Senior Report 5.24

Case Presentation by Dr. Matt Steimle

You are starting your shift at a small rural hospital with limited resources.

At the start of your shift during transition of care, you receive sign out about a 63-year-old male who has chest pain, is undergoing a cardiac workup, and is admitted to his own internal medicine doctor with a cardiology consult. You are told his first EKG has first-degree atrioventricular block unchanged from prior EKGs and that his first troponin I is negative. He has received aspirin and a dose of nitroglycerin.

His vital signs at the time of transition of care: BP 145/94, P 65, R 20, T 37.1, and 100% saturation on 2L O2 by nasal cannula

His repeat EKG and troponin I are ordered to be drawn in 3 hours.

2 hours into your shift you notice that the patient is lightheaded and confused, and the family and the nursing staff indicate that this is a sudden change. You examine him and order another 12-lead EKG.

Pertinent findings on repeat physical exam:

Vitals: BP 70/40, P 39, R 20, T 37.2, 100% saturation on 2L O2 by nasal cannula

General: complains of feeling presycopal and lightheaded

Cardiac: bradycardic, no M/R/G, s1 and s2 normal

Neuro: a+ox3, but is slow to respond; otherwise the rest of your neuro exam is unremarakable

Questions:

1. Which venous site is preferred for transvenous pacemaker placement?
a) brachial
b) left internal jugular
c) right internal jugular
d) right subclavian

2. What should the initial settings be on the pulse generator?
a) rate 60 beats/min or 10 beats faster than the underlying ventricular rhythm, output 5 mA, sensitivity 10 mV
b) rate 70 beats/min or 10 beats faster than the underlying ventricular rhythm, output 5 mA, sensitivity 10 mV
c) rate 80 beats/min or 10 beats faster than the underlying ventricular rhythm, output 5 mA, sensitivity 10 mV
d) rate 80 beats/min or 10 beats faster than the underlying ventricular rhythm, output 5 mA, sensitivity 3 mV

3. Which EKG lead do you connect the pacemaker to?a) II

b) III
c) AVL
d) V1

4. When do you inflate the balloon?
a) 10-12 cm for a subclavian or internal jugular insertion
b) 14-16 cm for a subclavian or internal jugular insertion
c) 16-18 cm for a subclavian or internal jugular insertion
d) 8-10 cm for a subclavian or internal jugular insertion

5. What will the EKG show when the pacemaker is in the right ventricle?
a) both the P-wave and QRS complex will be negative
b) P-wave becomes large and biphasic
c) P-wave becomes smaller and the QRS complex becomes larger
d) P-wave is larger than the QRS complex and deeply inverted

6. When the sensitivity control is in the demand (synchronous) mode, the pacemaker does not sense ventricular depolarizations.

a) False

b) True

Answers:

1. c

2. d

3. d

4. a

5. c

6. a

Discussion:

Heart block is a known complication of acute myocardial infarction (AMI).  15% to 19% of AMI patients progress to some degree of heart block. First-degree atrioventricular (AV) block progresses to second- or third-degree AV block 33% of the time, and second-degree AV block progresses to third-degree AV block about 33% of the time.

AV block occurring during anterior wall AMI is believed to occur due to diffuse ischemia of the septum and infranodal conduction tissue. These patients can progress to higher-degree AV block without warning, and consideration should be given to “prophylactic” cardiac pacemaker placement in such patients. Hemodynamically unstable patients unresponsive to medical therapy should be paced. One should try transcutaneous cardiac pacing until a transvenous pacemaker can be placed.

Temporary cardiac pacing for bradyarrhythmias in acute myocardial infarction may be necessary, even though permanent cardiac pacing may not be required. Revascularization strategies with thrombolysis and angioplasty have reduced the need for permanent pacing since there is less myocardial damage and a greater chance that bradycardia and conduction abnormalities will resolve. Therefore, there may be a need for temporary cardiac pacing.

