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Two aberrancies for the price of one
CARDIAC CONUNDRUM
Two aberrancies for the price of one George Nikolic´, MB, BS, FACC
T
he patient was a 29-year-old woman with unexplained persistent vomiting and mild (3.4 mEq/L) hypokalemia. Except for a regularly irregular pulse, there were no other abnormalities. A 12-lead electrocardiogram was obtained (Fig 1). The allorhythmia accounting for her pulse consists of repetitive triplets comprising a sinus beat and supraventricular ectopic beat followed by a junctional escape beat. Three premature supraventricular ectopic beats are probably present, judging from the P’ shape and the longer-than-sinus PR interval of atrial origin. The first beat has incomplete
left bundle branch block (LBBB) morphology, the second rsR’ has incomplete right bundle branch block (RBBB) morphology, and the third beat is only slightly aberrant, with a shorter S wave than the sinus beats. S-wave loss is the earliest sign of RBBB aberrancy.1 In all 3 cases, there is a long–short cycle sequence causing phasic aberrant conduction.2 This depends on the long–short discrepancy rather than the actual rate (which determines rate-dependent aberrancy). Here is the conundrum: All the staff were shown this electrocardiogram and asked how many kinds of aberrancy were present. Their answer was 2.
Fig 1 Admission electrocardiogram showing a 3-beat allorhythmia. From the Intensive Care Unit, The Canberra Hospital, Canberra, Australia. Corresponding author: George Nikolic´, MB, BS, FACC, 11 Birdwood Street, Hughes, Australian Capital Territory 2605, Australia. E-mail: [email protected] 0147-9563/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.hrtlng.2010.05.058
HEART & LUNG VOL. 39, NO. 6
www.heartandlung.org
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Nikolic´
Two aberrations
Fig 2 Another tracing from the same admission. A sinus P wave overlaps the onset of the fifth QRS complex.
Correct, but for the wrong reason! (The reader may want to reexamine Fig 1.) There are 4 more supraventricular ectopic beats in this trace, the junctional escape beats. All 4 have a slightly but consistently different contour from the sinus beats. Their aberrancy is non-phasic, which is thought to arise from a different activation front reaching the bundle of His and the ventricles from a junctional focus.3 The value of their recognition lies in separating dissociated junctional beats preceded by P waves from conducted sinus beats. Most junctional escapes, however, are identical to those of the dominant supraventricular rhythm; when non-phasic aberration is present, it is usually subtle and commonly overlooked. The 2 kinds of aberrancy in this trace are phasic and non-phasic, not RBBB and LBBB: The last 2 are different expressions of the phasic, long–short cycle variety. Subtle differences in morphology may be due to respiratory and other artefacts. It is always desirable to examine other traces. The aberrancy in Fig 2 confirms the distinctive contour only seen in junctional escape beats. The third escape complex is distorted by a dissociated sinus P wave at its
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onset, briefly breaking the allorhythmia. The phasic aberrancy is confined to LBBB morphology. The 2 traces show other, perhaps more serious, abnormalities: left axis deviation 35 degrees in the limb leads and (very) poor R-wave progression. The 2 may not be unrelated: Axis deviation in the frontal plane makes the chest leads very sensitive to the vertical placement of the electrodes.4 Is the left axis deviation due to left anterior hemiblock, its most common cause? The relatively small standard lead voltage and lack of secondary R wave in aVR and Rs morphology in V6 are against it. Then again, hemiblocks may be difficult, or even impossible,5 to diagnose on the grounds of an electrocardiogram alone. REFERENCES 1. Marriott HJL. Pearls & pitfalls in electrocardiography. Philadelphia: Lea & Febiger; 1990. p. 118. 2. Schamroth L, Chesler E. Phasic aberrant ventricular conduction. Br Heart J 1963;25:219-26. 3. Schamroth L. Disorders of cardiac rhythm. Oxford: Blackwell; 1971. p. 74-5. 4. Kwan A, Nikolic G. Rapid cure of silent ischemia. Heart Lung 1991;20:694-5. 5. Spodick DH. Fascicular blocks: not interpretable from the electrocardiogram. Am J Cardiol 1992;70:809-10.
