IBHRE: Basic ECGs

Basic ECGs Interpretation

Basic ECG Knowledge

ECG components and ECG leads. ▲

Lime leads and views of the heart
ref: Basic Electrocardiography: Normal and Abnormal ECG Patterns. Antoni Bayés de Luna. ▲

Chest leads and views of the heart
ref: Basic Electrocardiography: Normal and Abnormal ECG Patterns. Antoni Bayés de Luna. ▲

Intraventricular Conduction Delay

Possible Location of Intraventricular Conduction Abnormalities causing abnormal QRS complex
as labelled in number 1, 2, and 3. The abnormalities include left/right bundle branch block and left anterior/posterior fascicular block.
Marriott's Practical Electrocardiography. 13th edition, 2020. ▲

QRS duration ≥120msec
Lead V1 Late intrinsicoid (R′ peak or late R peak)
Lead V6 Early intrinsicoid (R peak), wide S wave

Marriott's Practical Electrocardiography. 13th edition, 2020.

Right Bundle Branch Block (RBBB)
in a patient with tetralogy of Fallot. Noted with prominent R' in V1 and wide S wave in V6. ▲

Fascicular Block
Compared with normal conduction in (A), fascicular block activates free wall from one site instead of two. Marriott's Practical Electrocardiography. 13th edition, 2020. ▲

Left anterior fascicular block
LAFB: left axis deviation (more than -60 degree), small Q in leads I and aVL, small R in leads II/III/aVF, and late intrinsicoid deflection in aVL (>0.045s).
Marriott's Practical Electrocardiography. 13th edition, 2020. ▲

Bifascicular Block
Left posterior fascicular block (LPFB) and RBBB.
LPFB: right axis deviation (>120 degree), small R in I/aVL, small Q in II/III/aVF, and late intrisicoid deflection in aVF (>0.0045s).
Marriott's Practical Electrocardiography. 13th edition, 2020. ▲

QRS duration ≥130msec in women or ≥140msec in men.
Lead V1: QS or rS
Lead I, V6: Monophasic R, no Q, mid-QRS slur or notch.

Marriott's Practical Electrocardiography. 13th edition, 2020.

Left Bundle Branch Block (LBBB)
Noted with wide QRS and mid-QRS notching in I, aVL, V5-6. ▲

Sinus Node Dysfuncion

Sinus Node Dysfunction
may present with severe sinus bradycardia, sinoatrial exit block, sinus pause, or tachy-bradyarrhythmia. Above is sinus pause. For those with symptoms, pacemaker is indicated. ▲

Sinoatrial exit block type II
SA Exit Block Type II: Sinus rhythm followed by a pause that is a multiple of P-P interval. Above, the pause duration was twice of P-P interval. ▲

Sinoatrial exit block: ECGs & Ladder Diagram
thoracickey.com ▲

Tachy-brady syndrome ▲

Atrioventricular Block

1st degree AV block
= excessive delay of impulse passing through AV node. Manifested in ECG by prolongation of PR interval. The prolonged PR is constant. ▲

2nd degree AV block type I or Mobitz I
PR interval progressively lengthens until the AV node fails to conduct. Usually benign. ▲

2nd degree AV block type II or Mobitz II
The tracing was obtained during exercise stress test. The AV block ratio was 2:1 alternating with 3:1 with constant PR intervals The QRS duration was wide. The block level was below AV node. ▲

3rd degree AV block or complete AV block
Atrial impulse fails to conduct to ventricle. Atrial rate is faster than ventricle. Atria and ventricles are totally dissociated. ▲

Tachyarrhythmias

Atrial Fibrillation
Fibrillatory wave seen in V1 with totally irregular ventricular rhythm. ▲

Atrial Flutter
Flutter waves seen clearly in II/III/aVF/V1. ▲

Supraventricular Tachycardia
Narrow complex tachycardia, rate approximately 150 bpm, P waves were visible after each QRS. ▲

Ventricular Tachycardia
Wide complex tachycardia rate approximately 200 bpm. No man's land axis. ▲

Polymorphic VT & VF
Sinus bradycardia with couplet PVCs followed by polymorphic VT which later progressed to VF. ▲

Monomorphic VT
Regular wide complex tachycardia, LBBB-like morphology, positive QRS in inferior leads consistent with VT from right ventricular outflow tract. In patients without structural heart disease, this condition is benign and may be cured by catheter ablation. ▲

Conditions that increase risk of sudden cardiac arrest

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC)
RBBB, T wave inversion in V1-V4, and presence of Epsilon waves (arrow). Epsilon wave is a low amplitude signal between end of QRS and onset of ST segment in V1-V3. ▲

Brugada ECG
J point elevation in right precordial leads with coved ST elevation and T wave inversion ▲

Hypertrophic Cardiomyopathy
High voltage in I, aVL, V4-6 with lateral ST depression and T wave inversion. ▲

Wolff-Parkinson-White Syndrome
Left: slurred upstroke of QRS complex or delta waves presented in leads II, III, aVF, and V2-V5.
Right: Irregular, wide-complex, and extremely fast tachycardia, consistent with AF with rapid conduction via accessory pathway causing extremely fast ventricular rate. Catheter ablation is indicated. ▲

