VF and PVT: Care of the Patient with a Shockable Rhythm

Defibrillation

In most cardiac arrests, the first provider immediately starts CPR with chest compressions while the second provider retrieves the defibrillator, attaches its pads to the patient, and checks the rhythm.^[2] The pads are placed directly on the skin at the anterior-lateral aspects of the chest. 

Alternative positions include anterior-posterior, anterior-left infrascapular, and anterior-right infrascapular regions of the thorax.

Defibrillator pads are typically placed in the anterior-lateral aspects of the chest.

Related Video – One Quick Question: Should You Choose CPR or Defibrillation?

The recommended defibrillator designs are biphasic truncated exponential (BTE) and rectilinear biphasic (RLB). They have different peak currents at the same energy settings. The energy outputs adjust based on the amount of patient impedance. RLB waveform defibrillators deliver more energy than the selected dose because energy is based on patient impedance. A 120J dose delivers around 150J. 

Studies show BTE and RLB defibrillators are highly effective in converting shockable cardiac arrest rhythms.^[3] The energy setting for the first shock is based on the manufacturer’s settings. First shock success occurs when the rhythm terminates five seconds after shock delivery. The success rate is between 85% to 98% when the energy setting of both BTE and RLB is 200J or less.

Defibrillator Technologies

Rhythm-Based Management

Rhythm checks must be brief. Clinicians perform pulse and rhythm checks in 10 seconds or less. If the provider is not sure they can feel a pulse, they should immediately perform chest compressions.^[4]

Ventricular Fibrillation

During VF, multiple areas in the ventricles chaotically depolarize and repolarize, causing a loss of pumping action to the heart. The ECG shows signs of voltage fluctuations. Coarser waves represent high amplitude waves while fine waves represent smaller amplitude waves. 

In its early stages, VF has coarser amplitudes. Left untreated, these coarse waves transform into finer amplitude waves until the victim converts into asystole. 

The heart rate during VF is very rapid and chaotic. The QRS complex cannot be appreciated, and the P wave is absent.

An ECG tracing outlines a rapid, chaotic heart rate during ventricular fibrillation.

Related Video – ECG Rhythm Review – Ventricular Fibrillation

Read: Ultimate Guide to ACLS Algorithms: Cardiac Arrest

Pulseless Ventricular Tachycardia

During pVT, the heart rate is fast with a regular rhythm. The QRS complex is wide, and the P waves are absent. There are three or more beats of ventricular origin in a row. P waves are sometimes present, but it’s not related to the QRS complex. 

Clinicians have difficulty differentiating ventricular tachycardia from supraventricular tachycardia with aberrant conduction. When in doubt, clinicians should assume the patient is in ventricular tachycardia.

In pulseless ventricular tachycardia, heart contractions are rapid but ineffective to sustain life.

Related Video – ECG Rhythm Review – Polymorphic Ventricular Tachycardia (Torsades de Pointes)

Shocking the Patient

Once VF or pVT is confirmed (via AED or ECG monitor), providers deliver a shock. First, clinicians charge the device while continuing CPR. Once charged, it is imperative that providers ‘clear’ the patient. Clinicians ensure there are no personnel touching the patient, the gurney, or any equipment attached to the patient before delivering the shock. 

Immediately following the shock, providers perform high-quality CPR for two minutes before checking for a pulse. First shock success rates are high, though it depends on how long the patient has been down. 

If the first shock fails, providers administer another shock after two minutes of CPR, following the defibrillator manufacturer’s instructions for shock dosage. Studies show a peak current of 150J fixed BTE or RLB waveforms terminates persistent VF. There is no change in return of spontaneous circulation or survival to hospital discharge when a fixed dose is given versus an escalating dose.

If a provider uses a defibrillator that allows for energy dose adjustment, the provider may increase the dosage for the second and subsequent shocks.

The single shock strategy with continued CPR for 2 minutes after administering the shock is preferred over the stacked shock strategy.^[5]

Intravenous Access

Epinephrine and other antiarrhythmic medications facilitate a perfusing spontaneous rhythm.^[6] An intravenous cannula or intraosseous cannula can be used to rapidly deliver fluids and medications into the central circulation during CPR. 

Clinicians should consider inserting an intravenous cannula after providing the first shock while minimizing interruptions in chest compressions. If intravenous access is not feasible, clinicians use intraosseous access. The medullary sinusoids of long bones are resistant to collapse and more than adequate to deliver the medications to the central venous circulation. 

When clinicians decide to gain an IV/IO access, they must remember high-quality CPR supersedes defibrillation and defibrillation supersedes establishing IV/IO access.

Other Access for Cardiac Arrest Drugs

If intravenous or intraosseous access cannot be established, the next step is central venous catheterization. Central venous catheterization directly delivers the drug to the central circulation via the subclavian or internal jugular veins that extend inferiorly towards the superior vena cava. 

