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A basic rhythm with normal PQRST intervals/durations. PR should be between 0.12-0.20 seconds; PR interval is normal and remains constant. QRS should be between 0.07 and 0.10 seconds. Regular R-R intervals should be present at a rate of 60-100 bpm (subject 6 years of age or older). Each QRS complex is preceded by a normal P-wave. QT: prolonged QT is noted to be 460 ms or longer in women; longer than 450 ms for men. Short QT is defined as 390 ms or shorter for both genders.

Borys Surawicz MD, FAHA, FACC; Rory Childers MD; Barbara J. Deal MD, FACC; Leonard S. Gettes MD, FAHA, FACC:  AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. Journal of the American College of Cardiology, Volume 53, Issue 11, 17 March 2009, Pages 976-981

Complete LBBB

1. QRS duration greater than or equal to 120 ms in adults, greater than 100 ms in children 4 to 16 years of age, and greater than 90 ms in children less than 4 years of age.
2. Broad notched or slurred R wave in leads I, aVL, V5, and V6and an occasional RS pattern in V5 and V6 attributed to displaced transition of QRS complex.
3. Absent q waves in leads I, V5, and V6, but in the lead aVL, a narrow q wave may be present in the absence of myocardial pathology.
4. R peak time greater than 60 ms in leads V5and V6but normal in leads V1, V2, and V3, when small initial r waves can be discerned in the above leads.
5. ST and T waves usually opposite in direction to QRS.
6. Positive T wave in leads with upright QRS may be normal (positive concordance).
7. Depressed ST segment and/or negative T wave in leads with negative QRS (negative concordance) are abnormal (see part VI of the AHA/ACCF/HRS Expert Consensus Document).
8. The appearance of LBBB may change the mean QRS axis in the frontal plane to the right, to the left, or to a superior, in some cases in a rate-dependent manner.

Incomplete LBBB

1. QRS duration between 110 and 119 ms in adults, between 90 and 100 ms in children 8 to 16 years of age, and between 80 and 90 ms in children less than 8 years of age.
2. Presence of left ventricular hypertrophy pattern.
3. R peak time greater than 60 ms in leads V4, V5, and V6.
4. Absence of q wave in leads I, V5, and V6.

Borys Surawicz MD, FAHA, FACC; Rory Childers MD; Barbara J. Deal MD, FACC; Leonard S. Gettes MD, FAHA, FACC:  AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. Journal of the American College of Cardiology, Volume 53, Issue 11, 17 March 2009, Pages 976-981

Complete RBBB

1. QRS duration greater than or equal to 120 ms in adults, greater than 100 ms in children ages 4 to 16 years, and greater than 90 ms in children less than 4 years of age.
2. rsr′, rsR′, or rSR′ in leads V1or V2. The R′ or r′ deflection is usually wider than the initial R wave. In a minority of patients, a wide and often notched R wave pattern may be seen in lead V1and/or V2.
3. S wave of greater duration than R wave or greater than 40 ms in leads I and V6in adults.
4. Normal R peak time in leads V5 and V6 but greater than 50 ms in lead V1.

Of the above criteria, the first 3 should be present to make the diagnosis. When a pure dominant R wave with or without a notch is present in V1, criterion 4 should be satisfied.

Incomplete RBBB

Incomplete RBBB is defined by QRS duration between 110 and 120 ms in adults, between 90 and 100 ms in children between 4 and 16 years of age, and between 86 and 90 ms in children less than 8 years of age. Other criteria are the same as for complete RBBB. In children, incomplete RBBB may be diagnosed when the terminal rightward deflection is less than 40 ms but greater than or equal to 20 ms. The ECG pattern of incomplete RBBB may be present in the absence of heart disease, particularly when the V1 lead is recorded higher than or to the right of normal position and r′ is less than 20 ms.

The terms rsr′ and normal rsr′ are not recommended to describe such patterns, because their meaning can be variously interpreted. In children, an rsr′ pattern in V1 and V2 with a normal QRS duration is a normal variant.

