ECG Puzzler A regular feature of the American Journal of Critical Care, the ECG Puzzler addresses electrocardiogram (ECG) interpretation for clinical practice. To send an eLetter or to contribute to an online discussion about this article, visit www.ajcconline.org and click “Respond to This Article” on either the full-text or PDF view of the article. We welcome letters regarding this feature.
HEART-RATE INDUCED CONDUCTION DEFECTS By Teri M. Kozik, RN, PhD, CNS, CCRN, Mary G. Carey, RN, PhD, CNS, Salah S. Al-Zaiti, RN, PhD, NP, and Michele M. Pelter, RN, PhD Scenario: Below are 2 rhythm strips taken from resting 12-lead electrocardiograms (ECGs) for a 73year-old man who came to the emergency department (ED) with complaints of a productive cough, shortness of breath, and chest discomfort for the past week. Leads II, V1 and V6 are shown below and were recorded on
ED admission (left) and on the day of discharge (right). His temperature on admission was 103.1°F. He has a history of hypertension, hyperlipidemia, and coronary bypass graft surgery. He was admitted to the medical telemetry unit with pneumonia and treated with supplemental oxygen and antibiotic therapy.
Day 1: ED admission II
Day 3: Hospital discharge II
v1
v1
v6
v6
Interpretation Questions: 1. Is the ECG properly calibrated (10 mm) and are leads properly placed? If no, interpret cautiously. 2. Is this a sinus rhythm (one P wave preceding every QRS complex)? If no, check for number of P waves in relation to QRS complexes. 3. Is the heart rate (R-R interval) normal (60-100 beats/min)? If no, check for supra-ventricular or ventricular arrhythmias. 4. Is the QRS complex narrow (duration < 110 milliseconds [ms] in V1)? If no, check for bundle branch blocks (BBBs), pacing, or ventricular arrhythmia. 5. Is the ST segment deviated (> 2 mm in V2-V3, or > 1 mm in other leads)? If yes, check for similar deviations in contiguous cardiac territories. 6. Is the T wave inverted in relation to the QRS (> 0.5 mV)? If yes, check for ST deviation or conduction abnormalities. 7. Is the QT interval lengthened (> 450 ms [women] or > 470 ms [men])? If yes, check for ventricular arrhythmias or left ventricular hypertrophy. 8. Is R- or S-wave amplitude enlarged (S wave V1 + R wave V5 > 35 mm)? If yes, check for axis deviation or other chamber hypertrophy criteria.
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
Teri M. Kozik is a nurse researcher at St. Joseph’s Medical Center, Stockton, California. Mary G. Carey is associate director for clinical nursing research, Strong Memorial Hospital, Rochester, New York. Salah S. Al-Zaiti is an assistant professor at the Acute and Tertiary Care Department, University of Pittsburgh, Pennsylvania. Michele M. Pelter is an associate professor at the Orvis School of Nursing, University of Nevada, Reno. ©2015 American Association of Critical-Care Nurses, doi: http://dx.doi.org/10.4037/ajcc2015343 www.ajcconline.org
AJCC AMERICAN JOURNAL OF CRITICAL CARE, January 2015, Volume 24, No. 1 Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
93
Day 1: ED admission
Day 3: Hospital discharge II
II
v1
v1
v6
v6
Answers: 1. Yes, the ECGs are properly calibrated. 2. Yes, there is one P wave for each QRS complex. 3. Yes, the heart rate is regular in both cases. The heart rate on ED admission is just above 100 beats/min. The heart rate on the day of discharge is approximately 65 beats/min. 4. No, the QRS on day 1 is not narrow and meets the > 120 millisecond bundle branch block (BBB) criteria. Lead V1 has an rS morphology and V6 has Rs morphology and lacks a q wave meeting the criteria for a left BBB (LBBB). On the day of discharge the QRS complex is normal width (lead V1 = negative QRS < 120 milliseconds). 5. Yes, The ST segments on admission appear depressed in leads II and V6 , and are normal at discharge. 6. No, the t waves are not inverted. 7. The QT interval cannot be assessed during LBBB, and is not prolonged during normal sinus rhythm (right). 8. Left ventricular hypertrophy cannot be assessed because lead V5 is not shown.
Interpretation and Rationale The ED admission ECG shows sinus tachycardia with LBBB. On the day of discharge, the ECG strip shows normal sinus rhythm. These ECGs demonstrate that this patient has a rate dependent LBBB (RD-LBBB). The ST-segment changes noted on ED admission are most likely secondary changes due to the presence of the LBBB.
