Sunday, March 16, 2014

An in-depth analysis of Rich Peverley's heart condition: What is atrial fibrillation and what does it mean for Peverley's hockey career?

Rich Peverley was a part of the huge Boston Bruins - Dallas Stars trade this past summer that sent Tyler Seguin to Dallas and Loui Eriksson and Reilly Smith to Boston (among other pieces). Peverley only missed one game last season and the Stars were happy to add the veteran to their otherwise young forward core.

DIAGNOSING ATRIAL FIBRILLATION 

As part of regular preseason testing, Peverley had an electrocardiogram (ECG/EKG), a simple test that records the heart's electrical activity. Unfortunately, Peverley's EKG was abnormal, showing that the player had atrial fibrillation (afib) - the most common cardiac arrhythmia (heart rhythm disorder/irregular heartbeat), present in about 5 million Americans.

EKG showing atrial fibrillation (top) compared with a normal sinus rhythm (bottom).
The bottom purple arrow shows a P wave (represent depolarization of the atria), which are absent in afib EKGs.
As described in the caption above, atrial fibrillation can be detected by certain abnormal characteristics on an EKG. One of the most common findings is the absence of P waves, which represent depolarization of the atria. Instead of a regular P wave, the EKG shows disorganized electrical activity before the Q wave and the large R waves. Another characteristic of afib is irregular R-R intervals, caused by an irregular conduction of impulses to the ventricles. The R-R interval on a EKG is shown below.


WHAT IS ATRIAL FIBRILLATION? 

To understand afib, you need to understand the heart's anatomy and electrical system. Your heart has four chambers - two atria (top) and two ventricles (bottom). The atria are small pumps that act as a primer, pushing blood into the ventricles which then pumps the blood out to the rest of the body. The electrical system is what causes the myocardium (muscle of the heart) to be stimulated and cause contraction in the chambers. 

The heart's electrical system controls the rate and rhythm of the heartbeat. With each heartbeat, an electrical signal spreads from the top of the heart in the atria to the bottom, causing the heart to contract and pump blood. In normal hearts, the electrical signal begins in the sinus node (or sinoatrial - SA node) which is located in the right atrium. The signal travels through the right and left atria, causing the atria to contract and pump blood into the ventricles, then moving to the atrioventricular (AV) node and slowing down slightly to allow the ventricles to fill up with blood. After the electrical signal leaves the AV node and travels down to the ventricles, causing them to contract and pump blood to the lungs and the rest of the body. This process is shown in the gifs below: 
A normal sinus rhythm
In atrial fibrillation, the electrical system is flawed. The signal doesn't begin in the SA node but rather at a different part of the atria or in several parts of the atria. The signals can clash and cause different impulses and don't travel normally, spreading throughout the atria in a rapid and disorganized manner. This causes the atria to fibrillate (quiver) and and the atria/ventricles to no longer beat in a coordinated way as the ventricles don't completely fill with blood.
Haywire electrical signals that occur during atrial fibrillation
As the electrical signal passes to the ventricles, they can beat too quickly (rapid ventricle response tachycardia) and the ventricle is pumping without completely filling with blood. With the heart beating so fast beyond normal range (tachycardia) and not pumping enough blood to the rest of the body, you become dizzy and nauseous. Eventually your blood pressure drops rapidly (hypotension) , your brain and muscles aren't receiving as much oxygen as they should, and you can pass out/collapse (syncope). 

Additionally, Afib increases the likelihood of a stroke because blood clots can form while swirling around the atria and not properly flowing through to the ventricles. 

TREATING ATRIAL FIBRILLATION 

Normally, afib resolves on it's own and the heart is able to reset and start pumping blood normally. Afib is fairly common and generally not life-threatening. The condition can be controlled with medications, starting with blood-thinners to prevent clots. It's highly unlikely Peverley was on an intense blood thinner such as warfarin but could have been taking low doses of aspirin. Doctors can also prescribe medications which can help control heart rate, such as beta blockers and calcium channel blockers. However, even with these medications, Peverley (as an NHL athlete) still faced huge risks due to the intense nature of the game which requires short bursts of activity.