NOVEMBER/DECEMBER 2010
HEART & LUNG
Two aberrancies for the price of one George Nikolic´, MB, BS, FACC
T
he patient was a 29-year-old woman with unexplained persistent vomiting and mild (3.4 mEq/L) hypokalemia. Except for a regularly irregular pulse, there were no other abnormalities. A 12-lead electrocardiogram was obtained (Fig 1). The allorhythmia accounting for her pulse consists of repetitive triplets comprising a sinus beat and supraventricular ectopic beat followed by a junctional escape beat. Three premature supraventricular ectopic beats are probably present, judging from the P’ shape and the longer-than-sinus PR interval of atrial origin. The first beat has incomplete
left bundle branch block (LBBB) morphology, the second rsR’ has incomplete right bundle branch block (RBBB) morphology, and the third beat is only slightly aberrant, with a shorter S wave than the sinus beats. S-wave loss is the earliest sign of RBBB aberrancy.1 In all 3 cases, there is a long–short cycle sequence causing phasic aberrant conduction.2 This depends on the long–short discrepancy rather than the actual rate (which determines rate-dependent aberrancy). Here is the conundrum: All the staff were shown this electrocardiogram and asked how many kinds of aberrancy were present. Their answer was 2.
Fig 1 Admission electrocardiogram showing a 3-beat allorhythmia. From the Intensive Care Unit, The Canberra Hospital, Canberra, Australia. Corresponding author: George Nikolic´, MB, BS, FACC, 11 Birdwood Street, Hughes, Australian Capital Territory 2605, Australia. E-mail: [email protected] 0147-9563/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.hrtlng.2010.05.058
HEART & LUNG VOL. 39, NO. 6
www.heartandlung.org
547
Nikolic´
Two aberrations
Fig 2 Another tracing from the same admission. A sinus P wave overlaps the onset of the fifth QRS complex.
Correct, but for the wrong reason! (The reader may want to reexamine Fig 1.) There are 4 more supraventricular ectopic beats in this trace, the junctional escape beats. All 4 have a slightly but consistently different contour from the sinus beats. Their aberrancy is non-phasic, which is thought to arise from a different activation front reaching the bundle of His and the ventricles from a junctional focus.3 The value of their recognition lies in separating dissociated junctional beats preceded by P waves from conducted sinus beats. Most junctional escapes, however, are identical to those of the dominant supraventricular rhythm; when non-phasic aberration is present, it is usually subtle and commonly overlooked. The 2 kinds of aberrancy in this trace are phasic and non-phasic, not RBBB and LBBB: The last 2 are different expressions of the phasic, long–short cycle variety. Subtle differences in morphology may be due to respiratory and other artefacts. It is always desirable to examine other traces. The aberrancy in Fig 2 confirms the distinctive contour only seen in junctional escape beats. The third escape complex is distorted by a dissociated sinus P wave at its
548
www.heartandlung.org
onset, briefly breaking the allorhythmia. The phasic aberrancy is confined to LBBB morphology. The 2 traces show other, perhaps more serious, abnormalities: left axis deviation 35 degrees in the limb leads and (very) poor R-wave progression. The 2 may not be unrelated: Axis deviation in the frontal plane makes the chest leads very sensitive to the vertical placement of the electrodes.4 Is the left axis deviation due to left anterior hemiblock, its most common cause? The relatively small standard lead voltage and lack of secondary R wave in aVR and Rs morphology in V6 are against it. Then again, hemiblocks may be difficult, or even impossible,5 to diagnose on the grounds of an electrocardiogram alone. REFERENCES 1. Marriott HJL. Pearls & pitfalls in electrocardiography. Philadelphia: Lea & Febiger; 1990. p. 118. 2. Schamroth L, Chesler E. Phasic aberrant ventricular conduction. Br Heart J 1963;25:219-26. 3. Schamroth L. Disorders of cardiac rhythm. Oxford: Blackwell; 1971. p. 74-5. 4. Kwan A, Nikolic G. Rapid cure of silent ischemia. Heart Lung 1991;20:694-5. 5. Spodick DH. Fascicular blocks: not interpretable from the electrocardiogram. Am J Cardiol 1992;70:809-10.
NOVEMBER/DECEMBER 2010
HEART & LUNG