Borys Surawicz MD, FAHA, FACC; Rory Childers MD; Barbara J. Deal MD, FACC; Leonard S. Gettes MD, FAHA, FACC:  AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. Journal of the American College of Cardiology, Volume 53, Issue 11, 17 March 2009, Pages 976-981

Nonspecific or Unspecified Intraventricular Conduction Disturbance

QRS duration greater than 110 ms in adults, greater than 90 ms in children 8 to 16 years of age, and greater than 80 ms in children less than 8 years of age without criteria for RBBB or LBBB. The definition may also be applied to a pattern with RBBB criteria in the precordial leads and LBBB criteria in the limb leads, and vice versa.

Beats originating from ectopic pacemaking tissue within the atria. Conduction originates from the atrium with variable P wave morphology. Atrial rate is less than 100 bpm. PR interval is within the normal range. QRS conduction is of normal duration.

These beats originate from within the region of the AV node, resulting in an absence of p-waves, or abnormal  p-waves with PR intervals of <.12 secs. (these retrograde p-waves are typically inverted in leads II, III, and AVF).  Ventricular conduction is usually normal resulting in a normal QRS.  These beats are followed by a compensatory pause

Ventricular Ectopic Beat (VEBS)

All ectopic beats originating below the Atria and AV Node in the ventricles,bypasses the His-Purkinje system, and depolarises the ventricles directly.

When the rate of supraventricular impulses arriving at the AV node or ventricle is less than the intrinsic rate of the ectopic pacemaker, a ventricular escape beat may occur.  The QRS complexes of a ventricular escape beat are broad (≥ 120 ms) and can have a LBBB or RBBB morphology at a rate of 20-40 bpm. Note: escape complexes originating from the ventricular septum may have near normal duration and morphology.

A pacemaker lead wire placed in the right ventricle produces a left bundle branch morphology on the ECG. 

An event occurring anytime during an ECG recording (that is NOT marked unreadable); which is treated by the analysis algorithm as a heartbeat of supraventricular or ventricular origin.

An event occurring anytime during an ECG recording (that is NOT marked unreadable); which is treated by the analysis algorithm as a heartbeat of supraventricular or ventricular origin.

Ectopic impulses which are premature in relation to the expected impulse of the basic rhythm. QRS is abnormal in duration (>120ms.) and configuration with accompanying ST segment and T wave changes. Not occuring on the T-wave of the preceeding beat. Typically followed by a compensatory pause. Retrograde capture of the atria may or may not occur.

Two types of 2nd degree AV block are identified as:
Mobitz Type I (Wenckeback) AV Block -  A second degree AV Block in which a singular ventricular beat is dropped in a cyclic fashion. With the first atrial impulse of the cycle, there is usually a normal P-R interval. With each succeeding beat, the P-R interval becomes progressively longer, until after several beats an atrial contraction fails to initiate a ventricular response (which results in a long diastolic pause). The P-P interval remains relatively constant.  The RR interval progressively shortens with each beat of the cycle.  The number of beats in each cycle is not necessarily constant.
Mobitz Type II AV Block - Recordings in which a single ventricular beat is dropped periodically. However, the P-P and P-R intervals are constant throughout. A 2nd degree AV Block with intermittent non-conducted P waves without progressive prolongation of the PR interval.   The PR interval in the conducted beats remains constant.  However, First Degree AV Block may also be present.  The P waves ‘march through’ at a constant rate.   The RR interval surrounding the dropped beat(s) is an exact multiple of the preceding RR interval (e.g. double the preceding RR interval for a single dropped beat, treble for two dropped beats, etc).  There may be no pattern to the conduction blockade, or alternatively there may be a fixed relationship between the P waves and QRS complexes, e.g. 2:1 block, 3:1 block.   More severe heart blocks in which the ventricular response is variable, resulting in mixed 2:1, 3:1, or 4:1 AV Block or even higher grade AV Block is often called Advanced Heart Block. The atrial rate (P-P interval) is usually constant. First Degree AV Block may also be present. 

