The PR intervalA period measured on rhythm strip paper that measures a wave and a segment; the distance measured is equal to time taken as an ECG is voltage over time; a PR interval for example is measured from the beginning of... is the time from the beginning of the atrial wave to the beginning of myocardial depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... of the ventriclesThe larger chambers of the heart (3 times the volume and muscle thickness than the atria), responsible for the pumping of blood to the lungs and the rest of the body.. Normally this takes 0.12 – 0.20 seconds. When the time taken is over 0.20 seconds, this is called a long PR interval.
Following the wave of atrial depolarization which produces a P wave on an ECGElectrocardiogram; also called an EKG; a representation of electrical voltage measured across the chest over a period of time. 1. Six Second ECG Guidebook (2012), T Barill, p. 196, is the time for the impulse to proceed across two small structures – the AV nodeIs located in the inferior aspect of the right atria; functions to slow the conduction speed to allow for atrial conduction prior to ventricular conduction (atrial kick); also serves as a pacemaker if the SA node fails to fire. The... and the bundle of HisPart of the AV junction, the bundle of His conducts the impulse through the fibrous plate that separates the atria and the ventricle; the bundle of His is also a pacemaker, firing at 40-60/minute. The bundle of His serves as... – that connect the atriaRight and left atria (1/3 volume and muscle mass of the ventricles) pump blood to the ventricles. Chambers and Layers of the Heart 1. Six Second ECG Guidebook (2012), T Barill, p. 190 to the ventricles. Like the SA nodeThe SA node, usually the dominant pacemaker, is located in the right atrium at the opening of the superior vena cava. The SA (sinoatrial) node is a clump of hundreds of specialized cardiac cells that have the ability to self-initiate..., these two structures – called the AV junctionConducts the impulse through the fibrous plate that separates the atria and the ventricles; consists of the AV node and the bundle of His; functions also to slow the conduction speed to allow for atrial conduction prior to ventricular conduction... – are too small to generate enough voltage to produce an electrical wave. The time taken to cross these structures are captured in the PR line.
The expected conduction speed measured from the beginning of atrial depolarization (beginning of the P wave) to the beginning of the ventricular depolarizationThe depolarization of the myocardium is represented on an ECG by a series of waveforms, one for atrial depolarization and soon after a larger waveform for ventricular depolarization. Normal ventricular depolarization begins with the septal fascicle of the left bundle... (beginning of the QRS complexThe electrical representation of ventricular depolarization; the atrial repolarization is also a part of the QRS. ECG interpretation relies heavily on the QRS complex. The QRS complex represents the depolarization of the ventricles. The repolarization of the atria is also...) is captured in the PR interval. This is typically .12-.20 seconds (3-5 mm on a rhythmOften refers to a discernible pattern in time or distance between QRS complexes and/or P waves. strip).
A long PR interval is usually caused by a longer PR line than a wider P wave that is longer. The PR line is most reflected from the time taken for the impulse to cross the AV junctionConnects the atria to the ventricle and slows the impulse conduction speed sufficiently to allow for atrial kick; the junction consists of the AV node and the bundle of His; the junction is a supraventricular structure. 1. Six Second ECG.... For a PR interval longer than .20 seconds, consider how and why this is so. Might a medication be having considerable effect on nodalCommonly refers to the junction; for example, junctional rhythm is also known as nodal rhythm; may also refer to the sinoatrial node. 1. Six Second ECG Guidebook (2012), T Barill, p. 200 conduction speed (ABCD – amiodarone, beta blocker, calcium channel blocker, digoxin)? Might there be nodal structural disease or ischemiaInsufficient supply of oxygen to meet the oxygen demands of tissue. Anaerobic metabolism becomes increasingly important during periods of ischemia. Ischemia results from an inadequate blood flow that fails to meet the oxygen demands (energy demands) of tissues. If tissues... effecting the area? Occasionally, this is caused simply because a person has a larger heart – larger person or enlarged heart – that takes a little longer for an impulse to cross. This can also be an unexplained phenomena as well.
Atrioventricular blocksAtrioventricular blocks (AV blocks) result from a conduction disturbance at or just below the AV junction. The 3rd step of the 3 step process prompts us to check the P waves and the PR interval. Abnormal PR intervals and lonely... (AV blocks) result from a conduction disturbance at or just below the AV junction. The 3rd step of the 3 step process prompts us to check the P wavesA wave generated from the depolarization of the atria; the P wave is upright when originating from the SA node. The P wave represents the depolarization of the right and left atria. The P wave begins with the first deviation... and PatternPattern refers to the repeating components of an ECG rhythm in a predicative order. An ECG rhythm that is initiated by one of several intrinsic pacemaker sites of a heart will often generate a regular, even rhythm pattern. This can... with a focus on the PR interval. Abnormal PR intervalsThe time and interval measured from the beginning of the P wave to the beginning of the QRS; should be called the PQ interval; normal PR interval is 0.12-0.20 seconds. The PR interval is measured from the start of the... and lonely ‘P’ waves define the type of AV block.
From a clinical perspective, the severity of a block is similar to the severity of burns. The higher the degree of burn the more aggressive the treatment. Similar escalation in treatment is required for higher levels of AV blocks. The affects of 2nd degree type II and 3rd degree AV blocks on cardiac outputWhat is it? Why is it Vital? The amount of blood pumped out of the ventricle in a minute (most often refers to the blood pumped by the left ventricle) What is cardiac output? Simply, cardiac output is the amount... can be much more significant than the affects of 2nd degree type I and 1st degree AV blocks.
First degree AV block is simply conducts slower through the AV junction. First degree AV block can be a benign finding (particularly athletes). Other causes include ischemia, increased vagal tone, and the effects of medications that slow conduction across the AV junction: digoxin, calcium channel blockers, and beta blockers for example. As a result of the slowed junctional conductivityThe ability of a cell to receive and transmit an electrical impulse. 1. Six Second ECG Guidebook (2012), T Barill, p. 194, the PR interval of first degree AV block is longer than normal (> 5 mm in width).
The significance of 1st degree block is revealed in its position in the naming of a rhythm. The underlying rhythmWhile a rhythm as a whole may be irregular, segments may be regular. These regular periods are often referred to as the underlying rhythm. Apply the three step method to the underlying rhythm first. When naming a rhythm, the underlying... is identified first followed by descriptors of any abnormal components such as 1st degree AV block.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 125-126, 189