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Related Concept Videos

Cardiac Cycle01:29

Cardiac Cycle

The cardiac cycle refers to the sequence of events that occur in the heart from the beginning of one heartbeat to the next. It's characterized by alternating periods of contraction (systole) and relaxation (diastole) of the heart muscles.
During the cardiac cycle, blood flow through the heart is regulated entirely by changing pressure gradients. This sequence of events begins with the heart in a state of total relaxation, known as mid-to-late diastole, during which blood passively flows from...
The Cardiac Cycle01:13

The Cardiac Cycle

The heart beats rhythmically in a sequence called the cardiac cycle—a rapid coordination of contraction (systole) and relaxation (diastole).
The Process
Electrical signals—sent from the sinoatrial (SA) node in the right atrial wall to the atrioventricular (AV) node between the right atrium and right ventricle—cause both atria to simultaneously contract. When the signal reaches the AV node, it pauses for approximately a tenth of a second, allowing the atria to contract and empty blood into the...
Physiology of the Heart: The Cardiac Cycle01:18

Physiology of the Heart: The Cardiac Cycle

The cardiac cycle describes the events from one heartbeat to the next. It includes three main phases: diastole, atrial systole, and ventricular systole, all driven by changes in chamber pressures and the function of heart valves.
Diastole: The Relaxation Phase
During diastole, all four heart chambers relax. The atrioventricular (AV) valves open, and the semilunar valves close. This phase sees the lowest chamber pressures, promoting ventricular filling. Venous blood enters the heart through the...
Specialized Characteristics of Cardiac Muscles01:27

Specialized Characteristics of Cardiac Muscles

The primary role of cardiac muscles is to propel blood throughout the cardiovascular system. The cardiac muscle cells, or cardiomyocytes, exhibit specialized characteristics that allow them to perform this function.
Cardiac muscle cells are smaller than skeletal muscles, averaging 10–20 mm in diameter and 50–100 mm in length. However, they have large energy demands for continuous contraction and relaxation. This energy is almost exclusively derived from aerobic metabolism of energy reserves in...
Pathophysiology of Cardiac Performance01:29

Pathophysiology of Cardiac Performance

Typical heart performance is influenced by heart rate, rhythm, myocardial contraction, and metabolism or blood flow. The cardiac muscle exhibits distinct electrophysiological features, including pacemaker activity and calcium channel control, which play a vital role in the heart's response to various drugs. The autonomic nervous system, comprising the sympathetic and parasympathetic branches, regulates heart rate. Sympathetic activation increases heart rate, while parasympathetic activation...
Correlation between ECG and Cardiac Cycle01:25

Correlation between ECG and Cardiac Cycle

The electrical signals recorded on an electrocardiogram (ECG) occur before the mechanical processes of contraction and relaxation during the cardiac cycle.
A cardiac action potential originates in the SA node and spreads throughout the atria and the AV node in approximately 0.03 seconds. This results in the P wave in an ECG and triggers atrial contraction. The action potential is then briefly slowed at the AV node, allowing the atria to contract and fill the ventricles with blood before...

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Related Experiment Video

Updated: May 31, 2026

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery
04:48

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery

Published on: November 28, 2018

Time equals myocardium: are we in time?

S Mohan1, S Lynch, T A Cummings

  • 1Department of Medicine, Eric Williams Medical Sciences Complex Trinidad and Tobago, West Indies. shaun.s.mohan@gmail.com

The West Indian Medical Journal
|June 28, 2011
PubMed
Summary

Patients with ST segment elevation myocardial infarction experienced delays in door to thrombolysis times, averaging over two hours. Inadequate healthcare systems hinder timely treatment for cardiac events.

Area of Science:

  • Cardiology
  • Emergency Medicine
  • Healthcare Systems Analysis

Background:

  • ST segment elevation myocardial infarction (STEMI) is a time-sensitive medical emergency requiring rapid intervention.
  • Thrombolysis is a critical treatment for STEMI, aiming to restore blood flow to the heart muscle.
  • Assessing door to thrombolysis time is crucial for evaluating the efficiency of emergency cardiac care pathways.

Purpose of the Study:

  • To evaluate the door to thrombolysis time for patients with STEMI at the Eric Williams Medical Sciences Complex.
  • To identify factors influencing the timeliness of thrombolytic therapy in acute myocardial infarction cases.

Main Methods:

  • Retrospective review of patient records presenting with cardiac chest pain and STEMI.
  • Data collection included door to thrombolysis times and patient demographics.

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In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography
08:13

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

Published on: February 16, 2016

Related Experiment Videos

Last Updated: May 31, 2026

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery
04:48

Noninvasive Determination of Vortex Formation Time Using Transesophageal Echocardiography During Cardiac Surgery

Published on: November 28, 2018

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography
08:13

In Vivo Quantitative Assessment of Myocardial Structure, Function, Perfusion and Viability Using Cardiac Micro-computed Tomography

Published on: February 16, 2016

  • Analysis of 51 patients treated for STEMI between February 1 and May 31, 2008.

    • Main Results:

    • 78.4% of STEMI patients received thrombolysis.
    • Average door to thrombolysis time was 2 hours and 7 minutes.
    • Initial healthcare facility presentation impacted thrombolysis timeliness.

    Conclusions:

    • While many patients presented within the thrombolysis window, overall treatment delays were observed.
    • Deficiencies in patient recognition, transport, triage, and treatment systems require urgent improvement.
    • Systemic overhaul is necessary to meet recommended American Heart Association and American College of Cardiologist guidelines for STEMI care.