HEART BLOCKS

1
HEART BLOCKS

• CHAPTER 5

2
INTRODUCTION TO HEART BLOCKS

• OCCUR WHEN THERE IS A PARTIAL OR COMPLETE
  INTERRUPTION IN THE CARDIAC ELECTRICAL CONDUCTION
  SYSTEM.
• CAN OCCUR ANYWHERE IN THE ATRIA BETWEEN THE SA
  NODE AND THE AV JUNCTION.
• IN THE VENTRICLES BETWEEN THE AV JUNCTION AND
  PURKINJE FIBERS.

3
THE APPEARANCE OF THE P WAVE AND QRS COMPLEX
VARIES, DEPENDING ON THE TYPE OF HEART
BLOCK. RATE AND RHYTHM MAY VARY. LOCATION OF
THE BLOCK AND PATIENT SYMPTOMS DETERMINE IF THE
DYSRHYTHMIA IS LETHAL.
4
FIRST-DEGREE HEART BLOCK

• DELAY OF IMPULSE BETWEEN THE ATRIA AND BUNDLE OF
  HIS.
• OCCURS WHEN THERE IS A PARTIAL INTERRUPTION
  ANYWHERE IN THE ATRIAL OR AV JUNCTIONAL
  CONDUCTION SYSTEM.
• THE IMPULSE IS EVENTUALLY CONDUCTED BUT IS
  DELAYED.

5
FIRST-DEGREE BLOCK IS NOT A TRUE BLOCK BUT SIMPLY
A DELAY IN THE ELECTRICAL CONDUCTION SYSTEM. PROL
ONGED PRI GREATER THAN 0.20 SECONDS. THE P WAVE
OCCURS BEFORE EVERY QRS BUT THE PRI IS ALWAYS
GREATER THAN 0.20 SECONDS. P TO P AND R TO R
INTERVALS ARE USUALLY REGULAR DEPENDING ON THE
UNDERLYING RHYTHM.
6
MAY BE FOUND IN ANY RHYTHM THAT HAS A P
WAVE BEFORE THE QRS COMPLEX. RATE MAY BE NORMAL,
BRADYCARDIC, TACHYCARDIC. MUST IDENTIFY THE
UNDERLYING RHYTHM FIRST. USUALLY NOT SERIOUS BUT
MUST BE ASSESSED. THE PATIENTS MYOCARDIUM MAY
HAVE BEEN DAMAGED. MAY BE CAUSED BY M.I. OR
DRUGS.
7
(No Transcript)
8
MOBITZ I HEART BLOCK

• MOBITZ I ( WENCKEBACH OR SECOND-DEGREE HEART
  BLOCK, TYPE I).
• PROGRESSIVE BLOCK.
• IMPULSE FROM THE ATRIA IS INTERRUPTED AT THE AV
  JUNCTION.
• THE INTERRUPTION BECOMES LONGER WITH EACH IMPULSE
  DELAYING DEPOLARIZATION OF THE VENTRICLES UNTIL A
  COMPLETE INTERRUPTION BLOCKS THE IMPULSE.

9
THE CYCLE OF PROGRESSIVELY DELAYED CONDUCTION IS
THEN REPEATED. THE PRI BECOMES LONGER WITH EACH
QRS UNTIL A DROPPED QRS OCCURS. THE P WAVE IS
SEEN WITHOUT A QRS COMPLEX. A QRS FOLLOWS EACH P
WAVE UNTIL A QRS IS DROPPED.
10
THE OVERALL RHYTHM IS IRREGULAR. THE RATE
MAY VARY. NOT A LETHAL DYSRHYTHMIA, THE PATIENT
MAY BECOME MEDICALLY UNSTABLE. MAY BE SERIOUS
WHEN IT INDICATES A RECENT CHANGE IN THE
CONDUCTION SYSTEM FOLLOWING INJURY TO THE CARDIAC
MUSCLE. MAY BE CAUSED BY INFECTION, M.I., DRUG
TOXICITY.
11
(No Transcript)
12
MOBITZ II HEART BLOCK

• OCCURS DUE TO AN INTERMITTENT INTERRUPTION NEAR
  OR BELOW THE AV JUNCTION.
• INTERRUPTION IS NOT PROGRESSIVE, BUT OCCURS
  SUDDENLY AND WITHOUT WARNING!!
• P WAVES BEFORE EVERY QRS COMPLEX AND ALL ARE THE
  SAME SIZE AND SHAPE.

