Polymorphic Ventricular Tachycardia and Repolarization  

Polymorphic Ventricular Tachycardia

It is a cardiac emergency, QRS shape varies because the origin of arrhythmogenic focus varies.QT prolongation is a significant factor that contributes to polymorphic ventricular tachycardia. 

Ventricular activation sequence is changing continuously, as indicated by the QRS structure in PVT, which will be continuously altering from beat to beat.  PVT suggests that there is not a permanent structural abnormality.  No single focal point of abnormality.
Clinical characteristics: palpitations, syncope, and syncopal episodes
Diagnosed by ECG. The most common forms of treatment include catheter ablation, anti-arrhythmic medications, and implantable cardiac devices (ICDs).

Potential Mechanisms

Reentry occurs on a regular basis.  There is constant change in the reentry pathway.  There are multiple auto-focus points.  The multiple reentry pathway is most frequently found in close proximity to regions of cardiac fibrosis.

Etiology 

Acute myocardial infarction or ischemia.  A scar develops after MI, and several reentrant pathways around or inside the scar can cause PVT.  Hypertrophied septum or apex: a region with many paths for reentry. Multiple automatic foci;  Genetic abnormality affecting cardiac ion channels;  Ventricular hypertrophy, or HOCM. 

Acute myocardial infarction

10% of individuals with acute MI develop PVT.  One of the Common Causes of PVT.

Also Read: Aortic Aneurysm- Thoracic And Abdominal Aortic Aneurysm

Mechanism of Myocardial infarction

Returning to the infarct boundary area, seldom do the remaining Purkinje cells additionally cause automaticity to be triggered from several locations. 
The first hour following an acute MI is when PVT risk is highest.
Patients who survive acute MI and are released from the hospital do not face the risk of sudden cardiac death.  PVT/VF that occurs within 48 hours of acute MI is linked to very high hospital mortality.

Also Read: High-Yield NEET SS Medicine Cardiovascular Questions

Treatment of Myocardial infarction

ACLS Protocol-compliant defibrillation. The following needs to be addressed right away: medication management; beta blockers; correction of electrolyte abnormalities; and hypokalemia.  It's critical that myocardial reperfusion happen quickly.

Repeated episodes 

Insist on a continuing myocardial infarction.  Evaluate whether or not myocardial reperfusion happened as intended.  Left ventricular function dictates the course of long-term therapy for post-infarct ventricular arrhythmia.  If EF is less than 35%, an ICD should be placed.

Also Read: Drugs and Toxins Induced Cardiomyopathies 

Repolarization Abnormality and Genetic Arrhythmia Syndrome

1. Long QT syndrome
   • Acquired
   • Genetic causes
2. Short QT syndrome
3. Brugada syndrome 
4. Catecholaminergic ventricular tachycardia
5. HOCM 
6. Genetic dilated cardiomyopathies

1. Acquired Long QT syndrome

Torsades de Pointes, or polymorphic VT, is linked to abnormal lengthening of the QT interval.  PVC after a sinus beat with a typical QT interval.  Long pause after PVC, then sinus beat with QT prolongation.  The long QT interval is where PVT first appears.  The first beat of PVT, or premature ventricular contraction, occurs following a lengthy Qt interval.  PVC has pauses, which is the reason this characteristic beginning is known as pause dependent PVT.

Also Read: Super Specialty in Medicine : Merits, Demerits, Scope, Career Outside India

Causes of QT prolongation 

Bradycardia; drugs; electrolyte abnormalities; hyperkalemia, hypocalcemia, hypermagnesemia.

Presentation 

• Near syncope
• Syncope
• Cardiac arrest 

Progression

• PVCs; Non-Sustained VT; Sustained VT; PVT; VF; • Defibrillation is necessary for patients who have developed ventricular defibrillation.

Treatment of Long QT interval

• Suppress recurring episodes; magnesium sulfate, IV, 1-2 g.  If magnesium sulfate doesn't work, try isoproterenol injection to raise heart rate.

PACING

• Heart rate is raised to between 100 and 120 beats per minute.
• When a patient is in a PVC state, their heart rate increases.
• When the person displays PVCs
• Overdrive pacing inhibits PVCs, which inhibits PVT formation.
• Steer clear of medications that lengthen QT.
• AAD Class I; AAD Class III 

Causes of QT Prolongation 

• Congenital
• Electrolyte disturbances
• Drugs 
• Endocrine causes
• Cardiac conditions
• Intracranial conditions

Congenital cause of QT Prolongation

The primary cause is mutations in the genes that code for the cardiac ion channels that cause ventricular repolarization.  Type 1 Long QT syndrome  and mutation of the potassium channel gene, KCNQ1. 