An important consideration in the setting of AMI is that bradycardia, even if asymptomatic or transient, can cause decreased coronary blood flow and reduced myocardial perfusion.

Guidelines from the American Heart Association and American College of Cardiology recommend temporary cardiac pacing in patients with AMI and the following cardiac rhythms and conduction abnormalities:

1.            Asystole

2.            Symptomatic bradycardia due to sinus node dysfunction, or Mobitz type I             (Wenckebach) second degree AV block that is not responsive to atropine therapy

3.            Mobitz type II second degree or complete heart block

4.            Bilateral or alternating bundle branch block, including right bundle branch block             with left anterior fascicular block or left posterior fascicular block

5.            A new bundle branch block with either old or new first degree AV block

6.            An old right bundle branch block with first degree AV block and a new fascicular             block

There are complications with the insertion of a endocardial pacemaker in a patient who has received thrombolytic therapy and is being treated with aggressive anticoagulant and antiplatelet therapy. In these settings, transcutaneous pacing is preferred. Insert endocardial pacemaker only if warranted due to recurrence of symptoms.

Avoid temporary pacing:

1. When the risks outweigh the benefits

2. When there are intermittent, mild or rare symptoms, and the bradycardia is well tolerated. This includes mildly symptomatic (mild or rare symptoms) complete heart block with an adequate and “stable” escape rhythm or symptomatic sick sinus syndrome with only rare pauses

3. In the presence of a prosthetic tricuspid valve or right ventricle infarct (remember to obtain right-sided leads RV3 and RV4), a circumstance in which it may not be possible to achieve right ventricle capture

4. In a patient with AMI who has received thrombolytic therapy and is being aggressively treated with anticoagulation or antiplatelet agents. Insertion of the pacemaker by a cutdown or the right internal jugular may be associated with significant bleeding in such patients.

5. When there is no informed consent, unless temporary pacing is considered life-saving

Procedure basics:

Continuous electrocardiographic monitoring is recommended. Fluoroscopy is desirable, safer, and insures proper placement under direct fluoroscopic guidance, but is not always feasible. If fluoroscopy is not available, a balloon-tipped catheter is recommended as long as the patient has intact circulation to help “float” the pacemaker wire to the desired location within the right ventricle.

Access site- the best access site for temporary pacing is via the left subclavian vein or right internal jugular vein. Brachial and femoral vein approaches are not recommended because of the risk of cardiac puncture and instability using a brachial approach, and the risk of deep vein thrombosis and infection using the femoral approach. The right internal jugular and the left subclavian veins have the straightest anatomic pathway to the right ventricle and are generally preferred for transvenous pacing. You will need an introducer set or sheath. Some pacing catheters are prepackaged with the appropriate equipment, others require a separate set. The introducer sheath must be larger than the pacing wire to allow it to pass!

Obtain pacing generator:

The rate control or (top control) is where you set the rate or beats per minute.

The ouput control (middle control) allows the operator to vary the amount of electrical current (amperage, amps) delivered to the myocardium; increasing this setting increases the output and improves the likelihood of capture.

The pacing control/sensitivity (the most inferior control), is determined by adjusting the gain setting for the sensing function of the generator. By increasing the sensitivity one can convert the unit from a fixed-rate (asynchronous mode) to a demand (synchronous mode) pacemaker. The voltage setting represents the minimum strength of electrical signal that the pacer is able to detect. Decreasing the setting increases the sensitivity and improves the likelihood of sensing myocardial depolarization.

In the fixed-rate mode(asynchronous) the unit fires despite the underlying intrinsic rhythm, the unit does not sense any intrinsic electrical activity. In the full demand mode, (synchronous mode similar idea to synchronized cardioversion) the pacemaker senses the underlying ventricular depolarizations and the unit does not fire as long as the patients ventricular rate is equal to or faster than the set rate of the pacing generator.

