ECG rate and rhythm

64,905views

test

00:00 / 00:00

ECG rate and rhythm

Back to the Basic Sciences

Core acute presentations

Anatomy of the abdominal viscera: Kidneys, ureters and suprarenal glands
Kidney histology
Renal system anatomy and physiology
Renal failure: Pathology review
Anatomy clinical correlates: Anterior and posterior abdominal wall
Anatomy clinical correlates: Inguinal region
Anatomy clinical correlates: Peritoneum and diaphragm
Anatomy clinical correlates: Viscera of the gastrointestinal tract
Anatomy clinical correlates: Other abdominal organs
Appendicitis: Pathology review
Complications during pregnancy: Pathology review
Diverticular disease: Pathology review
Gallbladder disorders: Pathology review
GERD, peptic ulcers, gastritis, and stomach cancer: Pathology review
Inflammatory bowel disease: Pathology review
Mood disorders: Pathology review
Pancreatitis: Pathology review
Anatomy clinical correlates: Female pelvis and perineum
Cervical cancer: Pathology review
Complications during pregnancy: Pathology review
Uterine disorders: Pathology review
Extrinsic hemolytic normocytic anemia: Pathology review
Intrinsic hemolytic normocytic anemia: Pathology review
Macrocytic anemia: Pathology review
Microcytic anemia: Pathology review
Non-hemolytic normocytic anemia: Pathology review
Anatomy clinical correlates: Heart
Anatomy clinical correlates: Mediastinum
Anatomy clinical correlates: Pleura and lungs
Anatomy clinical correlates: Thoracic wall
Aortic dissections and aneurysms: Pathology review
Coronary artery disease: Pathology review
Deep vein thrombosis and pulmonary embolism: Pathology review
GERD, peptic ulcers, gastritis, and stomach cancer: Pathology review
Pleural effusion, pneumothorax, hemothorax and atelectasis: Pathology review
ECG cardiac infarction and ischemia
Pigmentation skin disorders: Pathology review
Skin cancer: Pathology review
Papulosquamous and inflammatory skin disorders: Pathology review
Anatomy of the abdominal viscera: Esophagus and stomach
Anatomy of the abdominal viscera: Large intestine
Anatomy of the abdominal viscera: Small intestine
Anatomy of the gastrointestinal organs of the pelvis and perineum
Gastrointestinal system anatomy and physiology
Enteric nervous system
Colorectal polyps and cancer: Pathology review
Diverticular disease: Pathology review
Laxatives and cathartics
Anatomy clinical correlates: Pleura and lungs
Anatomy clinical correlates: Thoracic wall
GERD, peptic ulcers, gastritis, and stomach cancer: Pathology review
Lung cancer and mesothelioma: Pathology review
Nasal, oral and pharyngeal diseases: Pathology review
Obstructive lung diseases: Pathology review
Pneumonia: Pathology review
Tuberculosis: Pathology review
Amnesia, dissociative disorders and delirium: Pathology review
Cerebral vascular disease: Pathology review
Dementia: Pathology review
Electrolyte disturbances: Pathology review
Mood disorders: Pathology review
Hypothyroidism: Pathology review
Mood disorders: Pathology review
Anatomy of the abdominal viscera: Large intestine
Anatomy of the abdominal viscera: Small intestine
Anatomy of the gastrointestinal organs of the pelvis and perineum
Bile secretion and enterohepatic circulation
Enteric nervous system
Gastrointestinal system anatomy and physiology
Inflammatory bowel disease: Pathology review
Malabsorption syndromes: Pathology review
Bacillus cereus (Food poisoning)
Campylobacter jejuni
Clostridium difficile (Pseudomembranous colitis)
Clostridium perfringens
Escherichia coli
Norovirus
Salmonella (non-typhoidal)
Shigella
Staphylococcus aureus
