CPD II: cardiac arrhythmias and conduction defects

this section in CPD's cardiology lectures covered the various arrhythmias that can occur with various conduction defects. arrhythmias are essentially abnormal heart rhythms that can come in many different flavors, all detected primarily by the ECG. they can be regularly irregular (always abnormal), regularly regular (just fast or slow), irregularly irregular (randomly abnormal). much of the conduction defects that cause arrhythmias occur because of ectopic pacemakers, which are sites in the myocardium other than the standard pacemaker sites which depolarize and cause contraction of heart muscle. alternatively, the myocardium can be damaged by ischemia or necrosis and the conduction pathway can reenter the atrium (or simply blocked from entering the ventricles).

sinus arrhythmias occur when the conduction pathway begins normally in the atrium and thus P wave morphology on the ECG is normal. sinus bradycardia has a rate less than 60bpm, is often benign and results from increased vagal tone which might simply be the result of meditation or exercise. on the other hand, sinus tachycardia is higher than 100bpm and is the result of emotion, sympathetic stimulation, hyperthyroid, or drugs. sinus arrhythmia is an oscillation in heart rate resulting from cyclic vagal tone which is non-pathologic except in cases of increased intracranial pressure or digitalis use.

supraventricular arrhythmias all have some connection with ectopic foci in the atrium which generally result in abnormally shaped P waves and a narrow QRS wave. atrial premature beat is an early atrial contraction which can be benign or due to hypoxia of the myocardium. this would appear on the ECG as random early P waves, resulting in a longer PR interval, and some unconducted P waves (meaning, no QRS waves). atrial escape beats are somewhat the opposite, with a slower heart rate and shorter PR intervals. "wandering atrial pacemaker" is a condition that results from firing of multiple ectopic foci in the atria and thus has different P waves for every beat. multifocal atrial tachycardia is the same condition, just with a heartrate over 100bpm.

PVST is a condition in which the conduction pathway undergoes reentry either at the AV node or beyond it, in which case it is called Wolff-Parkinson-White syndrome. this manifests in young-mid aged patients with sudden episodes of palpitations. tachycardia, and other general symptoms (dyspnea, chest discomfort), between which they are completely normal. the ECG of PVST and WPW have regular tachycardia, variable P waves and a narrow QRS.

atrial fibrillation is an extremely common arrhythmia that occurs more commonly in caucasian men and is characterized by dysfunctional atrial contraction and irregular heart rate that is caused by multiple ectopic foci. people with underlying heart disorders such as HTN or cardiomyopathy are at a higher risk for getting a-fib, as well as alcoholics. since the atrial contraction is dysfunctional, blood stasis can occur and this increases chance for thrombus formation. patients are often asymptomatic, but can experience palpitations, fatigue, chest discomfort, etc. the ECG shows absent or indiscernable P waves, and irregular R-R intervals (irregular rhythm).

atrial flutter is a similar phenomenon but is caused by a large re-entry circuit rather than multiple ectopic foci. in this condition the atriums are contracting at such a fast pace, 250-300 bpm, that the ventricles only contract 1 time per every 2-3 atrial contraction. this results in an ECG that has 2-3 sawtooth-shaped P waves per 1 QRS wave. atrial flutter is associated with underlying heart disease such as CAD, MI, inflammatory disease, rheumatic heart disease, but may often appear asymptomatic (or just present the symptoms of the underlying disease). it is less thrombogenic than atrial fibrillation due to the regular atrial contraction.

moving to the ventricle: ventricular premature beat is the analogous defect to atrial premature beat, also caused by sympathetic stimulation or drugs. patients with this condition often feel a "missed beat" or "flip flop" sensation. "bigeminy" and "trigeminy" refers to one premature beat per every normal 2 or 3 beats, respectively. the QRS wave is highly abnormal, being widened, notched, and slurred, with an inverted T wave following it and no P wave preceding it.

generally, more than 2-3 VPB's in a row is considered very serious and can be classified as ventricular tachycardia. VT can be caused by CAD, MI, drugs and can present with an irregular thready pulse, jugular waves in the neck, and palpitations. the most serious arrhythmia and the most common arrhythmia seen right before cardiac arrest is ventricular fibrillation, uncoordinated quivering of the ventricles due to multiple re-entry pathways. the ECG of VF looks like armageddon.