Initial settings: Set Rate (80 beats/min or 10 beats faster than the underlying ventricular rhythm, output 5 mA, sensitivity 3 mV)

Obtain central venous access with an introducer. Attach the still-compressed sterile sheath to the introducer hub (make sure the connector of the sheath is firmly attached to the hub of the introducer), open the hub of the introducer by turning it counter clockwise to allow passage of the pacing wire.

Inflate then deflate the balloon on the pacing wire before it is introduced to test for integrity. There is a valve that keeps the balloon inflated; it must be turned to inflate /deflate the balloon. Use 1.2-1.5 mL of air for the balloon. An assistant attaches the proximal pacing wire to the nonsterile energy source. Use the demand mode and turn on the pacer output to the highest level, rate about 80/min, with the balloon deflated.

Insert the pacing wire into the still collapsed sheath and into the hub of the introducer. Slowly advance the wire through the introducer. Inflate the balloon when the tip of the pacing wire is in the superior vena cava (10-12 cm) and continue to advance. Close the valve to keep the to keep the balloon inflated. Watch the ECG and look for capture, demonstrated by a wide QRS pattern after each pacer spike. The right ventricle should be encountered by 15-20 cm as noted by markings on the pacer wire. If no capture is seen by 25 cm, deflate the balloon, withdraw the wire and try again. When consistent capture is seen, deflate the balloon and advance the wire 1-2 cm more to seat the wire in the endocardium. Tighten the valve on the sheath introducer to stop subsequent movement of the wire, and extend the sheath its full length. If required suture the wire in place. The lead should be tied down in at least two different sites, one where the lead exits from the skin and other to a loop formed with the lead.

Turn down the output control (middle control), then slowly turn it up to determine pacing threshold (first sign of capture). Set the output at two to three times the stimulation threshold and set the desired rate. Leave the pacer in the demand mode until stability is assured.  Obtain chest x-ray and 12-lead EKG.

EKG Guidance: The patient should be connected to the limb leads of an EKG machine, The pacemaker may be attached to any of the V leads (usually V1 or V5)

When the pacing wire enters the superior vena cava (10-12 cm for a subclavian or internal jugular insertion) the balloon is inflated.

The V lead ( usually V1 or V5) should be monitored. The P wave and QRS complex should be observed to ascertain the position of the catheter tip. As the pacing wire passes through the tricuspid valve, the P-wave becomes smaller and the QRS complex becomes larger. After successful passage of the pacing wire into the right ventricle, the tip should be advanced until contact is made with the endocardial wall. When this occurs, the QRS segment will show ST segment elevation.

Complications related to Central Venous Catheterization:

1.            Inadvertent arterial puncture (compress)

2.            Venous thrombosis and thrombophlebitis uncommon (Femoral vein thrombosis             more common)

3.            Pneumothorax

4.            Hemothorax

5.            Thoracic duct laceration chylothorax (left-sided insertion)

6.            Air embolism

7.            Wound infection

8.            Pneumomediastinum

9.            Hydromediastinum, hemomediastinum

10.            Phrenic nerve injury

11.            Fracture of guide wire and embolization

Complications of right-sided heart catheterization:

1.            Dysrhthymia with pvc’s bing a common occurrence

2.            Ventricular tachycardia

3.            Pacer in pulmonary artery

4.            Pacer in coronary sinus

5.            Left ventricle through ASD,VSD

6.            Septal puncture

7.            Extraluminal insertion

8.            Arterial insertion

9.            Perforation of the ventricle can result in loss of capture, hemopericardium,             tamponade

10.            Local infection

11.            Balloon rupture

12.            Pulmonary infarction

13.            Phrenic nerve pacing

14.            Rupture of the chordae tindinae

Defibrillation and cardioversion are safe in patients who have temporary pacemakers

References:

1. Roberts: Clinical Procedures in Emergency Medicine, 5th ed; 2009

  1. UpToDate: temporary cardiac pacing; 2012
  2. LearnTheHeart.com

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