A Patient Is In Pulseless Ventricular Tachycardia. Two Shocks

Ventricular tachycardia (VT) is a rapid, life-threatening heart rhythm originating in the ventricles, the lower chambers of the heart. When VT is pulseless, meaning the heart is beating so rapidly and inefficiently that it doesn't produce a palpable pulse, it becomes a critical emergency requiring immediate intervention. Two shocks, delivered via defibrillation, represent a cornerstone of the treatment algorithm for pulseless VT. Understanding the underlying mechanisms, the procedural steps, and the rationale behind this approach is vital for healthcare professionals involved in resuscitation.

Understanding Pulseless Ventricular Tachycardia

Ventricular tachycardia occurs when the ventricles fire electrical impulses at an abnormally high rate, typically exceeding 100 beats per minute. This rapid firing disrupts the normal sequence of cardiac contractions, hindering the heart's ability to effectively pump blood to the body. Pulseless VT signifies that the heart's contractions are so disorganized and rapid that they are unable to generate sufficient cardiac output, leading to the absence of a detectable pulse.

Several factors can trigger VT, including:

• Ischemic Heart Disease: Coronary artery disease, leading to reduced blood flow to the heart muscle, is a primary culprit.
• Prior Myocardial Infarction: Scar tissue from a previous heart attack can create electrical instability, predisposing to VT.
• Cardiomyopathy: Diseases affecting the heart muscle, such as hypertrophic or dilated cardiomyopathy, can disrupt normal electrical conduction.
• Electrolyte Imbalances: Abnormal levels of electrolytes like potassium, magnesium, and calcium can destabilize the heart's electrical activity.
• Drug Toxicities: Certain medications, particularly those affecting the heart's electrical system, can trigger VT.
• Congenital Heart Conditions: Some individuals are born with structural heart defects that increase the risk of VT.

Pulseless VT rapidly leads to:

• Cessation of Blood Flow: The ineffective heart contractions fail to deliver oxygen and nutrients to vital organs.
• Loss of Consciousness: Reduced blood flow to the brain results in immediate loss of consciousness.
• Organ Damage: Prolonged lack of perfusion leads to irreversible damage to the brain, heart, kidneys, and other organs.
• Death: If not promptly treated, pulseless VT invariably progresses to cardiac arrest and death.

The Role of Defibrillation: Electrical Reset

Defibrillation is the delivery of a controlled electrical shock to the heart with the goal of terminating the abnormal electrical activity causing the pulseless VT. The shock momentarily depolarizes the entire myocardium, effectively "resetting" the heart's electrical system. This allows the heart's natural pacemaker, the sinoatrial (SA) node, to regain control and restore a more organized and effective rhythm.

The success of defibrillation hinges on several factors:

• Timely Delivery: The sooner the shock is delivered, the greater the chances of successful rhythm conversion.
• Appropriate Energy Level: Delivering sufficient energy is crucial to depolarize the entire myocardium.
• Proper Pad Placement: Correct placement of the defibrillator pads ensures that the electrical current passes through the heart.
• Good Skin Contact: Adequate contact between the pads and the patient's skin minimizes resistance and maximizes current delivery.

Two Shocks: The Protocol for Pulseless VT

The two-shock protocol for pulseless VT is a standardized approach outlined in advanced cardiac life support (ACLS) guidelines. It involves delivering an initial shock, followed by a second shock if the first is unsuccessful in restoring a perfusing rhythm. This strategy is based on extensive research and clinical experience, aiming to maximize the chances of successful defibrillation while minimizing delays in treatment.

Step-by-Step Procedure: Two Shocks for Pulseless VT

Here's a detailed breakdown of the steps involved in administering two shocks for pulseless VT:

1. Recognition and Activation:

   • Upon encountering a patient who is unresponsive, immediately assess for breathing and pulse.
   • If there is no pulse, recognize that the patient is in cardiac arrest.
   • Activate the emergency response system (call for help) and retrieve a defibrillator.

2. Initiate CPR:

   • Begin chest compressions at a rate of 100-120 compressions per minute, with a depth of at least 2 inches (5 cm) but no more than 2.4 inches (6 cm).
   • Ensure complete chest recoil after each compression.
   • Provide ventilations with a bag-valve-mask device, delivering 1 breath every 6 seconds (10 breaths per minute), without interrupting chest compressions.

3. Attach Defibrillator:

   • As soon as the defibrillator arrives, power it on and attach the defibrillator pads to the patient's chest.
   • The preferred pad placement is:
     • Anterolateral: One pad placed below the right clavicle and the other pad placed on the left lateral chest, with the center of the pad in the midaxillary line.
     • Anteroposterior: One pad placed on the anterior chest (over the heart) and the other pad placed on the posterior chest (between the scapulae).
   • Ensure good contact between the pads and the skin by applying firm pressure.

4. Analyze Rhythm:

   • Stop chest compressions briefly and allow the defibrillator to analyze the patient's heart rhythm.
   • If the defibrillator indicates "ventricular tachycardia" or "ventricular fibrillation" (which is treated identically to pulseless VT in this context), proceed to defibrillation.
   • Confirm that the rhythm is truly VT and not a false reading.

