Imdur

Answer the questions, then check your responses against the answers that follow.

If you were caring for these two patients, would you make the right calls?

CASE STUDY #1

Mrs. Kramden, 70, has just returned to your coronary care unit (CCU) from the cardiac catheterization lab. Testing showed a 90% occlusion of her right coronary artery, which was treated with angioplasty, and a 40% occlusion of her left anterior descending coronary artery. Her medical history includes hypertension and chronic bronchitis. You prepare to attach Mrs. Kramden to the cardiac monitor.

1. Which electrocardiogram (ECG) lead would you select for continuous monitoring?

a. lead I or a VL b. lead II or III c. lead V^sub 2^/MCL^sub 2^ d. lead V^sub 6^/MCL^sub 6^

About 2 hours after her return from the cardiac catheterization lab, Mrs. Kramden starts complaining of severe squeezing retrosternal chest pain that radiates to her neck. Pale and diaphoretic, she rates the pain as a 9 on a pain scale of 0 (no pain) to 10 (the most pain). Her blood pressure is a normal 120/64 and her cardiac rhythm is a normal sinus rhythm at 78 beats/ minute. You notify the cardiologist, who orders sublingual nitroglycerin (0.4 mg every 5 minutes, up to three doses if pain persists and a stat 12-lead ECG.

After three nitroglycerin tablets, Mrs. Kramden's pain has lessened only slightly, to a 7 in the apin scale. The cardiac monitor shows ST-segment elevation in lead II. Looking at her 12-lead ECG, you notice STsegment elevation and T-wave inversion in leads II, III, and aVF and ST-segment depression in lead aVL.

2. What type of myocardial infarction (ME) would you suspect Mrs. Kramden is experiencing?

a. anterior-wall b. posterior-wall c. lateral-wall d. inferior-wall

You start an intravenous (I.V.) nitroglycerin infusion and prepare to send the patient for an emergency catheterization. While preparing her, you note that her cardiac rhythm changes to sinus bradycardia at 56 beats/minute. Her blood pressure drops to 116/44.

3. Sinus bradycardia indicates

a. a rapid decompensation of the left ventricle and the need to initiate emergency pacing.

b. a hypersensitivity reaction to the nitroglycerin infusion, which should be stopped. c. a rhythm disorder that's to be expected after an inferior-wall MI.

d. an extension of the MI to the right ventricle, calling for immediate administration of atropine.

Ten minutes later, the rhythm deteriorates to third-degree atrioventricular (AV) block with a ventricular rate of 54 beats/minute and narrow QRS complexes (less than 0.1 second). Mrs. Kramden still has chest pain (now a 4 on the pain scale), despite the I.V. nitroglycerin. Her blood pressure is 104/54. The cardiologist orders 4 mg of morphine I.V.

4. You'd expect the cardiologist to also order

a. emergency insertion of a transvenous pacemaker.

b. close patient monitoring and a backup transcutaneous pacemaker.

c. atropine, 0.5 mg I.V. over 1 minute.

d. an isoproterenol (Isuprel) infusion, titrated to maintain heart rate between 70 and 100 beats/minute.

Mrs. Kramden is sent to the catheterization lab, where a stent is placed in her right coronary artery, which had reoccluded. After the procedure, her cardiac rhythm stabilizes and returns to a normal sinus rhythm. She has no complications and is discharged the next day on medications with an appointment for outpatient follow-up.

ANSWERS: CASE STUDY #1

1. b. Mrs. Kramden's more serious occlusion was the 90% occlusion of her right coronary artery, which delivers blood to the right atrium, right ventricle, and inferior wall of the left ventricle. Leads II, III, and aVF all look at the inferior wall of the heart.

Leads I, aVL, and V^sub 6^/MCL^sub 6^ monitor the lateral wall of the left ventricle, which is primarily supplied by the circumflex artery. Lead V^sub 2^/MCL^sub 2^ monitors the anterior wall of the left ventricle, which is supplied by the left anterior descending coronary artery.

2. d. Mrs. Kramden is having an inferior-wall MI, as reflected by the ST and T-wave changes in leads II, III, and aVF. The ST depression in lead aVL is a common reciprocal change seen during an acute inferior-wall MI.

An anterior-wall MI is identified with ST and T-wave changes in the precordial leads (V^sub 1^ through V^sub 4^). An acute posterior-wall MI is identified by large R waves with ST-segment depression in leads V^sub 1^ and V^sub 2^ or ST-segment elevation and T-wave inversion in leads V through V^sub 9^. An acute lateral-wall MI is identified by ST and T-wave changes in leads I, aVL, V^sub 5^, and V^sub 6. ^

3. c. Sinus bradycardia is an expected rhythm disorder with an inferior-wall MI. The right coronary artery supplies the inferior wall of the left ventricle and, in most people, the sinoatrial (SA) and AV nodes as well. If this artery is occluded, the SA node may be ischemic, slowing its firing rate.