As a basic definition, Pacemaker Rhythm is the propagation of cardiac depolarization by an implanted electrical device; as well as the interaction of such devices with a patient’s native cardiac conduction system. Atrial and/or ventricular pacing can be detected in an ECG as a pacemaker spike occurring before a P-wave (atrial) or before a QRS (ventricular) or both (Dual chamber). A pacemaker lead wire placed in the right ventricle will produce a left bundle branch block pattern on the ECG. A lead wire in the left ventricle will produce a right bundle branch pattern.

Dual chamber pacemakers use two leads, with one lead in the right atrium and the other in the right ventricle.

Bi-ventricular pacemakers use three leads, one for each ventricle and one for the right atrium; used for cardiac resynchronization therapy to restore synchronous ventricular contractions. 

Fixed rate (Asychronous) pacing occurs at a pre-determined rate regardless of the patient's heart rate.

Demand (Synchronous) pacing occurs only when the patient's heart rate falls below a specific rate.

Wolff-Parkinson-White syndrome is associated with an accessory pathway that bypasses normal conduction through the AV node, bringing about a direct connection between the atrial electrical system and ventricles (resulting in a more rapid depolarization of the ventricles). This “pre-excitation” results in a shortened PR interval, and a slurring of the upstroke of the QRS complex (delta wave) on the ECG. The ability to bypass the AV node, or the establishment of a reentry circuit involving the accessory pathway, can result in the production of paroxysmal tachycardias, often referred to as atrioventricular reentry tachycardias (AVRT). The following definition is taken from the following AHA/ACCF/HRS Expert Consensus Document:
Borys Surawicz MD, FAHA, FACC; Rory Childers MD; Barbara J. Deal MD, FACC; Leonard S. Gettes MD, FAHA, FACC: AHA/ACCF/HRS Recommendations for the Standardization and Interpretation of the Electrocardiogram: Part III: Intraventricular Conduction Disturbances A Scientific Statement From the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. Journal of the American College of Cardiology, Volume 53, Issue 11, 17 March 2009, Pages 976-981

Ventricular Preexcitation of Wolff-Parkinson-White Type
Whether preexcitation is full or not cannot be determined from the body surface ECG, but the following criteria are suggestive of full preexcitation:
1. PR interval (assuming no intra-atrial or interatrial conduction block) less than 120 ms during sinus rhythm in adults and less than 90 ms in children.
2. Slurring of initial portion of the QRS complex (delta wave), which either interrupts the P wave or arises immediately after its termination.
3. QRS duration greater than 120 ms in adults and greater than 90 ms in children.
4. Secondary ST and T wave changes.

Ventricular Flutter: is an extreme form of VT often seen at  rates > 300  BPM.  The QRS complexes show a typical sinusoidal pattern that looks the same when turned upside down.  Ventricular Flutter often degenerates into Ventricular Fibrillation

Sustained Ventricular Tachycardia:  an episode of ventricular tachycardia with a heart rate of greater than 120 beats per minute, persisting more than 30 seconds.  In Monomorphic VT, all ventricular beats have the same QRS configuration. A right bundle branch block (RBBB) pattern is defined by a mono-, bi-, or triphasic R wave or qR in V1; LBBB pattern is defined by a QS, rS, or qrS in V1.  In Polymorphic VT, ventricular beats may have multiple QRS configurations

Non-sustained Ventricular Tachycardia (NSVT): an episode of ventricular tachycardia with a heart rate greater than 120 beats per minute, lasting for at least three beats and terminating spontaneously in < 30 seconds. In Monomorphic VT, all ventricular beats have the same QRS configuration. A right bundle branch block (RBBB) pattern is defined by a mono-, bi-, or triphasic R wave or qR in V1; LBBB pattern is defined by a QS, rS, or qrS in V1. In Polymorphic VT, ventricular beats may have multiple QRS configurations.