AV blocks refer to a partial or complete block in the conduction pathway between the atria and ventricles. a first degree block is a partial block that is generally benign, from increased vagal tone but can be from organic heart disease. a second degree "Mobitz I" or "Wanke-bach" block is one in which the ECG shows a progressively widening PR interval leading up to a dropped QRS. a second degree Mobitz II ECG shows a regular PR interval with intermittent dropped QRS- more likely to be pathological than the Mobitz I. finally, the third degree AV block is completely decapitation of the atria and ventricles, with the ventricles firing at a much lower rate. this results in an ECG with some P waves hidden in T waves and wide QRS waves that are similar to PVC's.

lastly, bundle branch blocks are blocks in conduction of branches of the Bundle of His on either side of the heart. a right sided BBB (RBBB) occurs in otherwise healthy people while a LBBB is often the result of a structural heart disorder such as a cardiomyopathy. because the contraction of one ventricle is delayed, the ECG shows a double peaked QRS wave, resembling rabbit ears.

questions
introduction...
1. what is the normal conduction pathway of the heart?
2. what are the inherent conduction rates of the SA, AV nodes and ventricles?
3. what is an ectopic pacemaker?

arrhythmias...
4. what are some general symptoms that patients with arrhythmias might have?
5. what is the best way to test for an arrhythmia?
6. what are three types of rhythms of arrhythmias?
7. how does the QRS wave indicate the type of arrhythmia?
8. how are bradyarrhythmias defined and what can cause them?
9. how are tachyarrhythmias defined and what usually causes them?
10. what is the reentry phenomenon and what is it caused by?

sinus arrhythmias...
11. what is a sinus bradycardia?
12. how serious is a sinus bradycardia?
13. what causes a sinus bradycardia?
14. what are some pathological causes of sinus bradycardia?
15. what are the emergency levels of heart rate in bradycardia?
16. what is sinus tachycardia and what causes it?
17. what are some potential etiologies for sinus tachycardia?
18. what is a sinus arrhythmia and what is it from?
19. when might sinus arrythmia be a concern?

supraventricular arrhythmias...
20. what are atrial premature beats?
21. what is a pathological etiology of atrial premature beats? how is this detected?
22. what are some causes of atrial premature beats?
23. what does the ECG of a patient with an atrial premature beat look like?
24. what is an atrial escape beat?
25. what is a wandering atrial pacemaker? what is it characterized by?
26. what is multifocal atrial tachycardia?
27. what is atrial tachycardia? what is it due to?
28. what does the ECG of atrial tachycardia look like?
29. what are some common etiologies for atrial tachycardia?

PVST...
30. where in the heart does reentry of the conduction pathway occur in PVST?
31. what is Wolff-Parkinson-White syndrome?
32. what is the clinical picture of patients that present with PVST?
33. what does the ECG of PVST look like?
34. WPW syndrome patients are more prone to what condition?

atrial fibrillation...
35. what is atrial fibrillation?
36. a-fib is more likely to occur in which gender and race?
37. what are the risk factors for a-fib?
38. patients with a-fib are at a higher risk of...
39. what are the different classifications of atrial fibrillation?
40. what are the symptoms of atrial fibrillation?
41. what does the ECG of a-fib look like?
42. what are the treatment goals for atrial fibrillation patients?

atrial flutter...
43. what is atrial flutter and what is it caused by?
44. describe the quality of the heartbeat in atrial flutter.
45. describe the ratio of depolarization of the atria and ventricles in atrial flutter.
46. what other conditions is atrial flutter associated with?
47. which has a greater risk for thrombus formation, atrial flutter or atrial fibrillation? why?
48. describe the symptom picture of patients with atrial flutter.
49. what does the EKG of atrial flutter look like?
50. what are the treatment goals for patients with atrial flutter?

