Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / @xirurgi_2025 / @xirurgi_2025 - 952 - файл
.pdf
32 PART I PATIENT EVALUATION
ABCD
https://t.me/medicina_free
Lead II
Figure 3-7. A, With a sinus rhythm, the P wave is positive (upright) in lead II because the wave of depolarization is moving
toward the positive electrode. The P wave associated with a junctional beat (in lead II) may be B, inverted (retrograde) and
appear before the QRS; C, be hidden by the QRS; or D, appear after the QRS. (From Grauer K: A practical guide to ECG
interpretation, ed 2, St Louis, 1998, Mosby.)
R-R interval
QT interval
Figure 3-8. Measuring the QT, and R-R intervals. (From Jenkins D, Gerred SJ: ECGs by Example, ed 3, Edinburgh, 2011,
Churchill Livingstone.)
11. What is a corrected QT interval?
Due to the variability of the QT interval with the patient’s heart rate, the QT interval can be
measured more accurately if it is corrected for the patient’s heart rate. The corrected QT interval
is calculated as the measured QT interval divided by the square root of the R-R interval and is
noted as QTc. It is considered prolonged if it is 0.45 seconds or longer in men, and 0.46 seconds
or longer in women. A QTc of 0.50 seconds or longer is associated with a higher risk of ventricular
dysrhythmias.
12. How can one determine if the QT interval is prolonged, and what is the significance of a prolonged QT interval?
The QT interval represents ventricular depolarization through repolarization.
13. What is the meaning of narrow and wide QRS complexes?
The width of the QRS complex could be used to categorize tachycardia on the electrocardiogram. Nar-
The QT interval is measured from the Q wave to the end of the T wave. If the Q wave is not
present, then measure from the beginning of the R wave. The QT interval will shorten when the heart
rate increases and lengthen when the heart rate slows. To quickly estimate the QT interval, measure
the interval between two consecutive R waves. If the measured QT interval is less than half of the R-R
interval of that QRS complex and the R wave of the following complex, it is most likely normal, as long
as the heart rate is less than 95 beats/min. If the QT interval is more than half the R-R interval, it is
probably prolonged. A prolonged QT interval is associated with a greater risk of ventricular dysrhythmias, such as torsades de pointes (Figs. 3-8 and 3-9).
row QRS complex arrhythmias (<80 ms) means rapid activation of the ventricles via the His-Purkinje
system, suggesting supraventricular arrhythmia (e.g., supraventricular tachycardia). Wide QRS
complex (>80 ms) is secondary to slow ventricular activation.
CHAPTER 3 ELECTROCARDIOGRAM 33
https://t.me/medicina_free
Figure 3-9. Polymorphic ventricular tachycardia. (From Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.)
The arrhythmia originates below the His bundle (e.g., ventricular tachycardia). The impulse
originates from an ectopic site within the ventricle and takes longer to activate the entire mass of the
ventricle.
There are exceptions like aberrant supraventricular tachycardia, which can produce a widened
QRS if there are either preexisting or rate-related abnormalities within the His-Purkinje system (e.g.,
supraventricular tachycardia with aberrancy) or if conduction occurs over an accessory pathway. Thus,
wide QRS complex tachycardias may be either supraventricular or ventricular in origin.
14. What is a Q wave, and when is it significant?
The Q wave is the first downward stroke of the QRS complex. An insignificant Q wave is less than
0.04 seconds and represents mid-septal depolarization. A significant Q wave indicates necrosis and
is diagnostic for an infarction. For a Q wave to be significant, it must be at least 0.04 seconds or onethird of the entire QRS amplitude.
15. What medications can cause a prolonged QT interval?
Medications are a common cause of a prolonged QT interval. The major classes of drugs include:
• Antiarrhythmics(e.g.,quinidine,sotalol,dofetilide,amiodarone,disopyramide)
• Certainantihistamines(terfenadine,astemizole)
• Certainantibiotics(uoroquinolones,macrolides,metronidazole)
• Certainpsychotropicmedications(someantipsychotics,someSSRIs,andtricyclicantidepressants)
• Analgesics/sedatives:methadone,oxycodone,chloralhydrate
• Certaingastricmotilityagents(cisapride)
There are many drugs that cause prolonged QT interval, and the list is constantly expanding. All
medications should be carefully scrutinized for potential QT interval prolongation as a side effect.
