Click image for larger version (will open in new window)
Patient/anamnesis: n/a
ECG interpretation/discussion: This ECG is a printout from a telemetry station, derived from a 5 lead patient monitoring. So, what have we here? The underlying rhythm is sinoatrial, but both PR and RR interval varies. Remember, Wenckebach is not the name of a certain type of block, but rather a type of conduction. This is often misunderstood, as Second Degree AV Block Type 1 or Mobitz 1 is also often labelled Wenckebach block. A more precise term would be Wenckebach periodity, phenomenon, conduction. Wenckebach conduction is usually considered benign and can be recognized by the following criteria:
1) PR interval is progressively prolonged until a P wave is blocked
2) The shortest PR interval is the one immediately following the dropped beat. The longest PR interval is the one immediately before the dropped beat. The incremental change in PR interval is in the beginning of the Wenckebach cycle, thus between the first and second PR interval in a sequence.
3) The RR intervals progressively shorten until a QRS is ‘dropped’ due to the non-conducted atrial/sinoatrial impulse.
Now, looking at this ECG, the two first beats are at the end of a Wenckebach cycle. After the second QRS a non-conducted P wave occurs. The following beat is wide and bizarre and is a ventricular escape beat that occurs due to the long preceding pause. After the escape beat, a new Wenckebach cycle starts. The PR interval lengthens until a P wave is blocked. After this pause, a narrow QRS is preceded by a P wave with a very, very short PR interval. This is a junctional escape beat. Then, the Wenckebach cycle restarts.
When counting P waves and QRS complexes in the cycles, we’ll see that for every three QRS complexes there are four P waves, since one of the QRS complexes gets dropped repeatedly. This gives a 4:3 atrioventricular (AV) ratio, which is also called 4:3 conduction.
What a beauty! Thanks to my colleague and fellow ECG-dork for bringing me this rare gem!
September 6, 2009
This case displays the a relatively young, male patient with a recent myocardial infarction who developes junctional tachycardia. Three 12 lead ECGs are presented: One that is 9 days prior to this admittance, one that is obtained on scene by EMS and finally the ECG obtained in on arrival in the ER. The three ECGs are compared to obtain the correct diagnosis.
Patient: Male, 45 y/o. Non-smoker, non-drinker. Diabetes Mellitus type I with early stage retinopathy. Previous anterior infarction (two months prior to this admittance), followed by PCI to the LAD. Now presented in the ER with minor pressing chest pain. The pain occured when he was bicycling home from work. Having had a previous MI he immediately called EMS, who arrived quickly and recorded a 12 lead ECG. EMS adminstered 0.4 mg Nitro sl and 2.5 mg Morphine iv, which relieved the patient of his pain. He was transported to the hospital for blood tests and a check-up. On arrival in the ER he was pain free, with no dyspnea, normal aand dry skin. Vital stats on initial assessment were BP 135/85, regular pulse, RF 16/min, SpO2 97% with O2 2 ltr/min.
This is the 12 lead ECG (LP12) that was obtained by EMS:
Click image for full scale version (will open in a new window)
Click image for full scale version (will open in a new window)
The ECG is at 50 mm/s and shows:
- a regular, narrow complex bradycardia at 46 bpm
- no P waves
- left axis deviation (LAD)
- Left Anterior Fascicle Block
- poor R wave progression (PRWP); late precordial transition zone: lead V6.
- normal ST-T segments
- minor baseline noise
Intepretation:
RHYTHM: This narrow, complex bradycardia has no visible P waves. The rhythm is regular and in the bradycardic range. What is the rhythm here? Narrow QRS complexes tell us that the rhythm is supraventricular, and added up with the regularity of the RR intervals, one should immediately suspect a junctional rhythm. The ventricles are paced at 46 bpm, which is slow enough to call this a bradycardia. Every myocardial cell has the ability to pace the heart, and each type of cell has its own intrisic rate that is slower than the type of cell preceding it. The fastest pacer is the SA node. Junctional and AV nodal cells pace in the range of ca. 45-50 bpm. Which means that this rate of 46 bpm also supports the theory of this being a junctional rhythm. As with all supraventricular impulses, the atria is usually depolarized. With junctional automaticity, the atria is normally depolarized in a retrograde fashion. With junctional rhythms, the P wave is therefore often found right after the QRS complex or in the following T wave, unless retrograde conduction is delayed, creating a prolonged RP interval. If visible, the P wave occuring from the retrograde atrial activation should be inverted in the inferior leads II, III and aVF.
