CardioDefender

According to the Joint Committee of the AHA/ACC (American Heart Association/American College of Cardiology) guidelines, anyone aged 40 years or older (approximately 42% of the US population) should have their heart rhythm evaluated.  In United States, India, and China alone there are ~849 million people eligible for ECG monitoring:

• ~129 million Americans over 40 years or older
• ~320 million Indians over 40 years or older
• ~400 million Chinese over 40 years or older

The first ECG a patient receives serves as a screening tool to detect any cardiac problems and as a baseline for comparison of future ECGs.

Guidelines issued by medical authorities around the world typically recommend ECG monitoring for all of the following patient categories.  A complete list of who should obtain an ECG, called Guidelines for ECG, is published by the Joint Committee of the AHA/ACC):

• To assess the response of patients to anti-arrhythmic treatment, e.g. the rate of atrial fibrillation, or pro-arrhythmic responses to drugs
• To assess the response of a patient to coronary artery bypass surgery or the function of a pacemaker device or implantable cardio-version device
• To assess patients with suspected variant angina.
• In the evaluation of patients with chest pain, who are unable to exercise
• In pre-operative assessment for vascular surgery
• In patients prior to discharge from hospital after a myocardial infarction
• In patients with congestive heart failure
• In patients with hypertrophic cardiomyopathy
• In patients with syncope, near syncope or recurrent dizziness
• In patients with recurrent palpitations
• In patients who have had a cerebrovascular accident in whom paroxysmal atrial fibrillation or atrial flutter is suspected
• In patients with episodic chest pain, shortness of breath or fatigue with no other obvious cause

The heart’s electrical system triggers the heartbeat.   An electrocardiogram, or ECG, is a non-invasive test that records the heart's electrical activity. With each heartbeat, an electrical signal spreads from the top of the heart to the bottom.   As it travels, the signal causes the heart to contract and pump blood. The process repeats with each new heartbeat.

The heart's electrical signals set the rhythm of the heartbeat. An ECG shows:

• How fast your heart is beating
• Whether the rhythm of your heartbeat is steady or irregular
• The strength and timing of electrical signals as they pass through each part of your heart

Doctors use ECGs to detect and study many heart problems, such as heart attacks, arrhythmias, and heart failure. The test's results also can suggest other disorders that affect heart function.

Each beat of the heart is represented on the electrocardiogram by a wave arm (or heart wave pattern), which appears on a computer screen and is recorded on an ECG report.  The normal heart rhythm (normal sinus rhythm) shows the electrical activity in the heart is following the normal pathway.   The normal electrocardiogram is characterized by the wave form.  Each of the individual segments of the wave is designated by a letter (or letters), and each represents a distinct phase of the cardiac cycle, illustrated below:

P wave. The P wave represents the electrical activity associated with the impulse generation at the SA node and its subsequent spread through the atria. When the P wave is of normal size and shape, it is assumed that the impulse began in the SA node. When P waves are absent or of abnormal size or shape, it is likely that the impulse originated outside the SA node.

PR interval. The period from the start of the P wave to the beginning of the QRS complex is called the PR interval. During this interval, which normally does not exceed 0.20 second, the impulse traverses the atria and the AV node. QRS complex. The QRS complex represents depolarization of the ventricular muscle, and consists of an initial downward deflection (Q wave), a large upward deflection (R wave), and a second downward deflection (S wave). Together these waves reflect the time necessary for the impulse to spread through the bundle of His and its branches to complete ventricular excitation. The duration of the QRS complex is normally less than 0.12 second. If the duration is increased, it is an indication of bundle branch block, a condition in which the ventricles are stimulated in a delayed, abnormal manner.

ST segment. The ST segment represents the period between the completion of depolarization and the beginning of repolarization of the ventricular musculature. The ST segment may be elevated or depressed by either ischemia or infarction.

T wave. The T wave represents the normal repolarization of ventricular myocardium that occurs after ventricular contraction. Tissue injury or ischemia may cause abnormal repolarization and inversion of the T wave. The EKG records the electrical impulses that stimulate the heart to contract and gives us a valuable permanent record of electrical cardiac activity during resting and recovery periods. The electrocardiogram is inscribed on a paper strip ruled in one-mm squares. The electrocardiograph plots millivolts ( ↕ vertical axis ) over seconds ( ↔ horizontal axis ). Each vertical space represents a voltage change of 0.1 (one-tenth) mv; the voltage between two of the heavy horizontal lines is 0.5 (one-half) mv. Each small square represents 0.04 (four-hundredths) of a second: the time interval between the heavy lines is 0.2 (two-tenths) seconds in duration. By measuring along the horizontal axis, we can determine the duration of any part of the cardiac cycle. depolarization repolarization.

As illustrated in the ECG below, the rhythm is regular and the node is normal (about 50 to 100 beats per minute).

Rate: 60-100 beats per minute.

Rhythm: Regular.

P wave: Normal contour and precedes each QRS complex.

PR interval: Normal and constant (0.12-0.20 sec.).

QRS complex: Normal and constant (0.06-0.10 sec.). The impulse originates in the SA node and travels through the AV node and ventricles in a normal fashion.

Examples of irregular fast and irregular slow heart rhythms:

Sinus Tachycardia:  As illustrated in the ECG below, the heart is experiencing a fast heart rhythm (greater than 100 beats per minute)

 

Rate: Above 100 beats per minute.

Rhythm: Regular.

