Electrocardiograms
How to read electrocardiograms
Important considerations for reading electrocardiograms
- Is the rhythm regular and consistent?
- Is the rate fast, slow, or normal?
- Are P waves present and look the same?
- Is the PR interval normal and consistent?
- Are the QRS complexes normal and immediately follow the P wave?
- Is the T wave present and normal in appearance?
Multi-lead strips: when viewing a multi-lead strip, use lead II or whichever lead shows the pattern most clearly.
Inverted waveforms: when a lead that is normally upright shows its P waves, QRS complexes, and T waves all inverted (lead I when the arm electrodes are swapped, for example), the cause is usually improper lead placement, not a heart problem. Have the electrodes checked and focus on the pattern listed above in 1-6. Some leads, such as aVR, are normally inverted, while a newly inverted T wave on its own can be a sign of ischemia and should be reported to the supervising PT.
Calculation of heart rate with EKG
Calculations as follows for a 6-second strip method:
The 6-second method works for both regular and irregular rhythms (such as atrial fibrillation), because it averages beats across the strip. It’s the go-to method when the rhythm is irregular.
Count the number of QRS complexes in 6 seconds and multiply by 10
Example:
7 QRS peaks noted in 6 seconds x 10 = 70 bpm (heart rate). This is in the normal range of 60-100.
Common EKGs
Sinus bradycardia (slow heart rate, below 60 beats per minute at rest)
PT implications
- Common to see this rhythm in well-conditioned athletes, in those taking beta-blockers, and in the elderly population
- If present and the patient has no symptoms, it is generally OK to start or continue activity:
- Will need to use the perceived exertion scale (RPE) to assess tolerance to activity, since beta-blockers blunt the normal heart rate response to exertion
- Monitor for symptoms of dizziness, lightheadedness, and pallor
- If these symptoms develop, or heart rate fails to rise (or drops) with increasing activity, stop the activity, recheck vitals, and notify the supervising PT
Sinus tachycardia (fast heart rate, > 100 beats per minute at rest)
PT implications
- Common to observe this rhythm during exercise
- If present before exercise notify supervising PT
- Pay attention if the individual develops a headache, dizziness, or lightheadedness with tachycardia
- If these symptoms develop, stop the activity, recheck all vital signs, and notify the supervising PT
A-fibrillation (A-fib)
An irregularly irregular rhythm in which the atria quiver erratically; the ventricular rate may be normal or rapid. On the EKG, discrete P waves are absent and are replaced by chaotic fibrillatory (f) waves.
PT implications
If not previously recognized, stop activity and notify
If identified previously:
- Use ECG or auscultation rather than the radial pulse alone, since the rate may be irregular; monitor heart rate, blood pressure, and oxygen saturation closely.
- Use rate of perceived exertion (RPE) rather than heart rate alone, and start with low to moderate intensity, avoiding high-intensity or sudden exertion early in rehab.
- Stop signs: dizziness, fatigue, palpitations, chest pain, or dyspnea.
A-flutter
A regular, tachycardic contraction of the atrium; constant atrial contraction produces a sawtooth pattern of flutter (F) waves in place of P waves.
PT implications
If not previously recognized, stop activity and notify
If identified previously, follow the same vital sign monitoring and exercise progression guidance as atrial fibrillation (above), with these flutter-specific notes:
- A-flutter typically presents with a regular but rapid atrial rate (240-400 bpm); ventricular response may be regular or irregular depending on AV block.
- Patients may suddenly shift into more dangerous rhythms (e.g., atrial fibrillation or rapid ventricular response), so use ECG or telemetry when possible, especially in acute care settings.
Premature ventricular contraction (PVC)
An early, wide, bizarre QRS complex from an ectopic ventricular focus, occurring before the next expected sinus beat and typically followed by a compensatory pause.
PT implications
- Singular PVC at rest and exercise (no restriction): initiate or continue with activity, as this can be an anomaly
- Can be caused by stress, caffeine, or idiopathic causes
- Couplet (2) (precaution): stop and rest for 5 minutes; resume exercise only if resolved
- Three or more PVCs in a row at rest or with exercise (contraindication): do not initiate activity and discontinue exercise, as this could lead to fatal heart rhythms
- Bigeminy - a PVC every other heartbeat (contraindication): do not initiate activity and discontinue exercise, as this could lead to fatal heart rhythms
- Monitor for symptoms: heart fluttering, heart pounding, missed heartbeats
Ventricular tachycardia
A rapid heart rhythm originating from the ventricles. The ventricles contract at a fast rate and may not fill effectively, which can significantly reduce cardiac output and impair blood flow to the body.
PT implications
- Medical emergency: stop activity immediately, activate emergency response, and check responsiveness and pulse.
- If the patient is unresponsive and has no pulse or is not breathing normally (only gasping), begin CPR and apply the AED.
Ventricular fibrillation
Ventricular fibrillation is a life-threatening dysrhythmia characterized by rapid, chaotic electrical activity causing ineffective quivering of the ventricles. Because there is no coordinated ventricular contraction, the heart is unable to produce effective cardiac output or blood flow to the body.
PT implications
- Medical emergency: activate emergency response, begin CPR, and apply the AED as soon as it’s available.
AV heart blocks
AV (atrioventricular) blocks are delays or interruptions in conduction from the atria to the ventricles, seen as changes to the PR interval or a mismatch between P waves and QRS complexes.
- First-degree: PR interval is prolonged (over 0.20 seconds) but constant, and every P wave is followed by a QRS complex. Usually benign; continue activity and monitor.
- Second-degree, type I (Wenckebach): the PR interval progressively lengthens until a QRS complex is dropped. Usually well tolerated; monitor symptoms and notify the supervising PT if new.
- Second-degree, type II: PR interval stays constant but QRS complexes are intermittently dropped without warning. Higher risk of progressing to complete block; stop activity and notify the supervising PT.
- Third-degree (complete): no relationship between P waves and QRS complexes; the ventricles beat independently at a slow rate. Medical emergency: stop activity and notify the supervising PT immediately.