ventricular premature beats...
51. what are ventricular premature beats?
52. what are "bigeminy" and "trigeminy" patterns in the context of VPB's?
53. three VPB's in a row = ...
54. patients with VPB often sense...
55. symptoms of VPB often increase with...
56. what does the ECG of VBP's look like?
57. how can the ECG distinguish between multiple vs. single ectopic foci?

ventricular tachycardia and fibrillation...
58. what are the symptoms and PE findings of ventricular tachycardia?
59. what does the ECG of ventricular tachycardia look like?
60. what are the risk factors of VT?
61. what is ventricular fibrillation and how serious is it?
62. VF is the most common rhythm with...
63. what does the eCG of VF look like?
64. what is the treatment for VF?

AV blocks...
65. what is a first degree AV block?
66. what is the seriousness and symptom picture of a first degree AV block?
67. what does the EKG of a first degree AV block look like?
68. what does the EKG of a second degree AV block (Mobitz I) look like?
69. what is the symptom picture of a second degree Mobitz I block?
70. what does the EKG of a second degree AV block (Mobitz II) look like?
71. what is the symptom picture of a second degree Mobitz II block?
72. what is a third degree AV block?
73. when does third degree AV block occur?
74. what does the EKG of a third degree AV block look like?

bundle branch blocks...
75. what is a "bundle branch block"?
76. LBBB vs. RBBB: which is more likely to be pathological?
77. what does the EKG of a bundle branch block look like?
78. what causes bundle branch blocks?
79. what might be heard upon auscultation of BBB's?

answers
1. SA node to AV node to Bundle of His to bundle branches to purkinje fibers.
2. 75/min, 60/min, 35/min.
3. a site in the myocardium other than the main conduction nodes that fires its own conduction signal, normally suppressed by the higher rate of conduction from the SA node.

4. many patients are asymptomatic, but some have palpitations, general symptoms of hemodynamic compromise, sometimes polyuria.
5. 12 lead ECG (or 24 hour ECG), serum electrolytes, nutritional analysis, food sensitivities.
6. regularly regular, regularly irregular, irregularly irregular.
7. a narrow QRS wave indicates supraventricular origin and a wide QRS wave indicates ventricular origin. [narrow high wide low]
8. heart rate below 60bpm, from either decreased pacemaker rhythm or or conduction blocks.
9. heart rate above 100bpm, usually due to reentry phenomenon.
10. when the conduction impulse is blocked from reaching the ventricles, due to ischemia, hypertrophy, or sympathetic stimulation.

11. heartbeat less than 60/min with normal P wave morphology.
12. often benign; interpret based on age and presentation of person.
13. increased vagal tone (can be from parasympathetic stimulating activities such as meditation)
14. myxedema, jaundice, and recovery from tachycardiac states.
15. below 30: send to ER (unless athlete). below 20: fatal.
16. greater than 100bpm, either from decreased vagal tone or increased sympathetic tone.
17. emotion, exercise, anemia, thyroid, hemorrhage, infection.
18. cyclic vagal tone that causes oscillation in heart rate, is generally non pathological in younger people.
19. if the patient also has increased intracranial pressure or digitalis use.

20. a type of ectopic supraventricular arrhythmia in which the atrial contraction comes early; can be non pathological.
21. hypoxia of myocardium; would hear S4 and premature beat.
22. emotion, fatigue, alcohol, tobacco, caffiene.
23. random early P waves, longer PR interval, may have unconducted P wave (no QRS).
24. an uncommon arrhythmia characterized by an abnormal P wave, short PR interval, and slower heart rate.
25. irregularly irregular rhythm due to multiple ectopic foci which results in differing P waves beat to beat.
26. essentially the same as wandering atrial pacemaker but with heart rate above 100bpm as opposed to below 100bpm.
27. a rare condition that leads to an elevated heartrate (150-200bpm) with a regular rhythm with a single ectopic foci, due to "enchanced atrial automaticity"
28. P waves of different morphology that may be hidden in previous T waves.
29. usually due to structural heart disorder, but also can be from drugs (digitoxin), alcohol, toxic gas inhalation.

