EKG Final

EKG Basics and Interpretation

EKG (Electrocardiogram) is a non-invasive test that records the electrical activity of the heart. It provides critical information about heart rate, rhythm, and structural or electrical abnormalities.

1. Steps to Systematically Read an EKG Strip

A systematic approach ensures accurate interpretation:

1 Rate: Calculate the heart rate.

◦ Normal Rate: 60-100 beats per minute (bpm).

◦ Bradycardia: Below 60 bpm.

◦ Tachycardia: Above 100 bpm.

2 Rhythm: Determine if the rhythm is regular or irregular.

◦ Measure R-R intervals (for ventricular rhythm) and P-P intervals (for atrial rhythm).

◦ Regular rhythm implies consistent intervals.

3 P Waves:

◦ Are P waves present?

◦ Are they upright and uniform?

◦ Is there one P wave for every QRS complex?

◦ Do all P waves look alike? (Indicates they originate from the same atrial pacemaker).

4 PR Interval:

◦ Measure from the beginning of the P wave to the beginning of the QRS complex.

◦ Normal PR Interval: 0.12-0.20 seconds (3-5 small squares).

◦ Consistent PR intervals suggest normal AV conduction.

5 QRS Complex:

◦ Measure the duration of the QRS complex.

◦ Normal QRS Duration: 0.06-0.10 seconds (1.5-2.5 small squares).

◦ Are all QRS complexes uniform?

◦ Are they wide or narrow? (Narrow suggests supraventricular origin, wide suggests ventricular origin or bundle branch block).

6 ST Segment:

◦ Is the ST segment at the isoelectric line? (The baseline between the T wave and the next P wave).

◦ ST elevation: Suggests myocardial injury (e.g., STEMI).

◦ ST depression: Suggests myocardial ischemia.

7 T Waves:

◦ Are T waves present and upright?

◦ Tall, peaked T waves might indicate hyperkalemia.

◦ Inverted T waves might indicate ischemia.

8 QT Interval:

◦ Measure from the beginning of the QRS complex to the end of the T wave.

◦ Normal QT Interval: Varies with heart rate, generally <0.44 seconds.

◦ Prolonged QT can predispose to arrhythmias like Torsades de Pointes.

2. Heart Rate Calculation Methods

1 300-150-100-75-60-50 Method (Sequence Method):

◦ Find an R wave on a thick line.

◦ Count down 300, 150, 100, 75, 60, 50 for each subsequent thick line.

◦ Useful for regular rhythms.

2 1500 Method:

◦ Count the number of small squares between two consecutive R waves.

◦ Divide 1500 by that number.

◦ Rate = 1500 / (\text{number of small squares between R-R})

◦ Most accurate for regular rhythms.

3 6-Second Method (for irregular rhythms):

◦ Count the number of R waves in a 6-second strip (usually marked by 3-second tick marks at the top or bottom, meaning 30 large squares [each large square is 0.2 seconds]).

◦ Multiply that number by 10.

◦ Rate = (\text{number of R waves in 6 seconds}) \times 10

3. Terminology

• Unifocal: Arising from a single ectopic focus. For example, unifocal PVCs all look alike because they originate from the same irritable site in the ventricle.

• Palpation: The act of feeling with the hands, especially for diagnostic purposes (e.g., palpating a pulse).

• Murmur: An unusual sound heard during a heartbeat, caused by turbulent blood flow. It can be a harmless innocent murmur or indicate a heart problem (e.g., valvular disease).

4. Basic EKG Waveforms, Intervals, and Segments

• P Wave: Represents atrial depolarization (contraction).

• PR Interval: Time from atrial depolarization to ventricular depolarization; reflects conduction through AV node.

• QRS Complex: Represents ventricular depolarization (contraction).

• ST Segment: Time from end of ventricular depolarization to beginning of ventricular repolarization; normally isoelectric.

• T Wave: Represents ventricular repolarization (relaxation).

• QT Interval: Total time for ventricular depolarization and repolarization.

5. Arrhythmias

5.1 Sinus Arrhythmias

• Normal Sinus Rhythm (NSR):

◦ Rate: 60-100 bpm.

◦ Rhythm: Regular.

◦ P waves: Present, upright, uniform, one before each QRS.

◦ PR Interval: Normal (0.12-0.20 s), constant.

◦ QRS: Normal (0.06-0.10 s), constant.

◦ EKG Strip Description: Consistent P-QRS-T complexes with regular spacing, normal shape, and rate between 60-100 bpm.

• Sinus Bradycardia:

◦ Rate: Less than 60 bpm.

◦ Other characteristics: Same as NSR.

