The PR interval of the surface electrocardiogram (ECG) is measured from the onset of atrial depolarization (P wave) to the beginning of ventricular depolarization (QRS complex). In the adult population, normal PR interval ranges from 0.12-0.20 seconds at normal heart rates. First-degree atrioventricular (AV) block is defined as a PR interval exceeding 0.20 seconds (see Image 1).
The PR interval represents the time needed for an electrical impulse from the sinoatrial (SA) node to conduct through the atria, AV node, bundle of His, bundle branches, and Purkinje fibers. Thus, as shown in electrophysiological studies, PR interval prolongation (ie, first-degree AV block) may be due to conduction delay within the right atrium, the AV node, the His-Purkinje system, or a combination of these. AV nodal dysfunction accounts for the majority of cases. First-degree AV block caused by conduction delay in the His-Purkinje system often is associated with bundle-branch block.
Structure and function of the AV node and His-Purkinje system
The AV node is the only normal electrical connection between atria and ventricles. It is an oval or elliptical structure, measuring 7-8 mm in its longest (anteroposterior) axis, 3 mm in its vertical axis, and 1 mm transversely. The AV node is located beneath the right atrial endocardium, dorsal to the septal leaflet of the tricuspid valve, and about 1 cm superior to the orifice of the coronary sinus. The bundle of His originates from the anteroinferior pole of the AV node and travels through the central fibrous body to reach the dorsal edge of the membranous septum. It then divides into right and left bundle branches. The right bundle continues first intramyocardially, then subendocardially, toward the right ventricular apex. The left bundle continues distally along the membranous septum and then divides into anterior and posterior fascicles.
Blood supply to the AV node is provided by the AV node artery, a branch of the right coronary artery in 90% of individuals and of the left circumflex coronary artery in the remaining 10%. The His bundle has a dual blood supply from branches of anterior and posterior descending coronary arteries. Likewise, the bundle branches are supplied by both left and right coronary arteries.
The AV node has a rich autonomic innervation and is supplied by both sympathetic and parasympathetic nerve fibers. This autonomic innervation has a major role in the time required for the impulse to pass through the AV node.
First-degree AV block is rare in young healthy adults. It is reported in 0.65-1.1% of young adults older than 20 years. Higher prevalence is reported in trained athletes (8.7%). The prevalence also increases with age; first-degree AV block is reported in 5% of men older than 60 years. The overall prevalence is 1.13 cases per 1000 lives.
No mortality or morbidity is related to isolated first-degree AV block. However, in the setting of acute inferior myocardial infarction (MI), first-degree AV block may herald higher degrees of AV block. Markedly prolonged PR interval in patients with left ventricular systolic dysfunction may impair ventricular filling and thus reduce cardiac output.
Incidence of first-degree AV block increases with age.
Patients with first-degree AV block are generally asymptomatic at rest. Markedly prolonged PR interval may reduce exercise tolerance in some patients with left ventricular systolic dysfunction. Syncope may result from transient high-degree AV block, especially in those with infranodal block and wide QRS complex.
The intensity of the first heart sound (S1) is decreased in patients with first-degree AV block.
Patients with first-degree AV block may have a short, soft, blowing, diastolic murmur heard at the cardiac apex. This diastolic murmur is not caused by diastolic mitral regurgitation, because it reaches its peak before the onset of regurgitation. The diastolic murmur is thought to be related to antegrade flow through closing mitral valve leaflets that are stiffer than normal. Administration of atropine may reduce the duration of this murmur by shortening the PR interval.
Athletic training: Well-trained athletes can demonstrate first-degree (and occasionally higher degree) AV block owing to an increase in vagal tone.
Coronary artery disease
Acute MI: First-degree AV block occurs in fewer than 15% of patients with acute MI admitted to coronary care units.
His bundle electrocardiographic studies have shown that, in most of these patients, AV node is the site of conduction block.
AV block is more common in the setting of inferior MI.
In the Thrombolysis in Myocardial Infarction (TIMI) II study, high-degree (second- or third-degree) AV block occurred in 6.3% of patients at the time of presentation and in 5.7% in the first 24 hours after thrombolytic therapy. Patients with AV block at the time of presentation had a higher in-hospital mortality rate than patients without AV block; both groups, however, had similar mortality rates during the following year. Patients who developed AV block after thrombolytic therapy had higher mortality rates both in-hospital and in the following year than patients without AV block. Right coronary artery was more often the site of infarction in patients with heart block than in those without heart block. Patients with AV block are believed to have larger infarct size. However, the prevalence of multivessel disease is not higher in patients with AV block.
