14 - ECG Recognition II Flashcards
What is an escape rhythm?
When a latent pace maker has been called into action
What is an atrial premature beat?
- The atria are depolarizing differently
- Morphology might or might not be different, it’s just coming before a normal p wave should come
- The premature atrial beat is followed by a pause period
- This is a protective mechanism by the heart
What are the features of a junctional escape rhythm?
- The depolarization is NOT coming from the SA node, but rather the level of the junction (AV junction)
- When the ventricles and atria receive depolarization impulse simultaneously: P wave can occur just before QRS (with a short PR interval), inside QRS complex (P wave buried), or just after QRS.
- QRS will be narrow (not wide)
- Retrograde P wave = after QRS
- Inverted P wave = down instead of up
Why do juncitonal escape rhythms occur?
If you depolarize the junction (AV junction) middle of the heart, it will spread in BOTH directions if the tissue is excitable
Why does bradycardia often accompany a junctional escape rhythm?
Latent pace makers are slower
In junctional escape rhythm, why are there sometimes QRS complexes without p waves?
Absence of a p wave before a QRS means that the impulse is not being generated at the SA node, but rather at the AV node
Describe the features of atrial fibrillation
- Fibrillation (f) waves vary in shape and polarity (come from multiple sites throughout atrial muscle)
- Irregularly irregular: variable f-f intervals and irregular ventricular (QRS) response
- Differentiate from atrial flutter
o Identical flutter (F) waves that time out regularly
o Constant QRS response (e.g. 2 F:1 QRS or 4 F:1 QRS) - Can increase risk for thrombo-embolus, due to uncoordinated movement of blood (especially stroke) and heart failure, due to short-term decrease in cardiac output and long-term mechanisms activated to compensate for reduced cardiac output
- Control rate, by pharmaceuticals or pacemaker; control rhythm, by ablation or cardioversion
Describe the features of supraventricular premature beats
- Can precede other supraventricular arrhythmias
- In atrial premature beat (APB), atrial depolarization occurs before next sinus p wave, termed p’ wave
- QRS complex of APB preceded by P wave that looks different from other P waves on strip (different morphology or PR interval); PR interval may be longer or short; P wave could be obscured by T wave
- After APB, a slight pause occurs before the normal sinus beat resumes (contrasted to the fully compensatory pause often seen after ventricular premature beats)
- QRS complex will be narrow (if no additional defects are present)
- May reach junction during refractory period and be blocked
Describe the features of multifocal atrial tachycardia
Multifocal Atrial Tachycardia
- multiple sites of atrial stimulation (ectopic foci)
- 3 or more consecutive non-sinus P waves with different shapes
- PR intervals vary
- Ventricular rate is irregular (some beats get through, some do not) and rapid.
- MAT can compromise filling and clinical symptoms of reduced perfusion (dizziness, shortness of breath) may be seen
Describe the features of a first degree AV block
First Degree AV Block
- P wave (usually sinus) followed by QRS complex with a PR interval > 200 msec
- PR interval is uniformly prolonged; all PR intervals are similar
- The number of P waves equals the number of QRS complexes
Describe the features of a second degree AV block (Type I)
Second Degree Type I AV Block (Wenckebach)
- Intermittently “dropped” QRS complexes (P wave not followed by a QRS complex)
- Each stimulus has progressively harder time traversing AV node until atrial stimulus is not conducted; PR interval will change progressively
- The pattern of conducted: dropped beats is regular (e.g. 3 P waves: 2 QRS complexes)
- Produces a strip with grouped or clustered beats
Describe the features of second degree AV block (Type II)
Second Degree Type II AV Block
- Sudden appearance of a single, “dropped” beat (P wave not followed by a QRS complex)
- Random (not progressive) lengthened (to infinity!) PR interval
Describe the features of a third degree AV block
Third Degree AV Block
- Complete heart block: no conduction from atria to ventricles; AV dissociation
- Atria continue to be paced by SA node, regular P waves
- Escape rhythm must pace ventricles (variable morphology, depending on location of escape pacemaker)
o Nodal pacemakers can generate higher rate of impulses and better coordinated (narrow QRS) depolarizations than infranodal escape rhythms
- More P waves than QRS complexes
Describe the features of a right bundle branch block (RBBB)
Right Bundle Branch Block (RBBB)
- Conduction occurs much more slowly in the right ventricle as compared to the left, generating a wide QRS complex
- Late QRS forces point toward the right ventricle (positive in V1 and negative in V6)
o V1: rSR’ complex with a broad R’ wave
o V6: qRS-type complex with broad S wave
o SECONDARY changes in T wave: inversions in right chest leads
- Found in pathologies that affect the right side of the heart (e.g., pulmonary embolism, COPD)
Describe the features of a left bundle branch block (LBBB)