Eighty to ninety percent of QT prolongation is caused by three types of gene mutations: Long QT 2, KCNH2 gene mutation, Long QT 3, and SCN5A (Sodium channel) gene mutation.  Compared to sodium channel abnormalities (Long QT 3), potassium channel abnormality (Long QT 1 and long QT 2) is more prevalent.

Corrected QT – QTc

• Corrected QT prolongation
• In Males - QTc > 440 m sec
• Females - QTc> 460 msec 

Presentation 

The typical appearance of syncope is typically observed in childhood.  Long QT 2 –occurs secondary to auditory stimuli or mental distress; Long QT 1 –occurs with exertion; particularly when swimming.  Sudden cardiac death while you're sleeping; long QT3. 

Patients who are asymptomatic may be found via family screening.  If the patient has a family history of sudden cardiac death, advise them to get their genotyping checked. 

Treatment 

Nonselective beta blockers; propranolol; naprolol; In addition to beta blockers, the patient needs an ICD indication.  In cases of recurrent syncopal attacks, ICD is also recommended.  Steer clear of medications that lengthen QT. AAD class I, class III, erythromycin, antihistamines, antidepressants, TCA, and SSRI 

Electrolyte disturbances predisposing to QT prolongation

• K+ < 3.5
• Ca+ < 9 mg/dl
• Mg+ < 1.7 mg/ dl 
• Treatment - 1-2 mg of magnesium sulfate 

Endocrine causes of QT prolongation

Bradycardia is a complication of hypothyroidism that may increase the risk of QT prolongation. Overactive parathyroidism -  Hypercalcemia reduces potassium channel activity, which is necessary for repolarization. QT prolongation results from the delayed repolarization that occurs as a result. 

Phenochromocytoma - Distinguished by elevated catecholamine levels.
Potassium channel activity is decreased when norepinephrine levels are raised above physiological thresholds. QT prolongation results from the delayed repolarization that occurs as a result.  Syndrome Conn - The defining feature of it is hyperaldosteronism.

Cardiac causes of QT prolongation

• Myocardial ischemia
• Myocardial Infarction
• Myocarditis o viral etiology

Intracranial disorders causing QT prolongation.

Thalamic hematoma; CVA/head injury; subarachnoid hemorrhage.  Encephalitis: These illnesses cause an increase in intracranial pressure, which triggers the Cushing's response and causes bradycardia. QT prolongation is predisposed by bradycardia.

Nutritional Disorders Causing QT Prolongation

• Anorexia Nervosa - Avoids food out of fear of gaining weight.
• Small Intestine-related autoimmune disease; celiac disease.
• Small Intestine affected by JI bypass and gastroplasty.
• Starvation - Electrolyte abnormalities that predispose to QT prolongation can be caused by any of these disorders.

Drugs causing QT prolongation

• Mnemonic - A2BCD2E
• Antiarrhythmics 
  • Class III Antiarrhythmics
    • AMIODARONE
    • SOTALOL
    • DRONEDARONE
    • IBUTILIDE 
    • DOFETILIDE
  • Class I Antiarrhythmics
    • QUINIDINE 
    • DISOPYRAMIDE
    • PROPAFENONE
    • FLECAINIDE
• Antianginal 
  • RANOLAZINE
• Antibiotics 
  • FLUOROQUINOLONE 
  • MACROLIDES 
  • AMINOGLYCOSIDES 
• Antipsychotics
  • HALOPERIDOL 
  • QUETIAPINE
  • RISPERIDONE
• Antidepressants
  • SSRIs
  • TCAs
  • Diuretics
  • Hydrochlorothiazide or loop diuretics
  • Cause hypokalemia 
• Antiemetics
  • ONDANSETRON
• Antihistamine
  • Astemizole 
  • DIPHENHYDRAMINE 
  • HYDROXYZINE

2. Short QT Syndrome

 It may make PVT more likely. They're extremely uncommon.  QTc < 360 msec;  QTc < 300 msec in severe type. 

Etiology- Genetic defect leading to potassium channel increase of function. Treatment for arrhythmias related to polymorphic ventricle tachycardia, atrial fibrillation, sudden cardiac death, and anti-arrhythmic medications.

Provide shock and stop PVT;  SOTALOL;  AMIODARONE; ICD;  QUINIDINE - class I. Shifts in lifestyle, Steer clear of triggers.
Patients with a family history of sudden cardiac death are referred for genetic counseling. Other risk factors include caffeine, alcohol, and strenuous exercise.