30. 50% of the time within the AV node and 40% of the time reentry bypasses AV node.
31. PVST where the reentry bypasses the AV node.
32. young adults to mid age with sudden episodes of palpitations (mb with dyspnea, pre-syncope, chest discomfort) with rapid heart rate, 160-240 bpm. asymptomatic between episodes of palpitation.
33. regular tachycardia, variable P waves, narrow QRS.
34. atrial fibrillation.

35. an extremely common supraventricular arrhythmia that results in a rapid, irregularly irregular rhythm due to multiple ectopic foci.
36. white men.
37. pre-existing heart condition such as HTN, valve disorder or cardiomyopathy, and alcoholism.
38. thrombus formation due to absent atrial contraction.
39. acute, paroxysmal, persistent, permanent.
40. often asymptomatic, but otherwise palpitations, chest discomfort, fatigue, heart failure or stroke symptoms.
41. absent or indiscernable P waves, irregular R-R intervals, possible rapid ventricular rate.
42. control the heart rate, control the rhythm, and prevent thrombus formation.

43. rapid atrial rate often caused by large re-entrant circuit in right atrium.
44. rapid and regular, up to 250-350 bpm.
45. the ventricles contract about every 2 to 3 times that the atria do.
46. CAD, MI, inflammatory diseases, rheumatic heart disease.
47. flutter has lower risk because atrial contraction is more regular.
48. if the rate is low, the patient is likely asymptomatic but if the rate is high then the symptoms will be similar to atrial fibrillation.
49. 2-3 sawtooth shaped P waves for every 1 QRS complex.
50. same as atrial fibrillation.

51. premature ventricular beats created by ectopic ventricular sites.
52. one VPB per every two heartbeats or three heartbeats, respectively.
53. v-tach.
54. missed beats or a "flip flop" sensation.
55. sympathetic stimulation, drugs, caffeine, electrolyte disturbances.
56. an abnormal, widened, notched, and slurred QRS wave with no P wave preceding and an inverted T wave.
57. if all the QRS waves have the same shape: single. different shapes: multiple.

58. irregular thready pulse, jugular waves in neck, palpitations, racing heart.
59. 3 or more PVC's in a row with fairly regular R-R intervals.
60. CAD, MI, drugs, torsade de pointes.
61. a cardiac emergency, uncoordinated quivering of the ventricle due to multiple re-entry.
62. cardiac arrest.
63. erratic voltages with or without P, QRS waves.
64. defibrillator or CPR.

65. a partial hear block; delay at the AV node that results from increased vagal tone or organic heart disease.
66. asymptomatic and can be physiologic in younger or atheletes.
67. longer PR interval. all else normal.
68. progressively widening PR interval until QRS dropped.
69. asymptomatic, can be physiologic in younger and atheletes.
70. regular PR intervals and intermittently dropped QRS, every 3 or 4 betas.
71. generally asymptomatic but may have signs of hemodynamic compromise. may indicate organic heart disease.
72. completely independent impulse generation in atria and ventricles.
73. in serious heart disease such as CAD or serious ischemic disease.
74. intermittently disappearing P waves (because hidden in T waves), wide QRS waves that look like PVC.

75. blocked conduction of one of the Bundle of His branches.
76. RBBB is often in otherwise healthy people but LBBB more often a structural heart disorder such as a cardiomyopathy.
77. 2 R wave peaks since one is side is delayed - results in "rabbit ears".
78. HTN, CAD, cardiomyopathy, ischemic heart disease.
79. wide S2 splitting.