Mechanism and Management A RD-LBBB is defined as a LBBB that develops during an increase in heart rate. The rate at which a RDLBBB occurs is called the critical heart rate. Interestingly, the critical heart rate that results in a RD-LBBB is often higher than the rate at which the RD-LBBB resolves. This conduction defect occurs when one of the bundle branches (left BB in this case) has a prolonged refractory (recovery) period resulting in delayed depolarization of the myocardium. When the heart rate
94
decreases, normal repolarization occurs, and the conduction defect disappears. Critical heart rates that result in RD-LBBB vary. In some patients, a minor heart rate change as little as 1 to 2 beats/min around the critical heart rate can result in a RD-LBBB. RD-LBBB is considered pathological. Prolongation of the refractory period in a BB was once thought to be due solely to intrinsic disease of the cardiac conduction system. However, other causes have been identified including hypertension, coronary artery disease, ischemia, aortic valve disease, and cardiomyopathies. This patient’s RD-LBBB was caused by sinus tachycardia that was most likely caused by his fever. After successful management of his pneumonia and return to normal sinus rhythm, the RD-LBBB disappeared. Given this patient’s history of hypertension and coronary artery disease, evaluation by a cardiologist is warranted to rule out ischemia or other cardiac pathology.
AJCC AMERICAN JOURNAL OF CRITICAL CARE, January 2015, Volume 24, No. 1 Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
www.ajcconline.org
Heart-Rate Induced Conduction Defects Teri M. Kozik, Mary G. Carey, Salah S. Al-Zaiti and Michele M. Pelter Am J Crit Care 2015;24:93-94 doi: 10.4037/ajcc2015343 © 2015 American Association of Critical-Care Nurses Published online http://www.ajcconline.org Personal use only. For copyright permission information: http://ajcc.aacnjournals.org/cgi/external_ref?link_type=PERMISSIONDIRECT
Subscription Information http://ajcc.aacnjournals.org/subscriptions/ Information for authors http://ajcc.aacnjournals.org/misc/ifora.xhtml Submit a manuscript http://www.editorialmanager.com/ajcc Email alerts http://ajcc.aacnjournals.org/subscriptions/etoc.xhtml
AJCC, the American Journal of Critical Care, is the official peer-reviewed research journal of the American Association of Critical-Care Nurses (AACN), published bimonthly by The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Telephone: (800) 899-1712, (949) 362-2050, ext. 532. Fax: (949) 362-2049. Copyright © 2015 by AACN. All rights reserved.
Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
HEART-RATE INDUCED CONDUCTION DEFECTS By Teri M. Kozik, RN, PhD, CNS, CCRN, Mary G. Carey, RN, PhD, CNS, Salah S. Al-Zaiti, RN, PhD, NP, and Michele M. Pelter, RN, PhD Scenario: Below are 2 rhythm strips taken from resting 12-lead electrocardiograms (ECGs) for a 73year-old man who came to the emergency department (ED) with complaints of a productive cough, shortness of breath, and chest discomfort for the past week. Leads II, V1 and V6 are shown below and were recorded on
ED admission (left) and on the day of discharge (right). His temperature on admission was 103.1°F. He has a history of hypertension, hyperlipidemia, and coronary bypass graft surgery. He was admitted to the medical telemetry unit with pneumonia and treated with supplemental oxygen and antibiotic therapy.
Day 1: ED admission II
Day 3: Hospital discharge II
v1
v1
v6
v6
Interpretation Questions: 1. Is the ECG properly calibrated (10 mm) and are leads properly placed? If no, interpret cautiously. 2. Is this a sinus rhythm (one P wave preceding every QRS complex)? If no, check for number of P waves in relation to QRS complexes. 3. Is the heart rate (R-R interval) normal (60-100 beats/min)? If no, check for supra-ventricular or ventricular arrhythmias. 4. Is the QRS complex narrow (duration < 110 milliseconds [ms] in V1)? If no, check for bundle branch blocks (BBBs), pacing, or ventricular arrhythmia. 5. Is the ST segment deviated (> 2 mm in V2-V3, or > 1 mm in other leads)? If yes, check for similar deviations in contiguous cardiac territories. 6. Is the T wave inverted in relation to the QRS (> 0.5 mV)? If yes, check for ST deviation or conduction abnormalities. 7. Is the QT interval lengthened (> 450 ms [women] or > 470 ms [men])? If yes, check for ventricular arrhythmias or left ventricular hypertrophy. 8. Is R- or S-wave amplitude enlarged (S wave V1 + R wave V5 > 35 mm)? If yes, check for axis deviation or other chamber hypertrophy criteria.