Idiopathic degenerative diseases of the conduction system
Lev disease: This is due to progressive degenerative fibrosis and calcification of the neighboring cardiac structures, "sclerosis of the left side of cardiac skeleton," including mitral annulus, central fibrous body, membranous septum, base of the aorta, and crest of the ventricular septum. Lev disease has an onset about the fourth decade and is believed to be secondary to wear and tear on these structures caused by the pull of the left ventricular musculature. It affects the proximal bundle branches and is manifested by bradycardia and varying degrees of AV block.
Lenègre disease: This is an idiopathic, fibrotic degenerative disease restricted to the His-Purkinje system. It is caused by fibrocalcareous changes in mitral annulus, membranous septum, aortic valve, and crest of the ventricular septum. These degenerative and sclerotic changes are not attributed to inflammatory or ischemic involvement of adjacent myocardium. Lenègre disease involves the middle and distal portions of both bundle branches and affects a younger population than Lev disease.
Drugs: Calcium channel blockers, beta-blockers, digoxin, and amiodarone all may cause first-degree AV block. Although first-degree AV block is not an absolute contraindication for administration of these drugs, extreme caution should be exercised in the use of these medications in patients with first-degree AV block, as they carry the risk of developing higher degree AV block on exposure to these drugs.
Mitral or aortic valve annulus calcification: The main penetrating bundle of His is located near the base of the anterior leaflet of the mitral valve and the noncoronary cusp of the aortic valve. Heavy calcium deposits in patients with aortic or mitral annular calcification is associated with increased risk of AV block.
Infectious disease: Infective endocarditis, diphtheria, rheumatic fever, Chagas disease, Lyme disease, and tuberculosis all may be associated with first-degree AV block.
Extension of the infection to the adjacent myocardium in native or prosthetic valve infective endocarditis (ie, ring abscess) can cause AV block.
Acute myocarditis caused by diphtheria, rheumatic fever, or Chagas disease can result in AV block.
Collagen vascular disease: Rheumatoid arthritis, systemic lupus erythematous, and scleroderma all may be associated with first-degree AV block.
Rheumatoid nodules may occur in the central fibrous body and result in AV block.
Fibrosis of the AV node or the adjacent myocardium in patients with systemic lupus erythematous or scleroderma can cause first-degree AV block.
Doppler echocardiographic signs of first-degree AV block have been demonstrated in about 33% of fetuses of pregnant women who are anti-SSA/Ro 52-kd positive. In most of these fetuses, the blocks resolved spontaneously. However, progression to a more severe degree of block was seen in 2 of the fetuses. Serial Doppler echocardiographic measurement of AV-time intervals can be used for surveillance of these high-risk pregnancies.
Infiltrative diseases such as amyloidosis or sarcoidosis
First-degree AV block occurs in about 10% of patients who undergo adenosine stress testing and is usually hemodynamically insignificant. Patients with baseline first-degree AV block more often develop higher degrees of AV block during adenosine stress testing. These episodes, however, are generally well tolerated and do not require specific treatment or discontinuation of the adenosine infusion.
Marked first-degree AV block may occur following catheter ablation of the fast AV nodal pathway with resultant conduction of the impulse via the slow pathway. This may result in symptoms similar to the pacemaker syndrome.
First-degree AV block (reversible or permanent) has been reported in about 2% of patients who undergo closure of atrial septal defect using the Amplatzer septal occluder.
First-degree AV block can occur following cardiac surgery. Transient first-degree AV block may result from right heart catheterization.
Abu Zubair meriwayatkan dari Jabir bin Abdullah bahwa Nabi Muhammad SAW bersabda:
"Setiap penyakit ada obatnya. Jika obat yang tepat diberikan dengan izin Allah, penyakit itu akan sembuh".
(HR. Muslim, Ahmad dan Hakim).
