Management
1. Rate Control:
a. Pharmacologic Options
Rate control consists of controlling the ventricular rate to slow down its response. The different rate control agents act on the atrioventricular (AV) node to prolong its refractory period and to slow its conduction. By doing so, one avoid the hemodynamic instability associated with tachycardia such as heart failure, and angina, and prevent long term tachycardia-mediated cardiomyopathy. Unfortunately, one may also have to face unwanted side effects, such as hypotension and bradycardia, for the same reason. In most situations, medication can be administered through the per os (PO or oral) or intravenous (IV) route. As expected the intravenous form provides a faster onset of action. The four main classes of rate control agents consist of; beta-blockers (metoprolol, atenolol, propanolol), calcium channel blockers (diltiazem, verapamil), sodium-potasium ATPase inhibitors (digoxin), and class III antiarrhythmic agents such as amiodarone. Beta-blockers, and calcium channel blockers are both effective at rest and during exercise, while digoxin is only effective at rest.
A special consideration should be given to patient with Wolff-Parkinson-White syndrome as administration of a beta-blocker, calcium channel blocker, adenosine, or digoxin would facilate antegrade conduction through the accessory conduction pathway and cause ventricular preexcitation. In this particular case, class I and III antiarrhythmic agents (amiodarone) become the best treatment option. The following tables give a list of possible rate control agents, along with their dosing and major side effects. I would recommend you to carry a version of it for when you are on call.
| Table 2. Rate Control Pharmacological Options | ||||
|---|---|---|---|---|
| Drug | Loading dose by route of administration |
Onset of action | Maintenance dose | Major side effect |
| Metoprolol | 2.5 to 5 mg IV bolus over 2 min, up to 3 doses |
5 mins | IV infusion n/a | Hypotension*, heart block, asthma/COPD**, heart failure |
| 25-100 mg PO bid |
4 to 6 hrs | 25 – 100 mg PO bid | Hypotension*, heart block, asthma/COPD**, heart failure |
|
| Propanolol | 0.15 mg/kg IV over 1 min |
5 mins | IV infusion n/a | Hypotension*, heart block, asthma/COPD**, heart failure |
| 80 – 240 mg/day in divided doses |
1 to 1.5 hrs | 80 – 240 mg/day in divided doses |
Hypotension*, heart block, asthma/COPD**, heart failure |
|
| Diltiazem | 0.25 mg/kg IV over 2 mins |
2 to 7 mins | 5 – 15 mg/hr infusion | Hypotension*, heart block, heart failure |
| 120 – 360 mg/day in divided doses |
2 to 4 hrs | 120 – 360 mg/day in divided doses |
Hypotension*, heart block, heart failure |
|
| Verapamil | 0.075 – 0.15 mg/kg IV over 2 mins |
3 to 5 mins | IV infusion n/a | Hypotension*, heart block, heart failure |
| 120 – 360 mg/day in divided doses |
1 to 2 hrs | 120 – 360 mg/day in divided doses |
Hypotension*, heart block, heart failure |
|
| Digoxin | 0.25 mg IV every 2 hrs up to 1.5 mg |
2 hrs | 0.125 – 0.25 mg/day | Digoxin toxicity***, heart block (bradycardia) |
| 0.25 mg PO every 2 hrs up to 1.5 mg |
2 hrs | 0.125 – 0.375 mg/day | Digoxin toxicity***, heart block (bradycardia) |
|
| Amiodarone | 150 mg IV over 10 mins |
days | 0.5 – 1 mg/min IV | Hypotension*, heart block, pulm toxicity, thyroid dysfct, warfarin interaction |
| 800 mg/day for 1 wk 600 mg/day for 1 wk 400 mg/day for 4-6 wks all PO |
1 to 3 wks | 200 mg/day | Hypotension*, heart block, pulm toxicity, thyroid dysfct, warfarin interaction |
|
* Do not use if systolic blood pressure less than 90 mmHg |
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