13
THIS OCCURS UNTIL A QRS COMPLEX IS DROPPED. THE
QRS MAY BE WIDER IF THE BLOCK OCCURS NEAR
THE BUNDLE OF HIS. CAN OCCUR IN ANY RHYTHM,
OVERALL RHYTHM IS IRREGULAR AND THE HEART RATE
VARIES DEPENDING ON THE UNDERLYING RHYTHM.
14
(No Transcript)
15
INTERPRETING THE BLOCK

• IDENTIFY THE UNDERLYING RHYTHM.
• DETERMINE THE RATIO OF P WAVES TO QRS COMPLEXES.
  THIS DETERMINES THE BLOCK. 21 BLOCK 2 P WAVES
  TO 1 QRS, 31 BLOCK 3 P WAVES TO 1 QRS.
• DETERMINE THE FREQUENCY OF OCCURRENCE. MAY OCCUR
  AT RANDOM OR IN A PATTERN.

16
A MOBITZ II WITH NO PATTERN (VARYING BLOCK) IS
MORE DANGEROUS. THIS INDICATES THE BLOCK IS
IRREGULAR AND MAY PROGRESS INTO A MORE SERIOUS
DYSRHYTHMIA. THIS IS A DANGEROUS BLOCK. THE
MYOCARDIUM IS INCREASED IRRITABILITY. IF THE
BLOCK IS SEVERE, THE VENTRICULAR RATE MAY BECOME
BRADYCARDIC.
17
A VENTRICULAR RATE OF 40 IMPULSES OR LESS IS
NOT SUFFICIENT TO MAINTAIN ADEQUATE CIRCULATION
TO THE ORGANS AND BODY. FREQUENT ASSESSMENT IS
IMPORTANT TO DETERMINE THE PATIENTS TOLERANCE OF
THE DYSRHYTHMIA. CAUSED BY M.I., HEART DISEASE,
OR DRUG TOXICITY.
18
THIRD-DEGREE HEART BLOCK

• COMPLETE HEART BLOCK OR COMPLETE AV DISSOCIATION.
• IMPULSE IS COMPLETELY BLOCKED BETWEEN THE ATRIA
  AND THE VENTRICLES.
• USUALLY TAKES PLACE BETWEEN THE AV JUNCTION AND
  BUNDLE OF HIS.

19
THE VENTRICLES MUST INITIATE THEIR OWN
IMPULSES. THE ATRIA AND VENTRICLES ARE
FUNCTIONING INDEPENDENTLY! PR INTERVALS ARE
CONSTANTLY CHANGING IN LENGTH. THE INTERVALS DO
NOT BECOME PROGRESSIVLY LONGER AS THEY DO IN
MOBITZ I NO TRUE PR INTERVAL OCCURS.
20
P WAVES AND QRS COMPLEXES APPEAR AS WELL AS
PR INTERVAL THAT ARE CONSTANTLY CHANGING IN
LENGTH. THE PRIS DO NOT BECOME PROGRESSIVELY
LONGER. NO RELATIONSHIP EXISTS BETWEEN THE P
WAVES AND QRS COMPLEXES. NO TRUE PR INTERVAL.
21
THE QRS COMPLEXES ARE WIDE AND BIZZARE WITH A
TIME FRAME OF gt0.12 SECONDS. DEPOLARIZATION IS AT
THE INHERENT RATE BUT THE P TO P AND R TO R
INTERVALS ARE NOT EQUAL. ATRIAL RATE 60 TO 100
VENTRICULAR RATE 20 TO 40. THIS IS A LETHAL
DYSRHYTHMIA. CAN LEAD TO ASYSTOLE.
22
Third degree heart block
23
BUNDLE BRANCH BLOCK (BBB)

