The Patient and the CT Scan
The patient is a 68 year old man with a past history of laparotomy that has left him with a colostomy bag.
He has a history of a heart murmur, but no other history of cardiac problems.
He saw his doctor one week ago because of a painless left flank mass that was increasing rapidly in size. His doctor ordered a CT scan of the abdomen, and then sent the patient to the Emergency Department (ED).
You are the consultant in the ED, and are shown the abdominal CT images (Figure 1).
The CT shows a large left sided cystic abdominal mass that probably arises from the left kidney. The heart is enlarged, the pericardium is thickened and there is a small quantity of fluid in the pericardial sac. There is an opacity near the apex of the heart.
The ECG & the Policy
While you are photographing the CT images you are shown the patient’s ECG (Figure 2). The ED policy is that each new ECG is shown to a consultant or a registrar who check and initial the ECG. They can also add their own written comments.
The other policy in the ED is that patients who need admission are sent to the ward within four hours of arrival
The ECG computer report mentions ventricular trigeminy, right bundle branch block (RBBB) and left anterior fascicular block (LAFB). The rhythm strip has a repeating QRS pattern and P waves that at first glance are conducted to the ventricles.
The patient does not have any chest discomfort, and his vital signs are normal. There are no previous ECGs for comparison. You want to look more closely at the rhythm strip while waiting for the result of the patient's serum troponin concentration.
You are now told that the patient has a bed under a Medical Unit, and that he should go to the ward now (under "interim orders") because his condition is stable and he is near the four hour time limit for being in the ED.
The Rhythm Strip
The rhythm strip (Figure 3) shows
- a ventricular rate of about 80 per minute
- QRS complexes with two different morphologies (rS and RS). There is a P wave before each rS complex but not before the RS complexes
- a trigeminal pattern (rS - rS - RS) of ventricular complexes
The PR interval of the second QRS complex in the rhythm strip is shorter than the PR
interval of the first complex, meaning that the second P wave is not conducted to the
second rS complex. At the end of the T wave of the second complex there is an
upward ‘bump’ that is a (non conducted) P wave. If we mark the position of the
second P wave and the ‘bump’ on a piece of paper we get a "P1 - P2" measurement.
If we put the P1 mark on the first P wave in the rhythm strip then P2 is (hidden) in the T wave of the first QRS complex. If we put the P1 mark on the bump at the end of the second QRS complex then P2 is obscured by the third (RS) complex in the rhythm strip.
The findings are consistent with AV dissociation and complete heart block.
After reviewing the ECG you talk to the Medical Registrar about referring the patient to the Cardiology Unit. The Medical Registrar does not agree with your ECG assessment, and also notes that the patient's condition is "stable" because the serum troponin level is normal. The patient is immediately transferred to the Ward.
Rhythm strips can be assessed by
- ‘eyeballing’ them
- using marks on a piece of paper strip to check intervals or find hidden P waves
- using calipers
- the laddergram approach
In this case I was intrigued by the regular pattern of the trigeminal rhythm, and decided to see if the laddergram would explain the pattern.
Under the rhythm strip we draw rectangles that represent atrial activity (A), conduction through the atrioventricular node (AVN) and ventricular activity (V) (Figure 4: Laddergram 1).
We then draw vertical lines from the start of each visible P waves to the bottom of the atrial zone (A). We leave out the AVN zone and V zone for the moment (Figure 5: Laddergram 2).
The interval between each line is calculated by multiplying the number of small squares between each line by the width [40 msec] of each small square. There are two groups of intervals: 620-640 msec and 1260 - 1280 msec. The longer interval is double the shorter interval.
The midpoint of the longer intervals is then marked by a dotted line that represents a possible P wave (Figure 6. Laddergram 3). Each dotted line (possible P wave) coincides with a T wave or QRS complex. We can assume that the solid and dotted vertical lines represent P waves.
Black dots are used to mark the start of visible or obscured P waves (Figure 7. Laddergram 4). The atrial rate is 94 - 97 beats per minute.
In Laddergram 5 (Figure 8) the AVN and V regions have been added, and vertical lines drawn from the start of every QRS complex in the rhythm strip to the lowest part of the ventricle zone. A green line is used for the rS complexes and a red line for the RS complexes. The intervals (in milliseconds) between eachP wave is shown above the A zone, and intervals between the various QRS complexes are shown in the V zone.