The central line is also a conduit for physiologic monitoring, such as central venous oxygen saturation and central pulse pressure to assess CPR quality. They’re also used to predict ROSC.

Related Video – Understanding the Post Cardiac Arrest Algorithm

Central line placement may cause a prolonged interruption in chest compressions. It is also a relative contraindication for fibrinolytic therapy if needed for ischemic stroke and acute coronary syndromes.

Absorption of drugs via an endotracheal tube is possible for naloxone, atropine, vasopressin, epinephrine, and lidocaine (remember NAVEL). No studies have determined the absorption efficacy of amiodarone.^[7]

Lower blood concentrations result via the endotracheal route compared to the intravenous route. This increases epinephrine’s beta-adrenergic effect and causes vasodilation, leading to hypotension and lower coronary pulse pressures and flow. It ultimately reduces the potential for ROSC. 

The dose of epinephrine administered via the endotracheal route must be 3–10 times the intravenous dose to achieve the same effect. It must be diluted in 5–10 mL of a sterile, normal saline solution and injected directly into the endotracheal tube.

Epinephrine

Epinephrine is an alpha-adrenergic drug that causes vasoconstriction. It increases coronary perfusion pressure and cerebral perfusion pressure during CPR and is administered at a dose of 1 mg IV/IO every 3–5 minutes during cardiac arrest.^[8] High doses of epinephrine may do more harm than good. At higher doses, it increases myocardial workload and decreases subendocardial perfusion. 

Providers must follow the bolus intravenous injection with a 20 mL flush of normal saline to facilitate the movement of the drug from the peripheral circulation to the central circulation. The provider elevates the extremity where the drug was administered, allowing gravity to assist in the drug’s delivery.

Related Video – Epinephrine – ACLS Drugs

Airway Management

All patients in need of CPR must be provided with positive pressure ventilations via a bag-mask device with supplemental oxygenation at 100% concentration. During the first few minutes of witnessed cardiac arrest, blood has an adequate concentration of arterial oxygen. Positive-pressure ventilation isn’t needed as much during this time, and chest compressions are more important to circulate oxygen.

A bag-mask device provides positive pressure ventilations.

When providing bag-mask ventilation, providers must make sure someone assists in opening the airway and producing a tight seal against the victim’s face to prevent air leaks during breath delivery. Mouth-to-mouth or mouth-to-mask ventilation is recommended for lone rescuers. Providers deliver about 600 mL with each breath. Visible chest rises connote adequate ventilation.

Related Video – Understanding Bag Valve Mask Usage During CPR

After the second shock, providers should consider advanced airway placement. Ventilations and chest compressions are important for victims who experience a prolonged cardiac arrest. Normal ventilation/perfusion relationships are maintained by providing positive-pressure ventilations while performing CPR. An advanced airway allows for asynchronous ventilations without interrupting chest compressions.

There’s no advantage to a bag-mask ventilation device versus an endotracheal tube. All providers must be proficient in providing positive pressure ventilations using a bag-mask device.

Refractory Ventricular Fibrillation and Pulseless Ventricular Tachycardia

After the third shock is administered, providers may administer Amiodarone. A 300 mg bolus is given for refractory ventricular fibrillation or pulseless ventricular tachycardia.^[9] A 20 mL saline flush helps facilitate the drug to the central circulation. If the first dose is ineffective after the next shock and 2-minute round of CPR, a second dose at 150 mg may be administered.

Outcome

If the patient recovers and achieves a return of spontaneous circulation, clinicians should proceed to post-cardiac arrest care.

 If the patient does not improve, providers should think about the possible reversible causes of cardiac arrest. They’re referred to as the Hs and Ts.

Prognostication During CPR

If a patient is intubated, providers measure the patient’s response to interventions by utilizing waveform capnography. The output is the end-tidal CO₂ measurement. End-tidal CO₂ is the partial pressure of exhaled CO₂ produced from gas exchange within the lungs’ alveoli, representing possible blood flow to the pulmonary vasculature as proof of good lung ventilation and perfusion.

Low end-tidal CO₂ (< 10 mm Hg) indicates CPR must be improved. It can also prognosticate a poor outcome if it remains low despite 20 minutes of high-quality CPR. Persistently low levels of CO₂ while providing CPR may indicate a problem with the equipment (such as a kinked endotracheal tube) or a physiologic disease such as tension pneumothorax.

Summary

There are different types of care for VF and pVT patients with shockable rhythms, including components of BLS, ACLS, and post-cardiac arrest care. Clinicians should perform CPR until it’s time to shock if they’re administering via manual defibrillator. Medication may be administered intravenously, intraosseously, through a central line, or through an endotracheal tube.