Cardiac Conduction Physiology

Pacemaker cells are primarily governed by Ca channels, while myocytes are governed by Na channels. Activation of β receptors leads to increased levels of cAMP which directly stimulates HCN channels to open, and through activation of PKA stimulates the activation of Ca channels. Cholinergic activation opposes this by activation of G_i.

Vaughan-Williams-Singh Antiarrhythmic Scale

• Class 1: Na Channel Blockers
  • 1a: Mixed Na and K Blockade (moderate dissociation), blocks open state of Na, widens QRS and prolongs QT
  • 1b: Fast dissociation, slightly shortens phase 2, minimal clinical impact
  • 1c: Strong (slow dissociation) Na blockade slowing 0, widens QRS
• Class 2: β-blockers
• Class 3: K Blockers
• Class 4: non-DHP CCBs

EKG Normal Values

Measure	Interval (ms)
PR Interval	120-200
QRS	80-120
QT*	380-460
QTc (Male)*	360-470
QTc (Female)*	360-480

*High risk of Torsades w/ QTc ≥ 500ms

$$QTc=\frac{QT}{\sqrt{60/HR}}$$

Sinus Bradycardia (Sick Sinus Syndrome)

A sinus, regular rhythm with a HR < 60 BPM

Risk Factors

• Myocardial infarction or ischemia
• Abnormal sympathetic or parasympathetic tone
• Electrolyte abnormalities
  • Hyperkalemia
  • Hypermagnesemia
• Drugs
  • Digoxin
  • ß-blockers
  • CCBs (Diltiazem, verapamil)
  • Amiodarone
  • Dronedarone
  • Ivabradine
• Idiopathic

SSx

• Hypotension
• Dizziness
• Syncope

Treatment

Only treat symptomatic patients

• Atropine 0.5mg q5min to max of 3mg or 0.04 mg/kg
  • Tachycardia
  • Urinary retention
  • Blurred vision
  • Dry mouth
  • Mydriasis
• Refractory to Atropine
  • Transcutaneous pacing
  • Dopamine 2-10 mcg/kg/min
  • Epi 2-10 mcg/min
• Long term treatment may require permanent pacemaker

Atrial Fibrillation

Characterized by an irregularly irregular rhythm with a ventricular rate of 120-180 BPM. P waves are often absent. A-fib is usually caused by abnormal atria or pulmonary vein automaticity sustained by atrial reentry circuits.

Classifications of A-fib

• Paroxysmal
  • Intermittent episodes
  • Episodes start suddenly and spontaneously, last for minutes to hours, and terminate suddenly and spontaneously
• Persistent
  • A continuous episode of AF that does not terminate spontaneously
  • May last > 7 days
• Long-standing persistent
  • Continuous AF > 12 months in duration
• Permanent
  • Pt never returns to sinus rhythm and cannot be converted
  • Usually a joint decision to stop escalating therapy
• Nonvalvular
  • Not accompanied by any valvular disease

Risk Factors

• HTN
• CAD
• CHF
• Old age
• DM
• Obesity
• OSA
• Valvular heart disease
• Rheumatic heart disease
• Smoking
• Genetic
• IdiopathicHyperthyroidism
• PE
• Thoracic Surgery
  • Coronary artery bypass graft (CABG)
  • Lung resection
  • Esophagectomy
• Excessive EtOH use

SSx

• Asymptomatic A-fib is somewhat common
• Palpitations
• Dizziness
• Fatigue
• Lightheadedness
• SOB
• Hypotension
• Syncope
• Angina (if pt has CAD)
• CHF exacerbation

Treatment Goals

Persistent A-Fib	Paroxysmal A-Fib	Permanent A-Fib
Ventricular Rate Control	Ventricular Rate Control	Ventricular Rate Control
Prevention of Stroke and Emoblism	Prevention of Stroke and Emoblism	Prevention of Stroke and Embolism
Convert to Sinus Rhythm	Maintain Sinus Rhythm

Treatment

Ventricular Rate Control

Treat to goal HR of < 110 BPM unless the patient is symptomatic or has HFrEF, then treat to goal of 80 BPM