Sabtu, 28 November 2009
Diposkan oleh FX di 18.31
The Holy Al-Qur'an (English version)
- Surah 1 - Al Fatiha THE OPENING
- Surah 2 - Al Baqarah THE HEIFER
- Surah 3 - Ali 'Imran - THE FAMILY OF 'IMRAN
- Surah 4 - Al-Nisa' THE WOMEN
- Surah 5 - Al Ma'idah THE REPAST
- Surah 6 - Al An'am THE CATTLE
- Surah 7 - Al A'raf THE HEIGHTS
- Surah 8 - Al Anfal THE SPOILS OF WAR
- Surah 9 - Al Tawbah THE REPENTANCE
- Surah 10 - Yunus JONAH
- Surah 11 - Hud THE PROPHET HUD
- Surah 12 - Yusuf JOSEPH
- Surah 13 - Al Ra'd THE THUNDER
- Surah 14 - Ibrahim ABRAHAM
- Surah 15 - Al Hijr THE ROCKY TRACT
- Surah 16 - Al Nahl BEES
- Surah 17 - Al Isra' THE NIGHT JOURNEY
- Surah 18 - Al Kahf THE CAVE
- Surah 19 - Maryam MARY
- Surah 20 - TA HA
- Surah 21 - Al Anbiya THE PROPHETS
- Surah 22 - Al Hajj THE PILGRIMAGE
- Surah 23 - Al Mu'minun THE BELIEVERS
- Surah 24 - Al Nur THE LIGHT
- Surah 25 - Al Furqan THE CRITERION
- Surah 26 - Al Shu'ara' THE POETS
- Surah 27 - Al Naml THE ANTS
- Surah 28 - Al Qasas THE NARRATIONS
- Surah 29 - Al 'Ankabut THE SPIDER
- Surah 30 - Al Rum THE ROMANS
- Surah 31 - Luqman LUQMAN
- Surah 32 - Al Sajdah THE PROSTRATION
- Surah 33 - Al Ahzab THE CONFEDERATES
- Surah 34 - Saba' SHEBA
- Surah 35 - Fatir THE ORIGINATOR OF CREATION
- Surah 36 - Ya Sin YA SIN
- Surah 37 - Al Saffat THOSE RANGED IN RANKS
- Surah 38 - Sad SAD
- Surah 39 - Al Zumar CROWDS
- Surah 40 - Ghafir FORGIVER
- Surah 41 - Fussilat EXPOUNDED
- Surah 42 - Al Shura CONSULTATION
- Surah 43 - Al Zukhruf THE GOLD ADORNMENTS
- Surah 44 - Al Dukhan THE SMOKE
- Surah 45 - Al Jathiyah THE KNEELING DOWN
- Surah 46 - Al Ahqaf WINDING SAND-TRACTS
- Surah 47 - Muhammad MUHAMMAD
- Surah 48 - Al Fath THE VICTORY
- Surah 49 - Al Hujurat THE CHAMBERS
- Surah 50 - Qaf QAF
- Surah 51 - Al Dhariyat THE WINDS THAT SCATTER
- Surah 52 - Al Tur THE MOUNT
- Surah 53 - Al Najm THE STAR
- Surah 54 - Al Qamar THE MOON
- Surah 55 - Al Rahman THE MOST GRACIOUS
- Surah 56 - Al Waq'iah THE INEVITABLE
- Surah 57 - Al Hadid IRON
- Surah 58 - Al Mujadilah THE WOMAN WHO PLEADS
- Surah 59 - Al Hashr THE MUSTERING
- Surah 60 - Al Mumtahinah THAT WHICH EXAMINES
- Surah 61 - Al Saff THE BATTLE ARRAY
- Surah 62 - Al Jumu'ah FRIDAY
- Surah 63 - Al Munafiqun THE HYPOCRITES
- Surah 64 - Al Taghabun THE MUTUAL LOSS AND GAIN
- Surah 65 - Al Talaq DIVORCE
- Surah 66 - Al Tahrim PROHIBITION
- Surah 67 - Al Mulk THE DOMINION
- Surah 68 - Al Qalam THE PEN
- Surah 69 - Al Haqqah THE SURE REALITY
- Surah 70 - Al Ma'arij THE WAYS OF ASCENT
- Surah 71 - Nuh NOAH
- Surah 72 - Al Jinn THE SPIRITS
- Surah 73 - Al Muzzammil THE ENFOLDED ONE
- Surah 74 - Al Muddaththir THE ONE WRAPPED UP
- Surah 75 - Al Qiyamah THE RESURRECTION
- Surah 76 - Al Insan MAN
- Surah 77 - Al Mursalat THOSE SENT FORTH
- Surah 78 - Al Naba' THE GREAT NEWS
- Surah 79 - Al Nazi'at THOSE WHO TEAR OUT
- Surah 80 - 'Abasa HE FROWNED
- Surah 81 - Al Takwir THE FOLDING UP
- Surah 82 - Al Infitar THE CLEAVING ASUNDER
- Surah 83 - Al Mutaffifin THE DEALERS IN FRAUD
