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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.

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.

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.

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.