JUNCTIONAL RHYTHMS

1. JUNCTIONAL RHYTHMS CHAPTER 4

2. INTRODUCTION • IF THE SA NODE AND ATRIA FAIL TO GENERATE IMPULSES THE ATRIOVENTRICULAR (AV) NODE MAY ASSUME THE ROLE OF SECONDARY PACEMAKER. • LOCATED IN THE LOWER RIGHT ATRIUM NEAR THE SEPTUM. • THE CARDIAC TISSUE SURROUNDING THE AV NODE IS USUALLY CALLED THE AV JUNCTION.

3. THE AV JUNCTION IS CAPABLE OF INITIATING ELECTRICAL IMPULSES. IMPULSES THAT START IN THE AV NODE OR AV JUNCTIONAL AREA ARE CALLED JUNCTIONAL OR NODAL RHYTHMS. THE AV JUNCTION IS NOT AS EFFICIENT AS THE SA NODE THEREFORE IT HAS A SLOWER RATE. THE INHERENT HEART RATE OF THE AV JUNCTIONAL AREA IS 40 TO 60 IMPULSES PER MINUTE.

4. NOT USUALLY A LETHAL DYSRHYTHMIA PATIENT ASSESSMENT IS ESSENTIAL TO DETERMINE THE PATIENT’S TOLERANCE OF THE DYSRHYTHMIA. THE IMPULSE TRAVELS IN A NORMAL PATHWAY FROM THE AV JUNCTION, BUNDLE OF HIS, BUNDLE BRANCHES, PURKINJE’S FIBERS TO THE VENTRICLES. QRS COMPLEX IS <0.12 SECONDS FOR THE ATRIA TO CONTRACT THE IMPULSE MUST TRAVEL BACKWARDS (RETROGRADE) FROM THE AV JUNCTION THROUGH THE ATRIA. THE P WAVE WILL BE INVERTED, BURIED, OR RETROGRADE.

5. INVERTED P WAVE • IF THE IMPULSE ORIGINATES HIGH IN THE AV JUNCTIONAL AREA THE ATRIA DEPOLARIZE QUICKLY IN A RETROGRADE MANNER. • THE P WAVE WILL BE UPSIDE DOWN OR RETROGRADE. • SINCE THE IMPULSE DISTANCE IS SHORTER TO DEPOLARIZE THE VENTRICLES THE PR INTERVAL IS LESS THAN 0.12 SECONDS.

7. BURIED OR HIDDEN P WAVE • IF THE IMPULSE ORIGINATES IN THE MID AV JUNCTIONAL AREA THE DISTANCE THE IMPULSE MUST TRAVEL UP THROUGH THE ATRIA AND DOWN THE VENTRICLES IS ALMOST THE SAME. • THIS CAUSES THE ATRIA AND VENTRICLES TO DEPOLARIZE AT ALMOST THE SAME TIME. • THE FORCE OF ATRIAL DEPOLARIZATION IS LESS THAN THE FORCE OF VENTRICULAR DEPOLARIZATION THE P WAVE IS HIDDEN BY THE QRS. • THE P WAVE IS HIDDEN AND A PRI WILL NOT BE SEEN.

8. Junctional Escape Beat

9. RETROGRADE P WAVE • IMPULSE ORIGINATES IN THE LOWER PART OF THE AV JUNCTIONAL AREA. • THE IMPULSE DISTANCE IS GREATER TO THE ATRIA THAN VENTRICLES. • THE ATRIA DEPOLARIZE SLIGHTLY LATER THAN THE VENTRICLES. • THE P WAVE APPEARS AFTER THE QRS COMPLEX. • NO MEASURABLE PRI, P WAVE IS INVERTED.

10. Find the retrograde wave

11. JUNCTIONAL BRADYCARDIA • ALL IMPULSES ORIGINATE FROM A SINGLE SITE WITHIN THE AV JUNCTIONAL AREA AT A RATE OF <40 IMPULSES PER MINUTE. • P WAVE CAN BE INVERTED, BURIED, OR RETROGRADE. • IF A PRI IS PRESENT IT WILL USUALLY BE LESS THAN 0.12 SECONDS. • THE QRS IS <0.12 SECONDS.

12. THE RHYTHM OF THIS DYSRHYTHMIA IS REGULAR. THE RATE CAN VARY, BUT MUST BE LESS THAN 40 PER MINUTE. THIS DYSRHYTHMIA MAY BECOME SYMPTOMATIC IS THE RATE FALLS SIGNIFICANTLY. ONLY A JUNCTIONAL RHYTHM WITH A RATE BELOW 40 CAN BE CALLED A JUNCTIONAL BRADYCARDIA.

