ECG Interpretation and Rhythm Analysis

Flashcards covering EKG/ECG basics, wave components, intervals, systematic interpretation steps, and classification of cardiac rhythms and blocks.

ECG (Electrocardiogram)

An electrical tracing of the cardiac activity within the heart that can indicate structural, mechanical, or electrical issues.

Rhythm strip

The electrical tracing of cardiac activity, typically made up of $6$-seconds split into two separate $3$-second portions.

12-lead ECG

The most common ECG type which utilizes $10$ electrodes to get $12$ different views of the heart.

Continuous telemetry monitoring

A monitoring method usually utilizing $3-5$ electrodes to view a few important leads, with a primary lead (usually Lead II) being continuously monitored.

P-wave

The electrical tracing that occurs during atrial depolarization, which causes the atria to contract.

QRS complex

The portion of the electrical tracing that signifies ventricular depolarization, when the ventricles contract.

T-wave

Representing ventricular repolarization, this is the phase where ventricular cells are electrically recharging for another contraction.

PEA (Pulseless Electrical Activity)

A condition where the electrical impulse is present on the monitor, but the heart does not have a mechanical response or contraction.

PR interval

The amount of time taken for the electrical impulse to go from the SA node in the atria until it reaches the ventricles; measured from the beginning of the P-wave to the beginning of the Q-wave.

Normal PR interval

A measurement between $120-200\,ms$, or $3-5$ small boxes on graph paper.

Normal QRS complex width

A narrow measurement between $80-100\,ms$, or $2-2.5$ small boxes.

QT interval

The length of time from the beginning of ventricular depolarization until the ventricles completely repolarize, normally between $350-450\,ms$.

QT-c (QT-corrected)

A measurement used to correct for heart rate variations, as the standard QT interval is not accurately reflected if the heart rate is abnormally slow or fast.

J-point

The specific point between the QRS complex and where the ST-segment begins.

ST-segment

The portion of the tracing indicating the beginning of ventricular recovery, which should baseline at the isoelectric line.

ST depression

Defined as greater than $0.5\,mm$ ($1/2$ small box) below the isoelectric line; often indicates cardiac ischemia, digoxin toxicity, or electrolyte abnormalities.

ST elevation

Defined as greater than $1\,mm$ ($1$ small box) in limb leads and $2\,mm$ in precordial leads above the isoelectric line; indicates myocardial necrosis (infarction).

T-wave inversion (TWI)

A nonspecific change where the T-wave is oppositely deflected from its expected direction, potentially indicating cardiac ischemia or irritability.

U-wave

A small hill following the T-wave representing the repolarization of the Purkinje fibers; may become prominent in conditions like hypokalemia or digoxin toxicity.

Ectopic beats (Ectopy)

Beats originating from outside the SA node, often caused by cells irritated from ischemia or damage.

PVC (Premature Ventricular Contraction)

A common type of ectopy originating in the ventricles, characterized by no P-waves, a wide QRS complex ($> 3$ small boxes), and usually an opposite deflection of the T-wave.

Bigeminy

A pattern where every other beat is a PVC.

Trigeminy

A pattern where every $3rd$ beat is a PVC.

Quadrigeminy

A pattern where every $4th$ beat is a PVC.

PAC (Premature Atrial Contraction)

A beat originating in the atria but outside the SA node, featuring a P-wave with different morphology that interrupts the underlying rhythm.

PJC (Premature Junctional Contraction)

A beat occurring within the AV node where P-waves are either absent or inverted.

Normal Sinus Rhythm (NSR)

Healthy cardiac conduction with a rate of $60-100\,bpm$, uniform P-waves preceding each QRS, and a narrow QRS complex.

Sinus Bradycardia

A rhythm identical to NSR but with a rate less than $60\,bpm$.

Sinus Tachycardia

A rhythm identical to NSR but with a rate greater than $100\,bpm$.

Junctional escape rhythm

A rhythm occurring when the AV node takes over as the pacemaker due to SA node dysfunction, resulting in a HR of $40-60\,bpm$.

Supraventricular Tachycardia (SVT)

A fast heart rate ($150-250\,bpm$) originating above the ventricles, characterized by a narrow QRS and P-waves often hidden in T-waves.

Ventricular Tachycardia (VTACH)

A serious rhythm with a rate of $100-250\,bpm$, no P-waves, and wide QRS complexes ($> 3$ small boxes).

Sinus Arrhythmia

An irregular but usually benign variant of NSR that often correlates with the respiratory cycle.