Drug	Loading Dose	Daily Dose	SEs	Notes
Diltiazem	0.25 mg/kg IV over 2 min	5-15 mg/hr or 120-360 mg ER PO QD	Hypotension Bradycardia HFrEF Exacerbation AV Blockade
Verapamil	0.075-0.15 mg/kg IV over 2 min w/ an addition 10 mg at 30 min if needed	0.005 mg/kg/min or 120-380 mg ER PO QD	Hypotension Bradycardia HFrEF Exacerbation AV Blockade Constipation	Increases levels of Digoxin and Dofetilide
Esmolol	500 mcg/kg IV over 1 min	50-300 mcg/kg/min IV	β-Blockade
Propranolol	1mg IV over 1min q2min Max of 3 doses	30-60mg PO Daily in divided doses	β-Blockade
Metoprolol	2.5-5mg IV over 2 min Max of 3 doses	Tartrate: 25-100mg PO BID Succinate: 50-400mg PO QD	β-Blockade
Digoxin	0.25mg IV q4hr Max of 1.5mg over 24hr	0.125-0.375mg PO or IV QD	N/V Anorexia Arrythmias	Amiodarone and Verapamil Increase Digoxin Levels
Amiodarone	300mg IV over 1hr	10-50 mg/hr over 24hr 100-200mg PO QD	Hypotension Bradycadia Photosensitivity Pulmonary Fibrosis Blue-Grey Skin Hepatotoxicity Hypo- / Hyperthyroidism	Increases levels of warfarin and digoxin

Sinus Rhythm Conversion

Drug	Loading Dose	Maintenance dose	SEs	Notes
DCC	120-200 J Biphasic 200 J Monophasic	n/a	Pain Risks of General Sedation
Amiodarone	150mg over 10 min 600-800mg QD in 2-3 divided doses for total loading dose of 10g	1 mg/min for 6hrs then 0.5 mg/min for 18 hr 200mg PO QD	Hypotension Bradycardia	Increases levels of Digoxin and Warfarin 24hr conversion
Dofetilide	See Table Below	n/a	TdP	Cimetidine HCTZ Ketoconazole Trimethoprim Verapamil (All raise levels of dofetilide) 24hr conversion
Ilbutilide	1mg IV over 10 min q10min x2 if needed < 60kg use 0.01 mg/kg	n/a	TdP	30min conversion
Propafenone	450-600mh PO x1	n/a	Dizziness Blurred Vision HFrEF	3-8hr conversion CI in HF
Flecainide	200-300mg PO x1	n/a	Dizziness Blurred Vision HFrEF	3-8hr conversion CI in HF

CrCl	Dofetilide A-Fib Dose
> 60	500 mcg PO BID
40-60	250 mcg PO BID
20-40	125 mcg PO BID
< 20	CI

Sinus Rhythm Maintenance

Anticoagulation

Anticoagulation is required for all A-Fib patients. Appropriate anticoagulants include warfarin, dabigatran, rivaroxaban, apixaban, and edoxaban. See Anticoagulants for appropriate dosing, monitoring, and therapy selection for these patients.

Paroxysmal Supraventricular Tachycardia

PSVT presents as a narrow complex, regular tachycardia which spontaneously initiates and terminates.

PSVT is most commonly due to re-entrant circuits within the:

• AV Node (60%)
• Accessory Pathways (WPW, 30%)
• Atria (4-8%)
• SA Node (4%)

PSVT is more common in women and those over the age of 65, and usually occurs in pts w/o a significant CV Hx.

SSx

• Neck-pounding
• Palpitations
• Dizziness
• Weakness
• Lightheadedness
• Near-syncope / Syncope
• Polyuria

Treatment

Cardioversion of Hemodynamically Stable Patients

1. Vagal Maneuvers and/or IV Adenosine
2. IV Rate Control Drugs (β-Blockers or nonDHP-CCBs)
3. Synchronized DCC

Drug	Dose	SEs	Notes
Adenosine	6mg IVPB w/ flush 12mg in 1-2min x2 if needed	Chest Pain Flushing SOB Sinus Pause Bronchospasm	Carbamazepine and dipyridamole alter adenosine response, decrease dose by 50%
Diltiazem	0.25 mg/kg IV over 2 min	5-15 mg/hr or 120-360 mg ER PO QD	Hypotension Bradycardia HFrEF Exacerbation AV Blockade
Verapamil	0.075-0.15 mg/kg IV over 2 min w/ an addition 10 mg at 30 min if needed	0.005 mg/kg/min or 120-380 mg ER PO QD	Hypotension Bradycardia HFrEF Exacerbation AV Blockade Constipation
Esmolol	500 mcg/kg IV over 1 min	50-300 mcg/kg/min IV	β-Blockade
Propranolol	1mg IV over 1min q2min Max of 3 doses	30-60mg PO Daily in divided doses	β-Blockade
Metoprolol	2.5-5mg IV over 2 min Max of 3 doses	Tartrate: 25-100mg PO BID Succinate: 50-400mg PO QD	β-Blockade
Amiodarone	150mg IV over 10 min	1 mg/min for 6hr then 0.5 mg/min for 18hr	Hypotension Bradycadia Photosensitivity Pulmonary Fibrosis Blue-Grey Skin Hepatotoxicity Hypo- / Hyperthyroidism