Vibrio cholerae (Cholera)
Yersinia enterocolitica
Anatomy clinical correlates: Facial (CN VII) and vestibulocochlear (CN VIII) nerves
Cardiomyopathies: Pathology review
Cerebral vascular disease: Pathology review
Heart blocks: Pathology review
Supraventricular arrhythmias: Pathology review
Valvular heart disease: Pathology review
Ventricular arrhythmias: Pathology review
Vertigo: Pathology review
ECG axis
ECG cardiac hypertrophy and enlargement
ECG intervals
ECG normal sinus rhythm
ECG QRS transition
ECG rate and rhythm
Kidney stones: Pathology review
Sexually transmitted infections: Vaginitis and cervicitis: Pathology review
Sexually transmitted infections: Warts and ulcers: Pathology review
Urinary tract infections: Pathology review
Central nervous system infections: Pathology review
Nasal, oral and pharyngeal diseases: Pathology review
Pneumonia: Pathology review
Shock: Pathology review
Urinary tract infections: Pathology review
Anatomy clinical correlates: Anterior blood supply to the brain
Anatomy clinical correlates: Temporal regions, oral cavity and nose
Central nervous system infections: Pathology review
Cerebral vascular disease: Pathology review
Headaches: Pathology review
Traumatic brain injury: Pathology review
Vasculitis: Pathology review
Anatomy clinical correlates: Arm, elbow and forearm
Anatomy clinical correlates: Axilla
Anatomy clinical correlates: Bones, fascia and muscles of the neck
Anatomy clinical correlates: Bones, joints and muscles of the back
Anatomy clinical correlates: Clavicle and shoulder
Anatomy clinical correlates: Foot
Anatomy clinical correlates: Hip, gluteal region and thigh
Anatomy clinical correlates: Knee
Anatomy clinical correlates: Leg and ankle
Anatomy clinical correlates: Median, ulnar and radial nerves
Anatomy clinical correlates: Wrist and hand
Seronegative and septic arthritis: Pathology review
Apnea, hypoventilation and pulmonary hypertension: Pathology review
Deep vein thrombosis and pulmonary embolism: Pathology review
Heart failure: Pathology review
Nephrotic syndromes: Pathology review
Renal failure: Pathology review
Anatomy clinical correlates: Anterior and posterior abdominal wall
Anatomy clinical correlates: Bones, joints and muscles of the back
Anatomy clinical correlates: Vertebral canal
Aortic dissections and aneurysms: Pathology review
Back pain: Pathology review
Anatomy clinical correlates: Inguinal region
Anatomy clinical correlates: Male pelvis and perineum
Penile conditions: Pathology review
Prostate disorders and cancer: Pathology review
Testicular and scrotal conditions: Pathology review
Testicular tumors: Pathology review
Complications during pregnancy: Pathology review
Anatomy clinical correlates: Eye
Eye conditions: Inflammation, infections and trauma: Pathology review
Eye conditions: Refractive errors, lens disorders and glaucoma: Pathology review
Eye conditions: Retinal disorders: Pathology review
Anatomy clinical correlates: Pleura and lungs
Coronary artery disease: Pathology review
Obstructive lung diseases: Pathology review
Pleural effusion, pneumothorax, hemothorax and atelectasis: Pathology review
Bronchodilators: Beta 2-agonists and muscarinic antagonists
Bronchodilators: Leukotriene antagonists and methylxanthines
Pulmonary corticosteroids and mast cell inhibitors
Anatomy clinical correlates: Ear
Anatomy clinical correlates: Temporal regions, oral cavity and nose
Nasal, oral and pharyngeal diseases: Pathology review
Sexually transmitted infections: Vaginitis and cervicitis: Pathology review
Vaginal and vulvar disorders: Pathology review

