To Pace or Not to Pace
Cardiac pacemakers represent one of the great accomplishments of 20th-century cardiology. Before pacemakers were available, there was no treatment for diseases that produced a slow heart rate—or no rate at all. Patients became dizzy, or fainted, or died when failure of the sinoatrial node or the AV conducting system dropped the heart rate below a level that could sustain health or life. Until the 1960s, physicians could only watch helplessly and prescribe drugs that had little effect. Then came pacemakers.
A cardiac pacemaker is simply an electrode attached at one end to the heart and at the other to an electric power pack that sends out an impulse very like the normal activating wave that makes the heart beat. The speed and intensity of the impulse can be controlled and a suitable heart rhythm can be restored.
Modern pacemakers are a triumph of engineering. With one electrode in the atria and one in the ventricle, a pacemaker can make the heart beat in a normal, synchronized manner. It can sense changes in hemodynamics and adjust itself to the needs of the patient. A pacemaker has safety features that permit it to recognize the patient’s own heartbeat and change accordingly. There are many different types of pacemakers to suit almost any clinical setting.
There are still technical problems—lead wires can break and power units can malfunction—but, on balance, the evolution of modern pacemakers has been a marvel of engineering.
On the medical side, things have sometimes been less than marvelous. There’s been confusion about the indications for permanent pacing, and it seems clear that a significant number of patients have received pacemakers who didn’t need them. Those of us who train physicians to interpret electrocardiograms have been deeply concerned about the failure of many cardiology training programs in recent years to teach this subject adequately. Experts in the field are lamentably sparse—a condition some of us are trying to correct. There really shouldn’t be any doubt about the indications for permanent pacing. They’ve been obvious for many years to every physician who has worked in the field of the arrhythmias. For all these reasons, the indications for implantation of a permanent pacemaker are spelled out here as plainly and simply as possible.
Important Note: Implantation of a permanent pacemaker is never an emergency. A temporary pacing wire can be floated into the heart easily and safely and can be kept there long enough to permit careful clinical evaluation and expert consultation. That pacemaker may be going in for a lifetime, and it’s not innocuous. Any patient deserves a couple of opinions and long, careful consideration before a pacemaker is implanted.
How to Tell When Someone Needs a Pacemaker
I had the privilege of serving as chairman of a committee of distinguished cardiologists who published guidelines for pacing in the Journal of the American Medical Association.1 It’s possible to condense these guidelines as follows:
Complete Heart Block in the Bundle Branch System
If nothing can travel from the atria to the ventricles because both bundle branches are permanently out of action and can’t conduct, permanent pacing is always indicated.
Mobitz Type II Block
Properly diagnosed, this means that one bundle branch is permanently blocked and the other fails now and then. The risk of catastrophe in these patients is over 30% per year. Permanent pacing is justified whether or not the patient has symptoms. Remember, Mobitz II block happens only in the setting of preexisting bundle branch block. Thus the QRS will be wide. If a physician makes a diagnosis of Mobitz II block when the QRS is narrow, the patient should run, not walk, to another, more competent physician. A narrow QRS means that both bundle branches are functioning normally. Mobitz II block in the presence of a narrow QRS is one of the rarest phenomena in electrocardiography.
Intrinsic, Permanent, or Severely Recurrent AV Nodal Block—High Degree or Complete (Rare)
This must be distinguished from insignificant AV nodal block. It’s not unusual for healthy people to have short periods of block in the AV node. Studies in Israel and Britain have documented Wenckebach and first-degree AV nodal block in healthy young people, especially at night. It’s a normal variant. Remember that the vagus nerve goes to the AV node and stimulation of the vagus nerve can produce transient AV nodal block. Retching and vomiting are common causes of vagal stimulation. Many normal people reading this have certainly had periods of AV nodal block during the peak of a hangover or while reacting to spoiled potato salad. Many drugs depress conduction through the AV node, such as digitalis, calcium blockers, and beta blockers, which all can produce AV nodal block alone. Add the vagal effect of retching and the block can be dramatic. Morphine, Demerol, and related pain-killing drugs stimulate the vagus powerfully. I have seen cases when pacemakers were implanted on the basis of periods of AV nodal block obviously produced by drugs, by the vagal stimulation of nausea and vomiting, or by both, sometimes with tragic results.
If AV nodal block appears during periods of intense vagal stimulation or drug effect, a temporary pacing wire can be inserted. The honest, competent physician will then wait for these temporary effects to wear off before recommending a permanent pacemaker. Ninety-nine times out of a hundred, the AV block will disappear. The word intrinsic in the
earlier heading means that there’s something wrong with the cells of the AV node itself. To justify pacing, the block must either be permanent or must recur often enough to be a hazard. The word permanent is especially important when a patient suffers an infarct involving the right coronary artery. This artery supplies the AV node most of the time. Temporary AV nodal block is common during an inferior myocardial infarct. Temporary pacing may be needed. Permanent pacing is never needed: the AV node always recovers. It may take up to 2 weeks, but the AV node will come back to normal.
earlier heading means that there’s something wrong with the cells of the AV node itself. To justify pacing, the block must either be permanent or must recur often enough to be a hazard. The word permanent is especially important when a patient suffers an infarct involving the right coronary artery. This artery supplies the AV node most of the time. Temporary AV nodal block is common during an inferior myocardial infarct. Temporary pacing may be needed. Permanent pacing is never needed: the AV node always recovers. It may take up to 2 weeks, but the AV node will come back to normal.
Now the words at the beginning of this heading should take on specific meaning. True, intrinsic, permanent, or severely recurrent high-degree or complete AV nodal block is rare.
Warning for patients and referring physicians: If AV block is present and if the QRS is narrow, the block must be in the AV node. The chances are then overwhelming that the block is caused by drugs or by some temporary effect such as ischemia or vagal effect. Don’t let anyone implant a permanent pacemaker until all these possibilities have been thoroughly excluded.
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