• INTERRUPTION IN THE ELECTRICAL CONDUCTION SYSTEM
  OF EITHER THE RIGHT, LEFT OR BOTH BUNDLE
  BRANCHES.
• CAUSES A DELAY TO THE VENTRICLES.
• THE INTERRUPTION FORCES THE IMPULSE TO DETOUR
  AND TAKE ANOTHER ROUTE TO THE VENTRICLES.

24
THIS EXTRA TIME CAUSES THE IMPULSE TO REACH
THE VENTRICLE LATER. THIS CAUSES TWO SEPARATE
DEPOLARIZATIONS. THE RHYTHM STRIP HAS A NOTCHED
QRS REFERRED TO AS RABBIT EARS. THE QRS
MEASURES WIDER THAN 0.12 SECONDS. IF BOTH
BRANCHES ARE BLOCKED THE IMPULSE TAKES LONGER TO
REACH THE VENTRICLES.
25
BBB MAY OCCUR IN ANY RHYTHM. P WAVES AND PRI IS
DETERMINED BY THE UNDERLYING RHYTHM. YOU MUST
IDENTIFY THE UNDERLYING RHYTHM FIRST. ARE NOT
LETHAL DYSRHYTHMIAS. A 12-LEAD EKG IS REQUIRED
TO DETERMINE IF THE BLOCK IS IN THE RIGHT OR LEFT
BUNDLE BRANCH.
26
(No Transcript)
27
MANAGEMENT

• BRADYDYSRHYTHMIAS PRESENT THE THREAT OF IMPAIRED
  CARDIAC OUTPUT RESUTLING IN CARDIOGENIC SHOCK AND
  POSSIBLE DEATH.
• IN 1ST AND 2ND DEGREE BLOCKS THE PATIENT IS
  USUALLY PERFUSING ADEQUATELY.

28
THERAPEUTIC MANAGEMENT WILL RESULT IN AN INCREASE
IN RATE. THE INCREASED RATE WILL DIRECTLY
INCREASE MYOCARDIAL OXYGEN DEMAND. PATIENTS ARE
MANAGED ONLY IF THEY ARE HEMODYNAMICALLY
SYMPTOMATIC. THESE ARE SHOCK SYMPTOMS DUE TO
LACK OF CARDIOVASCULAR PERFUSION.
29
SHOCK SYMPTOMS DIMINISHED LEVEL OF
CONSCIOUSNESS DIAPHORESIS FATIGUE DYSPNEA MUCOSA
AND NAIL BED BLANCHING
30
POSSIBLE MANAGEMENT SOLUTIONS

• 1ST DEGREE BLOCK ASSESS AND MONITOR THE
  PATIENT.
• MOBITZ I ( 2ND DEGREE, TYPE I) USUALLY DOES NOT
  REQUIRE TREATMENT, BUT IF THE PATIENT IS
  MEDICALLY UNSTABLE OR POOR CARDIAC OUTPUT
  ATROPINE IS USED IF THE OVERALL RATE IS
  BRADYCARDIC.

31
MOBITZ II (2ND DEGREE, TYPE II) OXYGEN, IV
FLUIDS, ATROPINE IF OVERALL RATE IS BRADYCARDIC,
ARTIFICIAL PACEMAKER, DOPAMINE OR
EPINEPHRINE. IF HEART RATE IS GREATER THAN 100
BUT LESS THAN 150 DILTIAZEM, DIGOXIN, OR BETA
BLOCKERS. 3RD DEGREE BLOCK OXYGEN, IV FLUIDS,
ATROPINE IF BRADYCARDIC, DOPAMINE, EPINEPHRINE,
OR ARTIFICIAL PACEMAKER. BBB- PATIENT ASSESSMENT