The sinus node is protected by a loose matrix of connective tissueConnective tissue in the heart provides structure, strength and protection to ensure efficient and effective electrical conduction and mechanical function. Connective tissue in the heart provides structure, strength and protection to ensure efficient and effective function. Connective tissue protects necessary.... In advanced age, this loose matrix can become denser. A possible result of this denser tissue is the sinus node initiated impulse(s) may be prevented from entering the atrium. If this occurs, a P waveA 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... is not generated. The next visible P wave, though, will arrive at an expected time as if the sinus node kept firing in sequence (and 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... does exactly that).
Sinus impulses can be inhibited from entering the right atrium due to dense tissue that surrounds the SA node. The next impulse that does enter the right atrium will begin a P wave right on time because the sinus node does not cease firing.
The sinus node does not produce enough voltage to generate its own electrical waveformA wave of an ECG. 1. Six Second ECG Guidebook (2012), T Barill, p. 209 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. The production of an upright P wave points to a sinus location for impulse generation (upright P wave in lead II is caused by the directed atrial 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... towards a positive electrode – in lead II this is the electrode placed near or on the left leg).
A sinus exit block can cause palpitations (i.e. missed beats) or even dizziness due to reduced heart rateThe number of QRS complexes per minute; note that HR may not equal perfused pulse rate. See also: - Step 1 Heart Rate - Rate - Rule of 300s (Triplicate Method) - Six Second Count - The Caliper Method 1.... and blood flowThe purpose of the cardiac cycle is to effectively pump blood. The purpose of the cardiac cycle is to effectively pump blood. The right heart delivers deoxygenated blood to the lungs. Here oxygen is picked up and carbon dioxide is.... A permanent implanted pacemakerAn electronic pulse generator that stimulates depolarization of the atria and/or the ventricles. 1. Six Second ECG Guidebook (2012), T Barill, p. 201 may be warranted.
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. 206