16. What is a U wave, and when is it clinically significant?
A U wave represents repolarization of the Purkinje fibers, and it may be occasionally seen following
the T wave on an ECG. When seen, the amplitude of a normal U wave should be approximately 11% of
the preceding T wave amplitude. Tall U waves may be caused by CNS disease, electrolyte imbalances,
hyperthyroidism, long QT syndrome, or certain medications (e.g., amiodarone, digitalis, procainamide,
phenothiazines). Inverted U waves in leads V2 to V5 are abnormal and may be seen in ischemic heart
disease. In hypokalemia, as serum potassium continues to drop below normal levels, the T waves on
an ECG flatten or become inverted, and a U wave may appear.
17. What is the J point on an ECG, and can you explain its significance?
The J point on an ECG is the point where the QRS complex and ST segment meet. The J point is sig-
nificant in the identification of ST elevation or depression. To evaluate for ST elevation or depression,
first identify the J point. Then use the TP segment to evaluate its position in relation to the isoelectric
line. ST depression of more than 0.5 mm in leads V2 and V3, or more than 1.0 mm in all other leads,
is suggestive of MI. ST elevation for acute injury can vary from 0.5 to 2.5 mm, depending on age,
gender, and ECG lead (Fig. 3-10).
18. What disorders can be evaluated perioperatively by the ECG?
Preoperative ECG, when indicated, can be used to evaluate and help diagnose the following conditions:
• Conductionabnormalities(AVblocks,prematureatrialcontractions[PACs],prematureventricular
contractions[PVCs])
34 PART I PATIENT EVALUATION
https://t.me/medicina_free
J point
Figure 3-10. Normal position of the J point. (Modified from Urden LD, Stacy KM, Lough ME: Critical care nursing: diagno-
sis and management, ed 7, St Louis, 2014, Mosby.)
• Myocardialischemia
• Myocardialinfarctions
• Ventricularandatrialhypertrophy
• Pacemakerfunction
• Preexcitation(e.g.,Wolff-Parkinson-Whitesyndrome)
• Drugtoxicity(digitalis,antiarrhythmics,tricyclicantidepressants)
• Electrolyteabnormalities(e.g.,disturbancesincalcium,potassium)
• Variousmedicalconditions(e.g.,pericarditis,hypothermia,pulmonaryemboli,corpulmonale,
cerebrovascular accidents, increased intracranial pressure)
19. Who should have a preoperative 12-lead ECG?
For the most part, this depends on many factors, including the clinical presentation of the patient and
the individual hospital regulations. However, it is generally agreed that the following patients may benefit from a preoperative 12-lead ECG to fully assess the surgical and anesthetic risks of these patients:
• Anypatientolderthanage50,oranypatientolderthanage40whenriskfactorsarepresent
• Anyotherpatientwhohassignsorsymptomsofcardiacdisease
• Patientswithpriorhistoryofcardiacischemia,dysrhythmias,orpacemakerplacement
• Patientswithhistoryofcocaineusewhoaretoundergoaprocedureundergeneralanesthesia
20. Why is lead II used for monitoring intravenous sedation?
Lead II is good for monitoring P waves, dysrhythmias, and inferior ischemia. Lead II is appropriate for
monitoring ASA I and ASA II patients.
21. What are some of the causes of intraoperative artifact on ECG monitoring?
Artifact can mimic cardiac dysrhythmias. It can be caused by loose electrodes, poor electrical contact,
broken lead wires, patient movement, shivering, and 60-cycle interference.
22. What are tachycardia and bradycardia?
Sinus tachycardia indicates a rate >100 beats/min, and bradycardia is a rate <60 beats/min.
23. What are typical ECG signs of ischemia, injury, and infarction?
Ischemia shows inverted T waves in the leads nearest the part of the affected myocardium most eas-
ily identified in the chest leads. ST depression may also be seen. Injury to heart muscle is indicated by
ST elevation and tall, positive T waves. Infarction shows Q waves that are 0.04 seconds or longer or
greater than one-third the size of the entire QRS complex. Location can be determined from the lead.
Anterior leads show Q waves in V1 and V2; inferior leads in II, III, and aVF; and lateral leads in I, aVL,
V5, and V6 (Table 3-1).