◦ EKG Strip Description: Looks like NSR but with widely spaced P-QRS-T complexes, indicating a slow rate.

• Sinus Tachycardia:

◦ Rate: Greater than 100 bpm.

◦ Other characteristics: Same as NSR.

◦ EKG Strip Description: Looks like NSR but with P-QRS-T complexes much closer together, indicating a fast rate.

• Sinus Arrhythmia:

◦ Rate: 60-100 bpm (can be outside this range).

◦ Rhythm: Irregular, often associated with respiration (rate increases with inspiration, decreases with expiration).

◦ Other characteristics: Same as NSR.

◦ EKG Strip Description: P-QRS-T complexes present, but the R-R intervals vary, appearing to lengthen and shorten with breathing.

5.2 Atrial Arrhythmias

• Premature Atrial Contraction (PAC):

◦ Premature P wave (often abnormal shape) followed by a normal QRS complex. The P wave comes earlier than expected, sometimes hidden in the previous T wave.

◦ EKG Strip Description: A premature, usually narrow QRS complex preceded by an abnormal or premature P wave. There might be a compensatory pause.

• Atrial Fibrillation (AFib):

◦ Rate (atrial): Very rapid, unmeasurable (>350 bpm).

◦ Rate (ventricular): Variable, often rapid and irregular.

◦ Rhythm: Irregularly irregular.

◦ P waves: Absent, replaced by fibrillatory waves (f waves) which are chaotic undulations of the baseline.

◦ PR Interval: Not measurable.

◦ QRS: Normal, but irregular.

◦ EKG Strip Description: Erratic, squiggly baseline (f waves), no discernible P waves, and irregularly irregular R-R intervals. QRS complexes are usually narrow.

• Atrial Flutter (AFlutter):

◦ Rate (atrial): Rapid, regular (250-350 bpm).

◦ Rate (ventricular): Variable, depends on AV block (e.g., 2:1, 3:1 conduction).

◦ Rhythm: Atrial regular, ventricular often regular (if consistent block) or irregular.

◦ P waves: Sawtooth pattern (flutter waves or F waves).

◦ PR Interval: Not measurable.

◦ QRS: Normal.

◦ EKG Strip Description: Distinct “sawtooth” pattern of flutter waves (F waves) between normal, usually regularly occurring QRS complexes. The ventricular rate depends on the number of F waves to each QRS.

• Supraventricular Tachycardia (SVT):

◦ Rate: Rapid (150-250 bpm).

◦ Rhythm: Regular.

◦ P waves: Often hidden within the QRS or T wave due to rapid rate; if visible, they may be abnormal.

◦ PR Interval: Not measurable.

◦ QRS: Narrow and uniform.

◦ EKG Strip Description: Very fast, regular narrow-complex tachycardia, often with P waves indistinguishable from the QRS or T waves.

5.3 Ventricular Arrhythmias

• Premature Ventricular Contraction (PVC):

◦ Premature, wide, bizarre QRS complex not preceded by a P wave. Often followed by a full compensatory pause.

◦ Unifocal PVCs: All PVCs look identical (same origin).

◦ Multifocal PVCs: PVCs have different shapes (different origins).

◦ Bigeminy: Every second beat is a PVC.

◦ Trigeminy: Every third beat is a PVC.

◦ EKG Strip Description: A wide (greater than 0.12 s), bizarre-shaped QRS complex that appears prematurely and is not preceded by a P wave. T wave is usually opposite in direction to the QRS.

• Ventricular Tachycardia (VTach):

◦ Rate: Rapid (100-250 bpm).

◦ Rhythm: Regular or slightly irregular.

◦ P waves: Absent, or dissociated from QRS.

◦ PR Interval: Not measurable.

◦ QRS: Wide (>0.12 s), bizarre, uniform (monomorphic VT) or varying (polymorphic VT).

◦ EKG Strip Description: A series of three or more consecutive wide, bizarre QRS complexes occurring at a rapid rate. P waves may be absent or appear dissociated.

• Torsades de Pointes:

◦ A type of polymorphic VT where the QRS complexes appear to twist around the isoelectric line. Associated with prolonged QT interval.

◦ EKG Strip Description: A distinctive form of polymorphic ventricular tachycardia characterized by QRS complexes that gradually change in amplitude and twist around the isoelectric line, giving a “corkscrew” appearance.

• Ventricular Fibrillation (VFib):

◦ Rate: Unmeasurable, chaotic.

◦ Rhythm: Chaotic, irregular.

◦ P waves: Absent.

◦ PR Interval: Not measurable.

◦ QRS: Absent, replaced by chaotic deflections.