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
❑ Yes
❑ No
❑ NA
Teri M. Kozik is a nurse researcher at St. Joseph’s Medical Center, Stockton, California. Mary G. Carey is associate director for clinical nursing research, Strong Memorial Hospital, Rochester, New York. Salah S. Al-Zaiti is an assistant professor at the Acute and Tertiary Care Department, University of Pittsburgh, Pennsylvania. Michele M. Pelter is an associate professor at the Orvis School of Nursing, University of Nevada, Reno. ©2015 American Association of Critical-Care Nurses, doi: http://dx.doi.org/10.4037/ajcc2015343 www.ajcconline.org
AJCC AMERICAN JOURNAL OF CRITICAL CARE, January 2015, Volume 24, No. 1 Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
93
Day 1: ED admission
Day 3: Hospital discharge II
II
v1
v1
v6
v6
Answers: 1. Yes, the ECGs are properly calibrated. 2. Yes, there is one P wave for each QRS complex. 3. Yes, the heart rate is regular in both cases. The heart rate on ED admission is just above 100 beats/min. The heart rate on the day of discharge is approximately 65 beats/min. 4. No, the QRS on day 1 is not narrow and meets the > 120 millisecond bundle branch block (BBB) criteria. Lead V1 has an rS morphology and V6 has Rs morphology and lacks a q wave meeting the criteria for a left BBB (LBBB). On the day of discharge the QRS complex is normal width (lead V1 = negative QRS < 120 milliseconds). 5. Yes, The ST segments on admission appear depressed in leads II and V6 , and are normal at discharge. 6. No, the t waves are not inverted. 7. The QT interval cannot be assessed during LBBB, and is not prolonged during normal sinus rhythm (right). 8. Left ventricular hypertrophy cannot be assessed because lead V5 is not shown.
Interpretation and Rationale The ED admission ECG shows sinus tachycardia with LBBB. On the day of discharge, the ECG strip shows normal sinus rhythm. These ECGs demonstrate that this patient has a rate dependent LBBB (RD-LBBB). The ST-segment changes noted on ED admission are most likely secondary changes due to the presence of the LBBB.
Mechanism and Management A RD-LBBB is defined as a LBBB that develops during an increase in heart rate. The rate at which a RDLBBB occurs is called the critical heart rate. Interestingly, the critical heart rate that results in a RD-LBBB is often higher than the rate at which the RD-LBBB resolves. This conduction defect occurs when one of the bundle branches (left BB in this case) has a prolonged refractory (recovery) period resulting in delayed depolarization of the myocardium. When the heart rate
94
decreases, normal repolarization occurs, and the conduction defect disappears. Critical heart rates that result in RD-LBBB vary. In some patients, a minor heart rate change as little as 1 to 2 beats/min around the critical heart rate can result in a RD-LBBB. RD-LBBB is considered pathological. Prolongation of the refractory period in a BB was once thought to be due solely to intrinsic disease of the cardiac conduction system. However, other causes have been identified including hypertension, coronary artery disease, ischemia, aortic valve disease, and cardiomyopathies. This patient’s RD-LBBB was caused by sinus tachycardia that was most likely caused by his fever. After successful management of his pneumonia and return to normal sinus rhythm, the RD-LBBB disappeared. Given this patient’s history of hypertension and coronary artery disease, evaluation by a cardiologist is warranted to rule out ischemia or other cardiac pathology.
AJCC AMERICAN JOURNAL OF CRITICAL CARE, January 2015, Volume 24, No. 1 Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
www.ajcconline.org
Heart-Rate Induced Conduction Defects Teri M. Kozik, Mary G. Carey, Salah S. Al-Zaiti and Michele M. Pelter Am J Crit Care 2015;24:93-94 doi: 10.4037/ajcc2015343 © 2015 American Association of Critical-Care Nurses Published online http://www.ajcconline.org Personal use only. For copyright permission information: http://ajcc.aacnjournals.org/cgi/external_ref?link_type=PERMISSIONDIRECT
Subscription Information http://ajcc.aacnjournals.org/subscriptions/ Information for authors http://ajcc.aacnjournals.org/misc/ifora.xhtml Submit a manuscript http://www.editorialmanager.com/ajcc Email alerts http://ajcc.aacnjournals.org/subscriptions/etoc.xhtml
AJCC, the American Journal of Critical Care, is the official peer-reviewed research journal of the American Association of Critical-Care Nurses (AACN), published bimonthly by The InnoVision Group, 101 Columbia, Aliso Viejo, CA 92656. Telephone: (800) 899-1712, (949) 362-2050, ext. 532. Fax: (949) 362-2049. Copyright © 2015 by AACN. All rights reserved.
Downloaded from ajcc.aacnjournals.org at KORNHAUSER LIBRARY on January 17, 2015
