Explained: Sudden Cardiac Arrest: What Causes It And Why Everyone Should Know CPR?

In recent times, the untimely and sudden death of a few celebrities has made everyone very anxious and concerned about cardiac health. The question that is troubling everyone is - why such healthy and young individuals are dying suddenly. Is it a heart attack? Or sudden cardiac arrest? What should have been done to try and save them? let me explain…

Heart attack vs Cardiac Arrest - what is the difference?
Heart attacks are very common. Every one of us has known of individuals who have survived a heart attack. Heart attacks occur when one of the three tubes (coronary arteries ) that supply blood to the heart gets clogged, reducing the blood supply to a portion of the heart muscle. The sudden reduction in blood supply weakens the heart pump, which if not restored quickly (by way of angioplasty and stenting) can also be permanently damaged.

Most people survive a heart attack and with advances in medical therapy and easy availability of cardiac speciality hospitals less than 10 % of heart attack, victims succumb. Now, the first hour of the heart attack is called the ‘Golden hour”, because most deaths occur within this first hour.

When the blood to a portion of the heart is acutely reduced, the heart can sometimes become electrically unstable and start beating at alarmingly fast rates, a condition called ventricular tachycardia or fibrillation. This is a life-threatening condition that causes the heart to stop suddenly - ‘Sudden cardiac Arrest’ or SCA. Thankfully, SCA is not a very common complication of a heart attack and occurs in less than 2-5% of the cases.

Sudden cardiac arrest can occur even in the absence of a heart attack. There are several other conditions where the heart may be electrically unstable. These include certain Cardiomyopathies (where the muscle is weak despite a normal blood supply) and Channelopathies (a condition where the electrical system of the heart is unstable despite normal blood supply and healthy heart muscle) . Some of these conditions are hereditary. It is important to understand that not every heart attack results in a sudden cardiac arrest and that not every sudden cardiac arrest is secondary to a heart attack.

How to identify an SCA and What should be done immediately?
When the heart stops, none of the organs receives any oxygen or blood. The victim usually collapses to the ground and shows no signs of life, I.e, no breathing, no pulse and no response to commands or stimulation. Quick identification of a possible SCA is vital as it is imperative to restart the arrested heart as early as possible. Restarting within one minute will result in a 90% chance of survival. Unfortunately, the chance of survival reduces by 10% with every passing minute and hence there is a near zero percent chance of survival if it takes more than 10 mins to restart a heart. That explains why most of these unfortunate victims don’t even reach the hospital alive and the dismal survival rates of <5% -10% even in countries with the best health care infrastructure.

So, coming back to the question, what can you do to restart the arrested heart?

The answer is CPR or cardiopulmonary resuscitation. CPR is an attempt to temporarily support the cardio-respiratory function and thereby the circulation by way of chest compressions and mouth-mouth or mouth-nose respiration. CPR per se may not restart a heart but can buy time till medical help arrives or automated defibrillators are employed to shock and restore the rhythm.

Who all should know CPR?
In my opinion, CPR is the most essential ‘life skill’ that every citizen should know! Just like one learns to swim or drive, anyone can learn CPR. It is easier than learning to swim! And ideally must be made mandatory in schools and workplaces. Studies have shown that children as old as 9 years learn and retain CPR skills. Many hospitals do provide free training for the general public in basic life support. Bystander CPR provided outside the hospital by first responders on on-lookers is the only hope for a cardiac arrest victim. Any delay in starting bystander CPR will result in the certain death of the victim.

Strengthening the “ Chain of Survival “ in SCA- The Rochester, Minnesota Model
Bystander CPR, rapid access to automated defibrillators and early access to emergency medical care are the three pillars that constitute the “Chain of Survival” in SCA. Interestingly, community participation in this “chain of survival” markedly improves the chances of survival in SCA. Rochester in Minnesota, USA has very high survival rates for out-of-hospital cardiac arrest victims when compared to the national average (40% vs < 9%). The credit goes to the relentless CPR training program where Police Personnel and other common public are trained in CPR and defibrillation and act as first responders in any Cardiac arrest. Bystander CPR and Early defibrillation when performed by the general public can drastically improve survival rates in SCA and is our only hope! A dedicated program similar to the Rochester program is the need of the hour in our country.

Implantable defibrillators and the SCA survivor -
Fortunate few who survive an SCA are usually implanted with a defibrillator. ICD or defibrillator is a small pacemaker-like device that is implanted beneath the left collar bone by way of a small operation that generally lasts less than an hour. The defibrillator once implanted monitors every heartbeat and in the event of any life-threatening rhythm will deliver a shock and save a life. ICD or defibrillator is the only proven therapy for preventing SCA in high-risk individuals or those who have already survived one cardiac arrest but are at risk of recurrence.

Identifying “High risk” individuals-

Although the most common cause of an SCA is a heart attack, unfortunately at present we are unable to predict the 2% who will succumb to an SCA. Certain other groups of heart patients can be screened, risk-stratified and prevented from developing an SCA. These include-

Patients with very low ejection fraction (EF). EF is the pumping capacity of the heart that is commonly assessed by an Echocardiogram. Damaged hearts which are very weak ( EF <35%) are traditionally said to be at a slightly higher risk of SCA and need to be risk stratified for further preventive intervention.

Those with cardiomyopathy or channelopathy and a family history of sudden cardiac arrest. SCA in one or more members of a family warrants screening of the family for any genetic condition that may predispose to SCA.

Since the survival chances of an SCA victim are dismal, screening for high-risk individuals is extremely vital. These high-risk individuals are risk stratified and then implanted with a prophylactic defibrillator if deemed suitable.

About the author: Dr Maneesh Rai is a Cardiac Electrophysiologist at KMC Hospital, Dr B R Ambedkar Circle, Mangalore. All views/opinions expressed in the article are of the author.