Assessments

Flashcards

0 / 11 complete

USMLE® Step 1 questions

0 / 1 complete

High Yield Notes

8 pages

Flashcards

ECG rate and rhythm

0 of 11 complete

Questions

USMLE® Step 1 style questions USMLE

0 of 1 complete

A 55-year-old man comes to the emergency department for evaluation of intermittent palpitations. He denies any episodes of syncope, chest pain, shortness of breath, or vomiting. Past medical history is significant for hypertension. An electrocardiogram (ECG) is performed which is shown. Which of the following is the most likely cause of observed findings in this patient’s ECG?  
 
Reproduced from: Osmosis notes

Transcript

Watch video only

An electrocardiogram - an ECG - or the dutch and german version of the word - elektrokardiogram or EKG, is a tool used to visualize “gram” the electricity “electro” that flows through the heart “cardio”.

An ECG tracing specifically shows how the depolarization wave moves during each heartbeat - which is a wave of positive charge - looks from the perspective of different sets of electrodes.

This particular set of electrodes is called lead II, with one electrode on the right arm and the other on the left leg, so essentially when the wave’s moving toward the left leg electrode, you get a positive deflection, like this big positive deflection correspond to the wave moving down the septum.

To read an ECG there are a few key elements to keep in mind, one of them includes figuring out the rate and rhythm. There are a couple ways of figuring out the heart rate on an ECG.

The first one is called the “box method” because you count the number of boxes between heartbeats. Each small box represents 0.04 seconds, and each big box is five small boxes, so each big box is 0.2 seconds.

To do that, you can count the number of small boxes between R waves since R waves are tall and pointy and easy to see in lead 2 of an ECG strip.

You can find an R wave that has a peak that falls at the beginning of a box, and then count up how many boxes until the same point on the next R wave.

Let’s say that there are 4 big boxes and 1.5 small boxes between two R waves, meaning there are 4 x 5 + 1.5 = 21.5 small boxes, and that means there’s 0.04 seconds x 21.5 or .86 seconds between heartbeats.

Now, to get something a little more meaningful we can take the inverse which is 1 over 0.86 beats per second, or 1.16 beats per second.

Now there’re 60 seconds in a minute, so multiplying that by 60 we end up with 70 beats per minute—the heart rate!

Now, if the distance between two R waves is exactly 1 big box, then the heart rate would be 300 beats per minute—really fast. If R waves are two big boxes apart or 0.4 seconds apart, then the heart rate is 150 beats per minute.

Three big boxes apart is 100 beats per minute, four, five, and six big boxes apart is 75, 60, and 50 beats per minute respectively.

Remembering these numbers makes it easier to make a rough estimate. For example, if there are three to four large boxes between R waves, then the heart rate must be between 75 and 100 beats per minute.

Another method to determine the heart rate is to count the number of beats in ten seconds, which is the standard length of time on the rhythm strip portion of a 12-lead ECG.

So in this case we’ve got 15. All you’ve gotta do is multiply this by 6 to get the heart rate, which would be 90 beats per minute.

The reason this little trick works is that you’ve got 15 beats per 10 seconds, and again to convert to per minute you multiply by 60 seconds in a minute. Looking at this we see that 60 / 10 equals 6 per minute. So 6 times 15 is 90 beats per minute.

If the heart rate is too slow or too fast, it could be because something other than the SA node is pacing the heart rate.

For example, there could be atrial flutter which is when an ectopic focus in the atria - like an irritated atrial cell - starts to spontaneously fire between 250-350 depolarizations per minute, with only one out of every few atrial depolarizations passes through to the ventricles *B*.

To calculate the atrial rate, you can use the same methods as before, except you look at P waves instead of R waves.

Summary

The heart is a muscle that regularly beats to pump blood throughout the body. An electrocardiogram (ECG) is a test that records the electrical activity of the heart, which shows how fast and strong the heartbeats are.

The heart rate refers to the number of contractions of the heart per minute. This one can vary according to an individual's age, but usually, the normal heart rate for adults falls between 60 and 100 beats per minute. The rhythm refers to the pattern of electrical impulses that cause the heartbeat. The normal cardiac rhythm is a regular sinus rhythm, which means that each heartbeat follows a predictable pattern. There may be abnormal rhythms, such as atrial fibrillation and ventricular fibrillation, both serious and life-threatening conditions.

Sources

  1. "Medical Physiology" Elsevier (2016)
  2. "Physiology" Elsevier (2017)
  3. "Human Anatomy & Physiology" Pearson (2017)
  4. "Principles of Anatomy and Physiology" Wiley (2014)
  5. "Inappropriate sinus node tachycardia following gastric transposition surgery in children" Pediatric Surgery International (2005)
  6. "The ECG" (2004)