R WAVE PROGRESSION: This patient’s previous anterior MI can be seen from the poor R wave progression in the precordial leads. To determine the R wave progression, one needs to identify the transition zone. This is the lead with equal R and S wave voltage (R/S=1). Normal R wave progression has an increasing R wave amplitude across the precordial leads, and a transition zone in V2, V3 or V4, where the voltage decreases again towards V6. Poor R wave progression is defined when the transition is late and doesn’t occur until V5 or V6. In this ECG the transition occurs in lead V6, indicating loss of myocardial tissue. Note that abnormal R waves and R wave progression can occur due to several other reasons, as for instance misplaced leads. However in this case, the PRWP correlates with the patient’s previous anterior MI.
Cherchez le P!
Again, those famous words by Dr. Marriott become useful. In this ECG the sinus node seems to be completely silent. There are no obvious P waves preceding any of the QRS complexes. By closely examining the QRS morphology in the right precordial leads V1 and V2, we find a small terminal R wave. These are actually pseudo R waves, and are called so because they are not really R waves, but instead retrograde P waves that occur right after the QRS complex.
Let’s compare to a previous ECG, taken 9 days prior to the first one:
Click image for full scale version (will open in a new window)
Click image for full scale version (will open in a new window)
- Sinus rhythm at 76 bpm
- Left Axis Deviation (LAD)
- Left Anterior Fascicle Block
- First Degree Atrioventricular Block (1AVB); the PR interval is 220 ms
- One non-conducted premature atrial contraction (PAC); best seen in lead V2 as a small bump on the initial part of the T wave after the third QRS complex from the left)
- Poor R Wave Progression (PRWP); late transition zone – the transition occurs in V6.
First of all, the most striking observation here, is that this ECG shows a normal sinus rhythm. This tells us that this patient’s heart was had a working sinoatrial node just 9 days ago. However, there is a 1AVB present, which could be a sign of AV nodal disease.
This next ECG is taken on arrival in the ER, only 50 minutes later than the prehospital ECG:
Click image for full scale version (will open in a new window)
Click image for full scale version (will open in a new window)
As we can see, the rate has increased. The rhythm is still junctional, but now pacing at a rate faster than the normal intrinsic rate of AV nodal and junctional pacemaker cells. The rate is 100bpm, making this an accelerated junctional rhythm (AJR). The retrograde atrial activation is still seen as pseudo R waves in lead V1.
March 26, 2009
Patient: n/a
ECG description:
- Sinus rhythm at 85 bpm
- Ventricular extra systoles in trigeminy pattern. Every third beat is a Premature Ventricular Complex (PVC).
- Marked First Degree AV Block. PR interval is 310 ms.
- Incomplete Left Bundle Branch Block (LBBB). QRS width 100ms.
- Axis normal at approx. 60°
ECG diagnosis: Ventricular trigeminy with marked (severe) 1° AV Block and incomplete LBBB.
ECG Comments:
PVC TRIGEMINY: When every third beat is a PVC, the term trigeminy is used. The PVCs here are unimorph and therefore unifocal, which means they all have the same morhpology and therefore arise from the same ectopic focus. Premature beats originates in irritable autmaticity foci that fires spontaneously. Such beats come earlier than expected in the rhythm. It is also important to understand that although PVCs in many ways are considered to be benign, they are early signs of hypoxia. 6 PVCs per minute is considered pathological. Remember that a continuous run of bigeminy or trigeminy will quickly exceed that criteria, and will then usually indicate that a very irritable focus is hypoxic and needs attention.
1° AV BLOCK: The PR interval in this ECG is 310ms. This is a so called marked First Degree AV Block. This term indicates that the PR interval is markedly prolonged. This is noted because sometimes the AV conduction delay becomes so severe that pacemaker insertion may be needed. I am not completely sure about the exact criteria here, but from what I have read permanent pacing is indicated when the patient is symptomatic and when the PR interval exceeds 300ms. This article from Emergency Medicine News discusses the matter, and says that those with a PR interval >300ms are at risk of developing complete heart block.
INCOMPLETE LBBB: The morphology here resembles LBBB, but the QRS is only 100ms. To diagnose BBB, the QRS complex must be at least 120 ms. Therefore, this LBBB must be considered incomplete.
November 19, 2008