seen as a P wave or QRS complex after the stimulus. Loss of capture means the pulse is not producing a contraction.

A device's ability to detect the heart's own electrical signals so it can decide when pacing is needed. Undersensing causes unnecessary pacing, while oversensing can cause pauses or inappropriate shocks.

Delivering a strong electrical shock to stop a disorganized, life-threatening ventricular rhythm and allow the heart's normal pacemaker to resume control. Early defibrillation is the key to survival in cardiac arrest.

A common arrhythmia in which the atria quiver chaotically instead of contracting in an organized way, producing an irregular pulse. It raises the risk of stroke and heart failure.

A consistent delay in conduction from the atria to the ventricles, shown by a PR interval longer than 0.20 seconds. Every atrial impulse still reaches the ventricles, so it is usually benign.

An early beat that starts in the ventricles and produces a wide, unusual QRS complex, often followed by a pause. Frequent or complex forms may need further evaluation.

A dangerous ventricular tachycardia in which the QRS complexes twist around the baseline. It is linked to a prolonged QT interval and is treated by correcting causes and giving magnesium.

Teaching patients about their rhythm disorder, medications, devices, and warning signs so they can take an active role in their care. It should use plain language and be checked for understanding.

Transmitting data from an implanted device to a clinic without an office visit. It allows early detection of device problems or arrhythmias and supports timely follow-up.

Practices that limit exposure to x-rays during procedures, including shielding, distance, and time limits. Staff should wear dosimeters and follow the principle of keeping exposure as low as reasonably achievable.

A brief, required pause before a procedure in which the team confirms the patient, the site, and the planned intervention. It is a core safety practice that prevents wrong-patient and wrong-site errors.