Old inferior and anterior wall myocardial infarction
Deep Q waves in III/aVF and V2-V4. May lead to scar-related VT. ▲

Long QT ECG
This ECG was from a patient with long QT 2 syndrome. Noted with prolong QT interval and notched T wave. ▲

Short QT
Short QT syndrome is an extremely rare, yet highly lethal condition. Marriott's Practical Electrocardiography. 13th edition, 2020. ▲

Cardiac rhythm device related ECGs

Ventricular pacing from different locations.
ECG patterns in LV pacing: R in V1, left-to-right frontal axis (negative in I and aVL and positive in III). ▲

LV only pacing to Biventricular pacing
Note with changes from left-to-right vector to left-to-superior vector. Leads I, aVL, and III became as negative. Lead II went from positive to negative as a result of RV apex pacing. ▲

Is CRT working properly?
Yes. This is the example of LV-RV pacing offset.
ECG revealed P synchronous biventricular pacing. The presence of biventricular pacing was evident by the presence of small Q in I, aVL; small R in III; and positive QRS in V1. There were 2 pacing spikes before the QRS, separated by 40ms. The pacing spikes were from LV pacing and RV pacing that were offset by 40ms. ▲

CRT system; DDD 60/120. Why did the device stop pacing?
The 1st part of the tracing showed P-synchronous biventricular pacing. The atrial rate was approximately 115 bpm.
Later in the tracing, the atrial rate speeded up to more than 120 bpm, above the upper rate limit. CRT, therefore, was unable to track and did not deliver biventricular pacing. ▲

Failure to fire
1st 6 beats: P synchronous ventricular pacing. Last 3 beats: P waves without any pacing spikes.
Generic Diagnosis: failure to fire. Potential causes: oversensing, battery depletion, loose connection, and etc.
In this case, failure to fire was due to lead noise oversensing from lead fracture. ▲

Atrial Undersensing ▲

Failure to fire, sense, and capture
This is a case of a VVI pacemaker with lead fracture. The lower rate was set at 60bpm. The first 4 beats were AF with slow ventricular response without any pacing spikes. After the 4th and 5th QRS, pacing spikes occurred in appropriately The last beat was PVC followed by a pacing spike which failed to capture. ▲

Atrial lead failed to properly pace.
Dual chamber system with A lead fell in to ventricle. Noted that for each QRS, there were 2 pacing spikes separated by 160ms, likely to equal AV delay.
The 1st spike captured ventricle. The 2nd spike was functionally not captured. Cannot exclude A/V leads switch in the header, though. ▲

Failure to properly pace and failure to fire
Dual chamber system. The first line showed 2 pacing spikes for each QRS. The 1st spike captured ventricle. The 2nd spike came at the interval of AV delay. There are 2 possible explanations, A lead in ventricle or A/V leads switch in the header. The latter was most likely. The 2nd and 3rd lines of the tracing showed P wave without QRS or V pacing, meaning that atrium signal was sensed. A lead in ventricle was therefore excluded. In this case, A and V leads were placed in to the wrong port in the header. When atrial rate was increased as in the 2nd line, ventricular channel was sensed and therefore inhibited the pacing from both A and V channels. ▲

DDD 50/110, PAV 150, SAV 120, PVARP 200
Upper Rate Behavior: Pacemaker "block".
ECG showed AS-VP with progressively increase in AV delay until drop beats. Atrial rate was faster than the upper tracking rate of 110bpm but slower than TARP rate. Wenckebach-like behavior was therefore seen. TARP = 120+200 msec; TARP rate = 188 bpm. Wenckebach window = 110-188 or 320-545msec. ▲

Pacemaker mediated tachycardia or endless-loop tachycardia.
Another upper rate behaviour of dual-chamber pacemaker. Noted with P-synchronous rapid V pacing, usually at the rate close to upper tracking rate.
Triggered by retrograde A which may be from PVC, long-AV delay, or non-A capture. In the above tracing, PMT was triggered by PVC. ▲

Managed Ventricular Pacing
The tracing began with AP-VS, followed by AP without AV conduction (the 3rd P wave). After the 3rd P wave, there were 2 pacing spikes very close to each other, one pacing A and another pacing V. The finding is typical for algorithm to reduce unnecessary RV pacing by switching AAI to DDD mode when conduction from atrium fails to conduct to ventricle. After the blocked AV, this algorithm is set to pace DDD with AV delay of 80ms. ▲

DDD 70/120, AVD 200ms
Appropriate AP-VP, followed by a PVC that timed perfectly at the lower rate interval. A pacing spike was seen at the beginning of the PVC with another pacing spike that came within 110ms. This is the behaviour of "safety pacing" feature. Any ventricular sensed event that occurs within the 110 millisecond window after AP event will result in a ventricular pace at the end of the 110 ms window. Atrial sensed (AS) events do not initiate a Ventricular Safety Pacing interval.
Medtronic Academy ▲

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