- Surah 84 - Al Inshiqaq THE RENDING ASUNDER
- Surah 85 - Al Buruj THE CONSTELLATIONS
- Surah 86 - Al Tariq THE NIGHT STAR
- Surah 87 - Al A'la THE MOST HIGH
- Surah 88 - Al Ghashiyah THE OVERWHELMING EVENT
- Surah 89 - Al Fajr THE DAWN
- Surah 90 - Al Balad THE CITY
- Surah 91 - Al Shams THE SUN
- Surah 92 - Al Layl THE NIGHT
- Surah 93 - Al Duha THE GLORIOUS MORNING LIGHT
- Surah 94 - Al Sharh THE EXPANSION OF THE BREAST
- Surah 95 - Al Tin THE FIG
- Surah 96 - Al Alaq THE CLINGING CLOT
- Surah 97 - Al Qadr THE NIGHT OF POWER
- Surah 98 - Al Bayyinah THE CLEAR EVIDENCE
- Surah 99 - Al Zalzalah THE EARTHQUAKE
- Surah 100 - Al 'Adiyat THOSE THAT RUN
- Surah 101 - Al Qari'ah THE GREAT CALAMITY
- Surah 102 - Al Takathur THE PILING UP
- Surah 103 - Al 'Asr TIME THROUGH THE AGES
- Surah 104 - Al Humazah THE SCANDALMONGER
- Surah 105 - Al Fil THE ELEPHANT
- Surah 106 - Quraysh THE TRIBE OF QURAYSH
- Surah 107 - Al Ma'un THE NEIGHBOURLY ASSISTANCE
- Surah 108 - Al Kawthar THE ABUNDANCE
- Surah 109 - Al Kafirun THOSE WHO REJECT FAITH
- Surah 110 - Al Nasr THE HELP
- Surah 111 - Al Masad THE PLAITED ROPE
- Surah 112 - Al Ikhlas THE PURITY OF FAITH
- Surah 113 - Al Falaq THE DAYBREAK
- Surah 114 - Al Nas MANKIND
- Acute Coronary Syndromes
- Angina Pectoris
- Anomalous Left Coronary Artery From the Pulmonary Artery
- Aortic Coarctation
- Aortic Dissection
- Aortic Regurgitation
- Aortic Stenosis
- Aortic Stenosis, Subaortic
- Aortic Stenosis, Supravalvar
- Ashman Phenomenon
- Atrial Fibrillation
- Atrial Flutter
- Atrial Myxoma
- Atrial Septal Defect
- Atrial Tachycardia
- Atrioventricular Block
- Atrioventricular Dissociation
- Atrioventricular Nodal Reentry Tachycardia (AVNRT)
- Benign Cardiac Tumors
- Brugada Syndrome
- Complications of Myocardial Infarction
- Coronary Artery Atherosclerosis
- Coronary Artery Vasospasm
- Digitalis Toxicity
- Dissection, Aortic
- Ebstein Anomaly
- Eisenmenger Syndrome
- First-Degree Atrioventricular Block
- HACEK Group Infections (Infective Endocarditis)
- Heart Failure - Decompensatio Cordis
- Holiday Heart Syndrome
- Hypertensive Heart Disease
- Junctional Rhythm
- Loeffler Endocarditis
- Long QT Syndrome
- Lutembacher Syndrome
- Mitral Regurgitation
- Mitral Stenosis
- Mitral Valve Prolapse
- Myocardial Infarction
- Myocardial Rupture
- Paroxysmal Supraventricular Tachycardia
- Patent Ductus Arteriosus
- Patent Foramen Ovale
- Pericardial Effusion
- Pericarditis Acute
- Pericarditis, Constrictive
- Pericarditis, Constrictive-Effusive
- Pulmonic Regurgitation
- Pulmonic Stenosis
- Right Ventricular Infarction
- Saphenous Vein Graft Aneurysms
- Second-Degree Atrioventricular Block
- Sinus of Valsalva Aneurysm
- Sudden Cardiac Death
- Tetralogy of Fallot
- Third-Degree Atrioventricular Block
- Torsade de Pointes
- Tricuspid Regurgitation
- Tricuspid Stenosis
- Unstable Angina
- Ventricular Fibrillation
- Ventricular Septal Defect
- Ventricular Tachycardia
- Wolff-Parkinson-White Syndrome