24. How do potassium and calcium affect the ECG?
Hypokalemia causes U waves (small, positive deflections following T waves). Hypokalemia may also
be seen as ST depression and flat T waves. Hyperkalemia causes tall, narrow, peaked T waves, QRS
widening, and P wave flattening and can progress to ventricular fibrillation. Hypocalcemia causes prolonged QT intervals. Finally, hypercalcemia causes shortened QT intervals, with or without ST segment
elevation (Figs. 3-11 to 3-15).
CHAPTER 3 ELECTROCARDIOGRAM 35
TU P
QRS QRS
https://t.me/medicina_free
Table 3-1. Localization of a Myocardial Infarction
LOCATION OF MI LEAD CHANGES AFFECTED CORONARY ARTERY
Anterior V3, V4 Left coronary artery
*LAD: diagonal branch
Anteroseptal V1, V2, V3, V4 Left coronary artery
*LAD: diagonal branch
*LAD: septal branch
Anterolateral I, aVL, V3, V4, V5, V6 Left coronary artery
*LAD: diagonal branch
*Circumflex branch
Inferior II, III, aVF Right coronary artery
*Posterior descending branch
Left coronary artery
*Circumflex branch
Lateral I, aVL, V5, V6 Left coronary artery
*LAD: diagonal branch
*Circumflex branch
Right coronary artery
Septum V1, V2 Left coronary artery
*LAD: septal branch
Posterior V7, V8, V9 Right coronary or circumflex artery
Modified from Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.
II
I mV
ABP Scale (0/40 0/80 0/120)
Figure 3-11. ECG tracing from a patient with hypokalemia. (Modified from Urden LD, Stacy KM, Lough ME: Critical care
nursing: diagnosis and management, ed 7, St Louis, 2014, Mosby.)
25. What is Wolff-Parkinson-White (WPW) syndrome?
WPW presents an abnormal ECG pattern caused by the presence of an accessory pathway that
bypasses the AV node. Early depolarization of the ventricles produces the following ECG characteristics (Fig. 3-16):
• WideQRScomplex
• ShorterPRinterval,asaresultofearlydepolarizationoftheventricles
• Deltawave,whichisseenintheupstrokeoftheQRScomplex
26. How is digitalis toxicity seen on ECG?
Digitalis toxicity has several ECG manifestations, including SA and AV node blocks, tachycardia, PVCs,
ventricular tachycardia, atrial fibrillation, and possible sloping of the ST segment.
36 PART I PATIENT EVALUATION
IIII
https://t.me/medicina_free
I
I
II
II
III
III
Figure 3-12. ECG of a patient presenting with hypokalemia. Note the prominent U wave after the T wave in leads V2 to V6.
(From Duke JC, Keech BM: Anesthesia secrets, ed 5, Philadelphia, 2016, Saunders.)
I
I
II
II
III
III
aVR
aVR
aVL
aVL
aVF
aVF
aVR
aVR
aVL
aVL
aVF
aVF
V1
V1
V2
V2
V3
V3
V1
V1
V2
V2
V3
V3
V4
V4
V5
V5
V6
V6
V4
V4
V5
V5
V6
V6
II
II
Figure 3-13. ECG of a patient presenting with hyperkalemia. Note the peaked T waves. (From Duke JC, Keech BM:
Anesthesia secrets, ed 5, Philadelphia, 2016, Saunders.)
27. What is the ECG manifestation of hypothermia?
Hypothermia is seen on ECG as sinus bradycardia, AV junctional rhythm, or ventricular fibrillation.
Typically, there is an elevated J point, and there may be an intraventricular conduction delay and
prolonged QT interval.
28. What are some of the common causes of PVCs?
Caffeine ingestion, anxiety, acid-base imbalance, ischemic heart disease, hypoxia, valvular heart
disease, heart failure, electrolyte imbalance, smoking, drug toxicity, cardiomyopathy, and medications.
29. What is the significance when the R wave of a PVC falls on the T wave of the
preceding beat?
There is a possibility that the PVC can precipitate VT or VF if it occurs during this period of the cardiac
cycle, associated with the relative refractory period. This is referred to as the R-on-T phenomenon.
CHAPTER 3 ELECTROCARDIOGRAM 37
V3
https://t.me/medicina_free
I
I
aVR
aVR
V1
V1
V4
V4
II
II
III
III
II
II
Figure 3-14. ECG of a patient presenting with hypocalcemia. The QT interval is prolonged. (From Duke J: Anesthesia
secrets, ed 4, Philadelphia, 2011, Mosby.)
