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Sunday, September 29, 2019

CRITICAL CARE NOTES ECG AND HEART


BASIC TIPS FOR HEART AND ECG


       Assesses the ECG for rate, rhythm, axis,  intervals, ischemia, and chamber enlargement

Rate
Normal adult HR is 60–100 bpm. HR < 60 bpm is bradycardia. HR >100 bpm is tachycardia. Common causes of sinus bradycardia are physical fit-ness, sick sinus syndrome, drugs, vasovagal attacks, acute MI, ↑ intracranial
pressure. Common causes of sinus tachycardia are anxiety, anemia, pain, fever, sepsis, CHF, PE, hypovolemia, thyrotoxicosis, CO2 retention, and sympathomimetics.

Rhythm

Sinus rhythm: Normal rhythm that originates from sinus node. It is characerized by a P wave (upright in II, III, and aVF; inverted in aVR) preceding every QRS complex and a QRS complex following every P wave. Sinus arrhythmia is common in young adults.

Axis

Can be determined by examining the QRS in leads I, II, and aVF.

Normal ECG 

Axis Deviation

ECG Axis interpretation QRS axis and frontal leads

Intervals
PR interval: Normally 120–200 msec (3–5 small boxes).
Prolonged = delayed AV conduction (eg, first-degree heart block).
Short = fast AV conduction down accessory pathway (eg, WPW
syndrome).

QRS interval: Normally < 120 msec. A normal Q wave is < 40 msec wide and < 2mm deep. Ventricular conduction defects can cause a
widened QRS complex (> 120 msec)


Left bundle branch block (LBBB): Deep S wave and no R wave in V1 (“W”-shaped); wide, tall and broad, or notched (“M”-shaped)
R waves in I, V5, and V6 . A new LBBB is pathologic and may be a sign of acute MI.

Left bundle branch 
block. Characteristic ECG findings are
seen in leads V1 (A) and V6 (B).


 Right bundle branch block (RBBB): RSR′ complex (“rabbit ears;” “M”-shaped); qR or R morphology with a wide R wave in V1; QRS
pattern with a wide S wave in I, V5, and V6

Right bundle
branch block. Characteristic ECG find-
ings are seen in leads V1 (A) and V6 (B).

 QT interval: Normally QTc (the QT interval corrected for extremes in heart rate) is 380–440 msec (QTc = QT/√RR). Long QT syndrome
(QTc > 440 msec) is an underdiagnosed congenital disorder that predisposes to ventricular tachyarrhythmias. Other common causes of prolonged QTc: acute MI, bradycardia, myocarditis, ↓ K+, ↓ Ca2+, ↓ Mg2+
, congenital syndromes, head injury, drugs.


Jervell and Lange-Nielsen syndrome: Long QT syndrome due to a defect in K+channel conduction. Associated with sensorineural deafness. Treat with β-blockers and pacemaker.

Ischemia/Infarction

Acute ischemia:
■ Within hours, peaked T-waves and ST segment changes (either depression or elevation).
■ Within 24 hours, T-wave inversion and ST-segment resolution.
■ Within a few days, pathologic Q waves (> 40 msec or more than one-third of the QRS amplitude). Q waves usually persist, but may resolve in 10% of patients. Because of this, Q waves signify either acute or prior
ischemic event
■ Non–Q-wave infarcts (also known as subendocardial infarcts) have ST and
T changes without Q waves.
■ In a normal ECG, R waves increase in size compared to the S wave between leads V1 and V5. Poor R-wave progression refers to diminished R waves in these precordial leads, and can be a sign of infarction, although it
is not specific

Chamber Enlargement

■ Atrial enlargement:

■ Right atrial abnormality (P pulmonale): The P-wave amplitude in lead II is > 2.5 mm.

■ Left atrial abnormality (P mitrale): The P-wave width in lead II is > 120 msec, or terminal ⊝ deflection in V1 is > 1 mm in amplitude
and > 40 msec in duration. Notched P waves can frequently be seen
in lead II.
■ Left ventricular hypertrophy

■ Amplitude of S in V1 + R in V5 or V6 is > 35 mm.
■ Alternative criteria: The amplitude of R in aVL + S in V3 is > 28 mm in men or > 20 mm in women.
■ Usually associated with ST depression and T-wave changes.
Right ventricular hypertrophy (RVH):
■ Right-axis deviation and an R wave in V1 > 7 mm.


Auscultation locations. Auscultation sites are shown with associated valves. A, aortic valve;
M, mitral valve; P, pulmonic valve; T, tricuspid valve.👇


Cardiac Physical Exam

Key exam findings that can narrow the differential include the following:
■ Jugular venous distention (JVD > 4 cm above the sternal angle): Most typically from volume overload, stemming from conditions such as right heart failure or pulmonary hypertension.
■ Hepatojugular reflux (distention of neck veins upon applying pressure to the liver): Seen in same conditions as JVD.
■ Kussmaul sign (↑ in jugular venous pressure [JVP] with inspiration): Often seen in constrictive pericarditis.
■ Aortic stenosis: A harsh systolic ejection murmur that radiates to the carotids.
■ Mitral regurgitation: A holosystolic murmur that radiates to the axilla.
■ Mitral valve prolapse: A midsystolic or late systolic murmur with a preceding click.
■ Flow murmur: Usually a soft murmur that is position-dependent (very common and does not imply cardiac disease).
■ Aortic regurgitation: An early decrescendo murmur.
■ Mitral stenosis: A mid to late low-pitched murmur.
■ Gallops:
■ S3 gallop: A sign of fluid overload (ie, heart failure, mitral valve disease); often normal in younger patients and in high-output states (eg,
pregnancy).
■ S4 gallop: A sign of decreased compliance (ie, hypertension, aortic stenosis, diastolic dysfunction); usually pathologic but can be normal in younger patients and in athletes.
■ Edema:
■ Pulmonary: Left heart failure (fluid “backs up” into the lungs).
■ Peripheral: Right heart failure and biventricular failure (fluid “backs up” into the periphery), nephrotic syndrome, hepatic disease, lymphedema, hypoalbuminemia, and drugs.
■ Hands:
■ Finger clubbing: Congenital cyanotic heart disease; endocarditis.
■ Infective endocarditis: Splinter hemorrhages; Osler nodes, Janeway lesions.

CARDIAC MURMURS
Visual representations of common heart murmurs are shown in relation to S1 and S2. MC, midsystolic click; OS, opening snap.


Peripheral pulses:
■ Increased: Compensated aortic regurgitation (bounding pulses); coarctation (greater in arms than in legs); patent ductus arteriosus.
■ Decreased: Peripheral arterial disease; late-stage heart failure.
■ Collapsing (“waterhammer”): Aortic incompetence; AV malformations; patent ductus arteriosus; thyrotoxicosis, severe anemia.
■ Pulsus paradoxus (↓ systolic BP > 10 mm Hg with inspiration): Cardiac tamponade; pericardial constriction; also seen in obstructive lung diseases
(eg, severe asthma), tension pneumothorax, and foreign body in airway.
■ Pulsus alternans (alternating weak and strong pulses): Cardiomyopathy; impaired left ventricular systolic function (LVF). Poor prognosis.
■ Pulsus parvus et tardus (weak and delayed pulse): Aortic stenosis.
■ Jerky: hypertrophic obstructive cardiomyopathy (HOCM).
■ Pulsus bisferiens (bifid pulse/“twice beating”): Aortic regurgitation; combined aortic stenosis and aortic regurgitation, HOCM.

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