A rapid decompensation of the left ventricle would trigger a faster heart rate, not bradycardia. As cardiac output decreases, compensatory tachycardia would develop. Mrs. Kramden's blood pressure is stable, which doesn't indicate left-ventricular decompensation.

Intravenous nitroglycerin causes venous and arterial vasodilation, which decreases blood pressure. Compensatory tachycardia is more likely to occur in an attempt to increase the cardiac output.

Right-ventricular MIs are commonly associated with inferior-wall MIs because the right coronary artery supplies both areas of the heart. Asymptomatic bradycardia doesn't require treatment with atropine.

4. b. Mrs. Kramden is hemodynamically stable, with a blood pressure of 104/54 and a heart rate of 54 beats/minute, so closely monitor her condition for deterioration and make sure a backup transcutaneous pacemaker is available. Because she's stable, emergency transvenous pacing isn't indicated.

Narrow-complex third-degree AV block commonly occurs with inferior-wall MI and usually doesn't require treatment. Wide-complex AV blocks are more common with anterior-wall MI and are more likely to require emergency pacing.

Atropine is indicated only for symptomatic bradycardia. Because it increases myocardial oxygen consumption and may cause tachycardia, use it cautiously in patients experiencing MI. Isoproterenol is indicated only for refractory symptomatic bradycardia.

CASE STUDY #2

You're caring for Mr. Frazier, a 56-year-old man with a history of angina. Before coming to your unit, he was treated in the emergency department (ED) for an evolving anterior-wall MI. The ED staff started infusions of nitroglycerin and a thrombolytic and administered 325 mg of aspirin.

On admission to the CCU, Mr. Frazier is in sinus rhythm with a blood pressure of 136/78.

5. The ECG lead you'd select for continuous monitoring is

a. lead II. b. lead III. c. lead Vl/MCL^sub 1^. d. lead aVL.

6. To monitor this lead, where should you place the positive ECG electrode? a. second intercostal space, left sternal border

b. second intercostal space, left midclavicular line

c. fourth intercostal space, right sternal border

d. fourth intercostal space, left sternal border

Fifteen minutes after Mr. Frazier is admitted to the CCU, the bedside monitor indicates that he's in type II second-degree AV block with QRS complexes of 0.16 second. His blood pressure is 74/40.

7. You notify the cardiologist and

a. prepare to initiate transcutaneous pacing. b. prepare for transvenous pacemaker insertion. c. continue to observe for changes in cardiac rhythm. d. discontinue the thrombolvtic infusion.

Mr. Frazier responds well to treatment. Two days later, he undergoes cardiac catheterization, which shows a signifigant occlusion in his left anterior descending coronary artery. He's discharged the next day on isosorbide mononitrate (Imdur), metoprolol tartrate (Lopressor), and aspirin. Because of the high risk of abrupt vessel closure following angioplasty on an unstable lesion, Mr. Frazier is scheduled for percutaneous transluminal coronary angioplasty the following week.

ANSWERS: CASE STUDY #2

5. c. Leads V^sub 1^ through V^sub 4^ are situated over the anterior wall of the left ventricle. You'll typically see acute ST and T-wave changes in lead V^sub 1^/MCL^sub 1^ during an acute anterior-wall MI. By continuously monitoring this lead, you can assess for resolution or extension of the MI.

Leads II and III monitor the inferior wall of the left ventricle; lead aVL monitors the lateral wall.

6. c. To monitor lead MCL^sub 1^, place the positive electrode at the fourth intercostal space, right sternal border. This allows you to accurately monitor the heart's anterior wall. If you're using a five-lead monitoring system, place the V electrode at the fourth intercostal space, right sternal border to monitor lead Vl.

7. a. Prepare to initiate emergency pacing with a transcutaneous pacemaker. Mr. Frazier is hemodynamically compromised, with a blood pressure of 74/40. His QRS complexes are wide (greater than 0.12 second), signifying that the block originates below the AV junction. This more serious block commonly progresses to complete heart block, so immediate treatment is indicated. Initiate transcutaneous pacing to prevent further hemodynamic deterioration or extension of the MI.

Inserting a transvenous pacemaker isn't the first treatment choice. Because Mr. Frazier is receiving a thrombolytic, inserting this type of pacemaker via a central vessel could lead to bleeding complications.

Reperfusion arrhythmias typically occur 45 to 60 minutes after a thrombolytic is initiated, when vessel patency is restored. Mr. Frazier has been receiving his infusion for only 30 minutes, so his arrhythmia is unlikely to be related to reperfusion. Also, second-degree heart block isn't a common reperfusion arrhythmia.

Don't discontinue a thrombolytic infusion if a reperfusion arrhythmia occurs. Usually transient, these arrhythmias signify that the artery has been opened. Continue giving the full thrombolytic dose to ensure maximum benefit from the drug.

BY CAROLYN L. STRIMIKE, RN, CCRN, MSN Cardiac Clinical Nurse Specialist St. Joseph's Hospital and Medical Center Paterson, N.J.

Copyright Springhouse Corporation Jun 1997
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