AMC: Albany Medical Review

EKG Case - 90 year old female unresponsive and pulseless

Andrew Turinsky, MD

History of Present Illness

A 90-year-old female was found unresponsive and pulseless. She was given atropine in the field, and cardiopulmonary resuscitation was started on the way to an outside hospital. Subsequently, transcutaneous pacing was initiated and she was transported to Albany Medical Center (AMC) for further evaluation and treatment. On arrival, the patient was found to have renal failure and shock liver. Her troponin level was done sequentially, and noted to be 0.66ng/ml, 0.75ng/ml, and 0.52ng/ml, respectively. At AMC, the patient was changed from transcutaneous pacing to transvenous pacing. Her past medical history was significant for hyperlipidemia, hypertension, mild Alzhiemer’s dementia, and a possible seizure disorder. The following EKG was obtained in the emergency department.

Determine the following conduction abnormality.

Diagnosis

Complete (3rd degree) atrioventricular (AV) heart block with junctional escape rhythm.

Discussion

The P waves are equally spaced and unrelated to the timing of the QRS complex. With third degree AV block atrial impulses do not reach the ventricle. This can be the result of a block in the AV node, the bundle of His, the fascicles, or the bundle branches. The location of the conduction block can be discerned by the morphology of the escape rhythm. Escape rhythms occur when foci other than the sino-atrial node have sufficient time to depolarize. Therefore, the pacing of the ventricles is generated distal to the block. Typically, if more than 2/3rds of the escape rhythms have a narrow QRS complex, the block is at the AV node, resulting in a junctional or AV nodal rhythm. Likewise, a narrow QRS complex can be generated with a block at the bundle of His. Wide QRS complexes are characteristic of subjunctional escape rhythms, rhythms generated as a result of a block in the bundle branches or fascicles.

The rate of the escape rhythm can provide information about the location of the block. As a general rule of thumb is; the slower the escape rhythm the more distal the block. Cells of the atrionodal area have a relatively fast depolarization rate (45-60/min) and are responsive to autonomic nervous system input. Therefore, the response of the block to atropine administration provides evidence to its location. Conversely, cells of the nodal-His region have a slower depolarization rate of approximately 40/min. Blocks in this distal region are less likely to respond to atropine administration.

Treatment of complete heart block involves correcting reversible causes, such as myocardial ischemia, increased vagal tone, or removal of drugs that depress conduction. If no reversible causes are present, pacemaker placement is indicated, particularly in infra-His bundle blocks as these escape rhythms are less reliably conducted. Atropine can be used in emergent setting by improving AV conduction, though may have variable success depending on the location of the block.

REFERENCES

Current Diagnosis and Treatment in Cardiology, 2nd edition, Micheal H. Crawford, 2003, Chapter 21

Harrison’s Principles of Internal Medicine, 16th edition Dennis L. Kasper, Eugene Braunwald, Anthony S. Fauci, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Kurt J. Isselbacher, Chapter 213. The Bradyarrhythmias: Disorders of sinus node function and AV conduction disturbances.

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