P wave: Present and precedes each

QRS complex. In very rapid rates, the P wave may be difficult to identify if it is buried within the preceding T wave.

PR interval: Normal and constant.

QRS complex: Normal duration.

Interpretation: The impulse originates in the SA node and follows normal conduction pathways. Since the rate is above 100 beats per minute, this is a tachyarrhythmia. In most individuals, stress, excitement, or exercise increases heart rate. Problems arise when this increased rate places a burden on a damaged heart. The goal of treatment is to lower the rate using drug therapy.

Sinus Arrhythmia:

 

Rate: May vary, but usually slower than normal.

Rhythm: Irregular.

P wave: Normal contour and precedes each QRS complex.

PR interval: Normal.

Interpretation: This rhythm is benign and requires no medical treatment. Phasic increases and decreases in heart rate are usually associated with inspiration and expiration, and are most noticeable during sleep.

Sinus Bradycardia:

Slow heart rhythm (less than 60 beats per minute)

Rate: Below 60 beats per minute.

Rhythm: Regular. P wave: Normal contour and precedes each QRS complex.

PR interval: Normal and constant.

QRS complex: Normal and constant.

Interpretation: The impulse originates in the SA node and follows the normal conduction pathways. Since the rate is below 60 beats per minute, this is a bradyarrhythmia. No medical treatment is necessary unless the rate is extremely slow and the patient becomes symptomatic (e.g., dizziness, hypotension, fainting). If treatment is necessary to increase heart rate, atropine is the drug of choice.

Ventricular Tachycardia:

Rate: The ventricular rate is usually 120–200 beats per minute.

Rhythm: Regular or slightly irregular.

P wave: Usually obscured by QRS complexes, but may be inverted (opposite of sinus rhythm) and not associated with the ventricular rhythm.

PR interval: Not able to determine.

QRS complex: Widened beyond 0.12 second. It has a bizarre configuration, with the T wave usually opposite in direction to the QRS complex.

Interpretation:  Ventricular tachycardia is defined as a series of three or more consecutive ventricular complexes. It may last seconds, hours, or days. In most cases the rate is too fast to provide an adequate cardiac output. Mental confusion, convulsions, or unconsciousness will reflect a decreased blood flow and oxygen supply to the brain. Immediate treatment is necessary if any of these symptoms occur. DC cardioversion is the treatment of choice if the patient is hemodynamically unstable. Otherwise, intravenous lidocaine, procainamide, or bretylium can be used.

Some arrhythmias create symptoms which a patient can feel; others produce few if any symptoms which a patient will notice.  In order to correctly diagnose and treat an arrhythmia it is essential that the type of arrhythmia is identified; this requires the patient to receive a quantitative ECG data, the patient’s physician will analyze this data to help them determine the correct diagnosis and treatment.

However, it is impossible to predict when a heart arrhythmia will occur.    Once one has occurred it is equally difficult to predict when the arrhythmia will reoccur.  Hours, weeks or months may elapse between arrhythmia events.  It is only when these arrhythmia events occur that a physician can collect important heart rhythm data required for an accurate diagnoses and treatment.

Consequently, to meet these performance requirements, ECG equipment must have several important capabilities, including:

1. Real-time, heart rhythm monitoring
2. Beat-by-beat analysis of heart rhythm (as opposed to sampling some heart beats or part of a heart beat)
3. Ability to perform up to 3 months of real-time, beat-by-beat quantitative patient monitoring and analysis
4. Fully mobile, real-time, beat-by-beat, fully automated, quantitative ECG monitoring and arrhythmia event reporting (so that monitoring of the heart rhythm is not confined to the hospital setting)
5. Comprehensive range of heart rhythm monitoring algorithms to enable automated detection and reporting of medically important arrhythmias to physicians
6. Access to full, detailed ECG data captured during the monitoring period, including post heart monitoring data processing for additional measurements
7. Ability to capture and report both symptomatic and asymptomatic arrhythmias

As illustrated in the table below and subsequently explained in more detail, none of the legacy ECG systems meets all of the required performance capabilities:

Required ECG Capabilities Versus Legacy ECG System Performance

1. The sampling period of hospital based ECG systems is usually too short (typically limited to a few days) to allow capture of an infrequent (but potentially serious) arrhythmia.
2. Although the period of observation could in theory be extended, to do so is impractical and expensive.  Patients are also resistant to long term hospital based ECG monitoring.
3. Observation of patients on a telemetry unit in the hospital also has severe limitations, especially poor patient acceptance.
4. Because the time-window of monitoring the heart rhythm is typically confined to a few days, the physicians’ ability to accurately diagnose and treat an arrhythmia is severely constrained.

 

Hospital Based ECG Systems

  

1. Portable ECG recorders and Holter monitors enable monitoring outside the hospital but none provide real-time, beat-by-beat, quantitative heart rhythm monitoring of symptomatic and asymptomatic events.
2. Portable ECG recorders and Holter monitors are typically limited to less than 4 hours or 6 events of actual event recording time.   This provides a relative short window of ECG recording time.
3. When the heart rhythm data is being transmitted to the monitoring center the ECG recorder cannot record new and potentially important data.
4. The process which patients have to follow in order to transmit heart rhythm data to a monitoring center can be complex and time consuming.
5. Because the time-window of monitoring the heart rhythm with portable ECG recorders and Holter monitors is typically confined to a short period of time the physicians ability to accurately diagnose and treat an arrhythmia is severely constrained.