3. Brugada Syndrome 

ECG shows that the sodium channel is impacted. It is a channelopathy.
V1 to V3 ST elevation > 0.2 mmol.  T wave inversion;  ST elevation shape: a curved pattern.  These patients may experience syncope episodes or cardiac arrest.  In patients with Brugada syndrome, structural heart disease is absent. Because of the SCN5A gene mutation, sodium cannot enter the cell. 

Various other disorders with ST segment elevation can be  

• STEMI
• LBBB
• Hyperkalemia
• Ventricular aneurysm
• Pericarditis
• ASVD - Arrhythmogenic Right Ventricular Dysplasia
• Brugada syndrome- Characteristic coved pattern of ST segment elevation 

Precipitating factors for Brugada syndrome

Increase of ST and T;  waxing and waning over time;  heightened waxing and waning in response to fever and acute illness.
Drugs that reveal brugada, the dispensing of medications that inhibit sodium channels-  Ajmaline; Procainamide; Flecainide.
Patients with Brugada may develop PVT, which increases the risk of cardiac arrest during sleep.  These medications also increase ST elevation.  Feverish sickness is the cause of cardiac arrest.  Men over women 
Mutation: found in the sodium channel, affecting more than 25% of patients.  SCN5A, a gene mutation, codes for sodium channel alpha.
Genes that encode potassium channels have other mutations.
The cardiac action potential can be changed by KCNE3, KCND3, sodium, and this type of potassium channelopathy, which increases the risk of arrhythmias and sudden cardiac death.

Treatment

Choice of treatment: ICD;  Indications- Unexplained syncope;  ECG demonstrating ST elevation. 

Antiarrhythmic medications: Epicardial right ventricular free wall; catheter ablation of aberrant areas; quinidine Ventricular tachycardia will be suppressed by catheter ablation of the epicardial right ventricular free wall.

4. Catecholaminergic ventricular tachycardia

Rare condition; two structures have undergone mutation.  Ryanodine receptors on the cardiac receptor  Less frequently, calsequestrin 2, a plasmoplasmic calcium binding protein.  The mutation will result in an abnormal increase in calcium sarcoplasmic influx..  Make one more prone to PVT.

Differential diagnosis of arrhythmia caused by elevated sarcoplasmic calcium. The toxicity of digoxin since it also raises calcium levels.  ECG - Bidirectional ventricular tachycardia, a distinctive alternating QRS shape, is present.  Features in clinical context,  Gifts from childhood.
Palpitations brought on by physical activity or emotional stress

Treatment

Non-selective beta blockers: NADALOL, PROPRANOLOL; For recurrent VT: CCBs; VERAPAMIL; FLECAINIDE – AADs. Surgical left cardiac sympathetic denervation should be planned.  It will lessen VT that recurs. The utility of ICDs in CPVT is debatable.  The ICD's shock could start a vicious loop.  Catecholamines are increased during shock, and this can lead to arrhythmia and death.

5. Hypertrophic cardiomyopathy

The condition is hereditary. Autosomal dominant inheritance is the type that the beta myosin gene is the most often mutated gene.  Rate: 1 out of 500.  It can potentially result in PVT-related abrupt cardiac death.
Sudden Cardiac Death typically occurs in people under 35, due to VF or PVT. Sustained monomorphic tachycardia is another possibility. The ventricular scar is the source. When a patient has an apical aneurysm, they most frequently present (in patients with apical hypertrophy).

SCD Risk Factors in HOCM

Under 35 years old, the existence of NSVT.  Failure of exercise-induced blood pressure rise;  Syncope history within the previous six months; Ventricular wall thickness greater than 3 mm;

Treatment- ICD in high-risk individuals. In CPVT, ICD is contraindicated. Release outflow obstruction; surgical myectomy; nonetheless, there is still a chance of septal ablation with alcohol
SCD still affects 1% to 5% of people. 

6.Genetic Dilated Cardiomyopathies 

Account between 30 and 40 percent of non-ischemic dilated cardiomyopathy; linked to muscular dystrophy. Becker's muscular dystrophy, Duchenne muscular dystrophy, and proximal muscle myopathy are medical conditions that can coexist.

The following conditions include: X-linked recessive; mitochondrial; gene mutation; coding for structural protein coding or nuclear lamina; LAMIN A/C; SCN5A; these genes encode proteins related to the heart's conducting system.  PVT resulting in cardiac arrest is one possibility for the patient.  Scar-related monomorphic tachycardia

ICD - recommended in patients with extended VT.  LV Ejection Fraction < 35% and heart failure in high-risk people.  A history of sudden cardiac death in the family. 

Hope you found this blog helpful for your NEET SS Medicine Cardiovascular Preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.