Lecture 19The Electrocardiogram

EKG/ECGHoldorf PhD, MPA, RDMS, RVT

Normal complex

• P wave-atrial systole

• QRS complex – ventricular systole (depolarization)

• T wave – Ventricular diastole (repolarization)

Hint:

• 1 small box = 0.04 seconds

• 1 big box = 0.2 seconds

• 5 big boxes = 1 second

• Normal values:

• R-R interval: between 3 to 5 big boxes (60-100 beats/minute

• QRS complex: less than 3 little boxes (less than .12 seconds

• PR interval: Less than 1 big box (less than 0.2 seconds)

• The ECG has which of the following rhythms?

• Normal sinus rhythm (via the SA node)

Method of analysisFind the P waves (they’re the big ones)

Assess at the QRS duration (< little boxes)Assess at R-R interval: between 3 and 5 big boxes

Look for P preceding each R waveCheck the PR interval (less than I big box)

ECG: Common abnormalities

• Normal sinus rhythm (R-R interval between 3 and 5 big boxes

• 60-100 BPM

• P-wave preceding each QRS

• PR interval and QRS complex within normal limits

SINUS BRADYCARDIA (more than 5 big boxesHeart rate less than 60 BPM

Otherwise all other findings of normal sinus rhythm

SINUS TACHYCARDIALess than 3 big boxes

Heart rate greater than 100 BPMOtherwise all other findings of normal sinus rhythm

If the cardiac electrical impulse is in the bundle branches, where are you on the ECG tracing?

The Purkinje fibersThe bundle of His?

• Answer for all

• PR interval

ARRHYTHMIAS OVERVIEW

• P waves

• Present or absent

• Relationship to QRS

• PR Interval

• Normal < 0.20 sec.

• QRS Duration

• Normal <0.12 sec.

Sinus arrhythmiaIrregular rhythm related to respiration (increase

rate with inspiration; decrease rate with expiration

In sinus arrhythmia, the heart rate varies with the phase of respiration.  The heart rate typically increases during inspiration and decreases during expiration.  Therefore, as observed, the R-R interval is longer during expiration.  These changes are mediated through vagal reflexes.  Sinus arrhythmia is more common in young healthy athletes.

Atrial fibrillation

• Rapid discharge of multiple foci in the atria, no discrete P waves, irregularly irregular rhythm.

Atrial flutterRapid discharge of an ectopic focus for atrial depolarization. Only occasional stimulus will

penetrate AV node. Saw-tooth pattern.

Ventricular FibrillationChaotic rhythm in which there are multiple areas exhibiting varying degrees of depolarization and repolarization. Absence of R-waves

Premature BeatsAtrial (PAC)

Electrical impulse originating in the atria outside of the SA node. Produces an abnormal P wave earlier than expected.

Ventricular (PVC-premature ventricular contractions)

Ectopic ventricular focus (anatomic source) produces an abnormal ventricular complex (usually larger and wider than normal complex).

A PVC occurring every other beast is called bigeminyA PVC occurring every 3rd beat is trigeminy

Ventricular tachycardiaThree or more beast of ventricular origin (PVC) occurring

in succession.

Bundle Branch BlockRight BBB= delay in depolarization of the right ventricle: QRS > 0.12 sec.

Left BBBDelay in depolarization of the left

ventricleV5 or V6 QRS > 0.12 sec.

Heart Block1st degree AV Block

PR interval >0.20 sec. (more than I big box) and of the same duration in every cycle. R-R interval is normal.

2nd degree AV BlockPR interval >0.20 sec. and gets progressively longer until a QRS is

dropped.In other words, the P moves further away from the QRS.

3rd degree AV block

• Complete absence of conduction between the atria and ventricles (also known as complete heart block (CHB).

• P-R interval gets progressively shorter.

• In other words, the P marches straight into the QRS complex.

PacemakersA high voltage, short duration pacing spike seen

before each ventricular conduction pattern.

Exercise Stress Testing• Indications

• To aid in the diagnosis of chest pain

• To determine the severity and prognosis of CAD

• To guide post MI rehab

• To evaluate cardiac arrhythmias

• To screen high risk professionals or asymptomatic patients

• Interpretation

• Morphology, degree and duration of ST-Segment depression (Mechanical / pressure)

• ST = segment elevation

• Duration of exercise

• Exercise-induced hypotension or arrhythmias