Prevention of Symptomatic PSVT

Drug therapy should only be initiated in SYMPTOMATIC patients

Premature Ventricular Complexes

PVCs present as irregular, wide QRS complexes that do not follow a P-wave. Prevalence of these arrhythmias increases with age, and they are indicative of increased cardiovascular risk in patients > 30yo. > 10k-20k PVCs QD is indicative of cardiomyopathy. PVCs occur due to increased automaticity of myocytes and/or purkinje fibers.

Risk Factors

• IHD
• MI
• Anemia
• Hypoxia
• Cardiac Surgery

SSx

• Usually Asymptomatic
• Palpitations
• Dizziness
• Lightheadedness

Treatment

Asymptomatic patients should NOT be treated

• Non CV Pts
  1. β-Blockers, Diltiazem, or Verapamil
  2. If unresponsive, antiarrhythmics
  3. Ablation
• CAD Pts
  1. β-Blockers, Diltiazem, or Verapamil
  2. If unresponsive, antiarrhythmics (Avoid Class 1C)
• HFrEF Pts
  1. β-Blockers

Ventricular Tachycardia

VTach presents as a regular, wide complex tachycardia defined as at least 3 consecutive PVCs at a rate of > 100 BPM. Sustained VTach is defined as either VTach lasting longer than 30s, or VTach requiring intervention w/i 30s due to hemodynamic instability. Otherwise, it is classified as non sustained. VTach in patients w/o SHD is referred to as idiopathic, and will either be verapamil sensitive or outflow tract VTach (β-blocker sensitive). VTach occurs as a result of increased myocyte automaticity which is sustained by reentry circuits.

Risk Factors

• Coronary artery disease
• Myocardial infarction
• HFrEF
• Hypokalemia
• Hypomagnesemia
• Drugs
  • Flecainide
  • Propafenone
  • Digoxin

SSx

• May be asymptomatic (nonsustained VT)
• Palpitations
• Hypotension
• Dizziness
• Lightheadedness
• Syncope
• Angina

Treatment

Termination of Hemodynamically Stable VTach

Drug	Loading Dose	Maintenance Dose	SEs	Notes
Procainamide	10-17 mg/kg IV at 20-50 mg/min	1-4 mg/min	Hypotension QT Prolongation TdP	Cimetidine, Ranitidine, and Trimethoprim inhibit procainamide elimination
Amiodarone	150mg IV over 10 min	1 mg/min for 6hr then 0.5 mg/min for 18hr	Hypotension Bradycardia Phlebitis	Increases levels of Digoxin and Warfarin
Sotalol	75mg IV Q12H	n/a	Hypotension Bradycardia QT Prolongation TdP
Verapamil	2.5-5mg IV Q15-30min at 1-3 mg/min	n/a	Hypotension Bradycardia HFrEF exacerbation	Inhibits the elimination of digoxin and dofetilide
Esmolol	500 mcg/kg IV over 1 min	50-300 mcg/kg/min IV	β-Blockade
Propranolol	1mg IV over 1min q2min Max of 3 doses	30-60mg PO Daily in divided doses	β-Blockade
Metoprolol	2.5-5mg IV over 2 min Max of 3 doses	Tartrate: 25-100mg PO BID Succinate: 50-400mg PO QD	β-Blockade

Prevention of VTach

• ICD
  • Preferred Therapy
• Amiodarone 400mg PO QD
  • Useful in pts w/ frequent ICD shocks
• Sotalol 80-160mg PO QD
  • Useful in pts w/ frequent ICD shocks
• Catheter Ablation
  • Recommended for pts w/ prior MI or who are intolerant to antiarrythmics

Ventricular Fibrillation

VFib presents as irregular, chaotic electrical activity with no palpable pulse and no QRS complexes

Risk Factors

• MI
• HFrEF
• CAD

Treatment

1. CPR x2min and obtain vascular access
2. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
3. CPR x2min
4. Epi 1mg
5. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
6. CPR x2min
7. Amiodarone 300mg in 20-30mL D5W
8. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
9. CPR x2min
10. Epi 1mg
11. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
12. CPR x2min
13. Amiodarone 150mg in 20-30mL D5W
14. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
15. CPR x2min
16. Epi 1mg
17. Defibrillation (120-200 J Biphasic or 360 J Monophasic)
18. Repeat steps 15-17 until the end of code