Left Bundle Branch Block (LBBB)
- Conduction occurs much more slowly in the left ventricle as compared to the right, generating a wide QRS complex
o Septal depolarization occurs from right to left due to the lag (lack) of impulse from the left side
o “Entire” ventricular depolarization event occurs right to left
- V1: wide QS complex (can be notched like an “M”)
- V6: wide R wave (can be notched like an “M”)
Describe the features of sinus tachycardia
Sinus Tachycardia
- Sinus rhythm with a HR exceeding 100 bpm
- Each P wave is followed by a QRS complex
- Can be related to sympathetic nervous stimulation or parasympathetic (vagal) withdrawal
- Causes can be multifactorial: physiologic, pain response, drug response (especially autonomic drugs), fever, volume or blood loss, CHF, pulmonary embolism, MI, hyperthyroidism, pheochromocytoma
Describe the features of sinus bradycardia
Sinus Bradycardia
- Sinus rhythm with a HR less than 60 bpm
- Each P wave is followed by a QRS complex
- Can be related to augmented vagal tone
- Causes can be multifactorial: physiologic, drug response (increasing parasympathetic tone or decreasing sympathetic tone), MI, hypothyroidism, hyperkalemia, sick sinus syndrome, age, hyper-vagotonia syndromes (vasovagal reactions, carotid sinus hypersensitivity, intracranial hypertension)
- Useful to assess the HR response to exercise to determine whether aggressive correction of bradycardia necessary
Describe the features of unifocal and multifocal premature ventricular complexes
Unifocal and Multifocal Premature Ventricular Complexes (PVC)
- PVC with similar appearance in any one lead (uniform) and different appearance (multifocal)
- PVC comes from ventricles, so the spread of depolarization is slow
- Usually precede sinus P wave, sometimes followed by retrograde (non-sinus) P wave
- 3 in a row is considered ventricular tachycardia (VT); can occur regularly or irregularly
- If the focus is in the LV, the QRS may appear as a RBBB; if in the RV, the QRS may appear as a LBBB
- QRS complex widens as origin is away from the middle of the heart
- Repolarization after PVC is discordant and ST segment can be elevated (differentiate from concordant T waves and ST segment elevation with myocardial injury)
- R on T Phenomenon: PVC falls near T wave, may precipitate VT or ventricular fibrillation
- Can be “normal” (benign) or abnormal (symptom of heart disease)
Describe the features of ventricular tachycardia
Ventricular Tachycardia
- 3 or more PVC’s in a row at a rate of 100 bpm
- Can be result of focal or reentrant mechanism, usually initiated by PVC
- Can be nonsustained (less than 30 sec) or sustained, monomorphic or polymorphic (with or without QT interval prolongation)
- Torsades de Pointes: usually from R on T due to prolonged QT interval
Describe the features of ventricular fibrillation
Ventricular Fibrillation
- Completely disorganized ventricular rhythm
- No cardiac output
- Coarse or fine nomenclature refers to amplitude of waves
- If left untreated, progresses to from coarse to fine VF to asystole
Describe the features of right atrial abnormality
Right Atrial Abnormality
- Results in abnormal amplitude of P wave (tall, > 2.5mm) but does not change duration
- Sometimes called P pulmonale due to association with pulmonary disease
Describe the features of left atrial abnormality
Left Atrial Abnormality
- Results in wide (>0.12 sec), sometimes notched P wave in one or more extremity leads and wide biphasic P waves in lead V1
- Can occur in the setting of valvular heart disease, hypertensive heart disease, cardiomyopathies and coronary artery disease
Describe the features of right ventricular hypertrophy
Right Ventricular Hypertrophy
- Tall right precordial R waves
- Right axis deviation
- Right precordial T wave inversions
- Can occur with pulmonary hypertension or pulmonic stenosis (increased pressure load); confirm by echocardiography
Describe the features of left ventricular hypertrophy
Left Ventricular Hypertrophy
- High voltage (abnormally tall) R waves in left chest leads; prominent S waves in right chest leads
- Exact voltage criteria vary
- Occurs with pressure overload on the left side of the heart: valvular disease, cardiomyopathies, systemic hypertension; confirm by echocardiography
Describe the features of a STEMI
STEMI
- Some MIs will occur without ST elevation. We will ignore these in our discussion.
- ST elevation most commonly occurs with transmural MI: ischemia and necrosis of a large area encompassing the entire ventricular wall
- Acute phase: ST segment elevation, sometime hyperacute T waves in 2 or more leads
- Evolving phase: hours or days later, deep T wave inversions in the leads that previously showed ST elevation
- Anterior infarct: ST elevation in anterior leads (chest leads); loss of normal R wave progression; prominent Q waves in area(s) of tissue death
o Antero-lateral infarct: ST elevation in V1→V4-6
- Inferior infarct: ST elevation in leads II, III, aVF; Q waves denote death of tissue and are found in the leads with ST segment elevation
- Reciprocal changes: inverse changes (ST depression) in the leads opposite the injury