Afib can also be treated with a procedure known as a cardiac ablation. Peverley had an ablation earlier during the preseason, however, even following a successful ablation, almost a 1/3 of patients will have recurring symptoms. An ablation is a procedure where a catheter is threaded up into the heart through vessels in the leg and to the problem location of the heart.  Once the catheter is in place, electrodes on the end measure the electrical activity (detect an arrhythmia), detect the problem area, and they are then ablated either using radiofrequency pulses (which burn the area) or through cryoablation (freezes).

UPDATE: Peverley apparently did not undergo an ablation this past preseason. Peverley underwent a cardioversion procedure. There are two forms of cardioversion; synchronized electrical cardioversion and pharmacologic (chemical) cardioversion. Synchronized electrical cardioversion uses two electrode pads to deliver a therapeutic reversion shock that is timed at a certain point in the cardiac cycle (synchronization). This differs from defibrillation which is supposed to re-start the rhythm of the heart. Pharmacological cardioversion uses agents such as sodium channel blockers, beta blockers and calcium channel blockers to stabilize the heart (rhythm control).

WHAT HAPPENED ON MARCH 10TH? 

Not even halfway through the first period, Peverley finished a shift and collapsed suddenly on the Stars bench. In a chaotic scene, the Stars players were frantic to get the refs attention and stop the game. The trainers and medical staff immediately picked Peverley up and hustled him down the tunnel. Information was very limited and the press, announcers and fans were confused as to what just happened.
Amazing, no? The Stars then released this bit of information:
And everyone started worrying. Eventually, people connected the dots that Peverley had missed the preseason due to his afib, and even missed a game last week due to "feeling strange," a possible recurrence of his condition.

The following day, Dr. Gil Salazar (emergency physician) from UT Southwestern released a statement with the Stars explaining the situation and what the medical staff did with Peverley:
"We provided oxygen for him. We started an IV. We did chest compressions on him and defibrillated him, provided some electricity to bring a rhythm back to his heart, and that was successful with one attempt, which is very reassuring."
So, within a matter of minutes, Peverley got almost instantaneous CPR and a shock from an automated external defibrillator (AED). The fact that he needed to be shocked means his arrhythmia turns from a fib into vfib. It's excellent news that Peverley was conscious and talking after just one shock which probably re-started his normal heart rhythm.

Peverley will undergo a battery of tests including another EKG and probably an echocardiogram. It was revealed that Peverley now has a device that can detect his heart rhythm and deliver a shock if necessary.
This device is probably an implantable cadioverter defibrillator, which uses electrical pulses or shocks to help control life-threatening arrhythmias. The ICD has wires with electrodes that connect to the heart chambers and has the ability to detect an abnormal rhythm. ICDs aren't the same as pacemakers which can only give low-energy electrical pulses to correct certain irregular heartbeats. ICDs can give high-energy pulses which are needed to correct dangerous arrhythmias in the ventricles. The image below displays the difference:

UPDATE: Peverley hasn't had an ICD implanted yet, nor has he had an ablation. It's likely that the procedure he'll undergo in Cleveland will be an ablation or another cardioversion.It's unlikely Peverley will get an ICD since it would be nearly impossible to play in the future with one (getting hit would dislodge the leads). 

 Two days after the chaotic event, the Stars announced that Peverley is out for the season and will undergo a procedure on his heart and pursue other treatments.
It's probably best that Peverley isn't playing. He'll probably undergo an ablation. Another surgical option is the maze surgery, an open-heart surgery that is usually only done if absolutely necessary (such as for heart valve disease). During this procedure, the surgeon makes small cuts and burns in the atria to prevent the spread of disorganized electrical signals. Considering Peverley's condition (NHL athlete) it's very unlikely he'll undergo this procedure.

It's unclear what this means for the rest of his career. Everyone in the NHL wishes Pevs the best in this scary situation and we're glad he's doing well.