13. Junctional Bradycardia

14. ACCELERATED JUNCTIONAL RHYTHM • RATE BETWEEN 61 AND 100 IMPULSES PER MINUTE. • P WAVES ARE INVERTED, BURIED, OR RETROGRADE. • PRI IF PRESENT IS <0.12 SECONDS. • R TO R INTERVALS ARE REGULAR, QRS IS <0.12 SECONDS. • THE RATE CAN VARY BUT MUST BE BETWEEN 61 AND 100 IMPULSES PER MINUTE. • JUNCTIONAL TACHYCARDIA HAS A RATE OF 101 TO 150 IMPULSES PER MINUTE.

15. Rate? Rhythm?

16. BOTH ACCELERATED JUNCTIONAL AND JUNCTIONAL TACHYCARDIA MAY BE CAUSED BY HEART DISEASE OR DRUGS SUCH AS ATROPINE, CAFFEINE, OR AMPHETAMINES. PAIN, FEVER, OR ACUTE ANEMIA CAN CAUSE THESE DYSRHYTHMIAS. EITHER OF THE CONDITIONS CAN BECOME SERIOUS IF THE RATE INCREASES SIGNIFICANTLY OR THE PATIENT BECOMES SYMPTOMATIC.

17. PREMATURE JUNCTIONAL CONTRACTION (PJC) • AN INDIVIDUAL COMPLEX. • ORIGINATES FROM A SINGLE SITE IN THE AV JUNCTIONAL AREA. • OCCURS EARLIER THAN THE NEXT EXPECTED COMPLEX OF THE UNDERLYING RHYTHM. • PJC’S ARE NOT RHYTHMS. • HAS THE SAME CHARACTERISTICS AS OTHER JUNCTIONAL COMPLEXES.

18. THE OCCURRENCE OF A PJC CAUSES THE RHYTHM TO BE IRREGULAR. THE PJC MAY BE FOLLOWED BY A COMPLETE COMPENSATORY PAUSE WHICH ALLOWS THE UNDERLYING RHYTHM TO DEPOLARIZE AT ITS NORMAL RATE. THE R TO R INTERVAL FROM THE COMPLEX BEFORE THE PJC TO THE COMPLEX AFTER THE PJC, IS AT LEAST TWO TIMES THE R TO R INTERVAL OF THE UNDERLYING RHYTHM. EASIER TO IDENTIFY IN SINUS OR BRADYCARDIC RHYTHM.

19. THE UNDERLYING RHYTHM MUST BE IDENTIFIED IN A STRIP CONTAINING A PJC. CAUSED BY INCREASED IRRITABILITY OF THE CARDIAC CELLS. MAY BE CAUSED BY: DIGITALIS, ATROPINE, NICOTINE, CAFFEINE, AND AMPHETAMINES. PAIN, FEVER, FEAR, ANXIETY, EXERCISE, SUDDEN EXCITEMENT.

21. ATROPINE • INCREASES HEART RATE, INCREASES SINUS NODE AUTOMATICITY, IMPROVES AV CONDUCTION. • TO CORRECT: SYMPTOMATIC BRADYCARDIA, ASYSTOLE, PULSELESS ELECTRICAL ACTIVITY, TO INCREASE HEART RATE TO AT LEAST 60 BEATS/MIN. IN A BRADYCARDIC RHYTHM WITH PVCs.

22. DIGITALIS • INCREASES MYOCARDIAL CONTRACTILITY; HELPS CONTROL VENTRICULAR RESPONSE TO ATRIAL DYSRHYTHMIAS. • USED FOR: ATRIAL FLUTTER, ATRIAL FIB, ATRIAL TACHYCARDIA INCLUDING PAT’S AND SVT, CHRONIC CONGESTIVE HEART FAILURE.

23. WANDERING JUNCTIONAL PACEMAKER • ORIGINATES FROM AT LEAST THREE SITES WITHIN THE JUNCTIONAL AREA. • SIZE AND SHAPE OF THE COMPLEX IS DETERMINED BY THE SITE OF ORIGIN OF EACH COMPLEX. • COMPLEXES ARE CHARACTERIZED BY P WAVES THAT ARE INVERTED, BURIED, OR RETROGRADE.

24. THE RHYTHM IS IRREGULAR WITH VARYING P TO P INTERVALS AND R TO R INTERVALS. RATE IS USUALLY 40 TO 60 IMPULSES PER MINUTE. MAY BE CAUSED BY HEART DISEASE, MYOCARDIAL INFARCTION, OR DRUG TOXICITY. HAS THREE OR MORE JUNCTIONAL SITES. IF BOTH ATRIAL AND JUNCTIONAL SITES – WAP.