Comprehensive Study Notes on SVT, Atrial Fibrillation, and Atrial Flutter

Supraventricular Tachycardia

• Conduction & Pathophysiology:

  • Supraventricular Tachycardia (SVT) originates at a site above or adjacent to the atrioventricular (AV) node, or results from extreme misfiring of the sinoatrial (SA) node.
  • It is classified as a narrow-complex tachycardia.
  • Extremely rapid heart rates (frequently exceeding $200\,\text{bpm}$) drastically shorten ventricular diastolic filling time. Consequently, the ventricles pump before filling adequately, causing a severe drop in stroke volume and cardiac output.

• Electrocardiogram (EKG) Characteristics:

  • QRS Complex: Typically very narrow and significantly skinnier than in normal sinus rhythm.
  • P Wave Analysis: No obvious or discernible P waves are visible. P waves may be present but are frequently buried under or obscured by preceding T waves.

• Clinical Presentation & Systemic Impact:

  • Patients present with lightheadedness, dizziness, syncopal or near-syncopal episodes, and an inability to speak.
  • Inadequate cardiac ejection leads to acute hypotension.
  • Compensatory Responses: Compensatory tachypnea occurs as the respiratory system attempts to counteract cerebral hypoxemia. Systemic hypoperfusion also affects renal perfusion, decreasing kidney function.

• Pharmacological Intervention: Adenosine:

  • Adenosine functions as an electrical disruptor to cardiac conduction (described functionally as "resetting the modem" or a "Control + Alt + Delete" for the heart).
  • The drug briefly terminates electrical activity through the AV node, creating a prolonged pause/asystole that typically lasts for up to $6\,\text{seconds}$ before normal sinus rhythm restores.

• Interventional Management:

  • Synchronized Cardioversion: Timed electrical delivery synchronized directly to a specific point on the QRS complex to prevent triggering ventricular fibrillation.
  • Radiofrequency Catheter Ablation: Performed via a femoral vascular approach (similar to a cardiac catheterization). A catheter is advanced into the right atrium to deliver targeted radiofrequency energy to cauterize and eliminate ectopic electrical pathways.

Atrial Fibrillation & Rapid Ventricular Rate

• Pathophysiology & Mechanical Dysfunction:

  • Atrial Fibrillation (AFib) represents chaotic electrical hyperexcitability ("cardiac hysteria") within the atria.
  • Instead of coordinated contraction, the atria fibrillate passively (described mechanically as shivering like a "terrified chihuahua").
  • Loss of the "atrial kick" prevents effective blood ejection into the ventricles. Blood trickles passively into the ventricular chambers rather than being forcefully pumped, reducing cardiac output.

• EKG Characteristics:

  • Rhythm: Completely and perpetually irregular (irregularly irregular).
  • P Wave Analysis: Absence of uniform, distinct P waves. Replaced by baseline chaotic fibrillatory activity (up to $100$ or more uncoordinated atrial impulses per ventricular response).
  • PR Interval: Undefined and unmeasurable due to the lack of identifiable P waves.
  • QRS Complex: Typically normal/narrow, occurring unpredictably as impulses randomly penetrate the AV node.

• Classification by Ventricular Rate:

  • Rate-Controlled AFib: Ventricular response rate remains within normal limits ($60-100\,\text{bpm}$).
  • AFib with Rapid Ventricular Rate (RVR): Ventricular response rate exceeds $100\,\text{bpm}$. Tachycardia combined with loss of atrial kick causes significant reductions in cardiac output.

• Etiology & Risk Factors:

  • Secondary complication following cardiac surgery.
  • Untreated hypertension.
  • Untreated pulmonary embolism (PE).
  • Sleep apnea.
  • Demographic trends demonstrate an elevated prevalence of chronic, rate-controlled AFib cases within East Tennessee populations.

Diagnostic Evaluation & Thromboembolic Risk

• Clinical Manifestations & Physical Assessment:

  • Lightheadedness, dizziness, and syncope.
  • Heart pounding or fluttering sensation in the chest.
  • Chest discomfort or chest pain (particularly in patients with underlying ischemic heart disease or prolonged rapid heart rates).
  • Shortness of breath (dyspnea) both at rest and with exertion, often accompanied by anxiety.
  • Pulse Deficit: A measurable disparity between the apical heart rate (auscultated at the apex) and the peripheral pulse rate (palpated at the radial artery), characteristic of AFib or vascular occlusion.

