The downward placement of the ST segmentSegment (line) between the end of the QRS complex and the beginning of the T wave; the end of the QRS is marked by the J point. Between the QRS complex and the T wave, lies the ST segment. The... greater than 1 mm from the isoelectric lineAlso called the baseline, the straight line that is present when no electrical activity is present. The baseline or isoelectric line is a reference point for the waves, intervals and segments.While the PR segment is often used as the baseline,...; suggestive of cardiac ischemiaThe ability to identify cardiac ischemia, injury and infarction is vital in the management of the majority of cardiac emergencies. Most sudden cardiac deaths are associated with an ischemic episode. Patient deaths due to an acute myocardial infarction (MI) typically..., but also may point to ventricular hypertrophyVentricular hypertrophy is reflected in QRS axis deviation towards the hypertrophied ventricle, increased amplitude in the QRS complex, altered R wave progression, and possibly signs of ventricular strain - ST depression and T wave inversion. Note that ST changes can..., digoxin use, and pericarditisThe presence of ST elevation in most views of a 12 lead ECG suggests pericarditis. Pericarditis, an inflammation to the pericardial lining of the heart often attributed to infection, also produces ST elevation on a 12 lead ECG. In fact,... among other possibilities.
Between 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... and the T waveThe wave that arrives after the QRS; is a graphical presentation of ventricular repolarization. Expect a T wave to follow every QRS complex. The T wave is a graphic representation of the repolarization of the ventricle. The T wave is..., lies the ST segmentA line between waves. Segments measure time between waves (waves are not included in a segment). While waves are fairly self-explanatory, intervals measure time from the start of one wave to the start of another wave (an interval includes at.... The ST segment usually follows the isoelectric line. The ST segment represents early repolarizationWhile an ECG is a superior diagnostic tool, experienced practitioners are witness to false positive and false negative ECGs. A false positive ECG occurs when ECG findings are abnormal for a patient that is quite healthy. An example of a... 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.. Early repolarizationFollows depolarization, involving the return to a pre-depolarization state; the myocardial cell’s electrical potential returns from +30 mV to its polarized state of –90 mV; the ions potassium, calcium and sodium are largely involved; note that contraction of the myocardial... includes a plateau phase where the cardiac cell membrane potential does not change.
During early repolarization, the positive ion potassium exits the cardiac cell while the positive ion calcium enters the cardiac cell, effectively negating any change in cell membrane potential. Because the cell membrane does not change its electrical potential, 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 leads do not record any electrical activity. As a result, the ST segment usually lies along the ECG baselineThe baseline or isoelectric line is a reference point for the waves, intervals and segments. While the PR segment is often used as the baseline, the TP segment - between the end of the T wave and the beginning of....
Determining where the ST segment begins is determined by the J pointA small notch in the QRS where the ST segment begins. The point where the S Wave ends and begins to flatten out. Figure 4.13 The QRS Complex, ST Segment and the T Wave Figure 4.13 depicts the component parts.... The J point, the juncture of the QRS and the ST segment, defines the starting point of the ST segment. The J point marks where the QRS complexA collection of waveforms (i.e. QRS complex and the ECG complex). 1. Six Second ECG Guidebook (2012), T Barill, p. 194 changes direction, forming a notch or bump in the ECG tracing. The ST segment is evaluated for any deviation from the ECG baseline 0.04 seconds (1 mm) after the J point.
While ST deviations may be a normal occurrence for a subset of the population, most often ST deviationWhile ST deviations may be a normal occurrence for a subset of the population, most often ST deviation is a sign of either myocardial ischemia, myocardial infarction and/or cardiac disease. It makes sense, then, to report any finding of ST... is a sign of either myocardial 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..., myocardial infarctionThe necrosis or death of myocardial tissue due to insufficient supply of oxygen to the infarcted region. The ability to identify cardiac ischemia, injury and infarction is vital in the management of the majority of cardiac emergencies. Most sudden cardiac... and/or cardiac disease. It makes sense, then, to report any finding of ST deviation from baseline in the ECG interpretation i.e. sinus rhythmAlso known as regular sinus rhythm or sinus rhythm, this cardiac rhythm is not a dysrhythmia; sinus rhythm originates in the sinoatrial (SA) node with a rate of 60-100/minute; P waves are upright in most leads and the QRS is... with ST depression.
ST depression of 1 mm or more in 2 contiguous leadsContiguous leads in a 12-Lead ECG refer to a group of leads that are sequentially connected on the body surface, with a common view of a region of the heart. For example, leads II, III and aVF are contiguous in... (neighboring leads) is suggestive of myocardial ischemia, injury or infarctionThe necrosis of tissue; acute myocardial infarction involves the acute death of myocardial cells. 1. Six Second ECG Guidebook (2012), T Barill, p. 198. ST elevationThe upward placement of the ST segment greater than 1 mm from the isoelectric line; suggestive of cardiac infarction or ischemia. Between the QRS complex and the T wave, lies the ST segment. The ST segment usually follows the isoelectric... of 1 mm or more in 2 contiguous leads is highly suggestive of a myocardial injury or infarction. Note that ST changes (elevation or depression) are highly suggestive of current events – the acute coronary events are happening now.
The shape of the ST segment, if depressed, bears mention. The depressed ST segment often presents horizontal (see the center QRS complex of Figure 4.17), sloping downwards or sloping upwards. Although all morphologies can indicate myocardial ischemia, the horizontal and downward sloping depressed ST segments are the more likely morphologies that point to ischemic events.
Note that ST changes can occur from conditions other than myocardial ischemia. As mentioned, ST elevation and depression may be a benign finding, although uncommon. For example, ST depression that is concave in shape – called a dig dip – can occur for patients taking digitalis (see Figure 4.17) even at normal blood levels. A depressed and upward sloping ST segment can represent ventricular hypertrophy.
ST segment elevation is a common finding in young healthy adults of African descent. This phenomenon is attributable to normal early repolarization and not a result of cardiac disease. Using an ECG to diagnose a disease state in the absence of direct contact with the patient, a patient’s clinical history and presentation is fraught with peril.
The presence of ST elevation in most views of a 12 lead ECG suggests pericarditis. Ventricular rhythms and supraventricularLocated above the ventricle – includes the bundle of His, AV node, atria and the SA node. 1. Six Second ECG Guidebook (2012), T Barill, p. 206 rhythms with left bundle branch blockA bundle branch block must satisfy two criteria - a wide QRS complex and a notch in the QRS complex. To distinguish between a RBBB and a LBBB, first make certain that the rhythm is indeed supraventricular (P waves before... have wide and bizarre QRS complexes, making the detection of ST changes all but impossible.
Several conditions not linked to cardiac ischemia can produce ST changes. The bottom line: most ST changes indicate cardiac ischemia, requiring urgent treatment BUT every ECG interpretation is more robust when integrated with a patient’s clinical status and history.
Figure 4.13 depicts the component parts of the QRS complex. The QRS complex consists of a series of waves, the ‘Q’, ‘R’, and ‘S’ waves. The ‘Q’ wave is the first negative deflection from baseline. The ‘R’ wave is the first positive deflection above baseline. The ‘S’ wave follows the ‘R’ wave with a negative deflection. A QRS complex may or may not have all three waveforms. The ST segment begins at the J point and continues to the beginning of the T wave.
Figure 4.17 presents three examples of ST deviation. A digoxin dipST segment deviation (possible ventricular strain or digoxin dip) Between the QRS complex and the T wave, lies the ST segment. The ST segment usually follows the isoelectric line. The ST segment represents early repolarization of the ventricles. Early repolarization... is also called a “dig dip”.
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. 86-88, 204