Inotropy, Chronotropy, and Dromotropy

• Inotropy refers to the strength of cardiac muscle contraction; positive inotropic agents strengthen contraction, while negative inotropic agents weaken it.
• Chronotropy refers to heart rate; positive chronotropic agents increase heart rate, and negative chronotropic agents decrease it.
• Dromotropy refers to the rate of nervous impulse conduction; positive dromotropic agents speed impulse conduction, while negative dromotropic agents slow it.
• The heart uniquely generates its own electrical impulses through self-excitation, where individual cells can depolarize without external stimuli.
• The cell with the fastest rate of discharge (automaticity) within the cardiac system acts as the heart’s pacemaker, possessing the fastest rate of automaticity.

Cardiovascular

• Cardiac ischemia
• Pericarditis (viral or autoimmune)
• Aortic dissection

Respiratory

• Pulmonary embolism
• Pneumothorax
• Pneumonia
• Pleurisy (pleural irritation)

Gastrointestinal

• Cholecystitis
• Pancreatitis
• Hiatal hernia
• Esophageal disease
• Gastroesophageal reflux disease (GERD)
• Peptic ulcer disease
• Dyspepsia

Musculoskeletal

• Chest wall syndrome
• Costochondritis
• Acromioclavicular disease
• Herpes zoster (shingles)
• Chest wall trauma
• Chest wall tumors

Common Signs and Symptoms

• Discomfort
• Dyspnea
• Cough
• Syncope
• Palpitation
• Altered level of consciousness (ALOC)
• Diaphoresis
• Restlessness and anxiety
• Feeling of impending doom
• Nausea/vomiting
• Fatigue
• Edema
• Headache
• Anguished facial expression
• Activity limitations
• Trauma
• Diabetic patients with myocardial injury may not always experience chest pain.

Risk Factors

• Smoking and cocaine use
• Older age
• Family history of cardiac disease
• Hypertension
• Hypercholesterolemia
• Carbohydrate intolerance
• Male gender
• Lack of exercise
• Diet
• Obesity
• Oral contraceptives (birth control)
• Type A personalities
• Psychosocial tensions (stress)

Out-of-Hospital Treatment

• Point-of-care testing (POC)
• IV and fluids
• Medications like aspirin, nitroglycerin, fentanyl, and oxygen
• Medications for heart rate and rhythm management (adenosine, lidocaine)
• Other therapies include prescribed medications and lifestyle changes.

Cardiac Electrical Pathway

• The sinoatrial (SA) node is the primary pacemaker with an intrinsic rate of 60-100 bpm; the interatrial pathway allows the left atrium to contract, and the Intranodal pathway connects electrical junctions.
• The atrioventricular (AV) junction delays signals to allow full atrial depolarization and blood contraction into ventricles; it functions as a backup pacemaker with an intrinsic rate of 40-60 bpm.
• Signals proceed to the Bundle of His, then to the left and right bundle branches, and finally to the Purkinje fibers, which contract the ventricles and serve as a last resort pacemaker with an intrinsic rate of 20-40 bpm.
• Irritability occurs when a lower site on the pathway assumes pacemaker responsibilities.
• An escape mechanism activates when a lower pacemaker site takes over due to the failure of the normal pacemaker.

Pericarditis

• Pericarditis involves inflammation of the pericardium, leading to swelling and irritation of the sac surrounding the heart.
• This condition often results from the linings of the walls rubbing against each other, causing sharp or stabbing pain
• Heart attacks or heart surgeries are also potential causes.

Understanding inotropy, chronotropy, and dromotropy is crucial for comprehending heart function and the effects of various drugs. Inotropy relates to the force of contraction, chronotropy to heart rate, and dromotropy to conduction velocity. The heart has intrinsic electrical impulses through self-excitation.