A pause in the cardiac rhythm due to momentary failure of the sinus node to initiate an impulse. This will result in at least one (1) "dropped beat". The pause between normal conducted beats should be at least twice the immediately preceding P-P interval.  A differentiating factor between whether it is called Sinus Pause or Sinus Arrest  is that in Sinus Pause,  the pause is a multiple of the preceding R-R intervals;  and in Sinus Arrest the pause is not a multiple of the preceding R-R intervals.  The severest form of sinus arrest (the absence of 4 or more beats) is called Asystole.

A form of multifocal atrial rhythm at a rate of <120 BPM.   WAP exists when at least 3 ectopic foci in the atrium generate action potentials that result in ventricular conduction.  In WAP, each QRS will be preceded by a p-wave (with varying morphologies reflecting varying atrial ectopic foci).  At rates greater than or equal to 120 BPM WAP is called Multifocal Atrial Tachycardia.

A form of supraventricular tachycardia associated with the generation of impulses from a focus in the region of the atrioventricular node due to A-V disassociation. The AV junction's intrinsic rate is 40-60 bpm. Therefore, an Accelerated Junctional rhythm is from 60-100 bpm, and becomes junctional tachycardia at a rate of >100 bpm. It can coexist with other supraventricular tachycardias due to the disassociation between the SA node and the AV node. Junctional tachycardia can appear similar to atrioventricular nodal reentrant tachycardia (AVNRT), where when a reentrant circuit forms within or just next to the AV node “The surface electrocardiographic findings of Juctional Ectopic Tachycardia (JET) can be variable, depending on whether the tachycardia is paroxysmal or incessant, and on whether ventriculo-atrial (VA) conduction occurs during tachycardia. An incessant JT with 1:1 VA conduction will present as a regular narrow-QRS tachycardia with short RP interval and retrograde P waves, mimicking typical AV nodal reentrant tachycardia (AVNRT). By contrast, in paroxysmal JET without VA conduction, the electrocardiogram (ECG) will show an irregular narrow-QRS tachycardia with intermittent sinus capture beats. During periods of frequent irregular junctional ectopy without obvious P waves or with variable distortion of sinus P waves, the surface ECG can mimic the appearance of multifocal atrial tachycardia or atrial fibrillation. Finally, JT with bundle branch block can mimic ventricular tachycardia involving the specialized conduction system, particularly if VA conduction is absent.” From: Douglas P Zipes, M.D. and Jose’ Jalife, M.D.: “Cardiac Electrophysiology From Cell to Bedside”; Sixth Edition; 2014 Elsevier Ltd. ISBN: 978-1-4557-2856-5

Junctional Tachycardia presents:

• Narrow complex rhythm; QRS duration < 120ms (unless pre-existing bundle branch block or rate-related aberrant conduction).
• Ventricular rate usually >100 bpm.
• Retrograde P waves may be present and can appear before, during or after the QRS complex; and are usually inverted in the inferior leads (II, III, aVF), upright in aVR + V1.
• AV dissociation may be present with the ventricular rate usually greater than the atrial rate.

Ventricular Fibrillation: is characterized as a chaotic irregular unformed QRS deflections in the baseline with varying amplitudes in which there are no identifiable P waves, or T waves. Heart rates are usually >500bpm.

An ectopic P-wave occurring so soon after a normal sinus beat, that the ventricle is still in a refractory period and will not respond. A less than full compensatory pause will usually occur, and will be less than twice the preceding normal R-R interval.

A slow, undulating baseline in the ECG due to respiration, patient movement, or movement of the ECG electrodes/Lead Wires.  Generated waveforms can be broad, or narrow, brief, or prolonged (as well as any combination of these).

Fuzzy, irregular baseline often caused by physical tremors of a patient’s muscles/skin due to neurological disorders (like Parkinsons), chills, shivering, muscle strain, etc.

Jagged abrupt movement of the baseline in one or more ECG leads resulting from poor electrode contact, broken lead wires, patient movement.  

Complete loss of the ECG signal on one or more leads.