I
I
II
II
III
III
II
II
Figure 3-15. ECG of a patient presenting with hypercalcemia. The QT interval is shortened, and the ST-T segment is
elevated. (From Duke J: Anesthesia secrets, ed 4, Philadelphia, 2011, Mosby Elsevier.)
aVL
aVL
aVF
aVF
aVR
aVR
aVL
aVL
aVF
aVF
V2
V2
V3
V3
V1
V1
V2
V2
V3
V3
V5
V5
V6
V6
V4
V4
V5
V5
V6
V6
Figure 3-16. Typical Wolff-Parkinson-White (WPW) syndrome pattern showing the short PR interval, delta wave, wide QRS
complex, and secondary ST segment and T wave changes. (From Surawicz B, Knilans TK: Chou’s electrocardiography in
clinical practice: adult and pediatric, ed 6, Philadelphia, 2008, Saunders.)
38 PART I PATIENT EVALUATION
https://t.me/medicina_free
30. What are some of the causes of ST segment elevation?
All of the following can lead to ST segment elevation: normal variant, acute ST segment elevation
myocardial infarction, early repolarization pattern, hypercalcemia, hyperkalemia, pericarditis, Brugada
syndrome, left bundle branch block, and left ventricular hypertrophy.
31. What is Brugada syndrome?
Brugada syndrome is a hereditary condition caused by dysfunctional cardiac sodium channels respon-
sible for nearly one-half of sudden death in healthy individuals without structural heart disease. It is
characterized by a right bundle branch block (RBBB) and ST elevation in leads V1 to V3, with a peaked
downsloping shape in the elevated ST segments.
32. Can you describe bundle branch block?
Bundle branch block is impairment of conduction in either the left or right bundle system that leads to
a wide QRS interval. With complete bundle branch block, the QRS interval would be >0.12 seconds.
Incomplete bundle branch block is between 0.10 and 0.12 seconds. The orientation of the QRS vector
is usually in the direction of the myocardial area where depolarization is delayed. In RBBB, the QRS
vector is oriented to the right and anteriorly. Note the presence of a secondary R wave (R′) in V1 and
slurred S wave in lead V6. In left bundle branch block (LBBB), the QRS vector is directed to the left
and posteriorly. LBBB generates predominantly negative QS complexes in lead V1 and positive R
complexes in lead V6 (Fig. 3-17).
V
1
V
6
Normal
R′
R
R
RBBB
T
S
q
S
LBBB
T
Figure 3-17. Comparison of typical QRS-T patterns in right bundle branch block (RBBB) and left bundle branch block
(LBBB) with the normal pattern in leads V1 and V6. Note the secondary R wave (R′) in V1 and slurred S wave in V6 with
RBBB. Note the secondary T wave inversions (arrows) in leads with an rSR′ complex with RBBB and in leads with a wide
R wave with LBBB. (From Goldberger AL, Goldberger ZD, Shvilkin A: Goldberger’s clinical electrocardiography: a simplified
approach, ed 8, Philadelphia, 2013, Saunders.)
CHAPTER 3 ELECTROCARDIOGRAM 39
https://t.me/medicina_free
33. How can you determine left ventricular hypertrophy using a 12-lead ECG?
Add the depth of the S wave in V1 to the height of the R wave in V5 in mm. If the total is greater than
35 mm, then left ventricular hypertrophy is present. The T wave in V5 and V6 often show inversion and
asymmetry. Left axis deviation will be present.
34. What ECG changes may be seen in a patient who develops a pulmonary embolus?
Lead I: Large S wave
Lead II: ST segment depression
Lead III: Large Q wave with T wave inversion
T wave inversion may be seen in leads V1 to V4, along with an RBBB.
35. What rhythm is shown in Figure 3-18?
Sinus rhythm. This normal regular rhythm originates in the SA node, with a normal rate of 60 to
100 beats/min. The PR interval is 0.12 to 0.2 seconds. The QRS complex is 0.04 to 0.12 seconds.
36. What rhythm is shown in Figure 3-19?
Premature atrial contractions. PACs originate when an irritable atrial automaticity focus suddenly fires,
producing an early, ectopic P wave. The rate varies depending on the number of these contractions.