There are three types of relationship between the P waves and QRS complexes:
- A constant PR intervalis seen in complexes 1, 4 and 7. This PR interval appears long enough for the atrial impulseto be conducted through the AVN to the ventricles
- Non conductedP waves are seen at the end of the T waves of (therS) complexes 1, 2, 4, 5, 7 and 8.
- P waves that are too close to conduct through the AVN precede the rS) complexes 2, 5 and 8.
The 5th, 10th and 15th P waves in the series are obscured by the third, sixth and ninth QRS complexes (that have a RS configuration).
In AV dissociation the P waves “walk through” the QRS complexes; here the process is more like a tap dance. However I cannot come up with a process of conduction through the AVN that convincingly links the P wave activity with the ventricular activity. These findings are thus most consistentwith AV dissociation.
The ventricular conduction is repetitive, with two rS complexes followed by a single RS complex. The R-R interval between successive rS complexes is constant at 1160 msec, and the interval between each rS complex and the following RS complex is also constant (but decreased) at 1080 msec.
The constant (coupling) interval between the rS and RS complexes suggests that complexes 3, 6 and 9 are ventricular ectopic beats. This means that the complexes with the rS morphology are the underlying ventricular rhythm. We can assemble the complexes in the other leads that correspond to the the rS complexes in Lead II in the standard ECG layout
This shows a RBBB pattern witha very widened QRS (e.g. 0.16 seconds in Lead III) and marked LAFB. The originof the ventricular rhythm is most likely in the left posterior fascicle of the left bundle branch.
Laddergram 6 (Figure 10) shows sinus rhythm, AV dissociation, and rS ventricular complexes (numbers 1, 2, 4, 5, 7 and 8) arising between the AVN and the BOH. The (ventricular ectopic) origin of complexes 3, 6 and 9 is shown by a red dash arising from the bottom of the ventricular tier.
The final analysis of the rhythm is shown in Laddergram 7 (Figure 11).
The atria are beating at a rate of 95 per minute, but because there is AV dissociation the sinus beats do not activate the ventricles i.e. we do not have “normal sinus rhythm“ [NSR]. NSR is our shorthand term for a rhythm that arises (normally) from the SAN node and is conducted without delay (“normally conducted”) through the atria and the AVN and the His-Purkinje system to the ventricles. Since the P wave shape is normal we could describe the atrial rhythm as “sinus tachycardia with AV dissociation" to avoid confusion with the term NSR.
The underlying ventricular rhythm (complexes1, 2, 4, 5, 7 and 8) is shown arising below the AVN, and the (unifocal) ventricular ectopics (complexes 3, 6 and 9) forming a trigeminal pattern.
Summary of ECGAnalysis
- Atrial rhythm: Sinus tachycardiaat a rate of about 95 per minute
- Atrioventricular dissociation
- Ventricularescape rhythm at a rate of about 50 per minute. Theorigin of thisrhythmis (probably) theleft posterior fascicle of the left bundle branch
- Unifocal ventricular ectopicsthatproduce ventricular trigeminy
A previous ECG done 8 months earlier showed sinus rhythm, a PR interval of 0.21 seconds, RBBB and LAFB that was similar in shapeto the ECG taken in the ED
A transthoracic echocardiogram the day after admission was curtailed because “after starting the test in sinus rhythm the patient developed complete heart block with ventricular escape of 45-60 beats per minute”.
The echocardiogram study showed
- LV hypertrophywith moderately reduced LV systolic function
- Moderately thickened LV myocardium with increased echogenicity and circumscribed regions of reduced echodensity within the myocardium suggestive of malignant infiltration
- Normal RV size and systolic function
- Small pericardial effusion
It was decided to managethe patientwith palliative treatment. This includednot inserting a pacemaker
Comments on the Laddergram
The laddergram approach to analysis of rhythms was popularizedby Thomas Lewisin the 1920s, butTheodor Wilhelm Engelmann (1843-1909) was probably the first personto use this approach.
- Engelmann and his laddergram. Am J Cardiol 1977;39:464–465
- Theodor Wilhelm Engelmann. ClinCardiol 2006; 29: 518–520
A laddergram provides a more detailed analysis of ECG rhythm(s) that using marks on a piece of paper to identify the relation between atrial and ventricular activity . Laddergrams can bestraightforward and satisfying and instructive, but sometimes they are liketantric sex: complex and frustrating and not easily brought to a satisfying conclusion.