Atrial Fibrillation (AF)

An arrhythmia where the atria quiver instead of beating organizedly, resulting in unmeasurable P-waves, an irregular rhythm, and increased blood clot risk.

Atrial Flutter (Aflutter)

A rhythm featuring visible P-waves in a saw-tooth pattern (F-waves), commonly with a $2:1$ P to QRS ratio.

Ventricular Fibrillation (VFIB)

A cardiac arrest rhythm where the ventricles quiver and there is no pulse, requiring immediate code and defibrillation.

Torsades de Pointes

A polymorphic type of VTACH caused by QT prolongation, appearing to 'twist' around the isoelectric line.

Asystole

The characteristic 'flat-line' indicating no electrical conduction and no mechanical beating.

1st Degree AV Block

A delay in conduction where the PR interval is consistently longer than $200\,ms$ ($5$ small boxes), described by the mnemonic: 'If the R is far from P – then you have a 1st degree'.

2nd Degree Type 1 AV Block (Wenckebach)

A block where the PR interval progressively lengthens until a QRS is dropped, described by the mnemonic: 'Longer longer longer drop – Then you have a Wenckebach'.

2nd Degree Type 2 AV Block (Mobitz II)

A block where the electrical impulse occasionally fails to reach the ventricles but the PR interval remains consistent for the conducted beats, described by: 'If some Ps don’t get through – then you have a Mobitz II'.

3rd Degree AV Block (Complete Heart Block)

A condition where atria and ventricles do not communicate; P-waves and QRS complexes map out regular but unrelated to each other, described by: 'If Ps and Qs do not agree – then you have a 3rd degree'.

Bundle Branch Block

A block slowing conduction between the ventricles, resulting in an abnormally widened QRS complex ($> 3$ small boxes).

How do you interpret abnormal ST elevation in an ECG?

ST elevation greater than $1$ mm in limb leads or $2$ mm in precordial leads indicates myocardial necrosis (infarction). To solve this, assess for symptoms of cardiac ischemia, and prepare for immediate interventions such as contacting emergency services or applying medical treatments as prescribed.

What is the first step when you notice a patient in asystole?

Asystole, the characteristic 'flat-line', indicates no electrical conduction and requires immediate action. Solve this by starting CPR and calling for help, preparing to use an AED if available.

How do you manage a patient experiencing Ventricular Tachycardia (VTACH)?

VTACH is a serious rhythm with a rate of $100-250$ bpm, with no P-waves and wide QRS complexes. To solve this, first verify if the patient has a pulse; if not, initiate CPR and coordinate for defibrillation.

What steps should you take if you observe a patient's heart rate is below 60 bpm?

This could indicate Sinus Bradycardia. If symptomatic, monitor the patient closely, consider administering atropine, and prepare for transcutaneous pacing if necessary.

How do you approach a case of Atrial Fibrillation (AF)?

AF involves unmeasurable P-waves, an irregular rhythm, increasing the risk for clots. Solve this by assessing the patient's symptoms, managing the rate/rhythm using rate control medications like beta-blockers, and considering anticoagulation therapy.

How do you interpret a wide QRS complex greater than 100 ms?

A wide QRS complex ($> 3$ small boxes) can indicate a bundle branch block or ventricular ectopy. To solve this, assess the patient's history, monitor for symptoms of ischemia, and consider further imaging or cardiac evaluation if the wide QRS is new or associated with other clinical signs.

What does the presence of P-wave abnormalities indicate in the ECG?

P-wave abnormalities, such as varying morphology, may indicate atrial enlargement or ectopic atrial activity. To solve this, identify the underlying rhythm and evaluate the patient for potential atrial conditions or heart failure.

How do you approach ST depression greater than 0.5 mm?

ST depression exceeding $0.5$ mm can indicate myocardial ischemia or digoxin toxicity. To solve this, assess the patient's symptoms and clinical context and consider initiating treatment for myocardial ischemia or reviewing medication dosages if digoxin toxicity is suspected.

What does T-wave inversion signify in an ECG reading?

T-wave inversion can suggest myocardial ischemia, but may also occur with other conditions like structural heart changes. To resolve this, correlate with clinical symptoms and consider further testing, such as echocardiography or stress testing, to evaluate for coronary artery disease.

How do you interpret U-wave prominence in an ECG?

A prominent U-wave may be indicative of electrolyte imbalances such as hypokalemia or other cardiac conditions. To solve this, assess the patient's electrolyte levels and clinical presentation, and correct any identified imbalances promptly.