This ectopic P wave will appear premature and will be unusually shaped when compared to the
normal P waves; it may fall coincidently on the T wave and present as a taller T wave. A shortened PR
interval may be evident. The QRS complex is usually normal but may appear slightly widened due to
aberrant ventricular conduction in that premature cycle.
37. What rhythm is shown in Figure 3-20?
Sinus tachycardia. This rhythm originates from the SA node and occurs when the SA node paces the
heart at a rate greater than 100 beats/min. The P waves, PR intervals, and QRS complexes are normal.
The rhythm is regular.
38. What rhythm is shown in Figure 3-21?
Supraventricular tachycardia. Generally, the rate is 150 to 250 beats/min. The P waves differ from
normal, and the rate may be so rapid that the P waves may be coincident with the previous T waves,
with a noticeable lack of PR interval. Certain conditions may widen the QRS complex in SVT.
Figure 3-18. Normal sinus rhythm. (From Linton AD: Introduction to Medical-Surgical Nursing, ed 5, St. Louis, 2012,
Saunders.)
Figure 3-19. Sinus tachycardia with three premature atrial complexes (PACs). From the left, beats 2, 7, and 10 are PACS.
(From Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.)
40 PART I PATIENT EVALUATION
https://t.me/medicina_free
II
I
V1
Figure 3-20. Sinus tachycardia at 120 beats/min. (From Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.)
Atrial tachycardia
P'
Figure 3-21. Supraventricular tachycardia that ends spontaneously with the abrupt resumption of sinus rhythm. The P
waves of the tachycardia are superimposed on the preceding T waves. (From Goldberger AL, Goldberger ZD, Shvilkin A:
Goldberger’s clinical electrocardiography: a simplified approach, ed 8, Philadelphia, 2013, Saunders.)
Sinus rhythm
P
II
Figure 3-22. Atrial fibrillation. (From Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.)
39. What rhythm is shown in Figure 3-22?
Atrial fibrillation. It is caused by the continuous rapid firing of multiple parasystolic atrial foci, produc-
ing a rapid “irregularly irregular rhythm.” The rate is usually 300 to 500 beats/min, with a ventricular
capture rate of 150 to 180 beats/min. P waves are usually unidentifiable, and PR intervals are virtually
impossible to distinguish. The QRS complexes are normal.
40. What rhythm is shown in Figure 3-23?
Atrial flutter. P waves appear in a “sawtooth pattern” known as flutter or F waves. The atrial rate aver-
ages 220 to 350 beats/min and ventricular rate ranges around 100 to 220 beats/min. This rhythm is a
reentrant arrhythmia in the atria or an endless electrical loop. PR intervals are usually regular and the
QRS complexes normal.
CHAPTER 3 ELECTROCARDIOGRAM 41
https://t.me/medicina_free
II
I
III
Figure 3-23. Atrial flutter. (From Aehlert B: ECGs made easy, ed 5, St Louis, 2013, Elsevier.)
Figure 3-24. Sinus rhythm with a first-degree atrioventricular (AV) block. (From Aehlert B: ECGs made easy, ed 5, St Louis,
2013, Elsevier.)
41. What rhythm is shown in Figure 3-24?
First-degree AV block. This rhythm presents with a prolonged PR interval, >0.2 seconds.
42. What rhythm is shown in Figure 3-25?
Second-degree AV block, Mobitz Type 1 (Wenckebach). The atrial rate is usually fixed, but the
ventricular rate is slower. The PR interval prolongs until the point that it no longer conducts to the
ventricles and there is no QRS complex.
43. What rhythm is shown in Figure 3-26?
Second-degree AV block, Mobitz Type II. The atrial rate and P waves are normal, but the ventricular
rate is slower by a factor of two (2:1) or three (3:1) The PR interval is usually normal, but there are
missed QRS complexes for P waves.
44. What rhythm is shown in Figure 3-27?
Third-degree AV block: complete heart block. Atrial contractions are normal, but there is complete
electrical conduction dissociation with the ventricles. The ventricles generate a signal through an
escape mechanism. The ventricular escape beats are usually “slow” at a rate of 20 to 60 beats/min.
The P waves and QRS complexes are regular, but they do not coincide.
Соседние файлы в папке @xirurgi_2025