Degree AV Block

This is the failure of the Atrioventricular node to conduct an impulse. AV blocks can be classified as 1st, 2nd and 3rd degree AV blocks. These blocks can be temporary or permanent. 

A 1st degree AV block is a delay between depolarisation of the atria and ventricular depolarisation occurring in the AV node (Figs. 7.6,7.7 and 7.8). This is seen on the 

ECG as an increase in the PR interval of more than 0.20 s (5 small squares). Each P wave is followed by a QRS complex. The best leads to see this type of block in are lead 11 and Vi as the P waves are usually more easily visualised in these leads, especially when used as a rhythm strip at the bottom of the 12-lead ECG. 1st Degree AV block does not normally require treatment. 

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The hydantoins are contraindicated in patients widi known hypersensitivity to die drug s. Phenytoin is contraindicated in patients widi sinus bradycardia, sinoatrial block, second and diird degree AV block, and Adams-Stokes syndrome it also is contraindicated during pregnancy (ediotoin and phenytoin are Pregnancy Category D) and lactation. Ediotoin is contraindicated in patients widi hepatic abnormalities. 

Type II second-degree or third-degree AV block absent o Observe... 

Second- or third-degree AV block for diltiazem or verapamil... 

Symptoms of bradyarrhythmias such as second- or third-degree AV block consist of dizziness, fatigue, lightheaded ness, syncope, chest pain (in patients with underlying myocardial ischemia), and shortness of breath and other symptoms of heart failure (in patients with underlying left ventricular dysfunction). 

In patients with second- or third-degree AV block due to underlying correctable disorders (such as electrolyte abnormalities or hypothyroidism), management consists of correcting those disorders. 

On the basis of ECG findings, AV block is usually categorized into three different types (first-, second-, or third-degree AV block). 

Cardiogenic shock preexisting second- or third-degree AV block (if no pacemaker is present) congenital QT prolongation sick sinus syndrome hypersensitivity to disopyramide. 

Heart block If first-degree heart block develops, reduce dosage. If the block persists, drug continuation must depend upon the benefit compared with the risk of higher degrees of heart block. Development of second- or third-degree AV block or unifascicular, bifascicular, or trifascicular block requires discontinuation of therapy, unless ventricular rate is controlled by a ventricular pacemaker. 

IR Individually titrate on the basis of response and tolerance. Initiate with 150 mg every 8 hours (450 mg/day). Dosage may be increased at a minimum of 3 to 4 day intervals to 225 mg every 8 hours (675 mg/day) and, if necessary, to 300 mg every 8 hours (900 mg/day). The safety and efficacy of dosages exceeding 900 mg/day have not been established. In those patients in whom significant widening of the QRS complex or second- or third-degree AV block occurs, consider dose reduction. 

Adverse reactions occurring in at least 3% of patients include angina first-degree AV block CHF intraventricular conduction delay palpitations proarrhythmia ventricular tachycardia dizziness fatigue headache constipation dyspepsia nausea/vomiting unusual taste blurred vision dyspnea. About 20% of patients discontinued treatment due to adverse reactions. 

Preexisting second- or third-degree AV block, right bundle branch block when associated with a left hemiblock (bifascicular block), unless a pacemaker is present to sustain the cardiac rhythm if complete heart block occurs recent myocardial infarction (Ml) presence of cardiogenic shock hypersensitivity to the drug. 

If second-or third-degree AV block, or right bundle branch block associated with a left hemiblock occurs, discontinue therapy unless a ventricular pacemaker is in place to ensure an adequate ventricular rate. 

Oral Severe sinus-node dysfunction, causing marked sinus bradycardia second-and third-degree AV block when episodes of bradycardia have caused syncope (except when used in conjunction with a pacemaker). 

Parenteral Marked sinus bradycardia second- and third-degree AV block unless a functioning pacemaker is available cardiogenic shock. 

Oral verapamil - Oral verapamil may lead to first-degree AV block and transient bradycardia, sometimes accompanied by nodal escape rhythms. 

Hypertrophic cardiomyopathy (IHSS) Serious adverse effects were seen in 120 patients with IHSS (especially with pulmonary artery wedge pressure more than 20 mm Hg and left ventricular outflow obstruction) who received oral verapamil at doses up to 720 mg/day. Sinus bradycardia occurred in 11%, second-degree AV block in 4% and sinus arrest in 2%. 

Patients with decompensated cardiac failure requiring the use of IV inotropic therapy (such patients should first be weaned from IV therapy before initiating carvedilol) bronchial asthma (see Warninas) or related bronchospastic conditions second- or third-degree AV block sick sinus syndrome or severe bradycardia (unless a permanent pacemaker is in place) cardiogenic shock clinically manifest hepatic impairment hypersensitivity to the drug. 

Phenytoin Because of its effect on ventricular automaticity, do not use phenytoin in sinus bradycardia, sino-atrial block, second- and third-degree AV block, or in patients with Adams-Stokes syndrome. 

Bronchial asthma, a history of bronchial asthma, or severe chronic obstructive pulmonary disease sinus bradycardia second- and third-degree AV block overt cardiac failure cardiogenic shock hypersensitivity to any component of the products. 

Contraindications Sick sinus syndrome/second- or third-degree AV block (except in presence of pacemaker), severe hypotension (less than 90mmFIg, systolic), history of serious ventricular arrhythmias, uncompensated cardiac insufficiency, congenital QT interval prolongation, use with other drugs prolonging QT interval... 

CHF, second and third-degree AV block occur rarely. 

Contraindications Bronchial asthma or chronic obstructive pulomonary disease, cardiogenic shock, overt cardiac failure, second and third degree AV block, severe sinus bradycardia, hypersensitivity to dorzolamide, timolol, or any other component of the formulation... 

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