◦ EKG Strip Description: No discernible P waves, QRS complexes, or T waves. The baseline is represented by a wavy, chaotic line of varying amplitude and morphology, indicating complete disorganized electrical activity. This is a cardiac arrest rhythm.

• Asystole:

◦ Rate: Zero.

◦ Rhythm: None.

◦ P waves: Absent.

◦ PR Interval: Not measurable.

◦ QRS: Absent.

◦ EKG Strip Description: A flat line, indicating absence of electrical activity. Occasionally, fragmented P waves might be seen, but no QRS complexes. This is a cardiac arrest rhythm (true cardiac standstill). Always confirm in two leads.

• Agonal Rhythm:

◦ Rate: Very slow (<20 bpm) and erratic.

◦ Rhythm: Irregular (dying heart).

◦ P waves: Absent or occasional.

◦ QRS: Wide, bizarre, often polymorphic; erratic and decreasing in frequency.

◦ EKG Strip Description: Extremely slow, irregular escape rhythm originating from the ventricles. Characterized by wide, bizarre QRS complexes appearing sporadically, with no P waves. Often precedes asystole.

6. Heart Blocks

Heart blocks are conduction disorders where electrical impulses from the atria are partially or completely blocked from reaching the ventricles.

• First-Degree AV Block:

◦ PR Interval: Prolonged (>0.20 s), but constant.

◦ Other characteristics: All P waves are followed by a QRS.

◦ EKG Strip Description: Normal P-QRS-T sequence, but the PR interval is consistently longer than 0.20 seconds.

• Second-Degree AV Block, Type I (Wenckebach/Mobitz I):

◦ PR Interval: Progressively lengthens, then a QRS complex is dropped. The cycle repeats.

◦ EKG Strip Description: PR intervals get progressively longer with each beat until a P wave appears without a QRS complex (missed beat), then the pattern repeats.

• Second-Degree AV Block, Type II (Mobitz II):

◦ PR Interval: Constant (if present), but some P waves are not followed by a QRS complex.

◦ EKG Strip Description: P waves are regular and constant, but occasionally a QRS complex is absent after a P wave. The PR interval of conducted beats remains constant. This is more serious than Type I and can progress to third-degree block.

• Third-Degree AV Block (Complete Heart Block):

◦ P waves: Regular.

◦ QRS complexes: Regular, but at a slower rate than P waves.

◦ P waves and QRS complexes are completely dissociated (they march to their own beat). There are more P waves than QRS complexes.

◦ No relationship between P waves and QRS complexes.

◦ EKG Strip Description: P waves appear regularly (atrial rate) and QRS complexes appear regularly (ventricular rate), but there is no relationship between them. The atrial rate is faster than the ventricular rate, and some P waves will fall within or on the QRS complexes or T waves.

7. ST-Elevation Myocardial Infarction (STEMI)

• STEMI: Acute myocardial infarction characterized by ST-segment elevation on the EKG, indicating full-thickness myocardial injury.

◦ EKG Characteristics:

▪ ST-segment elevation (at least 1 mm in two contiguous leads, or 2 mm in V2-V3).

▪ T wave inversion or hyperacute T waves may be present initially.

▪ Pathological Q waves may develop later, indicating myocardial necrosis.

◦ EKG Strip Description: Significant elevation of the ST segment above the isoelectric line, often with T wave changes.

7.1 Medications to Treat MI (Acute Phase)

• Oxygen: If hypoxic (SpO_2 < 90\%).

• Nitroglycerin: For chest pain, vasodilator. Reduces preload and afterload.

• Aspirin: Antiplatelet, reduces clot formation.

• Morphine: For severe pain, vasodilator.

• Beta-blockers: Reduce myocardial oxygen demand and mortality.

• ACE Inhibitors/ARBs: Start within 24 hours to prevent ventricular remodeling.

• Statins: Lower cholesterol, stabilize plaque.

• Thrombolytics (Fibrinolytics): If PCI (Percutaneous Coronary Intervention) is not available within recommended time frame (e.g., within 90-120 minutes), to dissolve the clot.

• Anticoagulants: (e.g., Heparin) to prevent clot extension and re-occlusion.

8. Pulse Points

Locations where an arterial pulse can be palpated:

• Radial: Thumb side of the wrist (most common).

• Brachial: Inner aspect of the elbow (used for blood pressure measurement, infants).

• Carotid: Side of the neck (do not palpate both sides simultaneously).

• Femoral: Groin area.

• Dorsalis Pedis: Top of the foot.

• Posterior Tibial: Behind the medial malleolus (inner ankle bone).

• Popliteal: Behind the knee.

• Temporal: Temple area of the head.

• Apical: Apex of the heart, by listening with a stethoscope (not palpatory usually for peripheral pulse check).