5. Deliver First Shock:

   • Ensure that no one is touching the patient or the bed.
   • Yell a clear warning, such as "Clear!"
   • Press the "shock" button on the defibrillator to deliver the first shock.
   • The energy level for the initial shock is typically:
     • Biphasic Defibrillator: 120-200 joules (as per manufacturer's recommendations).
     • Monophasic Defibrillator: 360 joules.

6. Immediately Resume CPR:

   • Do not delay! Immediately resume chest compressions, starting with compressions.
   • Continue CPR for 2 minutes (approximately 5 cycles of 30 compressions and 2 breaths).
   • Administer oxygen as available.

7. Rhythm Re-analysis:

   • After 2 minutes of CPR, stop compressions briefly and allow the defibrillator to re-analyze the rhythm.

8. Deliver Second Shock (If Needed):

   • If the rhythm remains ventricular tachycardia or ventricular fibrillation, prepare to deliver a second shock.
   • Ensure that no one is touching the patient or the bed.
   • Yell a clear warning, such as "Clear!"
   • Deliver the second shock at the same energy level as the first shock (or escalate if using a biphasic defibrillator with escalating energy).

9. Immediately Resume CPR (Again!):

   • Do not delay! Immediately resume chest compressions, starting with compressions.
   • Continue CPR for another 2 minutes.

10. Subsequent Management:

    • After the second shock and 2 minutes of CPR, re-analyze the rhythm.
    • If the rhythm remains ventricular tachycardia or ventricular fibrillation, continue alternating between CPR and defibrillation (increasing energy if indicated by the defibrillator) as per ACLS guidelines.
    • Administer medications as indicated by ACLS guidelines, such as epinephrine and amiodarone.
    • Search for and treat underlying causes of the VT (the "Hs and Ts").

The "Hs and Ts" of Cardiac Arrest:

During resuscitation, it's essential to consider and address reversible causes of cardiac arrest, often remembered by the mnemonic "Hs and Ts":

Hs:

• Hypovolemia: Low blood volume.
• Hypoxia: Low oxygen levels.
• Hydrogen ion (acidosis): Excess acid in the blood.
• Hypokalemia/Hyperkalemia: Low or high potassium levels.
• Hypothermia: Low body temperature.

Ts:

• Tension pneumothorax: Air trapped in the chest cavity, compressing the lungs and heart.
• Tamponade, cardiac: Fluid accumulation around the heart, restricting its ability to pump.
• Toxins: Drug overdose or poisoning.
• Thrombosis, coronary: Blood clot in a coronary artery (heart attack).
• Thrombosis, pulmonary: Blood clot in a pulmonary artery (pulmonary embolism).

Rationale Behind the Two-Shock Strategy

The two-shock protocol is based on the following principles:

• Increased Probability of Success: Delivering a second shock shortly after an unsuccessful first shock increases the overall likelihood of converting the VT to a perfusing rhythm.
• Minimizing Delay: Repeating the shock quickly avoids prolonged interruptions in chest compressions, which are crucial for maintaining blood flow to the brain and other vital organs.
• Standardized Approach: The standardized protocol ensures that all healthcare providers follow the same guidelines, promoting consistency and efficiency in treatment.
• Evidence-Based Practice: The two-shock protocol is supported by research demonstrating its effectiveness in improving survival rates in patients with pulseless VT.

Considerations and Potential Complications

While defibrillation is a life-saving intervention, it's essential to be aware of potential complications:

• Skin Burns: The electrical current can cause burns at the site of the defibrillator pads. Proper pad placement and good skin contact can minimize this risk.
• Myocardial Damage: In rare cases, the electrical shock can cause damage to the heart muscle.
• Arrhythmias: Defibrillation can sometimes induce other arrhythmias, although these are typically transient.
• Embolization: Dislodgement of existing blood clots.
• Equipment Malfunction: Always ensure equipment is tested and functioning.

Advanced Considerations: Escalating Energy and Alternative Strategies

While the two-shock protocol is the standard initial approach, advanced cardiac life support (ACLS) guidelines also address scenarios where the initial shocks are unsuccessful.

• Escalating Energy: With biphasic defibrillators, escalating the energy level for subsequent shocks may be considered. Follow the manufacturer's recommendations for energy escalation.
• Medications: After the initial two shocks, medications such as epinephrine and amiodarone are typically administered to improve the chances of successful defibrillation and prevent recurrence of VT.
• Underlying Cause: Always search for and treat underlying causes, such as electrolyte imbalances, ischemia, or drug toxicities.
• Refractory VT: In cases of refractory VT (VT that does not respond to multiple shocks and medications), alternative strategies such as anti-arrhythmic drug infusions or overdrive pacing may be considered. Consultation with a cardiologist or electrophysiologist is often necessary.

Conclusion

The two-shock protocol for pulseless ventricular tachycardia is a cornerstone of emergency cardiac care. By understanding the underlying principles, the procedural steps, and the importance of rapid and coordinated action, healthcare professionals can significantly improve the chances of survival for patients experiencing this life-threatening arrhythmia. Ongoing training and adherence to ACLS guidelines are essential for ensuring optimal patient outcomes. Remember that the key to success lies in early recognition, prompt intervention, and continuous reassessment throughout the resuscitation process.