Needs. We all have them. Some needs are more important than others. Some are required all the time and some needs are only necessary part of the time. In fact, we might consider some of our needs to be time-dependent, meaning there is a right time and place for them. We need to breathe. But while swimming underwater, if we attempt to meet that particular need, there can be disastrous results. In this circumstance, before our need is met, we must first find oxygen by reaching the surface to take in a breath. The same holds true for matters of the heart. Some needs are time-dependent, especially when it comes to the treatment of Sudden Cardiac Arrest in the presence of ventricular fibrillation.
The Three Shades
Ventricular fibrillation (VF) is often taught as a single rhythm in the cardiac range of electrical conduction. Some might even break VF down into two types: “coarse” ventricular fibrillation or “fine” ventricular fibrillation. Beginning in 2002, studies began to show that VF can actually be broken down into three distinct, time-dependent “phases.” These phases are named according to the highest priority treatment needed based on the current time frame. The three “shades,” or phases, of ventricular fibrillation are:
- Phase I: The Electrical Phase
- Phase 2: The Circulatory Phase
- Phase 3: The Metabolic Phase
The ability to understand these phases and recognize them prior to treatment is important in improving the survival rate for victims of cardiac arrest.
Phase 1: The Electrical Phase – 0 to 4 minutes post cardiac arrest
During the first 4 minutes of ventricular fibrillation, the highest priority for resuscitation is the delivery of a defibrillation shock. At this point, the cells in the heart are functioning and contain enough oxygen to properly produce and transmit electrical energy. The problem here is that there is no organization to the transmittal of this energy. All of the heart’s pacemakers are firing at will, causing the heart to fibrillate or quiver instead of contract. In essence, there are too many leaders and not enough followers. What is needed is one pacemaker to electrically “subdue” all the others so they will start following orders instead of giving orders.
Imagine a bar fight in the Old West. When the Sheriff quickly arrives, he witnesses a scene of disorder and chaos, the result of which is certainly death or damage in the least. What does the Sheriff do? He takes out his service revolver, points it in the air and fires a single shot. Ideally, the shock from this action is enough to garner the immediate attention of each of the offending patrons so that order can be resumed. This is, in essence, what is needed during the Electrical Phase of VF. A defibrillation shock provided externally or internally within the first four minutes has the greatest chance of subduing the many offending pacemakers and restoring order to a chaotic heart. Many studies have been performed with defibrillation shocks occurring at varying points in the timeline of VF. The result of these studies shows us that for each minute that passes there is a 10% less chance of successful defibrillation. If VF is allowed to persist longer than four minutes, we then enter the second phase.
Phase 2: The Circulatory Phase – 4 to 10 minutes post cardiac arrest
From about four minutes to 10 minutes past the onset of VF, the greatest need is reperfusion of cardiac tissue by performing CPR, specifically effective chest compressions. At this point on the timeline, the cells in the tissues are still sending electrical signals, but due to a lack of oxygen-carrying blood flow they are becoming weak and unstable. It’s important to note that the average national EMS response time is eight to 10 minutes, meaning this is the phase that EMS providers are most likely to encounter upon arrival. Many EMS protocols have pushed for an immediate defibrillation shock, or “shock first,” upon arrival and this has actually had adverse results.
“CPR First” vs. “Shock First”
When AEDs were first introduced to EMS personnel in Seattle, Washington, the expectation was that the survival rate of cardiac arrest would increase. In fact, the opposite was true. A study revealed that when EMS arrived on scene during the Circulatory Phase of VF and provided an immediate defibrillation shock, the most likely result was the VF terminating into pulseless electrical activity or asystole. It wasn’t until these providers were directed to perform two minutes of CPR prior to delivering a shock, or “CPR first,” that survival rates began to improve. By providing one to three minutes of high quality CPR during the Circulatory Phase, providers are strengthening the cellular stability of the heart and moving the patient from Phase 2 into Phase 1 where the heart is healthy enough to respond to the shock in a positive manner. If the heart continues to fibrillate beyond about 10 minutes, the patient will enter Phase 3, which is the least understood phase.
Phase 3: The Metabolic Phase – 10+ minutes post cardiac arrest
Around the 10 minute mark, cellular ischemia, or lack of oxygen, begins turning into cellular death. At this point, increasing circulation has little effect, and according to some reports, may have adverse effects. The current therapies for the Metabolic Phase focus on limiting cellular damage and appropriately timed reperfusion of oxygenated blood flow. Some of the therapies being studied are:
- Induction of hypothermia to slow metabolic damage
- Extracorporeal Membrane Oxygenation (ECMO), also known as cardiac bypass
- Filtering of toxins in the blood during use of ECMO
- Use of vasopressors to increase coronary perfusion pressures
Meet the Right Needs at the Right Time
The ability to recognize that the treatment for ventricular fibrillation should be catered to the time-sensitive nature of the heart tissues is of the utmost importance. Time after time, studies show that a well-meaning provider, performing a treatment that is appropriate for a different phase of VF can produce unintended and, in some cases, life threatening results. Emergency Cardiovascular Care education should emphasize that if bystanders witness cardiac arrest, the immediate treatment should be “shock first,” and then provide CPR. EMS personnel should be reminded that they are most likely going to arrive within the Circulatory Phase of VF and need to provide “CPR first” to move the patient into the Electrical Phase where shocking is much more likely to successfully defibrillate the heart and return an organized, blood-pumping rhythm.