• Diagnostic Laboratory Testing:

  • TSH (Thyroid Stimulating Hormone) & Thyroxine ($T_4$): Assesses underlying hyperthyroidism as a metabolic cause of atrial dysrhythmias.
  • Complete Blood Count (CBC): Evaluates oxygen-carrying capacity, hemoglobin levels, and systemic infection markers.
  • Serum Creatinine: Assesses renal function and end-organ perfusion.
  • Blood Glucose: Identifies acute hyperglycemia, which can trigger atrial irritability.
  • International Normalized Ratio (INR): Coagulation test performed specifically to titrate therapeutic dosage for patients prescribed Warfarin.

• Diagnostic Cardiac Imaging:

  • Transthoracic Echocardiogram (TTE): Non-invasive ultrasound of the heart wall. Requires no signed consent form and takes approximately $10\,\text{minutes}$.
  • Transesophageal Echocardiogram (TEE): Endoscopic probe passed down the esophagus adjacent to the atria. Provides direct, high-resolution visualization of atrial appendages to detect microthrombi. Requires moderate (twilight) sedation and formal written informed consent.

• Thromboembolic Complications:

  • Stasis of blood within the non-contracting atrial chambers promotes thrombus formation.
  • Diagnosis of AFib increases stroke risk to $5 \times$ higher than in the general population.
  • Dislodged left atrial clots travel to cerebral circulation causing ischemic stroke; right atrial clots travel to pulmonary vasculature causing pulmonary embolism (PE).

Pharmacological & Lifestyle Management

• Anticoagulation Therapy:

  • Patients with persistent or paroxysmal AFib require lifelong oral anticoagulants (e.g., Warfarin, Apixaban) to prevent thromboembolic stroke.
  • AFib itself does not cause bleeding; the mandatory anticoagulant medications induce bleeding risks.

• Mandatory Patient Education & Bleeding Precautions:

  • Shaving: Instruct patients to use electric razors exclusively. Avoid safety razors or straight blades.
  • Oral Care: Use soft-bristle toothbrushes. Avoid vigorous toothbrushing and aggressive dental flossing.
  • Physical Activity: Avoid high-impact or contact sports (e.g., football, rugby) due to internal hemorrhage risks. Suggest low-impact activities such as golf.
  • Medication Compliance: Inform patients that effective anticoagulants will not change how they feel physically. Emphasize that feeling unchanged indicates the drug is working to prevent clots. Instruct patients never to stop anticoagulants abruptly without explicit provider orders.

• Substance & Supplement Precautions:

  • Stimulants: Eliminate caffeine and nicotine to avoid increasing heart rate and atrial excitability.
  • Herbal Supplements ("The G's" & Fish Oil): Patients must avoid or obtain provider clearance before taking supplements with natural anticoagulant properties:
  • Ginseng
  • Garlic
  • Gingko (Gingko Biloba)
  • Fish Oil
  • Co-administration of these herbal supplements with prescribed anticoagulants produces additive anti-hemostatic effects, leading to hyper-anticoagulation and uncontrollable bleeding.

Atrial Flutter

• EKG & Rhythm Characteristics:

  • Ventricular Rate: Can be rate-controlled (e.g., $70\,\text{bpm}$, within the normal range of $60-100\,\text{bpm}$).
  • P Wave Analysis: Characterized by multiple flutter waves ($F$-waves) for every QRS complex, creating a uniform "sawtooth" pattern resembling the edge of a saw blade or steak knife.
  • Organization: Demonstrates a more organized electrical re-entry circuit compared to the chaotic baseline of AFib.

• Clinical Considerations & Treatment:

  • Atrial Flutter is a direct subset and variation of Atrial Fibrillation.
  • Mechanical atrial contraction remains ineffective, leading to similar risks of blood stasis, intra-atrial thrombus formation, and embolic stroke.
  • Clinical etiology, risk factors, bleeding precautions, rate/rhythm control interventions, radiofrequency catheter ablation strategies, and lifelong anticoagulation protocols are identical to those utilized for Atrial Fibrillation.