Tag: heart block
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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
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Patient: Male, 84 y/o. No cardiac history. Acute onset of severe, pressing chest pain. No relief from large doses of intravenous morhpine.
ECG description:
- Broad complex bradycardia with third degree atrioventricular block (3AVB) and AV dissociation
- Ectopic pacemaker firing at 48 bpm.
- Atrial rate 52 bpm
- Axis at approx. 60°
- ST elevation > in leads II, III and aVF
- Reciprocal ST depression in leads I and aVL
ECG comments: This is 3AVB. If you march out the P waves here, you will see that there is regular and normofrequent atrial activity, but none of the atrial impulses gets propagated further down the conduction system. The atrias and ventricles are acting independently. This is called AV dissociation, and is a criteria for 3AVB, also referred to as complete heart block. Third degree heart block is caused by a conduction block most commonly in the bundle branch/Purkinje system. According to American Journal of Critical Care, the block most commonly occurs in the bundle branch/purkinje system (61%), at the level of the AV node(21%) or the His bundle (15%). When a block occurs, an automaticity focus below the block will assume pacemaking activity at its inherent rate. An escape rhythm above the His bundle normally would produce a heart rate at 40-60 bpm and narrow QRS complex. When the ectopic focus sits lower in the ventricles, the heart will be paced a slower rhythms at around 20-40 bpm, and the QRS will become broad.
In this ECG, the heart rate suggests that the ectopic pacemaker is junctional. But the QRS configuration is wide, so the block is probably below the AV junction after all. Yet, it is pacing faster than expected. This can be referred to as an accelerated idioventricular escape rhythm.
ECG interpretation: Acute Inferior STEMI with reciprocal change, Third Degree Atrioventricular Block and Accelerated Idioventricular Escape Rhythm.
Note: This patient was transferred to a cath lab, where he was revascularized. I will soon update the post with more info on the culprit vessel, a post pci ecg and more.
December 26, 2008
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Patient: Elderly woman, around 80 years. Unfortunately, I don´t have any clinical information on this patient. All i know is that she was rapidly admitted to a cath lab where the perfusionists did a successful revascularization. AV block is secondary to infarction, hence it is intermittent.
ECG description:
- ST elevation > 4 mm in leads I , II, aVF and > 1 mm in leads V5, V6
- Reciprocal ST segment depression in leads I, aVL
- Complete atrioventricular dissociation. No relation between P waves and QRS complexes. Regular PP interval, regular RR interval. PR interval is variable, hence there is no apparent relationship between P waves and QRS complexes.
- Junctional escape rhythm at 50 bpm.
ECG diagnosis: Inferior wall STEMI. Third degree atrioventricular block with complete AV dissociation that probably has appeared because of damage to the AV node during the infarction. Because of the complete AV dissociation, an accessory pacemaker has taken over the pacing. Based on the rate and the normally configured QRS complexes here, the escape rhythm is junctional/nodal.
The patient was then transferred to the cath lab, where the perfusionists did a successful revascularization. She was transferred to an ICU. This next ecg was recorded 25 hours later since the initial ecg showing the acute STEMI.
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ECG description:
- Normofrequent sinus rhythm at ca. 90 bpm
- PR interval is at 200 ms, so there is a borderline first degree AV block present.
- ST elevation ca. 2mm in II, III, aVF, and 1mm in V5 and V6
- Reciprocal changes still in I, aVL
ECG diagnosis: ST elevation and reciprocal ST depression due to inferior wall infarction. Third degree AV block has disappeared and the patient is in normal sinus rhythm. The AV block was transitory due to the infarction, and the AV node has recovered. The PR interval is 200 ms and signals a borderline first degree AV block which is may due to damage of the AV node.
Comments:
Now this is an interesting case, but also a classic display of heart block etiology. Coronary ischemia is the most common cause of third degree AV block. It is a known fact that acute inferior wall myocard infarction can sometimes cause damage to the AV node, causing third degree heart block. In such cases, the damage is often transitory and the AV node may be recovered if the perfusion is restored. This is the case here, where the patient was quickly admitted to a cath lab where revascularization was done successfully, and the AV node was then restored to a functioning state. The the heart block was terminated and reset into normal sinus rhythm. During the complete heart block, an accessory pacemaker takes over pacing control. The escape rhythm here probably originates in the AV junction, providing a narrow complex escape rhythm, aka a nodal or junctional escape rhythm.
Further reading on the web:
E-medicine: Third degree heart block
American Heart Association: Third degree heart block
The Merck Manuals: Atrioventricular blocks
E-medicine: Atrioventricular disassociation
Wikipedia: Third degree AV block
November 15, 2008